Presence of coagulase-negative Staphylococcus in dairy products : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science at Massey University, Palmerston North, New Zealand
Species within the genus Staphylococcus produce various virulence factors, including staphylococcal enterotoxins. Because of their production of enterotoxins, Staphylococcus is the third most common pathogen responsible for outbreaks of food poisoning worldwide. Whereas Staphylococcus aureus, a coagulase-positive Staphylococcus, is the leading cause of these outbreaks, coagulase-negative staphylococci (CNS) species are also present in food and are able to produce enterotoxins. More specifically, such CNS species have been linked with dairy-related food poisoning outbreaks. However, to date, no research investigating CNS species in New Zealand and their presence in food has been reported. This study therefore sets out to isolate, identify and characterise CNS from New Zealand milk and dairy products, and to evaluate their toxin-producing potential. The results from this study showed that MALDI−TOF MS is a rapid, reliable and accurate method for identifying CNS definitively to the genus level and, on most occasions, to the species level in dairy products and is therefore a potential alternative to the traditional phenotypic, such as commercial identification kits, and genotypic, such as sequencing, methods that are currently used. Of the 42 isolates analysed, none of the CNS isolates tested produced enterotoxin in vitro, however, 2 isolates were found to possess an enterotoxin gene. This shows a low propensity for CNS isolates in New Zealand dairy products to be a food safety risk.