Rarity of transferable beta-lactamase production by Klebsiella species

We report a survey of beta-lactamases and their transferability in Klebsiella spp, isolated from blood during 1992-95, beta-Lactamases were characterized by determination of isoelectric point (pI), by hybridization 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 isolates of K. pneumoniae had a chromosomally encoded SHV-1 beta-lactamase (or a closely related enzyme); K. oxytoca also produced chromosomal 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-Lactamase activities were relatively low (<100 nmoles nitrocetin hydrolysed per minute per mg of protein) and ampicillin MICs were less than or equal to 128 mg/L for most isolates of both species, However, all isolates of K. pneumoniae with plasmid-encoded beta-lactamases, three other isolates of K. pneumoniae and three isolates of K. oxytoca had high beta-lactamase activities (>100 nmoles/mg/min) and very high ampicillin MICs (greater than or equal to 1024 mg/L).