Rarity of transferable β-lactamase production by Klebsiella species

Abstract

We report a survey of β-lactamases and their transferability in Klebsiella spp. isolated from blood during 1992-95. β-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 β-lactamase (or a closely related enzyme); K. oxytoca also produced chromosomal β-lactamases, but these were distinct from SHV-1. Plasmid-encoded β-lactamases were rare in Klebsiella spp., being found in six (7.5%) isolates of K. pneumoniae and in none of the K. oxytoca. β-Lactamase activities were relatively low (< 100 nmoles nitrocefin hydrolysed per minute per mg of protein) and ampicillin MICs were ≤ 128 mg/L for most isolates of both species. However, all isolates of K. pneumoniae with plasmid-encoded β-lactamases, three other isolates of K. pneumoniae and three isolates of K. oxytoca had high β-lactamase activities (> 100 nmoles/mg/min) and very high ampicillin MICs (≤ 1024 mg/L).