Diversity of Multidrug Efflux Genes and Phenotypic Evaluation of the In vitro Resistance Dynamics of Clinical Staphylococcus Aureus Isolates Using Methicillin; a Model β-lactam.

John F Antiabong,Marleen M Kock,Marthie M Ehlers,Nontombi M Mbelle

doi:10.2174/1874285801711010132

Abstract

Objectives:Methicillin-resistant Staphylococcus aureus (MRSA) across the world often leave clinicians with little or no choice of treatment options. The multi-drug efflux (MDE) genes are bacterial survival mechanisms responsible for the pumping out of antibiotics and other biocides from the cytoplasm. Whilst effort is being made in the development of antibiotic adjuvants such as efflux pumps inhibitors, information is needed on the diversity of these MDEs in the circulating S. aureus and on the growth dynamics of the clinical isolates in response to antibiotics is not regularly examined.Methods:Here, we evaluated the diversity of MDEs in cinical S. aureus recovered in a tertiary academic hospital, Pretoria, South African hospital using PCR and also employed visual minimum inhibitory concentration and quantitative analysis of spectrophometric measurements of bacterial growth in the presence of a model β lactam antibiotic (methicillin), to phenotypically elucidate the resistance pattern of these isolates in response to methicillin.Results:Three major distribution patterns of MDEs were observed in the clinical isolates evaluated. Moreover, norA, nor B and tet38 were present in 98.9% of the isolates while other MDE were present in different proportions ranging from 40 to 98.6% of the isolates. In addition, S. aureus isolates, be it of MRSA or MSSA genotype did not habour the same set of MDEs despite being recovered from the same hospital setting. Finally, we showed that MSSA displayed phenotypic resistance to methicilllin despite the non-detection of the mecA resistance gene.Conclusions:Our data suggest that the growth of S. aureus may be enhanced by β lactams (methicillin) and that MSSA may also display resistance to methicillin and perhaps other β lactam antibiotics. The high prevalence of MDEs suggestive of resistance to a broad spectrum of biocides and fluoroquinolones are particularly disturbing.

Highlights

Methicillin-resistant Staphylococcus aureus (MRSA) is a Gram positive bacterium with a circular chromosome of 2.2-2.8 Mbp and varieties of extrachromosomal elements that include plasmids, phages and other mobile elements [1]
Our data suggest that the growth of S. aureus may be enhanced by β lactams and that MSSA may display resistance to methicillin and perhaps other β lactam antibiotics
The multi-drug efflux genes (MDE) are grouped into five families based on their structure and the kinetics of their activities: (i) the major facilitator superfamily (MFS), (ii) the small multi-drug resistance (SMR) family, (iii) the multi-drug and toxic compound extrusion (MATE) family, (iv) the resistance-nodulation-cell division (RND) superfamily and (v) the adenosine-triphosphate (ATP)-binding cassette (ABC) superfamily

Summary

Introduction

MRSA is a Gram positive bacterium with a circular chromosome of 2.2-2.8 Mbp and varieties of extrachromosomal elements that include plasmids, phages and other mobile elements [1]. The Open Microbiology Journal, 2017, Volume 11 133 chromosomal and extra-chromosomal virulence determinants, antibiotic resistance genes and multi-drug efflux genes (MDE) which play significant roles in the pathogenesis of S. aureus-associated infections and poor antibiotic therapeutic outcome [2]; thereby increasing patient suffering and sustained epidemics. The MDE genes are bacterial survival mechanisms responsible for pumping out antibiotics and other biocides from the cytoplasm [3]. These efflux pumps can either be chromosomal or plasmid encoded and are able to extrude specific and/or different classes of antimicrobial compounds including biocides [2]. Several MDEs have been described in S. aureus Table (S1) that contribute to the antimicrobial resistance mechanisms in this pathogen [2]

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Conclusion