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.