Behaviour and enterotoxin production by Staphylococcus aureus during the manufacture and ripening of raw goats' milk lactic cheeses

Abstract

To study the possible presence of staphylococcal enterotoxin A in raw goats' milk lactic cheese, milk was inoculated with an enterotoxigenic Staphylococcus aureus strain to a final concentration of 4, 5 and 6 log(cfu/ml). Cheese was prepared following industrial specifications and ripened for 42 d. Detection of the enterotoxins was by the Vidas Staph enterotoxin test (BioMérieux) and by an indirect double-sandwich ELISA technique using anti-enterotoxin monoclonal antibodies. Staphylococcal counts declined markedly after draining, and by the end of ripening they had disappeared from some cheeses. In contrast, aerobic mesophilic organisms grew well. The level of staphylococcal enterotoxin A recovered varied from 1 to 2·5 ng/g cheese made with an initial population of 105 or 106 cfu/ml. Only traces of enterotoxin A (0·5 ng/g) were detected in cheeses made with the lowest Staph. aureus inoculum used in this study. Enterotoxin A was also detected in cheeses from which Staph. aureus had disappeared.