The cyclohexane tolerance and Phe-Arg-b-naphtylamide susceptibility of multidrug-resistant Enterobacter cloacae clinical isolates, and the predominance of one PFGE clone in Hungary

Abstract

The report concerns the molecular epidemiology, cyclohexane tolerance and Phe-Arg-β-naphtylamide (PAβN) susceptibility of multidrug-resistant Enterobacter cloacae isolates, with high-level fluoroquinolone resistance collected from healthcare facilities in a nationwide survey. A total of 113 multidrug-resistant E. cloacae isolates (recovered in 1997–2005) were subjected to disc diffusion tests, ERIC-PCR and XbaI PFGE. Representatives of the ERIC-types (n = 67) were tested further with cyclohexane and PAβN, using ciprofloxacin as the substrate. Forty-four per cent of the isolates were derived from the urinary tract, 19% from the bloodstream, 17% from the respiratory tract, and 15% from wound infections. Four ERIC-types (A, B, C and D) were distinguished, but 109 isolates were found to belong to a single, epidemic ERIC type: A. PFGE results suggested that the epidemic-type isolates were of monoclonal origin. Forty-two patients were involved in four outbreaks caused by the epidemic-type strains. Eighty-one cases were found to be nosocomial. At least fourfold reduction in ciprofloxacin MICs was found in the presence of PAβN in 79% of representative isolates (representing types A, C and D); an eightfold or greater reduction in ciprofloxacin MICs in the presence of PAβN (PAβN+) was found in 37% of representative isolates, representing types A and C. Eighty-five per cent of the representative isolates were found to be cyclohexane-tolerant, representing types A, C and D. This is the first report of a wide distribution of cyclohexane-tolerant or PAβN+ strains of E. cloacae. These featureindicators of adaptive mechanisms that help bacteria to survive in hospital wards may have contributed to the nationwide spread of type A strains.