Enfermedades Infecciosas y Microbiología Clínica
Original articlePhenotypic and genetic characteristics of fluoroquinolone- and methicillin-resistant Staphylococcus aureusCaracterísticas fenotípicas y genéticas de Staphylococcus aureus resistente a meticilina y a fluoroquinolonas
Introduction
Methicillin-resistant Staphylococcus aureus (MRSA) causes a large number of infections.1 Its ability to adapt and acquire resistance to different antimicrobials has possibly favoured its spread both in hospitals and in the community.1 Methicillin resistance in S. aureus is coded by the mec gene, included in a genomic island called the staphylococcal cassette chromosome mec (SCCmec). The fluoroquinolones are among the therapeutic agents whose activity is not affected by SCCmec. However, rates of fluoroquinolone resistance have increased,2 mainly due to mutations in genes gyrA and grlA.2
S. aureus expresses surface proteins that are essential for its success both as a commensal and as a pathogen. The most important group of these proteins are the MSCRAMMs (Microbial Surface Components Recognizing Adhesive Matrix Molecules).3
The objective of this study was to analyse the increase in MRSA resistant to fluoroquinolones and its possible relation with a clonal selection. In addition, the characteristics of the MRSA isolates studied were analysed including the phenotypic hypermutability of the identified clones and the MSCRAMMs content.
Section snippets
Selection of microorganisms and patients for inclusion in the study
The University Hospital Complex of Pontevedra has a catchment population of 296,463. We selected two groups of MRSA isolates from the years 2009 to 2011: (i) those that presented resistance only to beta-lactams (oxacillin, OX-R), being susceptible to all other groups of antimicrobials; and (ii) those with resistance to oxacillin and to levofloxacin OX-R-LEV-R, being susceptible to all other antimicrobial groups. Only one isolate per patient was analysed in the study. A total of 192 isolates
Characteristics of the isolates and molecular typing of MRSA
Between 2009 and 2011, a total of 2587 S. aureus were isolated; 728 (28.1%) were MRSA. Of the 728 MRSA isolates, 49 (6.7%) were only resistant to beta-lactams (OX-R) and 143 (19.6%) were OX-R-LEV-R (Table 1). Throughout the three years of the study (2009–2011), an increase of 9.1% was identified in OX-R-LEV-R MRSA being statistically significant (p < 0.05), whereas OX-R MRSA isolates only increased by 2.1% (Table 1). A total of 60 MRSA were considered community-associated MRSA (CA-MRSA) strains
Discussion
MRSA infections are more common in older individuals with comorbidities.17 In our study, CA-MRSA was the cause of 31.3% of the infections. This figure is higher than that previously reported in several nationwide studies in Spain18 and in Europe.19 However, the rates in the United States are much higher, above 50%.20
The increase in the prevalence of resistance to fluoroquinolones has been associated with different factors21 including the persistent increase in quinolone prescriptions, as is the
Funding
This work was partially financed by Fondo de Investigaciones Sanitarias PI070812 and Consejería de Sanidad de la Junta de Galicia PS08/34.
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
We would like to thank Dr. Marta García Campello, Head of the Microbiology and Parasitology Laboratories Department of the University Hospital Complex of Pontevedra, for allowing us access to the strains under study. We would also like to thank Dr. José Pintado Valverde of Marinas de Vigo Research Institute (CSIC) for his collaboration in the running of the GelCompar II software. We would also like to thank Dr. Ángel Salgado Barreira for the statistical analysis.
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