Abstract:

Objective To investigate the characteristics of strains of AmpC β-lactamase (AmpC enzyme) production in pathogenic bacteria in blood stream and clinical presentations of the cases, and study the related ampC and ampD genes. Methods One hundred and eighty-one strains of gram negative bacillus in blood stream were collected, Cefoxitin screening test and three-dimensional test were performed for screening of strains of AmpC enzyme, production and those of AmpC enzyme hyperproduction retrospective analysis was condected in the strains with positive results. ampC and ampD gene PCR amplification, sequencing and sequence analysis of positive strains were performed, and gene homology of ampC positive strains was analysed by Rep-PCR. Results Among 181 strains in blood stream, strains of AmpC enzyme production were detected in 39 isolates by Cefoxitin screening test, with the detection rate of 21.5% (39/181). The detection rate of strains of AmpC enzyme hyperproduction by three-dimensional test was 43.6% (17/39). PCR revealed that the positive rates for ampC and ampD genes were 41% (16/39) and 56.4% (22/39), respectively. The ampC gene sequencing of 16 positive strains indicated that the homology was 98% to 100% by comparison with the GenBank, while the ampD gene sequencing of 2 strains of Enterobacter cloacae demonstrated that the suspected gene mutations existed in the carboxy-terminal of ampD gene. Conclusion The prevalence of drug-resistant pathogenic bacteria in blood stream in this study is due to nosocomial infection. The mutation of ampC gene is rare in the pathogenic bacteria in blood stream with production of AmpC enzyme, while the rate of gene mutation in Enterobacter cloacae is higher, and the deletion and amino acid substitutions in the carboxy-terminal of ampD is highly relevant to the depressed expression of AmpC enzyme.

Key words: AmpC β-lactamase, Cefoxitin screening test, three-dimensional test, ampD