Detection of Staphylococcal Cassette Chromosome mec -Associated DNA Segments in Multiresistant Methicillin-Susceptible Staphylococcus aureus (MSSA) and Identification of Staphylococcus epidermidis ccrAB4 in both Methicillin-Resistant S. aureus and MSSA

Abstract

Methicillin-susceptible Staphylococcus aureus (MSSA) can arise from methicillin-resistant S. aureus (MRSA) following partial or complete excision of staphylococcal cassette chromosome mec (SCCmec). This study investigated whether multiresistant MSSA isolates from Irish hospitals, where MRSA has been endemic for decades, harbor SCCmec DNA. Twenty-five multiresistant MSSA isolates recovered between 2002 and 2006 were tested for SCCmec DNA by PCR and were genotyped by multilocus sequence typing and spa typing. All isolates lacked mecA. Three isolates (12%) harbored SCCmec DNA; two of these (genotype ST8/t190) harbored a 26-kb SCCmec IID (II.3.1.2) remnant that lacked part of mecI and all of mecR1, mecA, and IS431; the third isolate (ST8/t3209) harbored the SCCmec region from dcs to orfX. All three isolates were detected as MRSA using the BD GeneOhm and Cepheid's Xpert MRSA real-time PCR assays. Six isolates (ST8/t190, n ‫؍‬ 4; ST5/t088, n ‫؍‬ 2), including both isolates with the SCCmec IID remnant, harbored ccrAB4 with 100% identity to ccrAB4 from the Staphylococcus epidermidis composite island SCC-CI. This ccrAB4 gene was also identified in 23 MRSA isolates representative of ST8/t190-MRSA with variant SCCmec II subtypes IIA to IIE, which predominated previously in Irish hospitals. ccrAB4 was located 5,549 bp upstream of the left SCCmec junction in both the MRSA and MSSA isolates with SCCmec elements and remnants and 5,549 bp upstream of orfX in the four MSSA isolates with ccrAB4 only on an SCC-CI homologous region. This is the first description of a large SCCmec remnant with ccr and partial mec genes in MSSA and of the S. epidermidis SCC-CI and ccrAB4 genes in S. aureus.

Distribution of SCCmec-associated phenol-soluble modulin in staphylococci

“…within mecI [11,12]. It was also negative in a S. vitulinus strain, which was mecR1-negative by array hybridisation.…”

“…This can be attributed to the insertion of a 1865 bp long IS1182 element and between the primers, M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 within mecI [11,12]. It was also negative in a S. vitulinus strain, which was mecR1-negative by array hybridisation.…”

“…This allowed characterising their SCCmec elements [10]. In addition, SCCmec elements of some isolates have previously been studied comprehensively [11,12]. PCR primers pr_psmMEC_02 (5'-CGAAAGCCTGAATGCAAGTCT-3') and pr_psmMEC_03…”

Evaluation of commercial chromogenic media for the detection of meticillin-resistant Staphylococcus aureus

“…This specificity rate is low in comparison to other studies where specificity rates of 95"99% have been reported for chromogenic agars. [11][12][13] However, these other studies confined investigations to clinical specimens only, whereas the current study included a diverse collection of MSSA strains. The recovery of these MSSA strains as presumptive MRSA isolates has implications for the diagnostic laboratory in terms of increasing the turnaround time and resource management.…”

“…[11][12][13] However, a challenge arose for the MRSA Select II and MRSA Brilliance 2 media: each failed to detect a small number of MRSA isolates (one and three isolates, respectively) exhibiting susceptible oxacillin MICs. A small increase in the prevalence of oxacillin-susceptible mecA-positive isolates has been previously reported elsewhere and similar isolates have been recovered in the National MRSA Reference…”