Abstract:
A programmable automated turbidimeter/colorimeter system for accurately measuring growth among multiple bacterial specimens is described which in a preferred embodiment includes a motor driven rotatable carousel assembly disposed within an aluminum housing, the carousel assembly including a plurality of evenly spaced peripheral holes for receiving a corresponding plurality of disposable culture test tubes, a light source and a light detector disposed in spaced confronting relationship to each other whereby the culture tubes pass therebetween, and a signal amplifier and a recorder for recording optical densities of each specimen as the carousel is continuously rotated. A concentric magnetic shield may be disposed on one side of the carousel for shielding experimental specimens from control specimens in measurements of magnetic effects on the cultures.

Description:
This application claims priority of the filing date of Provisional Application Ser. No. 60/106,906 filed Oct. 26, 1998, the entire contents of which application are incorporated by reference herein. 
    
    
     RIGHTS OF THE GOVERNMENT 
     The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to systems and methods for culture growth and testing, and more particularly to a fully programmable automated turbidimeter/colorimeter system for accurately measuring and comparing turbidity or growth and optical density, gradually changing or stable, among multiple bacterial specimens under carefully controlled conditions. 
     In the course of experiments for determining the behavior of bacterial cultures treated with antibiotics and exposed to varying combinations of magnetic fields, experimental specimens were exposed to magnetic fields and identically handled control specimens were not so exposed. In those experiments it was observed that, following treatment with antibiotic, neither experimental nor control cultures showed any measurable growth for about 12 hours, after which the cultures began to show growth but at different rates. Following the progress of the culture growth and making critical measurements at prescribed time intervals therefore required the attention of laboratory personnel substantially constantly for protracted periods of time of up to eighteen hours or more. No reliable conventional system existed for making the desired measurements automatically in a substantially continuous manner. 
     The invention solved or substantially reduced in critical importance problems in the prior art as just suggested by providing a fully programmable automated turbidimeter/colorimeter system. 
     It is a principal object of the invention to provide an improved turbidimeter for measuring bacterial growth. 
     It is a further object of the invention to provide a lightweight and compact turbidimeter. 
     It is yet another object of the invention to provide a fully programmable and automated turbidimeter. 
     It is another object of the invention to provide a programmable automated turbidimeter for measuring the magnetic effects on bacterial culture growth. 
     It is yet another object of the invention to provide a programmable automated turbidimeter for measuring antibiotic effects on bacterial culture growth. 
     These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds. 
     SUMMARY OF THE INVENTION 
     In accordance with the foregoing principles and objects of the invention, a programmable automated turbidimeter/colorimeter system for accurately measuring growth among multiple bacterial specimens is described which in a preferred representative embodiment includes a motor driven rotatable carousel assembly disposed within an aluminum housing, the carousel assembly including a plurality of evenly spaced peripheral holes for receiving a corresponding plurality of disposable culture test tubes, a light source and a light detector disposed in spaced confronting relationship to each other whereby the culture tubes pass therebetween, and a signal amplifier and a recorder for recording optical densities of each specimen as the carousel is continuously rotated. A concentric magnetic shield may be disposed on one side of the carousel for shielding experimental specimens from control specimens in measurements of magnetic effects on the cultures. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more clearly understood from the following detailed description of representative embodiments thereof read in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a partially exploded view of the essential components of a representative embodiment of the turbidimeter system of the invention built and operated in demonstration thereof; 
     FIG. 1 a  is a view of the demonstration system of FIG. 1 taken along lines A—A thereof; and 
     FIG. 2 is a top view of the carousel assembly of the FIG. 1 demonstration system. 
    
    
     DETAILED DESCRIPTION 
     Background information related to the invention and reports of experimental work utilizing a turbidimeter built in demonstration of the invention are presented in Stansell et al, “Increased Antibiotic Resistance of  E. coli  Exposed to Static Magnetic Fields,” (submitted for publication in the  Journal of Bioelectromagnetics ), the entire contents and teachings of which are incorporated by reference herein. 
     Referring now to the drawings, FIG. 1 shows a partially exploded view of the essential components of a representative embodiment of a turbidimeter system  10  built and operated in demonstration of the invention. Demonstration system  10  included a housing  11  having a body portion  12  and optional hinged lid  13  for closure of housing  11 , housing  11  preferably comprised of aluminum, wood, opaque plastic or other opaque non-ferrous material (the selected material should be opaque in order to exclude stray light) (in the demonstration system, portion  12  was 27×27 cm×15.5 cm high and lid  13  was 27×27 cm×7.5 cm high, and housing  11  was fabricated of aluminum, however, size and materials of construction are not considered limiting of the invention). Body portion  12  was divided into substantially equal volume upper and lower compartments  14 , 15  separated by horizontal wall member  16 . 
     A rotatable carousel assembly  17  was disposed within upper compartment  14  and mounted for rotation on an aluminum sleeve  18  secured to drive shaft  19  extending through wall member  16  from motor  20  in lower compartment  15  substantially as shown in FIG.  1 . Sleeve  18  may be secured to drive shaft  19  by suitable means such as set screws  21 . Flange  22  and spacer  23  supported carousel assembly  17  on sleeve  18 . Motor  20  may comprise any commercially available variable speed carousel drive motor suitable for the intended function, a Hurst Model PA 115 volt AC motor being selected for use in the demonstration system. Power supply  24  was disposed within lower compartment  15  and operatively connectable to a suitable external source  28  of electrical power. Power supply  24  provides regulated voltages for differential amplifier  26 , and timer/controller module  27  (Macromatic Time Delay Relay, SS65122, #9OF1397, Repeat Program Cycle Timer, in the demonstration system). The output from differential amplifier  26  connects to recorder amplifier and/or computer  25 . Suitable controls (not shown) were panel mounted in an outer wall of housing  11  and operatively connected to components  20 , 24 , 26 , 27  within lower compartment  15  for regulating amplifier gain, zero/100% transmittance positioning, on-cycle-off-cycle duration control, carousel rotation direction, power on/off, and recorder amplifier and/or computer inputs. 
     In the FIG. 1 demonstration system, carousel assembly  17  comprised a pair of plastic disk members  29 , 30  (each 23.8 cm dia×0.4 cm thick) held in spaced relationship (about 2.7 cm in the demonstration system) by a plurality of spacers  31 . A plurality ( 16  in the demonstration system) of evenly spaced holes  33  were defined in the periphery of disk members  29 ,  30  substantially as shown in FIG. 1, for receiving a corresponding plurality of disposable culture test tubes  32  as described more fully below in relationship to FIG  1   a.  A central hole  34  in carousel assembly  17  was sized to receive aluminum sleeve  18  and carousel assembly was secured to sleeve  18  by set screw  35  and washer  36  for rotation with sleeve  18  and drive shaft  19  of motor  20 . Carousel assembly  17  was disposed in selected spaced relationship to wall member  16  by placement of a selected number of spacers  23 . In the FIG. 1 system, holes  33  were sized to receive 17 mm diameter sterile plastic cappable culture tubes, although specific tube size is not considered limiting of the invention. Smaller diameter tubes could be used by inserting sleeves of appropriate inner/outer diameters within holes  33  for snugly receiving the smaller diameter tubes. 
     Concentric with the drive shaft hole  34  was placed a mu-metal shield (magnetic shielding)  37  to effectively isolate tubes containing control specimens on one side of carousel plate  17  from tubes with magnets containing experimental specimens on the other side. Shield  37  is used in applications involving the effects of magnetic fields on bacterial resistance to drugs as discussed below. FIG. 1 a  is a view along lines A—A of FIG. 1 of an experimental tube  32  and cylindrical magnet  43  assembly in place in carousel assembly  17 . Cylindrical magnets  43  may be cemented to a formed sheet copper frame  44  bent in the shape shown, and the assembly may be compression fitted to culture tube  32 . 
     Upper compartment  14  (FIG. 1) includes a light source  38  disposed substantially as shown in FIG. 1 near one side wall of housing  11 , and light detector  39  was disposed in confronting relationship to light source  38  and movably spaced (2.2 cm in the demonstration system) from source  38  sufficiently to allow tubes  32  to pass therebetween as carousel  17  is rotated. FIG. 2 shows a top view of carousel  17  and housing  11  of the FIG. 1 system illustrating the positions of source  38 , detector  39 , shield  37  and upper disk member  29 . In the demonstration system, light source  38  comprised one or more high intensity light emitting diodes (LED) and detector was a photodiode (PD) (VTB 6061, max 2000 pA dark current in the demonstration system), although other sources and detectors may be selected by a skilled artisan practicing the invention, such as an incandescent lamp, ultraviolet deuterium lamp, or infrared glower sources and visible range, ultraviolet specific or infrared specific detectors, the same not considered limiting of the invention. Amplifier  26  processed the output from detector  39 . Operation of system  10  may be preprogrammed and fully computer controlled, including the timing and stop/go control of carousel  17  rotation, system on/off periods, selection and control of light source  38 , detector  39  operation and the acquisition and analysis of culture growth data derived from the operation of system  10 . 
     In a typical application of the turbidimeter system of the invention such as described in Stansell et al, supra, bacteria (clinical isolate of  E. coli ) from a pure culture are inoculated into trypticase soy broth (TSB) at a concentration of 1.5×10 8  cfu/ml and grown at 37° C. until density reaches about 8×10 8  cfu/ml. The culture is then diluted with fresh TSB to 1.5×10 8  cfu/ml and allowed to grow at 37° C. until the density again reaches 8×10 8  cfu/ml. Then the culture is diluted once again with fresh TSB to give 1.5×10 8  cfu/ml and then further diluted 1000:1 to a concentration of 1.5×10 5  cfu/ml at 37°. Two ml aliquots of the diluted culture are transferred to prewarmed (37° C.) tubes mounted in carousel assembly  17 . Magnet and/or sham assemblies are attached to tubes  32  as appropriate. Carousel assembly  17 , with filled tubes, is immediately returned to the incubator and the aliquoted cultures allowed to grow for 90 minutes at 37° C. After the initial incubation, caps of tubes  32  are temporarily removed and standardized quantities of antibiotic solution are added with mixing. The caps are replaced and the timer controls set for desired on-time/off-time durations. 
     Carousel assembly  17  rotates at any preselected speed (one rpm in the tests performed in the demonstration system) and the sensitivity is set to give a full scale reading (with pure TSB in the path) on the 0-5 volt scale of the strip chart recorder. The use of high output voltage from the differential amplifier provides an excellent signal to noise ratio. In addition to a selected number of experimental tubes  32  and a corresponding number of control tubes  32 , carousel assembly  17  may contain an opaque tube to set the baseline to zero transmittance and a tube containing pure TSB to set transmittance to 100%. As the center of a tube  32  passes through the light beam from source  38 , transmittance of the tube  32  reaches a maximum. The transmittance is a measure of the amount of turbidity (bacterial growth) in the specimen contained in the tube. As growth continues over time, the transmittance gradually decreases until a plateau is reached, indicating exhaustion of the TSB and stationary phase in the bacterial growth cycle. Additional experimental tests utilizing turbidimeter  10  are presented in Stansell et al, supra. 
     The invention therefore provides a fully programmable automated turbidimeter. It is understood that modifications to the invention may be made as might occur to one with skill in the field of the invention, within the scope of the appended claims. All embodiments contemplated hereunder that achieve the objects of the invention have therefore not been shown in complete detail. Other embodiments may be developed without departing from the spirit of the invention or from the scope of the appended claims.