distribution of mbl and serine-β-lactamase-producing pathogens in ventilator-associated pneumonia: insights into mdr and xdr strains

Background and objectives: ventilator-associated pneumonia (vap) caused by carbapenem-resistant gram-negative bacteria is a serious icu challenge. this study determined the prevalence, antimicrobial susceptibility profiles, and phenotypic carbapenemase resistance mechanisms of gram-negative isolates from vap patients in two tertiary hospitals in karachi, pakistan.materials and methods: we included 104 consecutive cases of vap (july 2021–january 2023). a total of 67 carbapenem-resistant gram-negative isolates were identified and tested. antibiotic susceptibility was assessed by disk diffusion and broth micro dilution, according to clsi and eucast guidelines. modified and enhanced carbapenem inactivation methods (mcim/ecim) were used to distinguish metallo-β-lactamase (mbl) and serine carbapenemase production.results: the mean age was 44.6 ± 18.3 years; 52.2% were male. early-onset vap accounted for 37.3% and late-onset for 62.7%. the most frequent pathogens were acinetobacter baumannii (49.3%, 33/67) and klebsiella pneumoniae (20.9%, 14/67). notably, 67% of isolates produced mbls, and 33% produced serine carbapenemases (phenotypically). the prevalence of multidrug-resistant (mdr), extensively drug-resistant (xdr), and pan drug-resistant (pdr) phenotypes was 42.6%, 31.3%, and 19.4%, respectively.conclusion: vap in our icus was dominated by a. baumannii and k. pneumoniae with high levels of mbl-mediated resistance. these findings highlight the urgent need for surveillance, stewardship, and new therapeutic options.