RARITY OF TRANSFERABLE BETA-LACTAMASE PRODUCTION BY KLEBSIELLA SPECIES

We report a survey of beta-lactamases and their transferability in Kle bsiella spp, isolated from blood during 1992-95, beta-Lactamases were characterized by determination of isoelectric point (pI), by hybridiza tion of plasmid DNA preparations with probes for SHV and TEM sequences and by PCR with SHV- or TEM-specific primers, There were 80 isolates of Klebsiella pneumoniae and 22 isolates of Klebsiella oxytoca, Most i solates of K. pneumoniae had a chromosomally encoded SHV-1 beta-lactam ase (or a closely related enzyme); K. oxytoca also produced chromosoma l beta-lactamases, but these were distinct from SHV-1. Plasmid-encoded beta-lactamases were rare in Klebsiella spp,, being found in six (7.5 %) isolates of K. pneomoniae and in none of the K. oxytoca. beta-Lacta mase activities were relatively low (<100 nmoles nitrocetin hydrolysed per minute per mg of protein) and ampicillin MICs were less than or e qual to 128 mg/L for most isolates of both species, However, all isola tes of K. pneumoniae with plasmid-encoded beta-lactamases, three other isolates of K. pneumoniae and three isolates of K. oxytoca had high b eta-lactamase activities (>100 nmoles/mg/min) and very high ampicillin MICs (greater than or equal to 1024 mg/L).