Molecular Characterization of Methicillin-Resistant Staphylococcus aureus from Outpatients in Northern Japan: Increasing Tendency of ST5/ST764 MRSA-IIa with Arginine Catabolic Mobile Element.

Arginine catabolic mobile element (ACME) is a genomic island of staphylococcus and is considered to confer enhanced ability to survive and growth on host bacterial cells. ACME has been typically identified in Panton-Valentine Leukocidin (PVL)-positive ST8 methicillin-resistant Staphylococcus aureus (MRSA) with SCCmec type IVa (USA300 clone), and it is also found in other lineages at low frequency. Prevalence and molecular characteristics of PVL+and/or ACME+ MRSA were investigated for 624 clinical isolates collected from outpatients in northern Japan from 2013 to 2014. Both PVL genes and ACME type I were detected in nine isolates (1.4%), which were ST8-MRSA-SCCmec IVa/spa type t008/agr-I; whereas solely PVL genes were positive in two isolates, ST30-MRSA-SCCmec IV and ST59-MRSA-SCCmec V. ACME type II' (previously referred to as ACME ΔII) was detected in 36 isolates (5.8%) with SCCmec II and V (32 and 4 isolates, respectively), exhibiting an increased rate within SCCmec II-MRSA (7.1%) compared with our previous studies (0.86-4.5%, 2008-2011). ACME II'-positive MRSA strains were classified into ST5-SCCmec IIa/V or ST764-SCCmec IIa belonging to five different spa types, with t002 being dominant. They harbored mostly enterotoxin gene clusters (seg-sei-sem-sen-seo-seu) and some more enterotoxin genes (seb1, seb2, sec3, sel, sep), showing resistance to more antimicrobials than ST8-MRSA-SCCmec IVa. ACME-SCCmec composite island (CI) of the 36 ACME II'-positive MRSA was classified into five types (ii)-(vi), among which type (ii) (orfX-ΨSCCΔJ1 SCCmec I-ACME II'-SCCmec II) was dominant and subdivided into the A3 variant and the less common A2 variant. CI types (v) and (vi) were considered novel genetic organizations having speG (acetyltransferase genes for polyamines) in inserted SCC4610/SCC266-like genetic elements. The present study revealed increased prevalence and genetic diversity of the ST5/ST764-MRSA-SCCmec II with ACME II' in northern Japan.

[MRSA clones identified in outpatient dermatology clinics].

To know the characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains disseminating through the Japanese community, we have determined types of Staphylococcal cassette chromosome mec (SCCmec) elements, Multi-Locus Sequence Typing (MLST), and carriages of four exotoxin genes (toxic-shock syndrome toxin, Panton-Valentine Leukocidine, and exfoliative toxins a and b) using 54 MRSA strains isolated from outpatients attending dermatology clinics at the four university hospitals of Juntendo University. Ten clonal complexes and 12 SCCmec types have been identified. As a result, more than 15 MRSA clones that were defined by the combination of genotype and SCCmec type, were identified. Among them, Clonal Complex (CC) 5-type IIa SCCmec strains were the most major (16 strains). In contrast to the fact that CC5- type IIa SCCmec strains known as a hospital-associated MRSA clone in Japan carried toxic-shock syndrome toxin gene (tst), only 2 of 16 strains have been shown to carry tst. Thirty-eight (70.4%) of isolates belonged to the clones distinct from the CC5-type IIa SCCmec strains. Among them, CC8 strains were major (12 strains), which contained 9 tst-positive CC8-type IVl SCCmec clones and a CC8-type IVa SCCmec strain carrying the Panton Valentine Leukocidin gene (lukS, F-PV). Clones related to impetigo were also identified: 7 exfoliative toxin b (etb) -positive clones, CC89-type IIa SCCmec and CC89-type V SCCmec strains; and 2 exfoliative toxin a (eta) -positive CC121-type V SCCmec strains. Other clones were as follows: CC1-type IVa SCCmec, CC8-type I SCCmec, CC81-type IVg SCCmec, CC97-type IVc SCCmec, CC91-type IVa SCCmec, CC59-type IVg SCCmec, CC45-type IIn SCCmec, CC89-SCCmec nontypeable, and CC8-type IVm, novel subtype of type IV SCCmec were identified in this study. Our data showed that many novel MRSA clones have emerged in the community.