Abstract:
A method and device for determining the presence and concentration of total microbial contamination or the presence and concentration of a specific microbial species on a surface is described. The method consists of a means of a collection device and fluid for removing the microbes from the surface and suspending them in a fluid phase. An aliquot of the fluid phase is introduced into a disposable test ticket which allows filtration of the sample to remove extraneous substances including somatic cells, and concentration of the microbes. The total concentration of microbes is determined by adding a somatic and bacterial releasing reagent to a disposable test device which comprises a membrane containing the luminescent reagents luciferin and luciferase, and introducing the disposable test device into a luminometer that can read the luminescence from the underside.

Description:
BACKGROUND 
     The following application is a continuation-in-part of U.S. application Ser. No. 08/370,093, filed Jan. 9, 1995, now U.S. Pat. No. 5,624,810, herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method for detecting the presence and determining the quantity of contaminants. More particularly, the invention relates to a method for rapidly determining the total microbial contamination or for determining the presence and quantity of specific microbial or chemical contaminant present on a wide variety of surfaces including surfaces of meat carcasses or other food, surfaces of equipment, surfaces where food is being processed or prepared, and surfaces of equipment, gloves and materials in medical situations. Airborne and liquid contaminants are also detectable. Furthermore, the invention relates to a method for determining the total microbial or specific microbial or chemical contamination by bioluminescence or chemiluminescence. 
     BACKGROUND OF THE INVENTION 
     Microbial contamination is a significant cause of morbidity and mortality. Rapid and routine procedures for quantitative determination of bacteria, particularly those present on surfaces, is frequently of vital importance, particularly in food processing and in hospitals. Food poisoning is often a result of microbial contamination of meat or food that occurs during processing. Contamination can be spread through contact of food with surfaces. In addition, spread of disease in hospitals and other facilities often occurs as a result of passage of infectious microbes on the surface of clothes or equipment. 
     A key feature of these applications is the requirement for rapid testing within minutes, a method that will overcome the potential contaminants from a variety of surfaces, liquids, and air, a requirement for no cross-over in the results from one test to a second, and a need for both general and specific testing for microbes, that is, the ability to test for contamination by both microbial counts and the ability to test for the presence of specific microbes. 
     Various methods have been utilized to measure microbial contamination on surfaces. Traditional procedures for assaying bacteria on surfaces are based on swabbing the surface followed by a culture of the swab for 24 to 48 hours in or on media that supports the growth of microbial species. The cultures are observed manually or with automated instrumentation to determine the number of colonies that have formed as an indicator of the number of microbes initially present on the surface. The disadvantages of this methodology are long assay times, requirements for specially trained personnel, and possible inadequate identification of the presence of certain potentially pathogenic microbes whose growth is not supported by the specific media or environment. In particular, it may be difficult to detect fungal contamination by this method. In addition, in many of the potential applications, the method does not give results in the time frame required for effective response. 
     Luminescent reactions have been utilized in various forms to detect bacteria in fluids and in processed materials. In particular, bioluminescent reactions based on the reaction of adenosine triphosphate (ATP) with luciferin in the presence of the enzyme luciferase to produce light (the &#34;firefly&#34; reaction) have been utilized. Since ATP is present in all living cells including all microbial cells, this method can be used in a rapid assay to obtain a quantitative estimate of the number of living cells in a sample. Early discourses on the nature of the reaction, the history of its discovery, and its general area of applicability are provided by E. N. Harvey (1957), A History of Luminescence: From the Earliest Times Until 1900, Amer. Phil. Soc., Philadelphia Pa. and W. D. McElroy and B. L. Strehler (1949) Arch. Biochem. Biophys. 22:420-433. Alternatively, chemiluminescent detection by isoluminol or similar compounds has been used. This method is based on the detection of iron-containing substances in microbes. 
     Test procedures exemplifying the use of bioluminescent reactions for bacterial determinations and, specialized instrumentation for measurement of the associated light emission, are known and have been disclosed. Plakas (U.S. Pat. Nos. 4,013,418, 4,144,134, and 4,283,490) teaches a bioluminescent assay for the detection of bacteria in a sample including the steps of lysing non-bacterial cells, effecting filtration by positive pressure, washing, lysing bacterial cells and detecting ATP released with a luciferin/luciferase/Mg2+ regent. The art in this patent does not deal with the specific problems associated with collection of material from a surface or with the detection of specific bacteria. No issue of the timing is mentioned and the invention as disclosed would require significant time. 
     Chappelle in U.S. Pat. No. 4,385,113 discloses a method for detection of bacteria in water based on bioluminescence. This test requires several hours to perform and is specifically addressed to the detection of total bacterial content in water. 
     Miller (PCT application US 88/00852) discusses a similar assay for use with urine samples, but does not discuss the issues of collection from a surface and the assay timing is not specifically set forward in this application. further, no method for detection of specific bacteria is elucidated. 
     Clendenning in his U.S. Pat. No. 3,933,592 discusses a method for bioluminescent detection of microbial contamination and in the examples refers to performing the procedure in less than 2 minutes. The procedure does not involve pre-treatment phases and the removal of somatic cell ATP. 
     AEgidius (U.S. Pat. No. 5,258,285) discloses a method for detection of bacterial concentration in a sample that utilizes a filtration step, a washing step to remove extraneous material including somatic cell ATP, establishing an extraction chamber in which luciferin/luciferase/Mg2+ is added and the reaction measured. This method does not mention time. In addition, it utilizes separate chambers for washing, extracting the bacterial ATP, and measuring the reaction. This may potentially result in decreased sensitivity due to loss of the material in the process of transferring the solution from chamber to chamber. Further, the method does not describe a means of collecting a sample from a surface. 
     Detection of bacteria on surfaces poses additional issues not addressed in these previous methods. First and foremost is the method for collecting a sample to be compatible with these test devices and materials. The method must effectively retrieve the bacteria from the surface and result in a liquid suspension of the microbes. 
     A second issue of main concern is that surfaces or other areas being monitored often are contaminated with materials that may interfere with the detection of the microbes. One main interfering material that can be present on surfaces, air, or liquids is somatic cells either from the food itself and including both animal and plant cells, or from the hands of an individual in contact with the surface. Since all living organisms including somatic cells contain ATP, the presence of these cells can mask or alter the reading obtained. 
     An additional source of interfering substances are those that interfere with the light producing reaction itself. These substances include a wide range of chemicals such as chlorine, oxidizing agents, free ATP, heavy metals, and other chemicals. As some of these chemicals are used for disinfecting of a surface, it is obvious that a reliable method for analyzing microbial contamination must include a means of eliminating these substances from the sample. 
     It is a further requirement in many cases in the food processing and hospital applications that the method for monitoring for microbial contamination of surfaces be rapid. For example, in the processing of beef carcasses, the carcasses are processed on a line and any testing of the material for microbial contamination must be performed within the time frame required for the carcass to move to further processing. 
     Previously disclosed luminescence based methodologies for microbial detection have not included any means for processing a sample from a surface and making a liquid suspension for testing. Further, the processes have required multiple devices or chambers for containment, filtration, and measurement of the reaction. Finally, the processes have not incorporated a disposable device that allows for minimizing cross-contaminations. Finally, in those assays for detecting specifically microbial ATP and other specific contaminants, previously disclosed inventions have relatively long time frames which are not consistent with on-line processing, quality control, and immediate verification of results. 
     SUMMARY OF THE INVENTION 
     The present invention is a method and device for determining the presence and/or concentration of total microbial concentration or the presence and/or concentration of a specific target analyte. The method firstly comprises collecting a surface sample by wiping a circumscribed area of a surface in a prescribed fashion using a collection apparatus means comprised of an absorbent or adsorbent material. The said collection apparatus means is placed into a container containing a fluid and agitated to release the surface contaminants from the collection apparatus means into the fluid. The collection apparatus means can be in the form of a sponge or a swab and the container can be a bag, tube, or small cup. An aliquot of the fluid phase is subsequently transferred to a disposable test device comprised of a translucent hollow cylinder, open on the top and having a porous filter attached on the bottom. The fluid phase is filtered through the disposable test device comprised of a translucent hollow cylinder, open on the to and having a porous filter attached on the bottom. The fluid phase is filtered through the disposable test device by applying either positive or negative pressure resulting in retention of microbes or target analytes on the surface of the filter. The filtration process results in the concentration of analyte and the removal of any interfering substances from the collectate prior to testing, such as inhibitors or any nonspecific materials to maximize test sensitivity and specificity. The filter retentate can be washed by adding appropriate wash solution and reapplying appropriate pressure to force the fluid phase through the filter. Another feature of the present invention is that the retentate captured on the filter of the disposable test device can be assayed by a chemiluminescent or bioluminescent test method. Said final step of said test method comprising addition of luminescent substrate to the retentate resulting in a chemiluminescent reaction and measuring the light output from said chemiluminescent reaction by using a photometer that accommodates the disposable device in a manner which allows its precise and reproducible positioning with respect to the surface of the photosensor and which precludes any possible loss of the final reaction mixture during and after the measurement cycle. 
     The present invention allows for a contaminant to be identified and/or concentration determined in less than 1 hour from time of collection to end result, and generally in less than 5 minutes. 
     More specifically, the present invention comprises a method for performing chemiluminescent assays such as bioluminescent assays for ATP, chemiluminescent immunoassay or DNA probe assays. One embodiment of the present invention is a method for determining the total microbial contamination comprising the steps of: 
     a) collecting a surface sample with a collection means and 
     b) agitating said collection apparatus means with a fluid phase to dislodge the surface contaminants into a fluid phase, said fluid phase the becoming the collectate and 
     c) placing an aliquot of said collectate into a disposable test device, and 
     d) adding a washing/lysing reagent that lyses any somatic cells present in the aliquot; and 
     e) applying a positive pressure to the top of the disposable test device or negative pressure to the bottom of the disposable test device to eliminate the liquid phase containing free ATP and any chemical inhibitors as well as concentrating the bacteria at the interface, and 
     f) adding a bacterial lysing reagent that perforates the bacterial cell walls allowing the release of microbial ATP, and 
     g) adding ATP free luciferin and luciferase reagent, and 
     h) determining the amount of ATP present by measuring the light emitted through translucent sides of said disposable test device. 
     The choice of collection fluids are well known to those skilled in the art. Generally the fluid is comprised of a detergent, salt, or buffer or any combination thereof that maintains the integrity of the microbial cell walls. A fluid consisting of 0.15M sodium chloride containing 0.5% Tween 20 detergent is one such choice. It is possible to use other formulations including phosphate or HEPES buffered saline and other detergents including zwitterionic detergents and non-ionic detergents. 
     It will be obvious to a person skilled in the art that mixing of reactant could be achieved in any of the steps through the use of a micropipette. The detection method of this invention specifically allows for both the concentration of analyte and any resulting chemiluminescent reaction caused by the presence of said analyte to occur within the chamber of the disposable test device. An added feature of the disposable test device is that the diameter of the filter is from 0.5 to 2.0 cm, preferably about 1.0 cm, so that the volume of bioluminescent or chemiluminescent substrate solution is minimized to maximize signal output to the photodetector means. The final volume of the substrate should be between 20 μl to 1000 μl, most preferably about 60 μl to 100 μl. The disposable test device can be inserted into a complementary device comprising a larger (liquid tight) at least two component chamber that can house the disposable test device and through which a volume of collectate greater than 500 μl can pass through the filter under positive or negative pressure and retain the microbes or the analytes of interest onto the surface of the filter. For example, the disposable test device can be inserted into the lower chamber of the two component device, said lower chamber having an outflow for the filtrate to which is attached a removable upper chamber of the two component device. The said upper chamber comprising a liquid tight seal to said lower compartment and having an intake valve. Said intake valve can be configured for a complementary Luer tip fitting for attachment of a Luer tipped syringe. Said syringe may include at least one series of prefilter(s) to remove any larger debris from entering the filter of the disposable test device. At completion of passing the collectate through the filter of the disposable test device, the two component device can be opened, and the disposable test device physically removed. Said disposable test device now containing the retentate from a large volume of collectate (i.e. 50 ml). The filtration of said large volume of collectate enables increased sensitivity for analyte detection of the collectate fluid. Said disposable test device is then processed as previously described. 
     The luciferin/luciferase chemiluminescent reactions for ATP are well known. Other chemiluminescent reactions employing bacterial luciferase reactions, or luminols for total microbial determinations can be easily adapted to the methods and devices of the present invention. 
     The luciferin/luciferase chemiluminescent reactions for ATP are well known. Other chemiluminescent reactions employing bacterial luciferase reactions, or luminols for total microbial determinations can be easily adapted to the methods and devices of the present invention. 
     The invention further concerns a detection method in which the presence and quantity of specific microbes on a surface can be detected in a time frame less than one hour, said method comprising the steps of: 
     a) Providing a clean disposable test device comprising an open top, translucent sides and a porous filter attached to the bottom side, 
     b) Adding an aliquot of collectate, said collectate being that described as above, 
     c) Adding an appropriate wash solution comprised of detergent, or buffered salts or a combination thereof, 
     d) Applying positive pressure to the top of the disposable test device, or negative pressure to the bottom of the disposable test device to remove fluid from the device and deposit microbes or target analytes directly or indirectly onto the surface of the porous filter, 
     e) Adding a specific labeled antibody directed against the specific microbes to be detected and incubating for an appropriate period of time, 
     f) Applying positive pressure to the top of the disposable test device, or negative pressure to the bottom of the disposable test device to remove fluid containing unreacted enzyme labeled antibody from the device, 
     g) Adding an appropriate wash solution comprised of detergent and buffered salts, 
     h) Applying positive pressure to the top of the disposable test device, or negative pressure to the bottom of the disposable test device to further remove fluid containing unreacted labeled antibody from the device, 
     i) Adding a chemiluminescent substrate and determining the amount of light emitted by the chemiluminescent substrate using a photometer that accommodates the disposable test device in a manner which allows its precise positioning with respect to the surface of the photosensor and which precludes any possible loss of the final reaction mixture during and after the measurement cycle. 
     The method described above can also be modified by adding capture particles such as latex spheres coated with a binder such as specific antibody to antigens of the target microbe into the target microbe into the disposable test device prior to performing step (d). The method can also be modified so that capture particles and enzyme labeled antibody and the collectate are all simultaneously reacted within the disposable test device, prior to performing step (f). 
     In yet another embodiment of the invention, all of the chemicals and solutions (except for the somatic cell releasing agent) are in a disposable membrane ticket. Such a device is easier to use, particularly in the field, than the use of a disposable test device or large volume concentration device. Utilization of membrane tickets significantly reduces the need for additional reaction reagents thus resulting in a more accurate and mobile test system. The membrane ticket also allows for the processing of iquid and air samples directly on the membrane. Virtually all of the elements of the invention are essentially self contained in the disposable membrane ticket. 
     The membrane ticket preferably comprises a hinged two sided plastic, cardboard, or paper support having a top and bottom section, and an absorbent pad or disk positioned on top of the inner side of the top section. On top of the absorbent disk is a glass filter membrane, which may be held in place by a plastic or paper rigid layer. 
     The bottom section of the membrane ticket preferably comprises a transparent window to which is affixed a semitransparent membrane (when wet) with immobilized luciferin-luciferase. 
     Various buffers for extracting antigens and washing immune complexes are well known to those skilled in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the collection apparatus means comprising a shaft, absorbent tip, and a container with fluid; 
     FIG. 2 is an angular side view of the collection apparatus means comprising a sponge and a bag with fluid; 
     FIG. 3 is a frontal view of a large volume concentrating apparatus; 
     FIG. 4 is an exploded perspective view of a large volume concentrating apparatus; 
     FIG. 5 is a cross-sectional side view of a negative pressure apparatus; 
     FIG. 6 is an exploded perspective drawing of a positive pressure apparatus, disposable test device and holder with absorbent disk; 
     FIG. 7 is a drawing of the disposable test device, its respective positioning into the complementary draw slide and the relationship to the photosensor means; 
     FIG. 8 is a graph of the total plate count obtained after 48 hours of incubation and the relative light units obtained from the 5 minute bioluminescent procedure outlined in the preferred embodiment with each data point representing a single beef carcass; 
     FIG. 9 is a cross section side view of the membrane ticket; 
     FIG. 10 is an angular overhead view of the membrane ticket; and 
     FIG. 11 is a cross-sectional view of te membrane ticket positioned over the photomultiplier. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a drawing of a collection apparatus means comprised of a shaft 1 and absorbent tip 2. The absorbent tip 2 is wetted with an excess of collection fluid 3 and used to wipe a circumscribed area of a surface to be monitored. After wiping the area, the absorbent tip 2 is placed into a container 4 and agitated to release any of the absorbed bacteria into the collection fluid 3. 
     As shown in FIG. 2 the collection apparatus means may be comprised of a sponge 5. The sponge 5 is wetted with collection fluid 3 and used to wipe a circumscribed area of a to be monitored. After wiping the area, the sponge 5 is placed into a plastic bag 6 containing excess fluid and squeezed several times to release any of the absorbed bacteria into the collection fluid 3. The volume of collectate fluid can vary depending upon the size of the absorbent and area wiped. The collection fluid 3 is selected to ensure transfer of the microbial contaminants from the test surface to the collection device and then to a disposable test device. Generally the ph of the collection fluid 3 is between 5 and 8, but preferably between 6.0 and 7.0 and contains salts such as sodium chloride between 0.1M and 0.3M, preferably about 0.25M NaCl to ensure survival of bacteria. The collection fluid 3 should contain a detergent such as 0.05% Tween 20 to ensure that the bacteria are easily removed from the test surface and collection apparatus. 
     Referring to FIG. 3 is a drawing of a large volume concentrating apparatus 7, in which a quantity of collectate fluid can be collected into a disposable test device. An appropriate sized Luer-tipped syringe is attached to the inlet 8 of large volume concentrating apparatus 7 and then positive pressure applied to the syringe plunger causing the collectate fluid to flow out of the outlet 9. 
     Referring to FIG. 4 is an exploded perspective view of the large volume concentrating apparatus 7, the collectate fluid flows through the filter bottom 11 of the disposable test device 10 &#34;O&#34; rings 14 and 15 provide a leakproof seal. After completion of concentrating the collectate, upper compartment 13 is separated from the lower compartment 16 to expose the lip 12 of the disposable test device 10. The disposable test device is then manually removed from the lower compartment 16. 
     Referring to FIG. 5 is a negative pressure device 17 in which the bottom portion of the disposable test device is inserted into holes 18. Appropriate volume of wash or somatic cell lysing solutions can be added and a vacuum can be applied to outlet 19 to remove fluid from the disposable test device 10. 
     Referring to FIG. 6 is an expanded perspective drawing of a positive pressure apparatus 20 comprised of a plunger 19 and a barrel 21, a disposable test device 10, and device holder 25 comprised of an absorbent pad or disk 26 to absorb the fluid waste. The disposable test device is inserted into holder 24. An aliquot of collectate fluid (i.e. 50 to 100 μl) is added and an appropriate volume of wash or somatic cell lysing solutions can be added. The rubber seal 23 of the positive pressure device is positioned on top of the disposable test device 10. Applying pressure to plunger 19 forces air through barrel 20 and out through outlet 22 displacing the fluid which passes into the absorbent disk 26. Additional wash solution can be added and the process repeated. 
     Referring to FIG. 7 is a drawing of the disposable test device 10, its respective positioning 28 into the draw slide 27, and the relationship to the photosensor means 30. The body of the disposable test device 10 is comprised of optically clean molded plastic material, such as polystyrene, which is capable of nearly complete transmission of light within a 500-600 nm wavelength range. Fused to the lower surface of the device is a semipermeable membrane 11 which is characterized by its strength and lack of deformation under pressure, and a pore size distribution which insures surface retention of bacterial cells, while facilitating complete passage of any associated liquidphase during pressurization. This membrane must also have sufficient surface tension to retain the measurement solution even after wetting. 
     The draw slide is an integral part of a luminometer instrument. The draw slide is pulled out and the disposable test device is positioned into hole 28 so that a window to the translucent wall of the disposable test device is exposed to the photosensor means when the draw slide is returned to a complementary dark chamber of the luminometer. 
     In a general bacterial screen based on bioluminescence, after a microbial sample has been concentrated in the disposable test device, a bacteriolytic reagent is added to lyse the bacteria and free the ATP. An appropriate volume of luminescent substrate (i.e. luciferin-luciferase) is added to the disposable test device and the draw slide is returned to the dark chamber of the luminometer. Measurement of light emission is made by digitalizing or converting the electrical signal from the photosensor means to a number of relative light units. If the method is to be used to detect specific bacteria, a specific antibody conjugated to a chemiluminescent or enzyme probe is added. In the preferred embodiment, the antibody is placed in the disposable test device and allowed to react for 10 minutes. Additional wash steps may be performed by adding a wash solution and evacuating the wash solution. A luminescent substrate solution is then added. In the preferred embodiment such substrate consists of a mixture of hydrogen peroxide and luminol. The draw slide is returned to the dark chamber of the luminometer. Measurement of light emission is made by digitalizing or converting the electrical signal from the photosensor means to a number of relative light units. 
     In another embodiment of the invention, all of the chemicals and solutions (except for the somatic cell releasing agent)are in a disposable membrane ticket 100. As with the systems described above, all systems and procedures described below involve the detection and quantification of bacteria in samples which may also contain somatic cells, free ATP, and constituents such as chloride ions which are known to inhibit the luciferin-luciferase enzyme reaction. 
     The membrane ticket 100 preferably comprises a hinged two sided plastic, cardboard, or paper support 101 having a top section 102 and bottom section 103. An absorbent pad 104 is positioned on top of the inner side 105 of the top section 104. The absorbent pad 104 is comprised of a material made of cellulose. The material may be cotton, corn silk, possibly fiberglass, or other absorbent material. On top of absorbent disk 104 is a glass filter membrane 106, which may be held in place by a plastic or paper rigid layer 107. 
     The bottom section 103 of the membrane ticket 100 preferably comprises a transparent window 108 on the outer side 109 of the bottom section, and a luciferin-luciferase solution immobilized on the membrane disk 111. The membrane disk fits in a hole 113 in the bottom section 103 of the ticket 100. 
     To form the membrane ticket 100 with the luciferin-luciferase immobilized on the membrane , it is important to prepare a luciferin-luciferase buffer solution. One of many possible cocktails is described as follows: The buffer solution is comprised of 1% trehalose, 0.05M dithiothreitol (DTT), and 0.025M HEPES Buffer. The quantity required of each designated raw material in this cocktail is calculated by multiplying the quantity to be made by the required weight (g) or volume per ml. The following formulae may be followed: ##EQU1## 
     The amount of water equivalent to 90% of the quantity of buffer solution to be made is determined by the formula: ##EQU2## 
     The water is measured poured into a suitable container comprising a stirring bar. Each of the above mentioned buffer materials is added to the water and stirred until dissolution is complete. While continuing to stir, the ph of the solution is adjusted with 0.1N NaOH to 7.8±0.01. An amount of processed water is added to the solution to bring the final volume to the desired amount. The luciferin Luciferase Spotting Reconstitution Buffer is passed through a 0.22μ membrane filter and, in a clean environment, collected in an autoclaved or other pre-sterilized screw cap container. 
     The required amount of luciferin-luciferase is then removed from the freezer and allowed to stand at room temperature for approximately 30 minutes. Working in a clean environment, the luciferin-luciferase is reconstituted in the Reconstitution Buffer 3.3 mol to a 5 ml. bottle or 10 ml for a 15 ml bottle of freeze dried material. The mixture is swirled gently, and allowed to equilibrate for approximately one hour. The reconstituted luciferin luciferase is filtered through a sterile 0.2μ syringe filter into sterile 12×75 tubes. The tip of a micropipette is dipped into methanol and the chamber of the micropipette is filled with Methanol. The methanol is expelled into a waste container and the chamber is rinsed with processed water in the same manner several times. The micropipette is filled with the luciferin-luciferase solution a number of times, preferably four, to clean the tip, and the pipetted solution is dispensed. 
     Each absorbent membrane or membrane disk 111 is then spotted with 10 μl of luciferin luciferase buffer until the desired number of disks have been spotted. 
     The spotted membrane disks 111, having been spotted in a suitable container, are then placed, while still in the container, into a -40° C. freezer for at least 45 minutes. The disks are then removed from the freezer and are lyophilized overnight (or for about at least 8 hours). The membrane disks 111 may be lyophilized while still in the containers, or removed from the containers during lyophilization. Once the spotted membrane disks 111 have been lyophilized, the containers containing the membrane disks 111 are stored in a container filled with desiccant. The membrane disks 111 should be stored in a refrigerator, being kept at about 4° C. 
     In another embodiment of the invention, somatic or bacterial cell releasing agent may be incorporated into the glass membrane 106 in much the same manner as the luciferin-luciferase solution is incorporated in to the membrane disks 111. 
     In assembling the ticket membrane 100 the assembler should take steps to avoid contamination of the membrane and the disks. Similarly, all work should be conducted in a clean environment. 
     The clean folded membrane tickets 100, are with the exception of the transparent window 108, manufactured by conventional means. 
     In a clean environment, and incorporating an adhesive tape to the bottom side of the plastic ticket, the membrane disk 111 is applied to the ticket 100 such that the membrane disk 111 is centered on the hole 113. 
     To use the membrane ticket 100, a sample volume of 25 μl, collected by normal means, is applied through a hole 110 in the rigid layer 107 onto the surface of the glass filter membrane 106. The glass filter membrane 106 retains bacterial and somatic cells on the surface of the glass filter membrane 106 while fluids pass into the absorbent disk 104. 
     Somatic cell releasing agent is then added onto the surface of the glass filter membrane 106. The somatic cell releasing agent is added dropwise onto the surface of the glass membrane 106 so as to avoid flooding the membrane ticket and washing the cells out of the glass filter membrane 106. 
     After the addition of the somatic cell releasing agent, the somatic cells have lysed and the released ATP from the somatic cells, along with free ATP and inhibitory materials which could have contaminated the results, are trapped in the absorbent pad. At this stage only bacterial cells are left intact on the surface of the glass filter membrane disk 106. In another alternative approach, somatic releasing reagent may be placed onto the swab used to streak the surface area being tested. 
     Next, 10 μl of bacterial releasing agent are applied, to the glass filter membrane 106, or the surface of a membrane 111 positioned on the inner side 112 of the bottom section 103 of the membrane ticket 100. The membrane 111 contains immobilized luciferin-luciferase. The luciferin-luciferase may be either saturated throughout the membrane 111, or found at the surface of the membrane 111. 
     The top section 102 and bottom section of 103 of the membrane ticket 100 are then compressed together, preferably upon the insertion of the disposable membrane ticket into the draw slide of the luminometer, and as the draw slide of the luminometer is pushed into the luminometer. As the top section 102 and bottom section 103 of the membrane ticket 100 make contact, the light producing reaction: ##STR1## is initiated. 
     This results in RLU&#39;s over a ten second integration period, which corresponds with the bacterial content of the sample. 
     As shown in FIG. 11, the membrane ticket 100 is preferably placed in the draw slide 200 of the luminometer with the luciferin-luciferase membrane face down, directly over a reading hole 201. The photomultiplier tube 30 is positioned directly under the hole 201. 
     This method may be used not just for the testing of surfaces, but also for the testing of fluids of all kinds, including air and liquids. 
     The invention is further illustrated by means of the following examples. 
     EXAMPLE 1 
     General Bacterial Screen on Hard Surfaces. 
     This example involves a procedure for testing a stainless steel surface for the presence of microbial contamination. 
     Escherichi coli were grown on tryptic soy agar for 18 hours at 30° C. A sample of the bacteria was introduced into 10 mls of peptic soy broth and incubated for an additional 18 hours. Bacteria were harvested by centrifugation and washed three times in 0.9% NaCl that had been sterile filtered. The optical density of the solution was measured at 650 nm and the concentration was adjusted so that the optical density was 0.300. Three serial 10-fold dilutions were prepared to arrive at a concentration of 10 5  microbes/ml. 100 μl of this solution was dribbled over an area of 10×10 cm demarcated on the surface of a stainless steel sheet that had been previously cleaned with bleach, alcohol and sterile distilled water. The solution containing the bacteria was allowed to dry for 5 hours at room temperature. Control demarcated areas were prepared with no bacteria. 
     Individual sponges of 10×10 cm were premoistened with approximately 750 μl of a collection fluid comprised of 0.15M NaCl containing 0.05% Tween 20 in a bag. This solution was just sufficient to completely wet the sponge. Each sponge was removed from a bag and wiped over demarcated areas of the surface with 10 strokes in each direction. The sponge was then returned to the bag and squeezed manually ten times yielding a collectate. An aliquot (25 μl) of the collectate was removed from the bag and placed in a disposable test device. 25 μl of bacterial releasing agent was added and 50 μl of a luciferin/luciferase/magnesium mixture was added. The draw slide was closed and the relative light units determined. 
     In a second set of experiments, swabs were premoistened with approximately 300 μl of collection fluid in a bag as outlined above. The swabs were used to wipe similarly demarcated areas of a stainless steel surface as described above. 
     In each case, control areas which had not had bacteria seeded on the surface were also tested. In addition, the bacterial solution that had been seeded onto the surface was placed directly into the collection fluid as a positive control Each data point represents the average of three samplings. Referring to Table 1, approximately 80% of seeded bacteria could be detected using either a sponge or a swab as a collection means. 
     
                       TABLE 1______________________________________             Positive  Negative   Control    Sample from                                 %  Control Surface             Direct Seeding                        Seeded Surface                                 RecoveryCollection  (Relative  (Relative  (Relative                                 of SeededDevice Light Units)             Light Units)                        Light Units)                                 Bacteria______________________________________Sponge 0          115         88      79%Swab   0          330        272      82%______________________________________ 
    
     EXAMPLE 2 
     General Bacterial Screen on Carcasses 
     This example involves a procedure for testing the surface of beef, pork, and poultry carcasses in a slaughterhouse for the presence of microbial contamination. 
     Testing of beef carcasses was performed in the slaughterhouse environment. Carcasses were sampled immediately before washing (after trimming) and after the final wash. A test area on the carcass was sectioned off with either a stainless steel template defining an area of 500 cm 2  or an area of that size was marked with edible ink. Random sites on the carcass were chosen for sampling. 
     Samples were taken with disposable sponges prepackaged in sterile bags. The sponges were premoistened by incubation with 25 ml of collection solution containing 0.085% NaCl with 0.05% Tween 20, pH 7.2. Before sampling, the excess collection fluid is mechanically expressed from the sponge. The marked area was sampled by wiping the sponge over the area approximately 15 times in both the horizontal and the vertical directions. The sponge was returned to the bag and mechanically agitated using a stomacher apparatus for two minutes. 
     50 μl of the sample was removed from the collection fluid and added to a disposable test device. 100 μl of wash solution comprising 0.05% saponin in 0.1M Hepes buffer, pH 7.75 was added. Using a positive pressure device, the fluidphase in the disposable test device was passed through the membrane onto a pad of paper towels. An additional 150 μl of wash solution was added and using positive pressure was passed through the membrane of the device onto a pad of paper towels. The disposable test device was placed into the drawslide of a luminometer and 30 μl of bacterial releasing reagent consisting of 0.1M benzyl sodium chloride in Hepes buffer, pH 7.75 were added followed by addition of 30 μl of luciferin/luciferase/magnesium solution. The draw slide of the luminometer was closed and the light emission was read. The entire procedure required under 5 minutes to perform per sample. The results were expressed in relative light units. An aliquot of the collectate was also treated in the conventional manner of streaking the material on tryptic soy agar plates and incubating the plates for 40 hours at 30° C. after which total plate counts were determined by an automated colony plate counter. 
     FIG. 8 shows the relative correlation between the plate counts determined by an automated plate counter compared with the relative light units for samples from 160 carcasses sampled at two sites. Each value is expressed as its arithmetic log. Similar data was collected for 400 carcasses at each of two sites. For this data, the correlation coefficient between the log of the relative units (log mATP) and the log of the aerobic plate counts (log APC) was 0.92. 
     Similar in-plant studies were performed on 320 pork carcasses taken in three commercial plants. The correlation coefficient between log mATP and log APC was 0.92. 
     Comparative mATP and APC data were obtained on 330 poultry samples from two commercial poultry plants at four locations in the plant: post-pick, post evisceration, post-final wash, and post chill. The correlation between log mATP and log APC was 0.85. 
     EXAMPLE 3 
     Chemiluminescent Salmonella Assays 
     This example involves a procedure for testing for the presence of salmonella. 
     Bacteria, either Salmonella typhimurium, ATCC 14028 or Aeromonas hydrophila, ATCC 7966, were streaked from frozen stocks onto tryptic soy agar plates and incubated for 18 hours at 26° C. Bacterial colonies were harvested into sterile 0.9% NaCl. The optical density of the solution was measured at 650 nm and the concentration was adjusted so that the optical density was 0.300 by diluting the bacteria in 0.05M Tris, 0.05M EDTA, 0.15M NaCl, pH 8.2. 
     An aliquot (10 μl) of a 0.5% solution of latex microspheres coated with antibodyto salmonella was added to the disposable test device. An aliquot, 100 μl, of the diluted bacteria were placed in a disposable test device with a filter on the bottom surface composed of 1.2 micron Biodyne C. After the aliquot of the bacteria was added the solution was allowed to sit for 10 minutes. 
     Positive pressure was applied and the fluid was evacuated onto an absorbent pad. The trapped antigens were washed by adding 200 μl of wash solution consisting of 0.01M PBS, pH 7.2 containing 0.05% Tween 20. Positive pressure was again applied and the fluid was evacuated onto an absorbent disk. A horseradish peroxidase labeled antibody directed against Salmonella was added to the disposable test device and allowed to sit for 10 minutes at room temperature. Positive pressure was again applied and the fluid evacuated from the disposable test device. A wash solution was added and evacuated with positive pressure two more times. The disposable test device was placed in a luminometer. 100 μl of Lumiglo Chemiluminescent substrate (Kirkegaard and Perry Laboratory, Gaithersburg, Md.) was added, the drawer slide was immediately closed and the light emission determined. 
     The results shown in Table 2 indicate that the concentrations as low as 10 5  organisms could be easily distinguished from a negative control using this system. 
     
                       TABLE 2______________________________________Results of a Test for Salmonella    Relative Light                 Relative Light    Units for    Units forTotal Number    Salmonella   Aeromonas  Signal toof Organisms    typhimurium  hydrophila Noise Ratio______________________________________10.sup.8 18,940       5,290      3.610.sup.7 13,780                  2.610.sup.6 10,720                  2.010.sup.5  9,220                  1.7______________________________________ 
    
     A second procedure was used similar to that detailed above, except that no latex beads were added to the disposable test device prior to the introduction of the aliguot of the bacteria. In this case, the signal to noise ration for a solution of S. typhimurium (10 8  organisms): A. hydrophila (10 8  organisms) was 5.91. 
     A third procedure was also tested. In this method, 40 μl of sample, and 40 μl of horseradish peroxidase labeled anti-salmonella antibody were added to a disposable test device. The mixture was incubated for 20 minutes at room temperature. Positive pressure was used to evacuate the fluid from the test device. The trapped material was washed three times by introduction of 200 μl of 0.01M phosphate buffered saline pH 7.2 containing 0.05% Tween 20 followed by evacuation of the fluid from the disposable test device using positive pressure. The disposable test device was placed in the luminometer and 100 μl of Lumiglo Chemiluminescent substrate (Kirkegarrd and Perry Laboratories, Gaithersburg, Md.) was added. The drawslide was immediately closed, and the light emission determined. The signal to noise ratio for a solution of S. typhimurium (10 6  organisms): A hydrophila (10 6  organisms) was 1.83. 
     All of the above examples and tests can be performed using the ticket membrane version of the device. 
     Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood within the scope of the appended claims the invention may be protected otherwise than as specifically described.