High frequency and molecular epidemiology of metallo-β-lactamase-producing gram-negative bacilli in a tertiary care hospital in Lahore, Pakistan

BACKGROUND: Metallo-β-lactamase (MBL)-producing isolates have a strong impact on diagnostic and therapeutic decisions. A high frequency of MBL-producing gram-negative bacilli has been reported worldwide. The current study was based on determining the incidence of MBL-producing imipenem-resistant clinical isolates and investigating the β-lactamase gene variants in strains conferring resistance to a carbapenem drug (imipenem). METHODS: A total of 924 gram negative isolates were recovered from a tertiary care hospital in Lahore, Pakistan, during a two-year period (July 2015 to February 2017). The initial selection of bacterial isolates was based on antibiotic susceptibility testing. Strains resistant to imipenem were processed for the molecular screening of β-lactamase genes. Statistical analysis for risk factor determination was based on age, gender, clinical specimen and type of infection. RESULTS: The rate of imipenem resistance was calculated to be 56.51%. Among the 142 strains processed, the phenotypic tests revealed that the incidence of MBLs was 63.38% and 86.61% based on the combination disc test and the modified Hodge test, respectively. The frequencies of bla(TEM), bla(SHV,) bla(OXA,) bla(IMP-1), and bla(VIM) genes were calculated to be 46%, 34%, 24%, 12.5% and 7%, respectively. The co-expression of bla(MBL) (bla(IMP) and bla(VIM)) and bla(ESBL) (bla(TEM), bla(SHV,) bla(OXA)) was also detected through multiplex and singleplex PCR. bla(OXA), bla(TEM) and bla(SHV) coexisted in 82% of the isolates. Co-expression of ESBL and MBL genes was found in 7% of the isolates. CONCLUSION: To our knowledge, this is the first report from Pakistan presenting the concomitant expression of bla(OXA), bla(TEM) and bla(SHV) with bla(IMP-1) and bla(VIM) in MBL-producing gram-negative bacilli.