1 School of Biochemistry and Microbiology, University of Leeds, Leeds LS2 9JT, UK; 2 Division of Geriatric Medicine, Department of Internal Medicine, Veterans Affairs Ann Arbor Healthcare System, The University of Michigan Medical School, Ann Arbor, MI, USA; 3 Division of Infectious Diseases, Department of Internal Medicine, Veterans Affairs Ann Arbor Healthcare System, The University of Michigan Medical School, Ann Arbor, MI, USA
Received 24 July 2005; returned 26 August 2005; revised 26 September 2005; accepted 28 September 2005
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Abstract |
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Patient and methods: A persistent carrier of mupirocin-susceptible MRSA participated in a trial of mupirocin for nasal decolonization among nursing home residents. During prophylaxis a high-level mupirocin-resistant MRSA emerged in the nasal isolates from this patient. S. aureus and coagulase-negative staphylococci were isolated prior to, during and after 14 days of mupirocin treatment. The staphylococcal isolates and their plasmids were examined by molecular genetic methods.
Results: All mupirocin-susceptible and -resistant MRSA isolates possessed the same genotype. The patient was also colonized by a single mupirocin-resistant Staphylococcus epidermidis strain. The mupirocin-resistant MRSA and S. epidermidis strains harboured identical plasmids that carried the mupA determinant and genes for conjugative DNA transfer in staphylococci. These plasmids could be transferred in vitro from both clinical isolates to S. aureus RN2677.
Conclusions: The MRSA strain contained a conjugative plasmid expressing mupA that was identical with that found in the S. epidermidis strain which colonized the patient. These findings suggest that transfer of mupA from S. epidermidis to MRSA probably occurred during mupirocin prophylaxis.
Keywords: MRSA , nasal decolonization , coagulase-negative , staphylococci
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Introduction |
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Widespread use of mupirocin has resulted in increased prevalence of high-level mupirocin resistance, particularly among coagulase-negative staphylococci (CoNS).4 Accordingly, it has been suggested that mupirocin-resistant CoNS might be an important source of the mupA determinant in MRSA, but evidence for transfer from CoNS during mupirocin prophylaxis has not been obtained.3
During a study to evaluate the efficacy of mupirocin in eliminating nasal carriage of S. aureus among nursing home residents, high-level resistance to mupirocin emerged in the MRSA that persistently colonized a participant in the study.1 Since the patient was also colonized by mupirocin-resistant CoNS, we investigated whether mupirocin resistance in MRSA originated from the mupirocin-resistant CoNS.
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Patient and methods |
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Staphylococcal nasal isolates recovered from the patient were also typed by PFGE1 and MRSA isolates were further characterized by spa typing.5 PCR amplification and sequencing of the native ileS genes of MRSA isolates were performed to detect mutations which may confer resistance to mupirocin.2 Filter matings were performed using S. aureus strains RN2677 (novobiocin- and rifampicin-resistant) as the recipient and RN4220 (pGO1) as a control donor.6 Plasmid DNA isolated from staphylococci using the Qiagen Midi Plasmid Extraction Kit (Qiagen, Crawley, UK) was analysed by Southern hybridization with the AlkPhos Direct kit (Amersham Biosciences, Buckinghamshire, UK).
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Results and discussion |
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All pre-therapy mupirocin-susceptible CoNS strains were eradicated by intranasal application of mupirocin within 3 days of starting treatment. These susceptible organisms were supplanted by a high-level mupirocin-resistant CoNS that persisted in all subsequent nasal samples obtained from the patient for the remainder of the study. PFGE analysis of CoNS isolates indicated that while mupirocin-susceptible isolates were distinct strains, all mupirocin-resistant CoNS isolates represented the same strain (data not shown). Therefore, the patient probably became colonized by a single mupirocin-resistant CoNS clone, which was identified as Staphylococcus epidermidis.
Mutations within ileS may confer resistance to mupirocin in S. aureus.2 However, no mutations were detected within PCR amplicons of the ileS from the mupirocin-resistant MRSA strain. The genetic basis of mupirocin resistance among staphylococcal nasal isolates (CoNS and MRSA) was examined by Southern hybridization using a mupA probe prepared by PCR amplification from the mupA-positive high-level mupirocin-resistant S. aureus strain, LZ-1.7,8 Only isolates that expressed high-level resistance to mupirocin contained plasmids that hybridized to the mupA probe (Figure 1).
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The increasing prevalence of transferable mupirocin resistance among CoNS species could be an important threat to the future use of mupirocin against MRSA.3,4 In this study we obtained direct evidence for the transfer of mupirocin resistance from S. epidermidis to S. aureus in a clinical situation involving the use of mupirocin. Indeed, it appears that after mupirocin prophylaxis had commenced, the patient became colonized with a single mupirocin-resistant S. epidermidis strain that transferred plasmid-borne mupA to mupirocin-susceptible MRSA resulting in mupirocin treatment failure. It is likely that mupirocin-resistant CoNS was a minor endogenous strain that was not detected upon initial screening and emerged under the selective pressure of mupirocin. In a prior study, 90% of our laboratory staff and patients had high-level mupirocin-resistant CoNS emerge during therapy that persisted following treatment.10
Studies of S. aureus colonization in our nursing home residents have shown that 82% of persistent carriers harbour the same strain for many months.11 Therefore, it is unlikely that the patient described here became recolonized with a different MRSA strain following treatment with mupirocin. It is also unlikely that he acquired a high-level mupirocin-resistant strain from other patients enrolled in the study, since mupirocin-resistant MRSA was not isolated from these participants.
In conclusion, it appears that high-level mupirocin resistance was acquired by the patient's pre-therapy MRSA strain through conjugative transfer of mupirocin resistance from S. epidermidis during nasal decolonization prophylaxis with mupirocin.
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Transparency declarations |
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Acknowledgements |
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References |
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2.
Hurdle JG, O'Neill AJ, Chopra I. The isoleucyl-tRNA synthetase mutation V588F conferring mupirocin resistance in glycopeptide-intermediate Staphylococcus aureus is not associated with a significant fitness burden. J Antimicrob Chemother 2004; 53: 1024.
3. Cookson BD. The emergence of mupirocin resistance: a challenge to infection control and antibiotic prescribing practice. J Antimicrob Chemother 1998; 41: 118.[Abstract]
4. Deshpande LM, Fix AM, Pfaller MA et al. Emerging elevated mupirocin resistance rates among staphylococcal isolates in the SENTRY Antimicrobial Surveillance Program (2000): correlations of results from disk diffusion, E test and reference dilution methods. Diagn Microbiol Infect Dis 2002; 42: 28390.[CrossRef][ISI][Medline]
5.
Harmsen DH, Claus WW, Rothganger J et al. Typing of methicillin-resistant Staphylococcus aureus in a university hospital setting by using novel software for spa repeat determination and database management. J Clin Microbiol 2003; 41: 54428.
6. Archer GL, Johnston JL. Self-transmissible plasmids in staphylococci that encode resistance to aminoglycosides. Antimicrob Agents Chemother 1983; 24: 707.[ISI][Medline]
7. Kauffman CA, Terpenning MS, He X et al. Attempts to eradicate methicillin-resistant Staphylococcus aureus from a long-term care facility with the use of mupirocin ointment. Am J Med 1993; 94: 3718.[CrossRef][ISI][Medline]
8. Janssen DA, Zarins LT, Schaberg DR et al. Detection and characterization of mupirocin resistance in Staphylococcus aureus. Antimicrob Agents Chemother 1993; 37: 20036.[Abstract]
9. Thomas WD, Archer GL. Identification and cloning of the conjugative transfer region of Staphylococcus aureus plasmid pGO1. J Bacteriol 1989; 171: 68491.[ISI][Medline]
10. Bradley S, Cinti S, Ramsey M et al. Mupirocin resistance (MUP-R) in Staphylococcus aureus and coagulase negative staphylococci (CNS). In: Abstracts of the Ninety-fifth Annual Meeting of the American Society for Microbiology, Washington, DC, 1995. Abstract A-29, p. 148. American Society for Microbiology, Washington, DC, USA.
11. Bradley SF, Terpenning, MS, Ramsey MA et al. Methicillin-resistant Staphylococcus aureus: colonization and infection in a long-term facility. Ann Intern Med 1991; 115: 41722.[ISI][Medline]
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