Coagulase negative staphylococci (CNS) are ubiquitous bacteria encountered in various environments, including animal and human skin and mucosae, food products of animal origin, soil, water, and hospital environment. Some CNS species play an important role in the fermentation of meat and milk products and are considered as food grade. The presence of risk factors in CNS and their increasing clinical significance raise questions about their current presence or use in food. Our goal was to assess risk factors in CNS by developing a diagnostic microarray. A set of 290 oligonucleotides was designed, targeting risk factors selected among staphylococcal and gram-positive species that may be in contact with CNS in foodstuffs. Risk factors include antibiotic resistance (72), staphylococcal enterotoxins (17) and toxins (46), biosynthesis of biogenic amines (22) and other toxins from gram-positive bacteria (113). After validation using genomic DNA of sequenced strains, the diagnostic microarray was used to screen 130 strains belonging to the 2 dominant species isolated from foodstuffs (S. equorum and S. xylosus) and the 2 main species common to food and clinical samples (S. epidermidis and S. saprophyticus). The selected strains were representative of the genetic diversity within each species as showed by PFGE analysis on 236 isolates. Risks associated with CNS are mainly limited to the presence of antibiotic resistance genes as no enterotoxin genes were found and only a few toxin genes were detected. Microarray data were further corroborated by antibiograms. Moreover, only 7% of the strains produced significant amounts of biogenic amines in vitro but the genes encoding the implicated enzymes were not detected. This work gives a first picture of risk assessment within four species of CNS frequently isolated from food or clinical environment.
This study was supported by « ANR- French National Research Agency », project SCN/BEER.