High-level carbapenem resistance in a Citrobacter freundii clinical isolate is due to a combination of KPC-2 production and decreased porin expression.
An imipenem-resistant isolate of Citrobacter freundii ZJ163 (MIC 256 microg ml(-1)) isolated from a Chinese hospital was investigated. The C. freundii ZJ163 isolate exhibited high-level resistance to carbapenems, penicillins, cephalosporins, cefoxitin, aztreonam, quinolones and aminoglycosides. Isoelectric focusing (IEF) demonstrated three beta-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 microg ml(-1)). IEF, specific PCRs and DNA sequence analysis indicated that the type A transconjugant produced CTX-M-14 beta-lactamase with a pI of 7.9, that the type B transconjugant produced KPC-2 beta-lactamase with a pI of 6.7 and that the beta-lactamase with a pI of 5.4 was TEM-1. PCR analysis and sequencing confirmed the presence of the ampC gene in the chromosomal DNA from C. freundii ZJ163, although no activity of AmpC beta-lactamase was detected by IEF. Urea/SDS-PAGE analysis of outer-membrane proteins revealed that the levels of the 41 and 38 kDa porins were decreased in C. freundii ZJ163. It was concluded that production of KPC-2 combined with decreased expression of porins contributes to high-level resistance to carbapenems in C. freundii ZJ163.
Zhang
Rong
R
Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China.
Yang
Lijiang
L
Huazhong University of Science & Technology, Wuhan, Hubei 430074, PR China.
Cai
Jia Chang
JC
Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China.
Zhou
Hong Wei
HW
Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China.
Chen
Gong-Xiang
GX
Second Affiliated Hospital of Zhejiang University, Zhejiang University, 88 JieFang Road, Hangzhou 310009, PR China.
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015780:Carbapenems / Q000494:pharmacology*; D016971:Citrobacter freundii / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification; D003227:Conjugation, Genetic; D024881:Drug Resistance, Bacterial; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D018272:Porins / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
D000900:Anti-Bacterial Agents; D015780:Carbapenems; D018272:Porins; D015378:Imipenem; C491478:beta-lactamase KPC-2; D001618:beta-Lactamases