JAC Advance Access originally published online on April 4, 2006
Journal of Antimicrobial Chemotherapy 2006 57(6):1259-1261; doi:10.1093/jac/dkl115
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Correspondence |
Klebsiella pneumoniae strains carrying the chromosomal SHV-11 ß-lactamase gene produce the plasmid-mediated SHV-12 extended-spectrum ß-lactamase more frequently than those carrying the chromosomal SHV-1 ß-lactamase gene
1 Department of Preventive Medicine, Kosin University College of Medicine 602-030, 34 Amnam-Dong, Seo-Gu, Busan, Korea 2 Department of Laboratory Medicine, Kosin University College of Medicine 602-030, 34 Amnam-Dong, Seo-Gu, Busan, Korea 3 Department of Laboratory Medicine, Pusan National University College of Medicine 602-739, 1-10 Ami-Dong, Seo-Gu, Busan, Korea
*Corresponding author. Tel: +82-51-990-6373; Fax: +82-51-990-3034; E-mail: kscpjsh{at}ns.kosinmed.or.kr
Keywords: chromosomal ß-lactamases , K. pneumoniae , SHV-1 , SHV-11 , SHV-12 , ESBLs
Sir,
Klebsiella pneumoniae produces species-specific class A chromosomal ß-lactamases that confer resistance to ampicillin, amoxicillin, carbenicillin and ticarcillin. Three families of chromosomal ß-lactamases, including SHV, LEN and OKP, have been identified in clinical K. pneumoniae isolates.1 Plasmid-mediated SHV-type extended-spectrum ß-lactamases (ESBLs) are widespread in K. pneumoniae isolates, and there has been a predominance of SHV-12 in south-east Asia.2 In this study, we investigated the diversity of chromosomal ß-lactamase genes in clinical K. pneumoniae isolates from Korean hospitals and the incidence of SHV-12 according to genotypes of chromosomal ß-lactamases.
From May to July 2002, 142 epidemiologically unrelated clinical K. pneumoniae isolates were collected from 10 teaching hospitals in 8 cities in Korea. The species identification and antimicrobial susceptibility tests were performed using the VITEK system (bioMérieux Vitek Inc., Hazelwood, MO, USA) and the disc diffusion method, respectively. Double-disc synergy (DDS) test was performed on Mueller–Hinton agar (Difco Laboratories, Detroit, MI, USA) with discs of ceftazidime, cefotaxime and aztreonam, each containing 30 µg of the drug, placed at distances of 20 mm (centre to centre) from a disc containing amoxicillin/clavulanic acid (20 µg/10 µg) in the centre of the plate.2 Mating experiments were performed as described previously with sodium azide-resistant Escherichia coli J53 AzideR as the recipient.2 Transconjugants were selected on MacConkey agar (Difco Laboratories) supplemented with ceftazidime (2 mg/L) and sodium azide (150 mg/L; Sigma, St Louis, MO, USA).
Chromosomal and plasmid DNAs were isolated by the cetyltrimethylammonium bromide and the alkaline lysis methods, respectively.3 PCR amplifications for the chromosomal ß-lactamase gene of K. pneumoniae were performed using the primers SHV-F (5'-CCG GGT TAT TCT TAT TTG TCG CT-3') and SHV-R (5'-TAG CGT TGC CAG TGC TCG-3'). Searches for genes coding for the plasmid-mediated class A ESBLs including TEM, SHV, CTX-M, PER-1, VEB, GES/IBC and TLA type enzymes were also performed by PCR amplification as described previously.2 The PCR products were subjected to direct sequencing. Both strands of each PCR product were sequenced twice using an automatic sequencer (model 373A; Applied Biosystems, Weiterstadt, Germany), as described previously.2
All 142 clinical K. pneumoniae isolates carried the class A chromosomal ß-lactamase gene. The most common types of chromosomal ß-lactamase gene in K. pneumoniae isolates were blaSHV-11 (n = 88, 62%) and blaSHV-1 (n = 50, 35%) genes. OKP-1, -2, -3 and LEN-2 ß-lactamase genes were also detected, each in one isolate (Table 1). K. pneumoniae strains carrying the blaSHV-1 gene were isolated from all 10 hospitals and those carrying the blaSHV-11 gene were isolated from 9 hospitals (not isolated in Jeju). K. pneumoniae strains carrying OKP-type or LEN-2 ß-lactamase genes were only isolated from hospitals in Seoul.
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The prevalence of ESBL-producing K. pneumoniae was 21.8% (31/142). Transfer of ceftazidime-resistance to the E. coli J53 AzideR recipient by conjugation was successful for only 38.7% (12/31) of the DDS-positive strains. The most common ESBL was SHV-12 (n = 18), and CTX-M-3, CTX-M-14, SHV-2a, SHV-5 and TEM-52 were detected in five, four, one, two and one strains, respectively. Three isolates carried multiple genes encoding ESBLs: one with CTX-M-3 and SHV-12; one with CTX-M-3, SHV-12 and TEM-52; and one with CTX-M-14 and SHV-12. Non-TEM and non-SHV type ESBLs including PER, VEB, IBC and TLA type ß-lactamases and members of CTX-M-2 and CTX-M-8 groups were not detected in this survey. For 4 out of 31 (12.9%) DDS-positive strains no ESBL was detected. These strains may have produced another ESBL, which was not determined in this study or might have given positive results for ESBL activity.
The incidence of ESBL was more predominant in K. pneumoniae strains carrying the blaSHV-11 gene (28.4%, 25/88) than in strains carrying the blaSHV-1 gene (12%, 6/50; P = 0.033). This phenomenon was more prominent in the blaSHV-12 gene. While 19.3% (17/88) of K. pneumoniae strains carrying the blaSHV-11 gene produced the SHV-12 ESBL, only 2% (1/50) of the strains carrying the blaSHV-1 gene produced the same type of ESBL (P = 0.003). It is not known why this over-abundance of SHV-12 in chromosomal blaSHV-11 gene-containing isolates has occurred, but the mechanism certainly warrants further study.
Transparency declarations
None to declare.
Acknowledgements
This work was supported by the Korea Research Foundation Grant (KRF-2004-042-E00117).
References
1
Haeggman S, Löfdahl S, Paauw A, et al. (2004) Diversity and evolution of the class A chromosomal ß-lactamase gene in Klebsiella pneumoniae. Antimicrob Agents Chemother 48:2400–8.
2
Ryoo NH, Kim EC, Hong SG, et al. (2005) Dissemination of SHV-12 and CTX-M-type extended-spectrum ß-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae and emergence of GES-3 in Korea. J Antimicrob Chemother 56:698–702.
3 Wilson K. (1988) Preparation of genomic DNA from bacteria. In Ausubel FM, Brent R, Kingston RE (Eds.), et al. Current Protocols in Molecular Biology (Green Publishing and Wiley Interscience, New York) pp. 241–5.
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