Abstract
BackgroundCoagulase-negative staphylococci (CoNS) are recognized as a large reservoir of staphylococcal cassette chromosome mec (SCCmec) harboured by Staphylococcus aureus. However, data of SCCmec in CoNS are relatively absent particularly in China.MethodsSeventy-eight CoNS clinical and 47 community isolates were collected in Beijing. PCR was performed to classify SCCmec types. Under oxacillin treatment, quantitative real-time reverse transcription PCR (qRT-PCR) was performed to compare mecA mRNA levels and mRNA half-life between isolates with single SCCmec element and those with multiple one. Their growth curves were analysed. Their bacterial cell wall integrity was also compared by performing a Gram stain. All ccr complex segments were sequenced and obtained ccr segments were analysed by phylogenetic analyses.ResultsAll 78 clinical isolates had mecA segments compared with 38% in community isolates (total 47). Only 29% clinical isolates and 33% community isolates (among mecA positive isolates) harboured a single previously identified SCCmec type; notably, 17% clinical isolates and 28% community isolates had multiple SCCmec types. Further studies indicated that isolates with multiple SCCmec elements had more stable mecA mRNA expression compared with isolates with single SCCmec elements. CoNS with multiple SCCmec elements demonstrated superior cell wall integrity. Interestingly, phylogenetic analyses of obtained 70 ccr segments indicated that horizontal gene transfer of the ccr complex might exist among various species of clinical CoNS, community CoNS and S. aureus.ConclusionsCoNS recovered from patients carried extremely diverse but distinctive SCCmec elements compared with isolates from the community. More attention should be given to CoNS with multiple SCCmec not only because they had superior cell wall integrity, but also because CoNS and S. aureus might acquire multiple SCCmec through the ccr complex.
Highlights
Coagulase-negative staphylococci (CoNS) are recognized as a large reservoir of staphylococcal cassette chromosome mec (SCCmec) harboured by Staphylococcus aureus
Most of the CoNS recovered from community were S. epidermidis (n = 40), and the other CoNS were few, including S. hominis (n = 5) and S. haemolyticus (n = 2)
Diverse SCCmec types and multiple SCCmec elements No mecC gene was detected in all these isolates
Summary
Coagulase-negative staphylococci (CoNS) are recognized as a large reservoir of staphylococcal cassette chromosome mec (SCCmec) harboured by Staphylococcus aureus. Coagulase-negative staphylococcus (CoNS) is a part of the commensal bacterial microflora of healthy people. The most common CoNS in nosocomial infection are Staphylococcus epidermidis, followed by Staphylococcus haemolyticus, Staphylococcus hominis and Staphylococcus capitis [4]. Another important reason for the increasing concern for CoNS is the fact that they harbour SCCmec elements, which are found in methicillin-resistant S. aureus (MRSA). SCCmec elements harbour mec genes (mecA/mecC), providing resistance to methicillin and most other beta-lactam antibiotics [5]
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