SCCmec typing for methicillin-resistant coagulase-negative staphylococci clinical isolates

Background: Methicillin-resistant coagulase-negative staphylococci (MR-CoNS) are opportunistic pathogens and serve as a large reservoir of staphylococcal cassette chromosome mec (SCCmec). SCCmec typing provides important information about the epidemiology of MR-CoNS.

Objective: To determine SCCmec types of MR-CoNS clinical isolates.

Methods: MR-CoNS were collected from various clinical specimens from West China Hospital, from March to May 2010. Identification and antimicrobial susceptibility were determined with the Phoenix system (BD). These isolates also grew on plates with 4 mg/L cefoxitin. Species identification of a few randomly-selected isolates was confirmed by sequencing 16s rRNA genes. SCCmec typing was performed using multiplex PCR published previously. For isolates in which SCCmec could not typed, classes of the mec complex were determined by additional PCR and the ccr genes (ccrA, ccrB and ccrC) were amplified with published primers and then sequenced.

Results: A total of 86 MR-CoNS were collected, including 38 S. epidermidis, 21 S. haemolyticus, 10 S. hominis, 6 S. capitis, 4 S. warneri, 2 S. cohnii, 2 S. saprophyticus, 1 S. kloosii, 1 S. simulans and 1 S. auricularis. All isolates had mecA detected by PCR. SCCmec types were assigned for 64 isolates by multiplex PCR and were assigned for 6 other isolates by PCR targeting the mec and ccr complexes. Among these 70 isolates with determined SCCmec types, 47 had a single type, including type III (n=19), IV (n=14), V (n=10), II (n=2), I (n=1) and VIII (n=1), while 22 isolates had two types, III+V (n=12), II+V (n=8) or II+IV (n=2), and 1 isolate had three types (two IV, IVa and IVb, plus V). Two isolates had a novel SCCmec type (ccr type 1 and mec type A). The SCCmec types of the remaining 14 isolates could not determined.  

Conclusions: SCCmec types III, IV and V were prevalent in MR-CoNS and many isolates could harbor more than one type. SCCmec of a substantial portion of MR-CoNS still could be typed based on schemes mainly targeting S. aureus, highlighting the need of developing new schemes with emphasis on MR-CoNS.