A variety of bakery products, including cakes, sweet puffs, vegetable puffs and cream buns, from five local bakeries were screened for their microbiological quality. The aerobic plate count varied between 102 to 104 CFU/g. The highest numbers were found in puffs containing vegetable fillings and least in bread and buns. Genera identified included Bacillus, Micrococcus, Staphylococcus, Enterobacter, Escherichia and Klebsiella. Staphylococci were not present in bread or buns; however, these organisms were isolated from cream-filled cakes and puffs containing coconut scrapings. These isolates were capable of producing enterotoxins of which enterotoxin B was most common.
Coagulase, DNase and enterotoxin production of 200 strains of staphylococci isolated from various foods were compared in order to see to what extent these biochemical tests can replace the enterotoxin assay for predicting food safety. Any degree of coagulase formation was not indicative of DNase activity also. However, all cultures having a 4' score of coagulase showed DNase. DNase activity decreased with heating. No correlation could be seen between coagulase and enterotoxin or DNase and enterotoxin production. In fact. a number of coagulase negative strains were found to produce enterotoxins. Reliability of coagulase or DNase activity for predicting food safety is therefore doubtful.Coagulase test is one of the most commonly used yardsticks for distinguishing the toxigenic and pathogenic staphylococci from the closely related saprophytic species [l, 21. In fact many of the laboratories monitoring routine quality control of foods rely mainly on this test for deciding food safety. Of late, however, more and more emphasis is being given to the t hermostable deoxyribonuclease (DNase) activity to distinguish the toxigenic strains of Sruphylococcus uureus [3, 41. However, there are reports that under certain conditions, S. uureus may lose these diagnostic characteristics, but still retain the toxigenicity and pathogenicity [4]. In the light of these reports, it is evident that the commonly employed criterion of relating the coagulase nature or DNase activity for diagnostic purposes must be viewed with reserve. We were therefore interested in finding as to what extent these biochemical tests are realistic in predicting their potential enterotoxigenicity or public health significance in foods.
Materials and MethodsA total of 200 strains isolated from various foods, food handlers and equipment surfaces in the laboratory were used. The foods screened included. accelerated freeze dried mutton mince, egg powder, dehydrated onions. curry mixes, ready to serve foods, canned fortified butter, mutton carcasses brought to the laboratory for making processed foods and bakery products from a few local bakeries. The strains isolated were purified as described earlier [5]. Only those cultures which were catalase positive, fermented glucose aerobically and anaerobically on HUGH and LEIFSON'S medium, VOGFS-PROSKAUER positive and produced phosphatase were taken for the studies. They were tested for coagulase formation, DNase activity and enterotoxin production using standard procedures 16-81. Standard enterotoxins and their specific antisera employed were very kindly supplied by Prof. M. S. BERGWLL,
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