Prevalence, molecular characterization, and drug susceptibility of extended-spectrum β-lactamase-producing Klebsiella pneumoniae, K. quasipneumoniae, and K. variicola in Japan

Abstract

Klebsiella pneumoniae is an extended-spectrum β-lactamase (ESBL)-producing bacterium (ESBL-KP). Recently, K. quasipneumoniae and K. variicola were reclassified from K. pneumoniae based on genome sequencing. However, the molecular characteristics and antimicrobial susceptibility patterns of ESBL-producing K. quasipneumoniae (ESBL-KQ) and ESBL-producing K. variicola (ESBL-KV) remain unclear. Here, we aimed to distinguish ESBL-KQ and ESBL-KV from ESBL-KP in terms of frequency, genomic characteristics, and antimicrobial susceptibility patterns. Of the 74 ESBL-KP isolates, 12 (16.2%) were reclassified as ESBL-KQ and 1 (1.4%) as ESBL-KV. Patients with ESBL-KP and ESBL-KQ infections were of similar age; ESBL-KQ infection was more frequent in men. Infection-associated mortality seemed to be similar in patients with ESBL-KQ and ESBL-KP infections, without a statistically significant difference (p = 0.99). Genetic analysis revealed that 19.1% of ESBL-producing Klebsiella isolates harbored AmpC. The prevalence of AmpC was higher with ESBL-KP (31.1%) than with ESBL-KQ (8.3%), although this difference was not statistically significant (p = 0.52). The frequency of ESBL-KQ with AmpC and quinolone-resistance-associated genes in clinical samples increased annually (p = 0.04). The prevalence of Klebsiella with fluoroquinolone-resistance genes did not differ significantly between species (p > 0.99). The gene profiles of ESBL-KQ and ESBL-KP differed, and the prevalence of antimicrobial resistance via AmpC and fluoroquinolone-resistance genes increased. Further studies are required to distinguish ESBL-KP and ESBL-KQ and determine the mechanism underlying the spread of AmpC and quinolone-resistance genes to prevent further spread of these genes.