Abstract
High-level carbapenem-resistant (Cpm R) mutants, with MICs for imipenem and carbapenem of > 128 μ g/ml , were selected in vitro from four carbapenem-susceptible (Cpm S) clinical isolates of Bacteroides fragilis. The Cpm S strains produced very low levels of β-lactamase activity, which was increased approx. 50- to 100-fold in the Cpm R mutants. Isoelectric focussing and enzyme kinetic analysis ( K m and V rel ) of the ‘carbapenemases’ from the Cpm R mutants and similarly resistant clinical isolates suggested a close relatedness of the enzymes. A probe covering most of the cfiA gene encoding such an enzyme (Thompson, J.S. and Malamy, M.H. (1990) J. Bacteriol. 172, 2584–2593) hybridized with DNA from the Cpm R mutants, their Cpm S parental strains as well as clinical Cpm R isolates, but not from randomly chosen carbapenem-susceptible strains. The possibility is considered that mutations leading to expression of the silent carbapenemase gene, and thereby to clinically relevant carbapenem resistance, may also occur in the clinical setting.
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