[Detection of the new type of aminoglycoside acetyltransferase gene in Enterobacter cloacae isolates].

OBJECTIVE: To investigate the prevalence of aac(6')-Ib-cr gene in Enterobacter cloacae isolates. METHODS: PCR and sequencing were performed on 81 strains of Enterobacter cloacae isolated clinically in Anhui province to identify aac (6')-IB-cr gene. Disk diffusion method was used to test the susceptibility of the Enterobacter cloacae isolates with aac (6')-Ib-cr gene to fluoroquinolones, aminoglycosides, and other antimicrobial agents. AmpC and extended-spectrum beta-lactamases (ESBLs) were detected by modified three-dimensional extract test, and the molecular typing was analyzed by ERIC-PCR. RESULTS: Aac (6')-Ib-cr gene was identified in 3 (3.7%) of the 81 Enterobacter cloacae isolates with different ERIC-PCR patterns. The isolates with aac (6')-Ib-cr gene were resistant to fluoroquinolones, aminoglycosides, chloramphenicol, ampicillin, cefoxitin, and second and third generation cephalosporins. Two of the 3 isolates produced AmpC and ESBLs, and 1 isolate produced only ESBLs. CONCLUSION: Aac (6')-Ib-cr gene is prevalent in Enterobacter cloacae isolates with resistance to most of antimicrobial agents and no clone spread in found in them.

[Identification and expression of blaCTX-M-14 and blaCTX-M-24].

OBJECTIVE: To identify the ESBL gene and the prevalence in Escherichia coli and Klebsiella pneumoniae strain isolated from Huashan Hospital, Shanghai. METHODS: Isolates were confirmed as an ESBL producing strain by double-disk synergy test and NCCLS Confirmatory Test. Antibiotic susceptibilities were determined by standard agar dilution procedure on Mueller-Hinton agar. To determine whether the resistance was transferable, the conjugation experiment was performed; plasmids were isolated from clinical isolates and transcojugants. The partial bla(gene) of ESBL producing isolates and their transcojugants were detected by PCR using universal primers for TEM, SHV, CTX-M-1group, Toho-1group, CTX-M-13group respectively. The entire bla(CTX-M-13) group were amplified by PCR using the primers outside the Open Reading Frame (ORF) of CTX-M-13group beta-lactamases; the PCR products of entire bla(CTX-M-13)group were cloned into vector and the recombinant plasmids were transformed into the recipient strain for expression; the PCR products were also directly sequenced and analyzed; the clinical isolates of ESBL producers were detected by PFGE. RESULTS: ESBL producers were resistant to most beta-lactams and non-beta-lactams. Most transconjugants were obtained at frequency of 10(-4) approximately 10(-5) and resistance to non-beta-lactams was cotransferred with the ESBL activity to the transconjugant. A plasmid of about > 23.1 kb was obtained from each tansconjugant by plasmid extraction. Partial gene amplification products of CTX-M-13 group gene were obtained from isolates and their transconjugants. The bla(CTX-M-13)group from 4 transconjugants were identified as bla(CTX-M-14), and other six were bla(CTX-M-24); those ESBLs were mediated by plasmids (> 23.1 kb); the transformants producing CTX-M-14 or CTX-M-24 were resistant to most beta-lactams, which were much more resistant to cefotaxime than to ceftazidine; PFGE patterns of those isolates were different. CONCLUSION: clinical isolate of Escherichia coli and Klebsiella pneumoniae isolated from Huashan Hospital, Shanhai produced CTX-M-14 or CTX-M-24, which caused the isolate resistant to most beta-lactams; no clone spread in those isolates was found.