An entirely new mixing device, particularly suitable for preparing bacterial suspensions from foods, fabrics, swabs, and other fairly soft materials, has been developed. With this technique the sample and diluent are put into an inexpensive, sterile plastic bag which is vigorously pounded on its outer surfaces by paddles when placed inside the machine. The resulting compression and shearing forces effectively remove even deep-seated bacteria. After samples are taken for analysis the bag and its remaining contents are thrown away. Labor involved in cleaning and sterilizing reusable homogenizer cups or probes is eliminated, and the device is immediately ready for reuse. Running costs are thus drastically reduced, compared with conventional homogenizers. Additional advantages of this device, which is simple and inexpensive to manufacture, are low noise level, negligible temperature rise, and the small storage space required for bags.

Summary. ATP levels were determined in micro‐organisms and in foods, either as purchased or after incubation or addition of living bacteria. ATP levels in foods were divided into intrinsic ATP (derived from the original tissue) and microbial ATP. Intrinsic ATP decreased during incubation while bacterial ATP increased. At sufficiently high levels of contamination ATP levels could be related to bacterial concentrations.

Factors affecting the membrane filtration of food suspensions were studied for 58 foods and 13 membrane filters. Lot number within a brand, pore size (0.45 or 0.8 pm), and time elapsed before filtration had little effect on filterability. Brand of membrane filter, flow direction, pressure differential, age (microbiological quality) of the food, duration of the blending process, temperature, and concentration of food in the suspension had significant and often predictable effects. Preparation of suspensions by Stomacher (relative to rotary blender) addition of surfactant (particularly at elevated temperature) and prior incubation with proteases sometimes had dramatic effects of filterability. In contrast to popular opinion, foods can be membrane filtered in quantities pertinent to the maximums used in conventional plating procedures. Removal of growth inhibitors and food debris is possible by using membrane filters. Lowering of the limits of detection of microorganisms by concentration on membrane filters can be considered feasible for many foods. The data are particularly relevant to the use of hydrophobic grid-membrane ifiters (which are capable of enumerating up to 9 x 10' organisms per filter) in instrumented methods of food microbiological analysis.

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An 0-antigen-specific monoclonal antibody, labeled by horseradish peroxidase-protein A, was used in a hydrophobic grid membrane filter-enzyme-labeled antibody method for rapid detection of Escherichia coli 0157 in foods. The method yielded presumptive identification within 24 h and recovered, on average, 95% of E. coli 0157:H7 artificially inoculated into comminuted beef, veal, pork, chicken giblets, and chicken carcass washings. In food samples from two outbreaks involving E. coli 0157:H7, the organism was isolated at levels of up to 103/g. The lower limit of sensitivity was 10 E. coli 0157 per g of meat. Specific typing for E. coli 0157:H7 can be achieved through staining with labeled H7 antiserum or tube agglutination.