{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,10]],"date-time":"2026-03-10T00:14:10Z","timestamp":1773101650728,"version":"3.50.1"},"reference-count":22,"publisher":"Microbiology Society","issue":"3","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2008,3,1]]},"abstract":"<jats:p>An imipenem-resistant isolate of <jats:italic>Citrobacter freundii<\/jats:italic> ZJ163 (MIC 256\u2005\u03bcg\u2005ml<jats:sup>\u22121<\/jats:sup>) isolated from a Chinese hospital was investigated. The <jats:italic>C. freundii<\/jats:italic> ZJ163 isolate exhibited high-level resistance to carbapenems, penicillins, cephalosporins, cefoxitin, aztreonam, quinolones and aminoglycosides. Isoelectric focusing (IEF) demonstrated three <jats:italic>\u03b2<\/jats:italic>-lactamases with pIs of 5.4 (TEM-1), 6.7 (KPC-2) and 7.9 (CTX-M-14). Two different transconjugants (types A and B) were obtained by conjugation studies. The type A transconjugant exhibited reduced susceptibility or resistance to penicillins, cephalosporins and aztreonam, but was susceptible to carbapenems, quinolones and aminoglycosides. The antimicrobial susceptibility patterns of the type B transconjugant were similar to that of type A, except for its significantly reduced carbapenem susceptibility (imipenem MIC 2\u2005\u03bcg\u2005ml<jats:sup>\u22121<\/jats:sup>). IEF, specific PCRs and DNA sequence analysis indicated that the type A transconjugant produced CTX-M-14 <jats:italic>\u03b2<\/jats:italic>-lactamase with a pI of 7.9, that the type B transconjugant produced KPC-2 <jats:italic>\u03b2<\/jats:italic>-lactamase with a pI of 6.7 and that the <jats:italic>\u03b2<\/jats:italic>-lactamase with a pI of 5.4 was TEM-1. PCR analysis and sequencing confirmed the presence of the <jats:italic>ampC<\/jats:italic> gene in the chromosomal DNA from <jats:italic>C. freundii<\/jats:italic> ZJ163, although no activity of AmpC <jats:italic>\u03b2<\/jats:italic>-lactamase was detected by IEF. Urea\/SDS-PAGE analysis of outer-membrane proteins revealed that the levels of the 41 and 38\u2005kDa porins were decreased in <jats:italic>C. freundii<\/jats:italic> ZJ163. It was concluded that production of KPC-2 combined with decreased expression of porins contributes to high-level resistance to carbapenems in <jats:italic>C. freundii<\/jats:italic> ZJ163.<\/jats:p>","DOI":"10.1099\/jmm.0.47576-0","type":"journal-article","created":{"date-parts":[[2008,2,20]],"date-time":"2008-02-20T17:08:55Z","timestamp":1203527335000},"page":"332-337","source":"Crossref","is-referenced-by-count":57,"title":["High-level carbapenem resistance in a Citrobacter freundii clinical isolate is due to a combination of KPC-2 production and decreased porin expression"],"prefix":"10.1099","volume":"57","author":[{"given":"Rong","family":"Zhang","sequence":"first","affiliation":[{"name":"Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lijiang","family":"Yang","sequence":"additional","affiliation":[{"name":"Huazhong University of Science & Technology, Wuhan, Hubei 430074, PR China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jia Chang","family":"Cai","sequence":"additional","affiliation":[{"name":"Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hong Wei","family":"Zhou","sequence":"additional","affiliation":[{"name":"Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Gong-Xiang","family":"Chen","sequence":"additional","affiliation":[{"name":"Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"345","reference":[{"key":"R1","doi-asserted-by":"crossref","first-page":"922","DOI":"10.1128\/AAC.32.6.922","article-title":"Clinical 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