Diversity of antibiotic resistance genes and staphylococcal cassette chromosome mec elements in faecal isolates of coagulase-negative staphylococci from Nigeria.

Luca Agostino Vitali,Adebayo Lamikanra,Manuela Prenna,Ezekiel Olugbenga Akinkunmi,Dezemona Petrelli

doi:10.1186/1471-2180-14-106

Abstract

BackgroundCoagulase-negative staphylococci (CoNS) are opportunistic pathogens found as colonisers of the human gut. This study was carried out to examine the genetic resistance mechanisms in faecal isolates of CoNS. The study investigated 53 non-duplicate CoNS isolates obtained from the fresh stool samples of apparently healthy subjects in the community of Ile-Ife, South-Western Nigeria. Antibiotic susceptibility testing was assessed by the disc diffusion test while antibiotic resistance genes were analysed by PCR. mecA positive isolates were analysed by Staphylococcal Chromosome Cassette mec (SCCmec) and cassette chromosome recombinase (ccr) complex typing methods.ResultsResistance genes were detected only in isolates that showed resistance by phenotypic screening. The aac(6′)–aph(2″) gene was detected in all the three isolates resistant to gentamicin. Four of the five erythromycin resistant isolates were positive for the ermC gene, the remaining isolate carried the msrA gene. The tetK gene was detected in 6 of the 7 tetracycline resistant isolates while 4 possessed the tetM gene. Three of the isolates (S. haemolyticus, S. xylosus and S. capitis) had both genes. Several SCCmec types were found: SCCmec I- ccrABβ2-α2 (4 isolates: 3 S. epidermidis, 1 S. warneri), SCCmecIVb- ccrABβ2-α3 (1 isolate: S. epidermidis), SCCmecIVd- ccrABβ2-α3 (8 isolates: 3 S. epidermidis, 2 S. xylosus, 1 S. saprophyticus, 1 S. warneri, 1 S. capitis), and untypable (2 isolates: S. epidermidis).ConclusionThis genetic background could be a reservoir for interspecies gene transfer among CoNS and S. aureus in the intestinal tract.

Highlights

Coagulase-negative staphylococci (CoNS) are opportunistic pathogens found as colonisers of the human gut
Bacterial strains CoNS isolates were obtained from freshly voided stool samples of apparently healthy children and adult subjects (n = 117) who came for immunizations at five healthcare institutions and households in the community of Ile-Ife, in South-Western Nigeria who gave consent for sample collection
Staphylococcal Chromosome Cassette mec (SCCmec) type comprised of SCCmecIccrABβ2-α2 (4 isolates: 3 S. epidermidis, 1 S. warneri), SCCmecIVb- ccrABβ2-α3 (1 isolate: S. epidermidis), SCCmecIVd- ccrABβ2-α3

Summary

Introduction

Coagulase-negative staphylococci (CoNS) are opportunistic pathogens found as colonisers of the human gut. This study was carried out to examine the genetic resistance mechanisms in faecal isolates of CoNS. Coagulase-negative staphylococci (CoNS) are opportunistic pathogens commonly associated with nosocomial infections [1]. Most CoNS strains have been reported to have acquired resistance to methicillin and almost all classes of antimicrobial agents [2,3]. In the vast majority of staphylococcal isolates, resistance to macrolides such as erythromycin has been to lincosamides and to streptogramin B compounds (MLSB phenotype). For full resistance to the streptogramine combination quinupristin-dalfopristin, strains need to carry additional resistance to streptogramin A compounds, which may be mediated by acetylation (acetyl transferase genes vat(A), vat(B) and vat(C), or by putative efflux pumps encoded by vga(A) and vga(B) [5,6]

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