What is it about?
Klebsiella pneumoniae is a common cause of urinary tract infections. However, two closely related species — Klebsiella variicola and Klebsiella quasipneumoniae — are frequently misidentified as K. pneumoniae in routine laboratory testing because standard identification methods cannot reliably distinguish between them. Whether these three species differ in their clinical behavior or antibiotic susceptibility has not been well studied, particularly in urine isolates. In this study, we analyzed 125 Klebsiella strains isolated from urine at a tertiary care hospital in Japan between March 2020 and June 2021. Species were identified using multiplex PCR targeting species-specific chromosomal beta-lactamase genes. We found that 84 strains (67.2%) were K. pneumoniae, 31 (24.8%) were K. variicola, and 10 (8.0%) were K. quasipneumoniae — a notably higher proportion of K. variicola than reported in bloodstream infection studies, consistent with K. variicola being isolated more frequently from urine. There were no significant differences in patient background or rates of bacteremia complications among the three species. However, K. pneumoniae was significantly less susceptible to ampicillin/sulbactam and piperacillin than K. variicola, and showed lower susceptibility to trimethoprim/sulfamethoxazole (79.8%) compared to K. variicola (96.8%) and K. quasipneumoniae (100%). All K. variicola and K. quasipneumoniae strains were susceptible to carbapenems and most cephalosporins. All 9 ESBL-producing strains (7.2% of total) were K. pneumoniae.
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Why is it important?
K. variicola and K. quasipneumoniae are routinely misidentified as K. pneumoniae in many clinical laboratories, meaning the true prevalence of each species and their respective resistance profiles are underestimated. This study demonstrates that these three species have meaningfully different antibiotic susceptibility patterns — particularly for trimethoprim/sulfamethoxazole, which is commonly used to treat urinary tract infections. Accurate species-level identification is therefore important not only for epidemiological surveillance but also for guiding appropriate treatment. The finding that ESBL production was confined exclusively to K. pneumoniae further supports the need for species-level distinction in clinical practice.
Perspectives
Clinicians treating urinary tract infections caused by Klebsiella should be aware that routine identification methods may not accurately distinguish K. pneumoniae from K. variicola and K. quasipneumoniae. When trimethoprim/sulfamethoxazole is considered as a treatment option, susceptibility testing results should be interpreted with the species identity in mind. Improving MALDI-TOF mass spectrometry database coverage for K. variicola and K. quasipneumoniae, or incorporating molecular identification into routine workflows, would help provide more accurate epidemiological data and guide antibiotic prescribing. Regional surveillance of ESBL prevalence stratified by Klebsiella species is also needed to better understand the local resistance landscape.
Dr Naoki Watanabe
Hirosaki University
Read the Original
This page is a summary of: Clinical characteristics and antimicrobial susceptibility of Klebsiella pneumoniae, Klebsiella variicola and Klebsiella quasipneumoniae isolated from human urine in Japan, Journal of Medical Microbiology, June 2022, Society for General Microbiology,
DOI: 10.1099/jmm.0.001546.
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