Abstract:
Described herein are methods and apparatus for rapid detection of microorganisms in biological samples (e.g. blood) for analysis to determine the presence or absence of infectious microorganisms in the samples. The apparatus includes a cartridge with a lid and a tray, a mechanism for isolating a bulk sample into multiple smaller samples, and a sensor disposed on the tray to determine the presence or absence of microorganisms. The cartridge lid includes projections that, in a first position, allow for sample to distribute evenly in the cartridge tray and, in a second position, isolate the sample into multiple smaller volume samples. The apparatus and method shorten the time-to-detection of a microorganism in a sample and reduce the steps required from sample collection to microorganism detection.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Sepsis is a significant healthcare issue due to its high frequency of occurrence and high mortality rate in hospitals. Sepsis is characterized by a whole-body inflammatory state, called a systemic inflammatory response (SIRS), and by the presence of a known or suspected infection. The immune system may cause this inflammatory response as a consequence of microbes in the blood, urine, lungs, skin, or other tissues, for example. One of the leading causes of sepsis is a bloodstream infection (BSI). BSI is most commonly diagnosed by a blood culture, in which a sample of blood is incubated with a medium in an atmosphere controlled to promote bacterial growth. 
         [0002]    Current automated blood culture systems can take 12-48 hours to detect the presence of infectious microorganisms in blood and can take up to 5 days to rule out the presence of any infectious microorganisms. It can take up to another 12-48 hours to identify the infectious microorganisms by sub-culturing the positive blood culture and performing identification and antimicrobial susceptibility tests. These results can be too late to alter the treatment course and result in the death of the patient. 
         [0003]    One approach to faster bacterial time to detection (“TTD”) is dividing the sample liquid together with growth media into a large number of smaller volume samples that are contained in closed small volume compartments (see U.S. Pat. Nos. 5,770,440 and 5,891,739 to Berndt, the entire contents of which are both hereby incorporated by reference herein). The added steps required to segregate the blood/media sample into smaller volume samples can be difficult and time consuming. Additionally, designing a product to address this increased workflow can be limited by considerations of manufacturability and cost. Consequently, a small-volume compartment BSI product design that is easy to manufacture, cost effective, less time-consuming to use and reduces TTD in a clinical sample is desired. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    Described herein are methods and apparatus for rapid detection of microorganisms in biological samples (e.g. blood) for analysis to determine the presence or absence of infectious microorganisms in the samples. The apparatus includes a cartridge with a lid and a tray, a mechanism for isolating a bulk sample into multiple smaller samples, and a sensor disposed on the tray to determine the presence or absence of microorganisms. 
         [0005]    According to the methods described herein, the cartridge lid is assembled onto the cartridge tray in a first position, the sample introduced into the cartridge tray and allowed to distribute across the volume of the cartridge tray, and the cartridge lid is moved into a second position creating a plurality of compartments isolating the bulk sample into multiple samples of a smaller volume. The method and apparatus allow for, inter alia, a reduced time-to-detection for microorganisms in a biological sample and obviates the need to manually dispense a sample into individual compartments of a detection device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  shows a perspective view of one embodiment of a portion of a top and bottom lid portion of a cartridge lid. 
           [0007]      FIG. 2  shows a perspective view of the top and bottom lid portions of  FIG. 1  assembled together. 
           [0008]      FIG. 3  shows a perspective view of a portion of a cartridge tray. 
           [0009]      FIG. 4  shows a perspective view of the cartridge lid assembly of  FIG. 2  mated to the cartridge tray of  FIG. 3  in a first position. 
           [0010]      FIG. 5  shows a perspective view of the cartridge lid assembly of  FIG. 2  mated to the cartridge tray of  FIG. 3  in a second position. 
           [0011]      FIG. 6  shows a perspective view of the entire top portion of the cartridge lid shown in  FIG. 1 . 
           [0012]      FIG. 7  shows a perspective view of the entire bottom portion of the cartridge lid shown in  FIG. 1 . 
           [0013]      FIG. 8  shows a perspective phantom view of the top and bottom portions of the cartridge lid shown in  FIGS. 6 and 7  prior to assembly. 
           [0014]      FIG. 9  shows a perspective phantom view of the top and bottom portions of the cartridge lid shown in  FIG. 8  assembled. 
           [0015]      FIG. 10  shows a perspective view of the entire cartridge tray shown in  FIG. 3 . 
           [0016]      FIG. 11  shows a side plan view of the cartridge lid assembly and cartridge tray shown in  FIG. 8  prior to assembly. 
           [0017]      FIG. 12  shows a side plan view of the cartridge lid and cartridge tray assembled in a first position, with an enlarged view of mating features. 
           [0018]      FIG. 13  shows the steps of collecting a blood sample. 
           [0019]      FIG. 14  shows a side view of a sample being introduced into the cartridge lid and tray in the first position. 
           [0020]      FIG. 15  shows a side view of the cartridge lid and tray transitioning from a first position to a second position. 
           [0021]      FIGS. 16A-B  show air escaping the cartridge tray during the transition from the first position to the second position. 
           [0022]      FIG. 17  shows a schematic view of the cartridge undergoing bacterial detection. 
           [0023]      FIG. 18  shows a top plan view of an alternate embodiment of the cartridge lid assembly shown in  FIG. 9  with enlarged views of individual compartments. 
           [0024]      FIG. 19  shows a side plan view of an alternate embodiment of the cartridge lid and cartridge tray of  FIG. 13  assembled in a first position. 
           [0025]      FIG. 20  shows a side plan view of the cartridge lid and cartridge tray of  FIG. 20  filled with sample and oil. 
           [0026]      FIG. 21A  shows a top plan view of an alternate embodiment of a cartridge lid and tray in a first position. 
           [0027]      FIG. 21B  shows a top plan view of the cartridge lid and tray of  FIG. 21A  in a second position. 
           [0028]      FIG. 22A  shows a top plan view of an alternate embodiment of a cartridge lid and tray in a first position. 
           [0029]      FIG. 22B  shows a top plan view of an alternate embodiment of a cartridge lid and tray in a first position. 
           [0030]      FIG. 23  shows a perspective phantom view of a bacterial detection cartridge with portions omitted according to one embodiment of the invention. 
           [0031]      FIG. 24  shows a sectional view of the cartridge of  FIG. 23  along a diameter of the cartridge. 
           [0032]      FIGS. 25A-B  show a sectional view of the cartridge of  FIG. 23  during and after sample introduction, respectively. 
           [0033]      FIG. 26A  shows a sectional view of the filled cartridge of  FIG. 25B  in a second position. 
           [0034]      FIG. 26B  shows the filled cartridge of  FIG. 26A  after vents are sealed. 
           [0035]      FIG. 27  shows two cartridges of the type illustrated in  FIG. 24  in a stacked configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Referring generally to  FIGS. 1-5 , a bacterial detection cartridge  10  according to an embodiment of the invention generally includes a cartridge lid assembly  16  and a cartridge tray  18 . The cartridge lid assembly  16  is composed of a top lid portion  12  and a bottom lid portion  14  which can be made separately, for example via injection-molding, and snapped together to form the cartridge lid assembly  16 . The cartridge lid assembly  16  is then positioned onto the cartridge tray  18  in an elevated first position ( FIG. 4 ). The cartridge lid assembly  16  can then be pushed down to lock the bacterial detection cartridge  10  into a second position ( FIG. 5 ) after sample  66  ( FIG. 16 ) has been introduced into the cartridge tray  18  through a sample injection port  20  ( FIG. 1 ) defined in top lid portion  12 . In one embodiment, the bacterial detection cartridge  10  containing the sample  66  is made ready for sample incubation. All compartments  24  are configured to allow for sample removal when the tray is in the second position. Therefore, any compartment  24  with sample  66  for which a positive detection result was obtained can be accessed for sample removal for further analyses. 
         [0037]    Referring generally to  FIGS. 1-2 , the cartridge lid assembly  16  includes a top lid portion  12  and a bottom lid portion  14 . The top lid portion  12  includes multiple top lid access apertures  22  positioned near the center of each compartment  24  of the bottom lid portion  14 . The top lid access apertures  22  allow a pipette, syringe or other device to access the sample  66  within a selected compartment  24 . The top lid access apertures  22  are integrated into the top lid  12  as thin circular areas. A sample injection port  20  is formed in the top lid portion  12  to allow a sample  66  to be introduced into the cartridge tray  18 . The port is configured to allow sample introduction into the lid assembly via a syringe or other sample introduction device. A separate re-sealable pressure escaping outlet  42  is also built onto the top lid portion  12  (shown in  FIGS. 6-12 ). 
         [0038]    The bottom lid portion  14  defines the compartments  24  in cooperation with the cartridge tray  18 . Specifically, each compartment  24  is defined by four downward projecting side-wall portions  24   a - d  in the bottom lid portion  14 , the top wall  24   e  of the bottom lid portion  14 , and the cartridge tray  18 . In other words, the bottom lid defines a grid of compartments  24  except for the bottom surface of the compartments, which is defined by the cartridge tray  18 . The bottom lid portion  14  also includes multiple bottom lid access apertures  26  positioned in the illustrated embodiment near the center of each compartment  24  and aligned with a corresponding top lid aperture  22 . The alignment of the top lid access apertures  22  with the bottom lid access apertures  26  permit an access device, such as a pipette or syringe, to penetrate through both the top lid portion  12  and bottom lid portion  14  to access the compartment  24  underneath. Also included on the bottom lid portion  14  are vents  28  for each compartment  24 . The vents  28  align with the seal rods  30  on the cartridge tray  18 . 
         [0039]    The top lid access apertures  22  can be covered with a pressure sensitive adhesive foil  72  (shown in  FIG. 18 ) to isolate the interior of the bacterial detection cartridge  10  from the environment. In use, after an access device penetrates the top and bottom lid portions  12 ,  14  to access the compartment  24 , the top lid access apertures  22  may be re-sealed, for example with an additional layer of pressure sensitive adhesive foil  72 , to again isolate the interior of the cartridge  10  from the environment to provide for safe handling, including disposal and/or autoclaving. In addition to reducing chances of contamination, providing a seal keeps sample components within the compartment  24 . For example, without a seal, CO 2  could escape from the compartment  24 , causing the sensor  36  (described below) to report inaccurate results of bacterial metabolism. Similarly, the bottom lid access apertures  26  may initially be sealed by a material, such as a pressure sensitive adhesive foil (not illustrated). A seal on the bottom lid access apertures  26  isolates the contents of a particular compartment  24  from the headspace between the top lid portion  12  and bottom lid portion  14  when the cartridge lid assembly  16  is in the second position, described more fully below. 
         [0040]    Referring generally to  FIGS. 3-5 , the cartridge tray  18  is a tray with seal rods  30  and an interior open vessel  32  built on the surface. The vessel  32  is configured to receive reagents such as resin gel pellets  34 . The seal rods  30  function to guide the cartridge lid assembly  16  on to the cartridge tray  18 , and serve to seal the vents  28  of the compartments  24  when the cartridge lid assembly  16  is moved from the first position to the second position. In one embodiment, the vessel is a raised rim on the surface of the cartridge tray  18 . In other embodiments, the resin gel pellets  34  can be applied directly to the cartridge tray without the use of vessels  32 . The exact location and the number of the vessels  32  and seal rods  30  are determined by the arrangement of the compartments  24  on the bottom lid portion  14  and is largely a matter of design choice. The cartridge tray  18 , top lid portion  12 , and bottom lid portion  14  can be made of various materials, such as clear polypropylene or similar optically clear plastic resins such as, but not limited to, polycarbonate, cyclic olefin polymer, and polystyrene. Although it is preferred that the top lid portion  12  and bottom lid portion  14  are a transparent material, other non-transparent materials are contemplated for use in the assembly described herein. 
         [0041]    In one embodiment, the cartridge tray  18  is preloaded with biosensor coating  36  on the bottom surface  37  outside the area of the interior open vessels  32 . Although a biosensor coating  36  is preferred for the sensor, other sensors known in the art can be used without deviating from the scope of the invention. The sensor  36  can detect, for example, O 2  and/or CO 2  changes collectively or independently (see U.S. Pat. No. 6,989,246 to Yeh, the entire contents of which are hereby incorporated by reference herein). Antimicrobial adsorption resin gel pellets  34  are dispensed inside the interior open vessels  32 . The resin gel pellet is made of, for example, antimicrobial adsorption resins mixed with water-soluble materials for ease of dispensing and resin release capability in aqueous environment. Such resins are known in the art. For example, U.S. Pat. No. 5,624,814 to Waters et al. describes resins added to culture media to isolate microorganisms from substances that have the potential to inhibit the growth of the microorganisms. Other references that contemplate combining a resin with a biological sample to remove growth inhibitors from a biological sample suspected of containing a target microorganism include U.S. Pat. Nos. 4,145,304 and 4,174,277, both to Melnick et al. The entire contents of these references are each hereby incorporated by reference herein. 
         [0042]    Referring to  FIGS. 6 and 7 , the top lid portion  12  and bottom lid portion  14  also include snap post apertures  38  and snap posts  40 , respectively, to allow the top lid portion to snap into the bottom lid portion  14  to form the cartridge lid assembly  16 , as illustrated in  FIG. 2 . 
         [0043]    As noted previously, once the cartridge lid assembly is positioned onto the cartridge tray  18  in the second position, a grid of segregated compartments  24  is formed. Vents  28  and pressure escaping outlet  42  maintain desired compartment conditions during the sample injection process and “push-down” action of the cartridge lid assembly  16  onto the cartridge tray  18 . Vents  28  allow the pressure among the compartments to equilibrate. Pressure escaping outlet  42  is configured to allow the bacterial detection cartridge  10  to vent if pressure builds up above a predetermined threshold. 
         [0044]    The seal rods  30  on the cartridge tray  18  are located such that each compartment  24  is adjacent to at least one seal rod  30 . The seal rod  30  in each compartment  24  aligns with the vent  28  of the bottom lid portion  14 . The seal rod  30  has a diameter that permits the seal rod  30  to fit within the vent  28 . The length of the seal rod  30  is such that, when the cartridge lid assembly  16  is in the second position, the seal rod  30  on the cartridge tray  18  seals the vent  28 . This is illustrated in  FIGS. 16A-B . The pressure escaping outlet  42  on the top lid portion  12  is kept open during sample injection and pushdown operation. Note that pressure escaping outlet  42  in top lid portion  12  overlies opening  43  in bottom lid portion  14  to permit pressure release through the bottom lid portion  14 . Pressure escaping outlet  42  is then re-sealed for incubation of the loaded bacterial detection cartridge  10 . This may be accomplished, for example, with the use of a re-sealable foil  45 . 
         [0045]    Referring generally to  FIGS. 6-10 , various aspects of the bacterial detection cartridge  10  in accordance with an embodiment of the invention are illustrated including top lid portion  12 , bottom lid portion  14 , of the cartridge lid assembly  16 , and cartridge tray  18 . 
         [0046]    As illustrated in  FIGS. 6-9 , the sample injection port  20  comprises a sample injection aperture  19  in the top lid portion  12  that aligns with a septum  21 . The septum  21  sits in a septum compartment  23  formed in the bottom lid portion  14 . 
         [0047]    Other features illustrated in  FIGS. 6-10  that are not illustrated in  FIGS. 1-5  include the pressure escaping outlet  42  previously described, raised block  44 , and raised inlet sample distributor  46 . As described above, the pressure escaping outlet  42  allows for pressure equalization during sample introduction and as the cartridge lid assembly  16  is moved from the first position to the second position. The bottom lid portion  14  also contains an open portion  43  that aligns with the pressure escaping outlet  42  in the top lid portion  12  to allow for pressure to escape from the bacterial detection cartridge  10  through pressure outlet  42 . The pressure escaping outlet  42 ,  43  is kept open as the cartridge lid assembly  16  is pushed down into the first and second positions on the cartridge tray  18 . Once in the second position, the pressure escaping outlet  42  is re-sealed. The raised block  44  aligns with the pressure escaping outlets  42 ,  43 . The raised block  44  prevents sample from flowing into the area occupied by the raised block. If there were sample  66 , resin gel  34  and sensor  36  in a compartment  24  instead of the raised block  44 , the entire sample  66  in the compartment  24  beneath the pressure escaping outlet  42 ,  43  would be exposed to the entire headspace between the top lid portion  12  and bottom lid portion  14  because of open portion  43 . This headspace could hinder bacterial detection, so the raised block  44  is preferred. 
         [0048]    The cartridge tray  18  also contains a raised inlet sample distributor  46 . The raised inlet sample distributor  46  is in fluid communication with the sample injection port  20 . As sample  66  is introduced by a syringe or other device, the sample  66  flows across the surface of the inlet sample distributor  46  in all directions into the cartridge tray  18 . This ensures more uniform sample distribution in the cartridge assembly as it fills with sample 
         [0049]    Referring generally to  FIGS. 11-18 , the steps by which the bacterial detection cartridge  10  according to an embodiment of the invention is assembled and filled are illustrated. The bacterial detection cartridge  10  is illustrated in side and side perspective views in these figures. The first step is to snap the top lid portion  12  into the bottom lid portion  14  to form the cartridge lid assembly  16 . The cartridge tray  18  is also prepared by inserting resin gel  34  into the vessels  32  of the tray cartridge and further by depositing the biosensor coating  36  on the surfaces previously described. The assembly steps may be completed by the manufacturer, rather than the end user. In such embodiments, the user begins with a pre-assembled cartridge lid  16  and cartridge tray  18 . Assembly by a manufacturer is preferred as the bacterial detection cartridge  10  is preferably sterilized and in the first position when provided to a user. 
         [0050]    The user then assembles the bacterial detection cartridge  10  into its first position, as shown in  FIG. 12 , by pressing down the cartridge lid assembly  16  partially onto the cartridge tray  18 . As mentioned above, this step is preferably performed by a manufacturer so that the components are sterilized and in the first position when provided to the user, but user assembly is still within the scope of the invention. The cartridge lid assembly  16  and cartridge tray each include features to lock them together. Failure to lock indicates that the cartridge lid assembly  16  and cartridge tray  18  are not in proper engagement. The locking features may include multiple locking features, such as protrusions and corresponding recesses, such that the cartridge lid assembly  16  and the cartridge tray  18  can lock in multiple discrete stages. Locking features may be, for example, sawteeth  47  on the cartridge lid assembly  16  and notches  48  on the cartridge tray  18 . The sawteeth  47  and notches  48  are configured in the illustrated embodiment to allow the cartridge lid assembly  16  to engage and lock on the cartridge tray  18  in the first and second positions. The sawteeth  47  initially snap in to the notches  48  in the first position, after which the cartridge lid assembly  16  can be further advanced to snap the sawteeth  47  into an additional set of notches  48  to move the bacterial detection cartridge  10  into the second position. 
         [0051]    Sample preparation is illustrated in  FIG. 13 . The sample  66  may be collected, for example, directly from the patient into syringe  50  or similar device pre-filled with growth media  56  and under a partial vacuum balanced with nitrogen or other preferred gas compositions for storage stability. In one embodiment, the syringe  50  can contain oil, described more fully below. A traditional butterfly needle  52  can be used with a first end located at the sample source in the patient  54  (e.g. in a vein) and with a second end connected to a needle in the syringe  50 . A plunger  58  and needle  60  are then connected to the syringe  50  for injecting the sample  66  into the bacterial detection cartridge  10 . The collection step may alternatively include multiple steps, wherein the sample is first collected from the patient, undergoes some sort of pre-processing, and is then introduced into the bacterial detection cartridge  10  via the collection tube. The sample  66  is not limited to blood, and can be any other biological sample such as spinal fluid, urine, saliva, etc. 
         [0052]    When the bacterial detection cartridge  10  is in the first position, the spacing between the bottom lid portion  14  and the cartridge tray  18  is such that sample  66  will flow across the cartridge tray  18  and relatively uniformly fill a portion of each compartment  24  as illustrated in  FIG. 15 . Sample  66  will not flow into the region occupied by raised block  44 . The user pierces the septum  21  in the sample injection port  20  with the needle  60  on the syringe  50 , and depresses the plunger  58  to inject the sample  66  into the bacterial detection cartridge  10 . Because the bacterial detection cartridge  10  is in the first position, the sample  66  can flow freely across the bottom of cartridge tray  18 , with uniform distribution of sample being assisted by the raised inlet sample distribution guide  46 , as shown in  FIG. 14 . During sample injection, the re-sealable foil  45  on the pressure escaping outlet  42  is in the open position, allowing for the pressure inside the bacterial detection cartridge  10  to equalize with the pressure outside the bacterial detection cartridge  10 . A cartridge and syringe docking station  62  may optionally be employed to provide additional stability to the bacterial detection cartridge  10  and to provide a guide for the syringe  50 . Automated robotic systems for providing sample to the compartments are contemplated. 
         [0053]    After the sample  66  is fully injected and after the sample volume has equilibrated among the compartments (the skilled person would appreciate that the “self-leveling” aspect of the distribution of sample within the tray is best achieved when the tray is in a level position), the user advances the cartridge lid assembly  16  on the cartridge tray  18  until the sawteeth  47  engage the next set of notches  48 , moving the bacterial detection cartridge  10  to the second position, as shown in  FIG. 15 . Although not specifically described herein, the assembly is easily configured to provide one or more intermediate positions. 
         [0054]    Referring to  FIGS. 16A-B , as the cartridge lid assembly  16  is advanced from the first position to the second position, the seal rods  30  advance further into the vents  28 , sealing them. Before the downward projecting walls  24   a - d  of the compartment  24  come into contact with the sensor  36  disposed on the cartridge tray  18  surface, air  64  escapes through the vent  28 . As the downward projecting walls  24   a - d  of the compartment  24  advance onto the sensor  36  on the cartridge tray  18 , the seal rods  30  simultaneously plug the vents  28 . Once the downward projecting walls  24   a - d  of the compartment  24  touch the cartridge tray  18 , the sample  66  is sealed into multiple compartments  24 . The re-sealable foil  45  is then re-sealed to isolate the sample inside the bacterial detection cartridge  10  from the environment. If desired, gaskets in the form of tapes can be used to seal between the cartridge lid assembly  16  and cartridge tray  18  to prevent potential leaks. 
         [0055]    Once the sample  66  is loaded into the bacterial detection cartridge  10  and sealed, the cartridge is placed into an incubator  70  to grow microorganisms in the sample. The sensor  36  detects growth, for example by detecting changes in concentration of O 2  and/or CO 2  from increased levels of bacterial metabolism, and reports each compartment  24  that tests positive for growth. As such detection techniques are well known in the art, they are not described in further detail herein. Ultrasound or similar mechanisms can be used to agitate the bacterial detection cartridge  10  during inoculation. 
         [0056]    As shown in the embodiment illustrated in  FIG. 18 , the compartments  24  of the bacterial detection cartridge  10  are arranged in a grid format, with each compartment including identifiers. For example, the compartments can include a row-identifying letter and column-identifying number (G 3 , G 4 , H 3 , H 4  etc.). Each compartment  24  that tests positive for bacterial growth by the incubator  70  is reported to the user. If any compartment  24  shows signs of bacterial growth, there is often a need for removal of the sample  66  from those compartments  24  for post-processing procedures such as identification or antibiotic susceptibility testing. The user identifies the specific compartment(s)  24  testing positive for bacterial growth, inserts a removal device such as a syringe or pipette into the desired compartment via the top and bottom lid access apertures  22 ,  26  respectively, piercing any adhesive foils or film  72  covering the apertures, and withdraws the positive sample  66 . The user then may perform desired post-processing of the positive sample to, for example, identify the bacteria in the blood sample  66 . One, some, or all of the above-mentioned steps may be automated. The bacterial detection cartridge  10  is not limited to a round dish, but can be other shapes including, but not limited to, oval or other polygons. 
         [0057]    An alternate embodiment of the bacterial detection cartridge  10  is shown in  FIGS. 19-20 . In this embodiment, the top lid portion  12  and cartridge tray  18  are substantially similar to embodiments previously described. The top of the bottom lid portion  14 , in the illustrated embodiment, is downwardly deflected towards the center of each compartment  24 . This downward deflection  74  provides a guiding mechanism for insertion of an access device, such as a syringe or pipette. The downward deflection  74  further provides a barrier from the sample  66  escaping if any splash-back occurs during manipulation of the bacterial detection cartridge  10 . Additionally, if a portion of sample  66  sticks to the top surface of the bottom lid portion  14 , for example while transporting bacterial detection cartridge  10 , the downward deflection  74  provides a path for the sample to flow down into the compartment  24 . This may be especially useful considering the small volumes of sample  66  in each compartment  24 . 
         [0058]      FIG. 20  shows another embodiment of the invention. Syringe  50  ( FIG. 13 ) is prepackaged with oil, for example mineral oil, in addition to growth media  56 . The sample  66  with growth media  56  and oil is loaded into the bacterial detection cartridge  10  as described above. Once loaded, the low density and low miscibility of the oil causes the oil to migrate to the upper surface of the sample  66 , creating an oil layer  76 . Other fluids can be used besides mineral oil, including, but not limited to, silicone oil and organic polymers. The oil layer  76  acts as a seal to isolate the sample  66  from the environment external to the oil layer  76 . This fluid seal can be used alternatively, or in addition to, sealable materials such as the adhesive foils described above. 
         [0059]    The operation of the bacterial detection cartridge  10  with two stages of pushing into a first and second position can be functionally replaced with alternate mechanisms. For example, a twist-down mechanism, or a slide-over mechanism, as shown in  FIGS. 21A-B  and  22 A-B, can be used with a similar result. Referring to  FIG. 21A , a top-down view of the bacterial detection cartridge  10  is shown. The cartridge tray includes vessels  32  as described above and additionally includes posts  80 . The bottom lid portion  14 , in the illustrated embodiment, has downward projecting walls  82 . The cartridge lid assembly  16  is placed onto the cartridge tray  18  in a first position, shown in  FIG. 21A , in which the walls  82  and posts  80  do not form a completely isolated compartment  24 . This is functionally similar to the first position described above, in which sample  66  may be introduced to the bacterial detection cartridge  10  and flow uniformly therethrough. Once the sample  66  has been introduced, the cartridge lid assembly  16  can be translated into a second position, illustrated in  FIG. 21B . In the second position, the walls  82  and posts  18  are positioned to isolate each compartment  24 , including the sample  66  therein. The specific shapes of the described components can vary, based on design choices, while accomplishing a similar result. For example,  FIGS. 22A-B  show yet another embodiment of the slide-over mechanism, except the posts  80   a  are rectangular projections instead of triangular projections as in  FIGS. 21A-B . The walls  82   a  shown in  FIGS. 22A-B  are shaped to correspond to the projections  80   a  such that the cartridge lid assembly  16  can be slid from a first position ( FIG. 22A ) in which sample  66  can freely flow to a second position ( FIG. 22B ) in which compartments  24  isolate the sample. 
         [0060]    A further embodiment of a bacterial detection cartridge  100  is illustrated in  FIG. 23 . In this embodiment, bacterial detection cartridge  100  is a circular disk with a plurality of radially extending walls  101 . A plurality of compartments  124  are created by the walls  101  in combination with the bacterial detection cartridge  100 , each compartment being defined by two adjacent walls  101  and the top, bottom, and side walls of the bacterial detection cartridge.  FIG. 23  illustrates a  32  compartment embodiment, with half of the compartments omitted for clarity of illustration. The top wall of each compartment  124  includes a vent aperture  128 , providing a venting mechanism as discussed below. The vent apertures  128  may act additionally as access apertures for a pipette or other withdrawal tool to withdraw sample  166  from the corresponding compartment  124 . Alternatively, each compartment  124  may include a separate access aperture (not illustrated) in addition to the venting apertures  128 . 
         [0061]    As illustrated in  FIG. 24 , each compartment  124  is preloaded with biosensor coating  136  on the bottom surface. The biosensor coating  136  may be provided in an annular pattern on the bottom surface of the bacterial detection cartridge  100 , or in other configurations. Although a biosensor coating  136  is preferred for the sensor, other sensors known in the art can be used without deviating from the scope of the invention. Each compartment further includes a vessel  132  configured to receive reagents such as resin gel pellets  134 . In one embodiment, the vessel is a raised rim on the bottom surface of the bacterial detection cartridge  100 . In other embodiments, the resin gel pellets  134  can be applied directly to the bottom surface of the bacterial detection cartridge without the use of vessels  132 . 
         [0062]    A plunger  190  is provided near the center of the bacterial detection cartridge above a raised inlet sample distributor  146 . The plunger  190  has an open first position, as illustrated in  FIG. 24 . In the first position, the space between the plunger  190  and the raised inlet sample distributor  146  creates a flow channel  192 . As sample  166  is introduced into the bacterial detection cartridge  100  when the plunger  190  is in the first position, the sample flows via the flow channel  192  into the compartments  124 . The plunger  190  includes a septum  121  to facilitate introduction of sample  166 . 
         [0063]    Sample preparation is similar to that discussed with reference to  FIG. 13 . Once the sample  166  is prepared, it is injected, for example using syringe  150 , through septum  121 , flows through the flow channel  192 , and fills the compartments  124 , as illustrated in  FIGS. 25A-B . During sample introduction, vent apertures  128  are open to allow pressure equalization. 
         [0064]    Once the sample  166  has been introduced, as illustrated in  FIG. 25B , the plunger  190  is moved to the closed second position, as illustrated in  FIGS. 26A-B . The user presses the plunger  190  in direction D to close the plunger in the second position. The bacterial detection cartridge  100  includes snap locks  198  to lock the plunger  190  in the second position. The bacterial detection cartridge  100  includes one or more apertures  194  located above the plunger  190 . These apertures  194  allow for pressure equalization to facilitate transition of the plunger  190  from the first position to the second position. Once the plunger  190  is in the second position, the flow channel  192  is sealed off, and each compartment  124  with sample  166  is sealed off to the environment with the exception of vent apertures  128 . After the plunger  190  has been moved to the second position, the vent apertures  128  can be sealed, for example with a re-sealable foil  145 . Similarly, the septum  121  can be sealed with, for example, a re-sealable foil  196 . Once the sample  166  has been fully introduced, the plunger  190  moved to the second position, and the vent apertures  128  sealed, the bacterial detection cartridge  100  can be placed into an incubator. The growth of organisms inside the bacterial detection cartridge  100 , as well as detection, removal, and processing is substantially similar to the procedures described with other embodiments above. The shape of the bacterial detection cartridge  100  allows for multiple cartridges to be stacked, as shown in  FIG. 27 , for easier storage and transportation. 
         [0065]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.