What is it about?
Extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae is a globally recognized antimicrobial-resistant pathogen that is increasingly difficult to treat. ESBL enzymes allow bacteria to break down many commonly used antibiotics, limiting treatment options. Some isolates can also produce a second enzyme called AmpC, which further narrows the choice of effective antibiotics. In this retrospective study, we analyzed 139 ESBL-producing Klebsiella isolates collected from two regions in Japan — Kameda Medical Center in eastern Japan and Sapporo Clinical Laboratory in northern Japan. Isolates were identified at the species level using a web-based tool, ESBL and AmpC genotypes were determined by multiplex PCR, and antimicrobial susceptibility was tested against 14 antibiotics. Of the 139 isolates, 135 (97.1%) were identified as K. pneumoniae and 4 (2.9%) as K. quasipneumoniae subsp. similipneumoniae. No K. variicola was detected. The CTX-M-1 group was the most prevalent ESBL genotype in K. pneumoniae (61.5%), followed by the CTX-M-9 group (33.3%). Resistance rates were high for quinolones (46.7–63.0%) and trimethoprim/sulfamethoxazole (78.5%), particularly in the CTX-M-1 group. All isolates were susceptible to carbapenems and amikacin. Of the 16 isolates positive on AmpC screening, only one K. pneumoniae isolate (0.7%) was confirmed to carry an AmpC gene (DHA type).
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Why is it important?
K. quasipneumoniae is frequently misidentified as K. pneumoniae in routine laboratory testing, meaning its true prevalence and resistance profile may be underestimated in Japan. Our study provides updated data on the species distribution and resistance patterns of ESBL-producing Klebsiella in Japan. The low prevalence of AmpC co-production (0.7%) in this cohort suggests that cefmetazole — a carbapenem-sparing option — may retain clinical utility against ESBL-producing Klebsiella in Japan. However, the high rates of quinolone and trimethoprim/sulfamethoxazole resistance, especially in the CTX-M-1 group, highlight the challenge of managing these infections with oral agents.
Perspectives
Continuous surveillance of ESBL genotypes and resistance patterns in Klebsiella is essential, as the epidemiology varies by region and changes over time. Clinicians treating ESBL-producing Klebsiella infections in Japan should be aware of the high likelihood of quinolone and trimethoprim/sulfamethoxazole co-resistance, particularly when CTX-M-1 is the dominant genotype. Carbapenems and cefmetazole remain reliable options in settings with low AmpC prevalence. Future studies incorporating broader geographic regions and larger sample sizes — particularly for K. quasipneumoniae and K. variicola — are needed to fully characterize the resistance landscape of ESBL-producing Klebsiella in Japan.
Dr Naoki Watanabe
Hirosaki University
Read the Original
This page is a summary of: Antimicrobial resistance and AmpC production in ESBL-producing Klebsiella pneumoniae and Klebsiella quasipneumoniae: A retrospective study in Japanese clinical isolates, PLOS One, May 2024, PLOS,
DOI: 10.1371/journal.pone.0303353.
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