Prevalence and Characteristics of Enterotoxin B-Producing Staphylococcus aureus Isolated from Food Sources: A Particular Cluster of ST188 Strains was Identified.

The aim of this study was to investigate the prevalence and characteristics of staphylococcal enterotoxin B (SEB) producing Staphylococcus aureus (S. aureus) isolated from food sources. A total of 412 S. aureus isolates were recovered from 1970 milk and dairy samples (n = 236) and 2450 meat samples (n = 176) in China from 2009 to 2014. Of the 412 isolates, 124 isolates were tested positive for 1 or more classical staphylococcal enterotoxin (SE) genes using PCR, and 31 isolates were positive for seb gene and further proved to be SEB-producing. Four SE profiles were observed among 31 SEB-producing isolates when investigated using ELISA kit, that is, SEB (16 isolates), SEA+SEB (6 isolates), SEB+SEC (6 isolates), and SEB+SED (3 isolates). Thirteen sequence types (STs) were identified in the 31 SEB-producing S. aureus isolates using multilocus sequence typing (MLST). The 3 most detected STs were ST1 (7 isolates), ST188 (6 isolates), ST59 (3 isolates). Two distinct clusters were identified by pulsed-field gel electrophoresis (PFGE), each of which showed excellent consistency with ST188 and ST1 achieved by MLST, respectively. In summary, this study reveals that various SE profiles are observed in SEB-producing S. aureus isolates and the great part of SEB-producing S. aureus isolates are showed as clusters. Especially, a particular cluster of ST188 strains was observed in SEB-producing S. aureus isolates which was associated with outbreaks of SFP and needs further attention.