{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,26]],"date-time":"2026-10-26T18:29:11Z","timestamp":1793039351262,"version":"4.5.0"},"reference-count":28,"publisher":"Public Library of Science (PLoS)","issue":"5","license":[{"start":{"date-parts":[[2024,5,14]],"date-time":"2024-05-14T00:00:00Z","timestamp":1715644800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS ONE"],"abstract":"<jats:sec id=\"sec001\">\n<jats:title>Introduction<\/jats:title>\n<jats:p>The study of <jats:italic>Klebsiella quasipneumoniae<\/jats:italic>, <jats:italic>Klebsiella variicola<\/jats:italic>, and AmpC production in extended-spectrum \u03b2-lactamase (ESBL)-producing <jats:italic>Klebsiella<\/jats:italic> in Japan is limited, and existing data are insufficient. This study aims to characterize <jats:italic>Klebsiella<\/jats:italic> species, determine AmpC production rates, and analyze antimicrobial resistance patterns in ESBL-producing <jats:italic>Klebsiella<\/jats:italic> isolates in Japan.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec002\">\n<jats:title>Methods<\/jats:title>\n<jats:p>A total of 139 clinical isolates of ESBL-producing <jats:italic>Klebsiella<\/jats:italic> were collected in Japan, along with their corresponding antimicrobial susceptibility profiles. The isolates were identified using a web-based tool. ESBL genes within the isolates were identified using multiplex PCR. Screening for AmpC-producing isolates was performed using cefoxitin disks, followed by multiplex PCR to detect the presence of AmpC genes. Antimicrobial resistance patterns were analyzed across the predominant ESBL genotypes.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec003\">\n<jats:title>Results<\/jats:title>\n<jats:p>The web-based tool identified 135 isolates (97.1%) as <jats:italic>Klebsiella pneumoniae<\/jats:italic> and 4 (2.9%) as <jats:italic>K<\/jats:italic>. <jats:italic>quasipneumoniae<\/jats:italic> subsp. <jats:italic>similipneumoniae<\/jats:italic>, with no instances of <jats:italic>K<\/jats:italic>. <jats:italic>variicola<\/jats:italic> detected. Among <jats:italic>K<\/jats:italic>. <jats:italic>pneumoniae<\/jats:italic>, the CTX-M-1 group emerged as the predominant genotype (83\/135, 61.5%), followed by <jats:italic>K<\/jats:italic>. <jats:italic>quasipneumoniae<\/jats:italic> subsp. <jats:italic>similipneumoniae<\/jats:italic> (3\/4, 75.0%). The CTX-M-9 group was the second most prevalent genotype in <jats:italic>K<\/jats:italic>. <jats:italic>pneumoniae<\/jats:italic> (45\/135, 33.3%). The high resistance rates were observed for quinolones (ranging from 46.7% to 63.0%) and trimethoprim\/sulfamethoxazole (78.5%). The CTX-M-1 group exhibited higher resistance to ciprofloxacin (66\/83, 79.5%) compared to the CTX-M-9 group (18\/45, 40.0%), a trend also observed for levofloxacin and trimethoprim\/sulfamethoxazole. Among the 16 isolates that tested positive during AmpC screening, only one <jats:italic>K<\/jats:italic>. <jats:italic>pneumoniae<\/jats:italic> isolates (0.7%) were confirmed to carry the AmpC gene.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec004\">\n<jats:title>Conclusion<\/jats:title>\n<jats:p><jats:italic>Klebsiella pneumoniae<\/jats:italic> with the CTX-M-1 group is the most common ESBL-producing <jats:italic>Klebsiella<\/jats:italic> in Japan and showed a low proportion of AmpC production. These isolates are resistant to quinolones and trimethoprim\/sulfamethoxazole, highlighting the challenge of managing this pathogen. The findings underscore the importance of broader research and continuous monitoring to address the resistance patterns of ESBL-producing <jats:italic>Klebsiella<\/jats:italic>.<\/jats:p>\n<\/jats:sec>","DOI":"10.1371\/journal.pone.0303353","type":"journal-article","created":{"date-parts":[[2024,5,14]],"date-time":"2024-05-14T17:27:58Z","timestamp":1715707678000},"page":"e0303353","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":9,"title":["Antimicrobial resistance and AmpC production in ESBL-producing Klebsiella pneumoniae and Klebsiella quasipneumoniae: A retrospective study in Japanese clinical isolates"],"prefix":"10.1371","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8609-4981","authenticated-orcid":true,"given":"Naoki","family":"Watanabe","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tomohisa","family":"Watari","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yoshihito","family":"Otsuka","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Masahiko","family":"Ito","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kazufumi","family":"Yamagata","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6872-5943","authenticated-orcid":true,"given":"Miyuki","family":"Fujioka","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2024,5,14]]},"reference":[{"key":"pone.0303353.ref001","doi-asserted-by":"crossref","first-page":"5575","DOI":"10.1099\/ijsem.0.001485","article-title":"Genome-based 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