Safety assessment of dairy microorganisms: coagulase-negative staphylococci.

The genus Staphylococcus is made up of 36 validated species which contain strains that are pathogenic, saprophytic, or used as starter cultures for the food industry. Staphylococci species used in cheese-making are novobiocin-resistant, coagulase-negative and are not usually identified at species level by routine laboratories. A bibliographic survey was conducted to assess safety status of CNS used in fermented dairy foods. Commercial kits based on phenotypic discrimination can't reliably identify these species because of the variable expression of some phenotypic traits. Several molecular targets, including 16S rRNA, hsp60, tuf, SodA and rpoB genes can be used for identifying species of the Staphylococcus genus. No coagulase-negative staphylococci isolated from milk or dairy products has ever been involved in a case of food poisoning or human pathology following ingestion of dairy products. Nevertheless, a few case of nosocomial infection caused by some species (S. caprae, S. capitis, S. sciuri) have been reported in patients with depressed immune systems or who have undergone long severe hospital treatments, or in the presence of an indwelling catheter or foreign materials such as cardiac prostheses. They may therefore be regarded as exceptional opportunistic pathogens in certain clinical situations.