First identification of an SHV-12 extended-spectrum beta-lactamase in Klebsiella pneumoniae isolated in Italy.

A clinical isolate of Klebsiella pneumoniae highly resistant to third- and fourth-generation cephalosporins, cephamycins and aminoglycosides, was isolated in 1991 from urine. Analysis of a crude extract showed the presence of three beta-lactamases with isoelectric points of 6.6, 7.5 and 8.2. The enzyme with pI 8.2 was transferred by conjugation into Escherichia coli K-12 J53 and was responsible for the resistance to third-generation cephalosporins and monobactams, but not to other antibiotics. Kinetic studies of partially purified beta-lactamase from the transconjugant strain confirmed that the enzyme was able to hydrolyse ceftazidime, cefotaxime and aztreonam but not cephamycins. Analysis of the transconjugant showed the presence of two small non-conjugative plasmids of 14 and 6 kb. A polymerase chain reaction was performed using primers specific for the bla(SHV) gene and a fragment of the expected size (about 961 bp) was obtained with both the K. pneumoniae clinical isolate and the transconjugant. Nucleotide sequence analysis of the fragment showed that it encoded the enzyme SHV-12, derived from SHV-5 (with Gln-35 to Leu). This is the first report of an SHV-12-like enzyme isolated in Italy.