Molecular Epidemiology and Identification of a Staphylococcus aureus Clone Causing Food Poisoning Outbreaks in Japan

Abstract

e Molecular characterization of isolates from staphylococcal food poisoning (SFP) outbreaks in Japan showed that the dominant lineage causing SFP outbreaks is clonal complex 81 (CC81), a single-locus variant of sequence type 1, coagulase type VII, positive for sea and/or seb, and positive for seh. Among various CC lineages producing staphylococcal enterotoxin A, CC81 showed the highest toxin productivity. Staphylococcal food poisoning (SFP), one of the most common food-borne diseases, results from the consumption of foods containing toxic amounts of staphylococcal enterotoxins (SEs) (1-4). SFP is associated with toxigenic Staphylococcus aureus strains that produce one or more members of a family of genes encoding heat-stable SEs. Recently, a superfamily of more than 23 different SEs and SE-like toxins (SEls) was studied for their biological activities (4-8). These bacterial toxins are also known as pyrogenic superantigens that stimulate polyclonal T-cell proliferation and can potentially cause toxic shock syndrome (1-4). The genes for SEs and SEls are harbored by various mobile genetic elements and/or genomic islands, including prophages, plasmids, S. aureus pathogenicity islands (SaPIs), and Sa␤. To date, in addition to the five classical types of SEs (SEA through SEE), 18 new types of SEs and SEls (SEG through SElX) have been described (4-8). Our recent study confirmed the emetic potential of SElK, SElL, SElM, SElN, SElO, SElP, and SElQ in the monkey, and these SEls were renamed SEK, SEL, SEM, SEN, SEO, SEP, and SEQ, respectively (9). Comparing SEs and SEls, SEA is considered the most important SE causing SFP. S. aureus is a common commensal bacterium of the skin and mucosal surfaces of humans, with estimates of 20% persistent and 60% intermittent colonization (10). Food handlers carrying enterotoxin-producing S. aureus in their nasal cavities or on their skin are important sources of food contamination during the cooking process (3). Contamination with S. aureus is believed to be associated primarily with improper handling of cooked or processed foods with improper storage under conditions that allow the growth of S. aureus and the production of SEs. Reports concerning the molecular epidemiology and genetic diversity of the isolates from SFP outbreaks are limited when clinical isolates are compared. In this investigation, we ex-

Positive Regulation of Staphylococcal Enterotoxin H by Rot (Repressor of Toxin) Protein and Its Importance in Clonal Complex 81 Subtype 1 Lineage-Related Food Poisoning

“…A recent study in Germany showed almost all of the isolates from food poisoning by ice cream were positive for seh as well as sea (9). Further, an epidemiology study in South Korea showed that S. aureus strains positive for seh formed one of the dominant groups causing SFP, similar to findings of our previous study (6,10). In the Netherlands, there was a report of an outbreak with S. aureus positive for seh only (3).…”

“…The sample was concentrated 25 times. Sandwich ELISA was performed to detect SEA, SEC, SEG-SEI, SEK, and SEM-SEQ as described by Omoe et al and Sato'o et al (6,13,16), with modifications. For detection, SuperSignal ELISA Femto maximum sensitivity substrate (Thermo Fisher Scientific, Waltham, MA) was used as the substrate.…”

“…Staphylococcus aureus was cultured in medium and on the meat product. Medium culture was performed as described previously (6), with some modifications. Staphylococcus aureus was precultured in 3 ml brain heart infusion (BHI) broth (Becton Dickinson, Sparks, MD) supplemented with 1% (wt/vol) yeast extract (Becton Dickinson) at 37°C overnight.…”

“…Almost all of the CC81 subtype 1 isolates carried sea and showed high SEA production (6). Moreover, another unique genetic characteristic is the presence of seh.…”

“…Moreover, another unique genetic characteristic is the presence of seh. All CC81 subtype 1 isolates carried seh (all 30 strains), while other isolates rarely carried it (1 strain in 341 strains) (6).…”