Prevalence and Genetic Characteristics of Staphylococcus aureus and Staphylococcus argenteus Isolates Harboring Panton-Valentine Leukocidin, Enterotoxins, and TSST-1 Genes from Food Handlers in Myanmar

Abstract

Asymptomatic carriers of toxigenic Staphylococcus aureus are potential source of diseases, including food poisoning. Toxigenic potential and genetic traits of colonizing S. aureus were investigated for 563 healthy food handlers in Myanmar. Carriage of S. aureus was found in 110 individuals (19.5%), and a total of 144 S. aureus isolates were recovered from nasal cavities (110 isolates) and hands (34 isolates). Panton-Valentine leucocidin genes (pvl) were detected in 18 isolates (12.5%), among which 11 isolates were classified into coa-VIa, agr type III, and ST1930 (CC96) that had been also detected in pvl-positive clinical isolates in Myanmar. A pvl-positive, ST2250 nasal isolate was identified as S. argenteus, a novel coagulase-positive staphylococcus species. Toxic shock syndrome toxin-1 (TSST-1) gene was detected in five pvl-negative isolates. All of the 144 isolates harbored at least one of the 21 enterotoxin(-like) gene(s). The most prevalent enterotoxin(-like) gene was selw (98%), followed by selx (97%), sei (28%), sely (28%), sem (26%), sel (24%), and sea and sec (22% each). Considerable genetic diversity with five groups was detected for selw. The present study revealed the relatively high rate of pvl, as well as the wide distribution of enterotoxin(-like) genes among colonizing S. aureus in Myanmar.

Keywords: Myanmar; Panton-Valentine leukocidin; Staphylococcus argenteus; Staphylococcus aureus; TSST-1; enterotoxin; enterotoxin-like gene; food handler.

Figure 1

Phylogenetic dendrogram of S. aureus and two S. aureus-related species S. argenteus and S. schweitzeri based on the concatenated sequences of seven MLST loci using the maximum-likelihood method. This dendrogram contains S. aureus STs commonly found in Myanmar and other countries in Asia [20,21,27], representative of 10 S. argenteus STs and ST2022 of S. schweitzeri type strain FSA084. ST2250 identified in the present study is marked with a black circle. Bootstrap values >80% are shown. Scale bar, 0.01 substitutions per nucleotide.

Figure 2

Phylogenetic dendrogram constructed from the nucleotide sequences of selw determined for 16 isolates in the present study, representative S. aureus strains reported previously [22]. Genetic groups assigned by this dendrogram are shown on the right. Bootstrap values >80% are shown. Scale bar, 0.005 substitutions per nucleotide.