Classification of enterococci and their roles in spoilage of pork products and as sanitary indicators in pork processing

Knudtson, Linda
Major Professor
Paul A. Hartman
Committee Member
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The genus Streptococcus, including the fecal streptococci, has received intensive scrutiny in recent years, resulting in a new genus Enterococcus, rearrangement of species within the genus, and addition of many new species. To clarify the roles of these bacteria in food microbiology, known strains were examined by using conventional tube tests and API Rapid Strep and MicroScan Pos ID panels. Identification schema were devised to identify 13 species of enterococci and S. bovis and S. equinus by using a minimum of supplemental tests. These schema were used for enterococcal species identification to pinpoint possible sources of fecal contamination. Enterococci were enumerated and isolates were identified from samples taken in three pork slaughtering plants at different stages of slaughter and at different sites on the pork carcasses. Enterococcal numbers varied with stage, site and plant. Enterococcus faecalis predominated at each sample category. Since Enterococcus faecium predominates in hog feces, source(s) other than fecal contamination was indicated. Processed pork also was examined. Spoiled processed pork sausage contained a predominance of E. faecium, whereas samples of fresh and expired pork contained relatively low numbers of enterococci. These were predominantly E. faecalis. fGTC and KF media were used to enumerate enterococci on the pork carcasses and on retail samples of pork, beef, and poultry. Significantly higher counts were obtained with fGTC agar than with KF agar for all sample types. Species distribution of presumptive-positive colonies on the two media were similar, and at least 95% of colonies counted on fGTC agar were enterococci (except for samples in which shelf life had expired and lactobacilli predominated). The results indicated that fGTC agar is a superior medium for the isolation of enterococci in foods, except in products such as vacuum-packaged meats, where large numbers of lactobacilli are expected. The antibiotic resistance patterns of enterococci from pork, water, and clinical sources also were examined. Isolates from all sources carried similar intrinsic resistance to certain classes of antimicrobials; the least amount of resistance was observed in isolates from pork samples. When antibiotic resistance was compared among enterococcal species, some differences were detected. Finally, four streptococcal grouping kits were compared for their abilities to accurately type the group Lancefield D.