The spread of a mupirocin-resistant/methicillin-resistant Staphylococcus aureus clone in Kuwait hospitals

High-level mupirocin- and methicillin-resistant Staphylococcus aureus (MRSA) isolated from five hospitals in Kuwait were studied by pulsed-field gel electrophoresis (PFGE) to determine their relatedness to one another and to high-level mupirocin-resistant MRSA isolated previously in a Burns Unit. The genetic location of mupirocin resistance determinant was also determined. All of the isolates were resistant to gentamicin, kanamycin, streptomycin, tetracycline and cadmium, and contained plasmids of 38, 26 and 2.8 kb. Two isolates contained additional 4.4-kb plasmids. Transfer experiments demonstrated that the 38-kb plasmid encoded high-level mupirocin resistance and the 4.4-kb plasmid encoded chloramphenicol resistance. PFGE typing of representative isolates from the five hospitals demonstrated that the majority of them had identical or closely related pulsed-field patterns suggesting that they had a common origin. However, they differed from high-level mupirocin-resistant MRSA isolated previously in the Burns Unit in their resistance and pulsed-field patterns. Whereas the majority of the previous isolates were susceptible to ciprofloxacin and resistant to trimethoprim and chloramphenicol, the majority of the current isolates were susceptible to trimethoprim and chloramphenicol, and resistant to ciprofloxacin. Only one of the current isolates had identical pulsed-field pattern to the majority of isolates obtained previously in the Burns Unit. The results suggested that a previously dominant clone of high-level mupirocin-resistant MRSA has been replaced in the Burns Unit by a new clone, which also spread in four other hospitals.