Main Differences in Behavior and Enterotoxin Production of Staphylococcus Aureus in Two Different Raw Milk Cheeses

Differences in behavior and enterotoxin production of Staphylococcus aureus in two cheese types namely lactic and Camembert type cheeses have been evaluated. A Staphylococcus aureus strain producing staphylococcal enterotoxin A was added to raw goat's milk. The initial staphylococcal counts were respectively 4, 5 and 6 log cfu ml(-1). Cheeses were prepared following the industrial specifications and ripened for 42 d. Numbers of Staphylococcus nureus and aerobic plate count were determined respectively using Baird-Parker medium supplemented with rabbit plasma and bovine fibrinogen and Plate Count Agar (P.C.A.) during manufacture and ripening of cheeses. Physico-chemical analysis : pH, dry matter and chloride were also measured. Detection of the enterotoxins was done by the Vidas SET test (bioMerieux) and by an indirect double-sandwich ELISA technique using anti-enterotoxin monoclonal antibodies.Aerobic mesophilic plate counts increased at a similar rate until the salting in both cheese types and remained stable and high during the ripening period. S. aureus counts declined markedly after draining and, by the end of ripening, they become zero in lactic cheeses. Conversely S. aureus counts increased until the salting and remained stable during ripening of Camembert type cheeses. The level of staphylococcal enterotoxin A recovered varied from 1 ng to 3.2 ng g(-1) in Camembert type cheeses made with an initial population of 10(4) to 10(6) cfu ml(-1) and from 1-2.5 ng g(-1) of cheese made with an initial population of 10(5) or 10(6) cfu ml(-1) in lactic cheeses. Staphylococcal standards should be replaced by enterotoxin detection in the regulations to assure the safety of raw milk cheeses.