title: Genetic analysis of methicillin-resistant Staphylococcus aureus expressing high- and low-level mupirocin resistance.
abstract: Clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) expressing high- and low-level mupirocin resistance were studied to determine the genetic location of mupirocin and other resistance determinants. Mupirocin resistance was confirmed by MIC determination with E-test strips. Curing and transfer experiments were used to establish the genetic location of the resistance determinants and the PCR with mupA-specific primers was used to detect the presence of mupA genes. High-level mupirocin-resistant isolates had MICs >1024 mg/L, whereas the low-level resistant isolates had MICs of 32-128 mg/L. The isolates carried plasmids ranging from 2.8 to 38 kb in size. All of them carried 26- and 3.0-kb plasmids, but only the high-level mupirocin-resistant isolates carried a 38-kb plasmid. Curing and transfer experiments revealed that the 26-kb plasmid encoded resistance to cadmium, mercuric chloride, propamidine isethionate and ethidium bromide and the 38-kb plasmid was a conjugative plasmid encoding high-level mupirocin resistance. One isolate, IBN287, carried both plasmid-borne high-level and chromosomal low-level mupirocin resistance. The mupA gene was detected on the 38-kb plasmid DNA but not in the genomic DNA of the low-level mupirocin-resistant isolates. The genomic DNA of strain IBN287 cured of the 38-kb mupirocin resistance plasmid did not contain mupA. The results suggest that different genes encoded low- and high-level mupirocin resistance in these isolates.
authors.affiliation: Department of Microbiology, Faculty of Medicine, Kuwait University, Kuwait.
authors.forename: E E
authors.initials: EE
authors.lastname: Udo
authors.affiliation: Department of Microbiology, Faculty of Medicine, Kuwait University, Kuwait.
authors.forename: L E
authors.initials: LE
authors.lastname: Jacob
authors.affiliation: Department of Microbiology, Faculty of Medicine, Kuwait University, Kuwait.
authors.forename: B
authors.initials: B
authors.lastname: Mathew
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003227:Conjugation, Genetic / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004352:Drug Resistance, Microbial; D018432:Drug Resistance, Multiple / Q000235:genetics*; D006801:Humans; D016106:Methicillin Resistance / Q000235:genetics*; D016712:Mupirocin / Q000494:pharmacology*; D010957:Plasmids / Q000737:chemistry; D016133:Polymerase Chain Reaction; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D001618:beta-Lactamases / Q000032:analysis / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D016712:Mupirocin; D001618:beta-Lactamases