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Aim: To investigate whether the Staphylococcus argenteus is present in Eastern China and to verify the utility of a new screening process., Materials & Methods: Phenotype observation, PCR assay targeting a hypothetical nonribosomal peptide synthetase (NRPS) gene, phylogenetic analysis of rpoB and multilocus sequence typing were used to screen and identify strains of S. argenteus from 839 presumptive S. aureus isolates., Results: Eighty-nine (89/839, 10.6%) of the presumptive S. aureus isolates produced white colonies on tryptone soya agar plates. Of the white-colony isolates, six (6/89, 7%) were S. argenteus, 75 (75/89, 84%) were S. aureus and eight (8/89, 9%) were other bacteria., Conclusion: The PCR-based method targeting the NRPS gene can simultaneously identify and distinguish S. argenteus and S. aureus. All representative sequences of rpoB generated in this study were deposited in GenBank under accession numbers SJTU F20002, KT767581; SJTU F20269, KT767582; SJTU F20419, KT767583; SJTU F20420, KT767584; SJTU F20124, KT767585; SJTU F21164, KT767586; SJTU F21285, KT767587; SJTU F21224, KT767588; SJTU F21155, KT767589; SJTU F21294, KT767590; SJTU F20030, KT767591; SJTU F20044, KT767592; SJTU F20135, KT767593; SJTU F20123, KT767594; SJTU F21319, KT767595, respectively. All the new sequence types (STs) were submitted to a multilocus sequence typing database and the assigned ST numbers are ST3261 (151-469-20-101-145-150-131), ST3262 (12-3-1-1-4-4-410) and ST3267 (2-471-2-2-6-3-2).

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.

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., (© 2016 Institute of Food Technologists®)

Purpose: This study aims to characterize the wild-type staphylococcal enterotoxin A (SEA)- producing Staphylococcus aureus. Materials and methods: We identified 29 wild-type sea-positive S. aureus isolates from dairy and meat samples, as well as from patients, measured the amount of SEA produced under favorable cultivation conditions using enzyme-linked immunosorbent assay and sea mRNA transcriptional level and investigated the phage type as well as genetic diversity by means of pulsed-field gel electrophoresis and multilocus sequence typing. Results: Among 29 sea-positive isolates, 22 were from food sources (including one outbreak case) and seven from clinical patients. Five enterotoxin gene profiles, namely, sea (14 isolates), sea+sec (9 isolates), sea+seb (4 isolates), sea+seb+sec (1 isolate) and sea+seb+sed (1 isolate), were identified. Multilocus sequence typing generated sequence type (ST)1 (13 isolates), ST6 (5 isolates), ST59 (3 isolates), ST239 (3 isolates), ST5 (2 isolates), ST188 (2 isolate) and ST15 (1 isolate). The amount of SEA per 108 colony-forming unit (CFU) after 24 h of incubation was 1.1-33.5 (mean, 8.74; SD, 7.7) ng/108 CFU. The amount of SEA per hour incubation in the log growth phase was 0.1-12.0 (mean, 2.37; SD, 3.06) ng/108 CFU. Overall, 54.2% of SEA was produced in the log growth phase. Both the transcriptional level of sea mRNA and the amount of SEA in the log growth phase correlated well with the amount of SEA after 24 h of cultivation. Four isolates, namely, SA-212, SA-217, SA-340 and SA-341, were categorized to be of high SEA production (877-1,109 ng/mL, 24 h). The total amount of SEA was mainly based on the amount of SEA in 108 CFU, not the relatively fixed bacterial cell counts (21.1-43×108 CFU/mL). Seven isolates from patients all carried the ФMu3A phage, whereas 21 of the 22 isolates from the environmental sources all carried the ФSa3ms phage. Conclusion: The present study exhibits varied SEA production capacity of the wild sea-positive S. aureus strains. An apparent boundary in phage types between strains from the clinical samples and strains from the environment was also identified. [ABSTRACT FROM AUTHOR]