Responding to a need for a guide for conducting Official Method validation studies of microbiological methods, AOAC utilized the experience of three microbiologists who have been active in the field of method validation. In collaboration, a document was prepared which covered the following areas: terms and their definitions associated with the Official Methods program (e.g., reference methods, alternative methods, and ruggedness testing), protocols and validation requirements for qualitative methods versus those for quantitative methods, the concept of the precollaborative study, ruggedness testing, tests for significant differences, performance indicators, and the approval process. After its preparation, this document was reviewed by the members of the Methods Committee on Microbiology and Extraneous Materials and by members of the Official Methods Board. Herein is presented the approved version of that document.
Using standard procedures, aerobic plate counts (APC), total and fecal coliform most probable number (MPN) determinations, and analyses for Salmonella, Arizona, Shigella and Edwardsiella tarda were performed on 335 fresh and 342 frozen sample units of channel catfish. APC values for 93.0% of the fresh and 94.5% of the frozen samples were
The behavior of microorganisms was studied in mung beans and alfalfa seeds before and after germination in modified, commercially available bean-sprouting kits. The microorganisms were enumerated by the aerobic plate count (APC) and by total yeast and mold count procedures. Salmonella species were artificially inoculated into selected samples and were enumerated by the most probable number (MPN) method. After germination of the beans or seeds into mature sprouts, significant increases were noted in APCs and in MPN values of Salmonella species. Although counts of yeasts and molds did not increase significantly after germination, these samples showed an increase in toxic Aspergillus flavus and potentially toxic Alternaria species. The presence of toxic Penicillium cyclopium molds also increased substantially in 5 samples of a single brand of mung beans. Analysis of selected sprout samples, however, showed no presence of aflatoxin.
Migration of Salmonella enteritidis through egg albumen to the yolk and its subsequent growth in the yolk were examined. Submersion of eggs in .1% mercuric chloride solution for 1 h followed by submersion in 70% ethanol for 30 min resulted in an eggshell surface from which no Salmonella organisms were recovered. The eggs were then inoculated with S. enteritidis under the shell membrane. Although growth of S. enteritidis was negligible in eggs refrigerated up to 16 days, the population level of the organism increased by more than 8 log10 units in unrefrigerated eggs stored for the same amount of time.
The relative effectiveness of Rappaport-Vassiliadis (RV) medium, selenite cystine (SC) broth, and tetrathionate (TT) broth for the recovery of Salmonella spp. from foods with a low microbial load was determined. RV medium made from its individual ingredients and incubated at 42 degrees C was compared with a commercial preparation of SC broth, incubated at 35 degrees C, and TT broth incubated at 35 and 43 degrees C, for the recovery of Salmonella spp. Twenty-one artificially contaminated food types that included dairy foods, spices, and egg products, as well as other low-microbial-load foods, were analyzed. The foods were inoculated with single Salmonella serovars at target levels ranging from 0.04 to 0.4 CFU/g. No significant differences (P< or =0.05) among the selective enrichment broths for the recovery of Salmonella spp. from 18 of the foods were observed. Significantly fewer Salmonella-positive test portions of gelatin, guar gum, and nonfat dry milk were recovered with RV medium than with SC broth incubated at 35 degrees C and TT broth incubated at 35 and 43 degrees C. TT broth incubated at 35 degrees C recovered the greatest number of Salmonella-positive test portions. For the recovery of Salmonella spp. from foods with a low microbial load, it is recommended that TT broth incubated at 35 degrees C and RV medium incubated at 42 degrees C be used.
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.