Identification and Distribution of the Clinical Isolates of Imipenem-resistant Pseudomonas aeruginosa Carrying Metallo-β-lactamase and/or Class 1 Integron Genes

To investigate the distribution of the genes of two major metallo-β-1actamases （MBL;i.e.,IMP and VIM） and class 1 integrons （intI） in the clinical imipenem-resistant Pseudomonas aeruginosa, a total of 65 isolates, from a university hospital in Sichuan between December 2004 and April 2005 were screened for MBL genes by PCR using primers specific for blaIMP-1, blaVIM and blaVIM-2 genes. The MBL-positive isolates were further assessed for class 1 integrons by PCRusing specific primers. The nucleotide sequences of several PCR products were also determined. The results revealed that the blaVIM gene was found in 81.5% （53/65） of all isolates, blaVIM-2 gene was found in only 1 isolate and the intl gene was observed in 45.3% （24/53） of blaVIM-positive isolates. One isolate carried simultaneously both blaIMP-1 and intl genes, and to the best of our knowledge this is the first report of such isolate in southwest China. These observations highlight that the genes for VIM β-1actamase and class 1 integrons were predominantly present among the imipenem-resistant P. aeruginosa tested, confirming the current widespread threat of imipenem-resistant, integron-borne P.aeruginosa.

Total Alkaloids from Sophora Alopecuroides L.Increase Susceptibility of Extended-Spectrum β-Lactamases Producing Escherichia coli Isolates to Cefotaxime and Ceftazidime

Objective： To evaluate the antimicrobial activity of total alkaloids extracted from Sophorea alopecuroides L. （TASA） against clinical isolated extended-spectrum beta-lactamases （ESBLs） producing Escherichia coil （E.. coil） strains. Methods： The antibacterial activity of TASA either itself or in combination with cefotaxime （CTX） or ceftazidime （CAZ） was investigated by using the microbroth dilution method and phenotypic confirmatory disk diffusion test against three clinical isolated ESBLs-producing E. coil strains; the interactions of TASA and C＇I＇X or CAZ were ascertained by evaluating the fractional inhibitory concentration index （FICI）. Results： The antibacterial activity of either TASA itself or in combination with C＇IX or CAZ was found. The minimum inhibitory concentration （MICs） of TASA against the ESBLs producing isolates was 12.5 mg/mL. In the combinations with a sub-inhibitory concentration of TASA, a synergistic effect on CTX and CAZ against the ESBLs producing isolates was observed. Similarly, the isolates exposed to lower dose of TASA yielded an increased susceptibility to CTX and CAZ by 8-16 folds determined by microdilution assay. Moreover, enzymatic detection of ESBLs demonstrated that TASA induced reversal resistance to CTX and CAZ partially by a mechanism of inhibition of ESBLs activity in these isolates. Additionally, in the tested isolates following the exposure of TASA, molecular analysis verified the SHV-type beta-lactamase encoding ESBL gene in these isolates, and no mutation was introduced into the ESBL gene. Conclusions： These results suggest that TASA could be used as a source of natural compound with pharmacological activity of reversal resistance to antimicrobial agent. These findings also indicated that the application of the TASA in combination with antibiotics might prove useful in the control and treatment of infectious diseases caused by the ESBLs producing enterobacteriaceae.