ST9 MRSA strains carrying a variant of type IX SCCmec identified in the Thai community

Abstract

Background: Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in Thailand occur most frequently in healthcare facilities. However, reports of community-associated MRSA are limited.

Methods: We characterized 14 MRSA isolates from outpatients (O-1 to O-14) by phenotypic and genotypic methods and compared them with 5 isolates from inpatients (I-1 to I-5). Thai MRSA isolates from a healthcare worker (N-1) and a pig (P-1) were also included as ST9 MRSA strains from other sources.

Results: All MRSA isolates from the outpatients and inpatients were multidrug-resistant (resistant to ≥3 classes of antimicrobials). All of them except strains O-2 and I-3 carried type III SCCmec and belonged to agrI, coagulase IV, spa type t037 or t233, which related to ST239. The strain O-2 (JCSC6690) carried type IX SCCmec and belonged to agrII, coagulaseXIc, spa type t337 and ST9, whereas the strain I-3 carried a type III SCCmec and belonged to ST1429. Nucleotide sequence determination revealed that the type IX SCCmec element in strain O-2 was distinct from that in a Thai ST398 strain (JCSC6943) previously identified in 2011; nucleotide identities of ccrA and ccrB were 93 and 91%, respectively and several open reading frames (ORFs) at the joining regions were different. PCR experiments suggested that strain O-2 and N-1 carried similar SCCmec element, whereas that of strain P-1 was different, suggesting that distinct ST9-MRSA-IX clones might be spreading in this province.

Conclusions: The SCCmecIX-ST9 MRSA clones of distinct SCCmec subtypes might have emerged in the Thai community and might also have disseminated into the hospital.

Figure 1

Structural comparison of type IX SCCmec elements carried by strains O-2 and JCSC6943. Structures of SCCmec are illustrated based on the nucleotide sequences deposited in databases DDBJ/EMBL/GenBank, under accession nos. AB505628 for JCSC6943, AB705452 (region 1, indicated by black bar) and AB705453 (region 2, indicated by black bar) for O-2. The red arrowhead indicates the location of ISS, and the nucleotide sequences are given below. ORFs are colored as follows: yellow, insertion sequences; red, cad operons; lawn green, genes for arsenical resistance operons; orange, copB; salmon, ORFs for ccr gene complexes. The three joining regions (J1, J2, and J3 regions) are indicated in green. The locations of DNA fragments amplified with three pairs of primers (a, b, and c) are indicated in red bars. Nucleotide sequences of primers used for amplification for three loci are listed in Additional file 1: Table S1.

Figure 2

Dendrographic analysis of Pulsed-field Gel Electrophoresis banding patterns of SmaI-digested chromosomal DNAs of MRSA strains from human and a pig. PFGE patterns of 14 MRSA strains from outpatients (O-1 to O-14), 5 MRSA strains from inpatients (I-1 to I-5), an MRSA strain from a healthcare worker (N-1) and an MRSA strain from a pig (P-1) were compared. Curve-based phylogenetic tree using Ranked Pearson Correlation was generated using BioNewmerics.