Genotypes of CTX-M-like-extended-spectrum and OXA-like-spectrum Beta-lactamase in Clinical Isolates of Gram-negative Bacilli in Guangzhou

OBJECTIVE To investigate the main genotypes and the epidemic characteristics of CTX-M-like-extended-spectrum beta-lactamases(ESBLs) and OXA-like-spectrum beta-lactamases(Bla) of the common Gram-negative bacilli in Guangzhou. METHODS The ESBLs phenotype of 3500 clinical isolates was primarily screened and confirmed by the NCCLS phenotypic confirmatory test according to guidelines of NCCLS(2001).PCR was performed on ESBLs phenotype-positive clinical isolates using primer specific for CTX-M1,CTX-M2, CTX-M9 and OXA,respectively,and the PCR products were purified and sequenced by ABI prism 377 DNA sequencer. RESULTS The positive rates of PCR results for CTX-M1,CTX-M2,CTX-M9,OXA,and two or more of them in all the ESBLs-phenotype-positive clinical Gram-negative isolates were 9.96%(108/1084),0,35.5%(385/1085),1.6%(17/1085),and 5.9%(64/1084),respectively.The PCR products for CTX-M1 and CTX-M9 were further identified as CTX-M-3(3.23%),CTX-M-22(3.7%),CTX-M-9(4.99%),CTX-M-14(3.32%),CTX-M-17(2.21%),CTXM-18(3.69%),CTX-M-21(2.95%),CTX-M-24(4.43%),TOHO-2(1.85%),and TOHO-3(1.48%).The prevalence of CTX-M-9 and CTX-M-24 was the highest in Guangzhou.All PCR products for OXA were further identified as OXA-2/PSE-2 gene(1.38%,15/1084).Besides above 8 strains which producing an unclassified CTX-M-like gene were detected in the present study(0.74%,8/1084).Among them,42.8%(151/353) of CTX-M-producing strains were Escherichia coli,36.3%(128/353) of CTX-M-producing strains were Klebsiella pneumoniae,while 80%(12/15) of OXA-producing strains were Pseudomonas aeruginosa. CONCLUSIONS CTX-M-like ESBLs,especially CTX-M-9 and CTX-M-24,are the prevalent genotypes of ESBLs of clinical Gram-negative bacilli in Guangzhou.But the CTX-M2-like ESBLs could not be detected in our city.Finally,one or more kinds of novel CTX-M-like ESBLs might be existed in Guangzhou.