Differential expression of blaSHV related to susceptibility to ampicillin in Klebsiella pneumoniae

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