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Variation in the behaviour of enterotoxigenic Staphylococcus aureus after heat stress in milk
Author(s) -
BATISH V.K.,
NATARAJ B.,
GROVER SUNITA
Publication year - 1989
Publication title -
journal of applied bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 0021-8847
DOI - 10.1111/j.1365-2672.1989.tb02450.x
Subject(s) - enterotoxin , staphylococcus aureus , coagulase , microbiology and biotechnology , deoxyribonuclease , subculture (biology) , casein , brain heart infusion , food science , biology , chemistry , agar , staphylococcus , enzyme , bacteria , escherichia coli , biochemistry , genetics , gene
The survival of several strains of Staphylococcus aureus after heat stress in different menstrua was not logarithmic and F‐values were determined to express their resistance to heat. Of the strains tested, Staph, aureus 234 (enterotoxin B) was the most heat resistant and Staph. aureus 790 (enterotoxin E) was the most heat sensitive. Buffalo milk gave the best protection to all the strains of Staph. aureus against heat, followed by cow's milk; phosphate‐buffered saline gave the least protection. Soyabean casein digest agar gave maximum recovery of survivors followed by brain heart infusion and Baird‐Parker medium. At 50°C there was no marked variation in coagulase production by the surviving strains but at 55 and 62–5dE C there was complete loss of coagulase activity. There was a decreased deoxyribonuclease (DNase) production by all the strains of Staph. aureus after heat stress. Heat‐treatment at 55 and 62mD5dE C resulted in loss of enterotoxin production by all the survivors except S 6 and 234, the surviving cells of which still prodused enterotoxin B after heat treatment at 55dE C. Most of the survivors regained lost characteristics such as coagulase, DNase and enterotoxin production after four to five passages through BHI which suggests that subculture of Staph. aureus recovered from heat‐processed milk is necessary to avoid false results.