A variety of chemical cleaning and sanitizing compounds were evaluated for their ability to remove and/or inactivate surface adherent Listeria monocytogenes. Adherent cells were obtained by incubating 1-cm2 chips of stainless steel or plastic conveyor belts with a multistrain cocktail of L. monocytogenes for 24 h at 25°C. Resistance of adherent cells to sanitizers was dependent upon the surface studied, being greatest on polyester/polyurethane followed by polyester and stainless steel. Biofilm removal with cleaners followed the same pattern as sanitizers with the polyester/polyurethane surface being most difficult to clean. Complete biofilm removal and/or inactivation was obtained in many cases where the surface was first cleaned prior to exposure to sanitizer. The data support conventional wisdom in that cleaning must precede sanitizing in order to remove and inactivate microorganisms. Listeria biofilms should be controllable by combining Good Manufacturing Practices with the discipline of a Hazard Analysis Critical Control Point Program.

An indirect enzyme-labeled antibody technique (ELAT), in which Salmonella typhimurium was used as a model, was developed as a method to detect Salmonella in food samples. A cellulose-acetate membrane filter, the matrix for detection, was placed on a membrane-filter base and overlaid with a multiwelled lucite template. Mixed broth enrichment cultures were dispensed in the template wells, and cells were spotted onto the membrane via suction. After fixation, the membranes were immersed in rabbit anti-S. typhimurium flagella antibody, washed, immersed in goat anti-rabbit antibody conjugated to peroxidase, and washed. Exposure of membranes to the substrates 3,3'-diaminobenzidine or benzidine resulted in development of brown or blue macroscopic reaction products, respectively, on spots containing S. typhimurium. ELAT results agreed with those of enrichment serology and cultural procedures on three food products containing known levels ofS. typhimurium. Because of the magnification effect of the enzyme-substrate reaction, fewer cells were needed for detection than with enrichment serology, thereby reducing the total analysis time. The ability to test 14 or more samples simultaneously on a 47-mm membrane filter would facilitate screening large numbers of samples. Pending the development of a pure H antisera pool for the common Salmonella serotypes free from 0 antibodies, the ELAT demonstrated potential as a Salmonella detection methodology.

The neurotoxin in cells of young Clostridium botulinum type A culture was extracted with lysozyme. Highly purified neurotoxin preparation, obtained by processing the extract in two chromatographic steps had only unnicked (single-chain) molecules of molecular weight comparable to that of the dichains isolated from type A crystals. Trypsinization converted the unnicked molecules into dichains whose component subunits were of sizes indistinguishable from those of the neurotoxin from crystals. The enzymatic treatment increased toxicity of crude extract 30-fold but did not activate the purified intracellular neurotoxin preparation. The results indicated that intracellular type A botulinum neurotoxin is unnicked, is not fully activated, and is activated in the time between its extraction and purification. Since trypsinization nicked all of the single chains without increasing toxicity, nicking was not causally related to toxicity activation.

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