Molecular Characterization and Transfer Among Staphylococcus Strains of a Plasmid Conferring High-Level Resistance to Mupirocin

Abstract

In this work, mupirocin resistance was correlated with the presence of plasmids in methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in the Rio de Janeiro Federal University Hospital in Brazil, where topical mupirocin has been used extensively since 1990. Of 19 strains studied, those exhibiting high-level resistance carried a large and relaxable plasmid of about 35 kb. Mupirocin-sensitive derivatives, obtained by growth at 42 C of a strain exhibiting high-level resistance, were devoid of the large plasmid, which was designated pMG1. Mupirocin resistance was transferred to strain RN8411 during overnight filter-matings at low frequencies (7.0 x 10(-9)/donor). The pMG1 plasmid was shown to be responsible for high-level mupirocin resistance in our isolates and to be incompatible with pGO1. Hybridization experiments suggested that mupirocin resistance in pMG1 is due to the presence of the ileS-2 gene. The pMG1 plasmid was successfully and bidirectionally transferred from Staphylococcus aureus to Staphylococcus epidermidis, suggesting that the latter may be a reservoir of this resistance plasmid. No transfer was detected to Staphylococcus haemolyticus. The development of self-transferable high-level mupirocin resistance should be considered when using mupirocin to control the spread of MRSA in hospitals.

Emergence of High-Level Mupirocin Resistance in Coagulase-Negative Staphylococci Associated with Increased Short-Term Mupirocin Use

“…However, the emergence of highlevel mupirocin resistance in CoNS isolates indicates an expanding reservoir of plasmids encoding mupirocin resistance. These plasmids can, in vitro, be transferred from CoNS strains to other CoNS strains, to MRSA, and to restriction-deficient S. aureus strains (1,12). The restriction system prevents the interchange of DNA with other bacterial species.…”

New Quadriplex PCR Assay for Detection of Methicillin and Mupirocin Resistance and Simultaneous Discrimination ofStaphylococcus aureusfrom Coagulase-Negative Staphylococci

“…CoNS are also among the most frequently isolated bacteria in clinical microbiology laboratories (29,31). More importantly, CoNS often serve as reservoirs of antimicrobial resistance determinants, since they usually have a high prevalence of multidrug resistance (5). Therefore, it is important to characterize and distinguish S. aureus strains and CoNS.…”

Low Concentrations of Mupirocin in the Pharynx following Intranasal Application May Contribute to Mupirocin Resistance in Methicillin-Resistant Staphylococcus aureus

“…Low-level and high-level mupirocin-resistant MRSA strains have been described previously (1,4). Mupirocin resistance in MRSA results from changes in the target enzyme, isoleucyltRNA synthetase, while high-level mupirocin resistance is plasmid encoded.…”