A medium for direct overnight isolation of hemorrhagic colitis (HC) strains of Escherichia coli from foods has been developed. It is a direct plating medium incorporating tryptophan (as tryptone), sorbitol, an indicator dye and a fluorogenic substrate for diagnostic purposes. Sodium chloride is included to raise the upper temperature limit for growth and a bile salt concentration lower than that usual for E. coli media but still inhibitory to non-enteric organisms is used. Colonies of HC strains grown overnight at 44.5°C on membrane filters placed on the medium are blue. Subsequent indole staining of the membranes yields red positive colonies. Replicate colonies are confirmed serologically. In contrast, E. coli Type I colonies are yellow and give apparently negative indole reactions. Recovery of HC organisms from artificially contaminated ground beef is ≥90%.
In rice, milk, and brain-heart-infusion cultures, 17 of 67 Bacillus cereus strains produced a heat-stable toxin causing morphological changes in cultures cells. All of the positive strains were associated with illness, eight with the emetic syndrome. Time-temperature studies indicated that toxin production was optimum at 25 to 30°C after 18 h in shaking culture, but low levels were produced at 15°C. Effects in cells included granulation, vacuole formation, cell rounding, acid production, and arrested cell multiplication. Of seven cell lines tested, Int 407, CHO, and HEp-2 were equally the most sensitive with the former being preferred for ease of interpreting results. The observed toxin had a molecular weight of about 14,000 and a pI of 5.9 as determined by Superose 12 chromatography and Mono P ion-exchange chromatofocusing, respectively.
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.
Heat treatment of raw milk in an HTST pasteurizer operated at 60.0 to 72.0 degrees C for a minimum holding time of 16.2 s rapidly inactivated mixtures of hemorrhagic Escherichia coli O157:H7, Yersinia enterocolitica and Campylobacter spp. (C. fetus, C. coli, and C. jejuni). Each of the three genera in the mixture was inoculated at a level of approximately 1.0 x 10(5) cfu/ml. At 60.0 degrees C, hemorrhagic E. coli showed a maximum 2 log10 reduction in counts and no viability at greater than or equal to 64.5 degrees C. Yersinia enterocolitica and Campylobacter spp. showed greater heat sensitivity with a 4 log10 reduction in counts at 60.0 degrees C and absence of viable cells at greater than or equal to 63.0 degrees C. These findings reiterate the need for stringent control of thermal processes in the manufacture of dairy products from raw or heat-treated (non-pasteurized) milk.
The heat stability of staphylococcal enterotoxins A, B and C (SEA, SEB, SEC) in phosphate buffered saline solution at a concentration of 100 ng per ml indicated that normal cooking times and temperatures are unlikely to completely inactivate the toxins. The order of heat resistance of the three toxins was SEC>SEB>SEA.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.