Antimicrobial Susceptibility Study
Genotypic and phenotypic characterization of methicillin-resistant Staphylococcus aureus (MRSA) clones with high-level mupirocin resistance

https://doi.org/10.1016/j.diagmicrobio.2016.02.021Get rights and content

Highlights

  • Mupirocin resistant MRSA isolates (HLMUPR-MRSA) were prevalent in skin and soft tissue samples.

  • HLMUPR-MRSA isolates showed higher gentamicin and tobramycin resistance rates than susceptible isolates.

  • All HLMUPR-MRSA were included in CC5, widely distributed in hospital and community settings in Spain.

  • An association between CC5/ST125/t067 and erythromycin resistance (encoded by msr(A) gene) was observed.

  • Nine IS257-ileS2 amplification patterns were identified in HLMUPR-MRSA, p3 pattern being the most frequent in CC5/ST125/t067.

Abstract

A high proportion of methicillin-resistant Staphylococcus aureus isolates recovered in one year period showed high-level mupirocin-resistance (HLMUPR-MRSA) in our environment (27.2%). HLMUPR-MRSA isolates were mainly collected from skin and soft tissue samples, and diabetes was the main related comorbidity condition. These isolates were more frequently found in vascular surgery. HLMUPR-MRSA was more resistant to aminoglycosides than mupirocin-susceptible MRSA, linked to the presence of bifunctional and/or nucleotidyltransferase enzymes with/without macrolide resistance associated with the msr(A) gene. Most of HLMUPR-MRSA isolates belonged to ST125/t067. Nine IS257-ileS2 amplification patterns (p3 was the most frequent) were observed in HLMUPR-MRSA isolates, suggesting the presence of several mupirocin-resistance-carrying plasmids in our environment and promoting the emergence of mupirocin resistance. The presence of the same IS257-ileS2 amplification pattern p3 in 65% of HLMUPR-MRSA, all of them ST125/t067, suggests a clonal spread in our hospital and community environment which could explain the high prevalence of HLMUPR-MRSA during the study period. An outbreak situation or an increase in mupirocin consumption was not observed.

Introduction

Mupirocin, also known as pseudomonic acid A, is a topical antibiotic that was originally isolated from Pseudomonas fluorescens. It is used for decolonization of nasal carriers of methicillin-resistant Staphylococcus aureus (MRSA) (Sutherland et al., 1985). The increased use of this antibiotic has been accompanied by outbreaks of mupirocin-resistant MRSA (Schmitz and Jones, 1997, Simor et al., 2007).

Mupirocin is an analogue of isoleucine that inhibits protein synthesis by competitively binding to the enzyme isoleucyl-tRNA synthetase (Yanagisawa et al., 1994). The high-level mupirocin-resistant isolates show a MIC greater than 512 mg/L. This resistance is mediated by the acquisition of a plasmid containing the ileS2 gene that encodes an alternative isoleucyl-tRNA synthetase enzyme and is generally flanked by copies of the insertion sequence IS257 (Pérez-Roth et al., 2010, Woodford et al., 1998).

The objective of the study was to identify the prevalence, clonal lineages, resistance mechanisms and virulence genes of high-level mupirocin-resistant MRSA (HLMUPR-MRSA) isolates recovered from inpatients and outpatients in our institution during one year.

Section snippets

Material and methods

One hundred forty-seven MRSA isolates were collected from clinical samples in the University Teaching Hospital “Lozano Blesa” (Zaragoza, Spain) from July 2009 to July 2010. Only one isolate per patient was included. The study was conducted retrospectively. Clinical records of all patients were reviewed. For each patient the following data were collected: gender, age, medical service, source of the culture sample and comorbid conditions during the year prior to MRSA isolation (dialysis,

Results and discussion

During the course of this study, MRSA prevalence in our hospital was 30.9%, consistent with other resistance rates found in different Spanish hospitals (Cuevas et al., 2008, González-Domínguez et al., 2015, Lozano et al., 2013). Forty MRSA isolates showed HLMUPR, representing 27.2% of the studied isolates (mupirocin MICs ≥ 256 mg/L). This percentage is higher than that found in other Spanish hospital (Daskalaki et al., 2009). Other isolates were mupirocin-susceptible (i.e. MIC, <8 mg/L).

Conclusions

Most of HLMUPR-MRSA isolates that are circulating in our environment belonged to ST125/t067. This specific lineage is predominant in our area and it is associated with resistance to aminoglycosides, and to a lesser extent, to macrolides. The presence of the same IS257-ileS2 amplification pattern p3 in 65% of HLMUPR-MRSA, all of them ST125/t067, suggests a clonal spread in our hospital and community environment which could explain the high prevalence of HLMUPR-MRSA during the study period. An

Funding

This work was supported by Departamento de Ciencia, Tecnología and Universidad del Gobierno de Aragón, Spain (Project DGA-FSE/Grupos consolidados, B24-211130). MGD received a grant from the S.E.I.M.C (Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica).

Conflict of interest

None.

Acknowledgments

We are grateful to Dr. E. Pérez-Roth for his technical assistance in the rapid typing method for strain characterization based on the heterogeneous IS257-ileS2 spacer regions and Dr. J Pintado for his helping with the GelCompar II® software.

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