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.

Staphylococcus aureus with the ability of staphylococcal enterotoxins (SEs) production is one of the most common causes of bacterial foodborne outbreaks worldwide. In our study, 336 S. aureus isolates were recovered from 3476 food samples during 2010-2014. A total of 86 S. aureus isolates were proved to be enterotoxin-producing strains with PCR and enzyme-linked immunosorbent assay. In the 86 isolates, 20 STs were identified using multilocus sequence typing (MLST) and 20 isolates were typed as sequence type 5 (ST5), which was the most prevalent ST using MLST. There were six SE profiles and high carrier rates of sec (50%) and sed (75%) genes in the 20 S. aureus ST5 isolates. Additionally, 8 antibiotic resistance patterns were observed, and 10 multidrug-resistant isolates (50%) and 4 methicillin-resistant S. aureus isolates were identified. Our findings illustrate high prevalence of S. aureus ST5 isolates from food sources and diversity in SE profiles and antibiotic resistance patterns. These results indicate that great difference in the ability of obtaining SE production and antimicrobial resistance may exist between different genetic lineages of S. aureus strains.

Salmonella enterica serotype Enteritidis (S. Enteritidis) is an important causative agent of nontyphoidal salmonellosis in human populations. In this study, we collected 72 S. Enteritidis strains from 2004 to 2014 in Ningbo, mid-east China. Of the 72 strains, we identified a dominant clone of 58 strains recovered from patient's feces (n = 48), blood (n = 1), pleural effusion (n = 1), chickens (n = 3), and dessert cakes (n = 5) by pulsed-field gel electrophoresis (PFGE) and variable-number of tandem repeat analysis (MLVA). The profile arrangements of MLVA were SE1-SE2-SE3-SE5-SE6-SE8-SE9: 4-4-3-11-10-1-3. These dominant strains were susceptible to ampicillin, chloramphenicol, tetracycline, ciprofloxacin, gentamicin, cefotaxime and trimethoprim-sulfamethoxazole, and resistant to nalidixic acid. Additionally, all isolates harboured virulence genes invA, sipA, sopE, and spvB when tested by PCR. Our results reveal that genetically similar S. Enteritidis strains which accounted for several outbreaks as well as blood infection and pleural cavity infection are prevalent in China for a long-term period. This situation calls for further attention in the prevention and control of foodborne disease caused by Salmonella species.

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