Differential expression of bla(SHV) related to susceptibility to ampicillin in Klebsiella pneumoniae.

Klebsiella pneumoniae usually shows intrinsic resistance to ampicillin and other beta-lactams. bla(SHV) is thought to be a key beta-lactamase gene responsible for this intrinsic resistance to ampicillin. Nevertheless, surveys of clinical strains reveal that some isolates of K. pneumoniae that carry bla(SHV) remain susceptible to ampicillin. To explore susceptibility to ampicillin in relation to bla(SHV) in K. pneumoniae, we analysed the existence and transcription of bla(SHV) and determined beta-lactamase activity as well as the susceptibilities to clinically relevant beta-lactams, including ampicillin in 160K. pneumoniae isolates from China. In total, 141 isolates (88.1%) were detected as bla(SHV)-positive, 20 (14.2%) of which were found to be broadly susceptible to all beta-lactams tested, including ampicillin. Among the 20 broadly susceptible isolates, sequencing of bla(SHV) revealed synonymous point mutations in 19 isolates and a premature stop codon in 1 isolate. Reverse transcription-polymerase chain reaction failed to detect bla(SHV) mRNA in five isolates (25%). The results demonstrate that differential expression of bla(SHV) in clinical isolates of K. pneumoniae can affect susceptibility to ampicillin.