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.