Abstract
Carbapenem-resistant Gram-negative (CR-GN) pathogens pose a critical threat to patient outcomes in high-dependency and intensive care environments. This study aimed to delineate species prevalence, antimicrobial resistance phenotypes, carbapenemase genotypes, and clinical-environmental transmission dynamics across critical-care units. Cross-sectional surveillance was conducted in six ICUs and HDUs of a tertiary-care hospital in Karachi, Pakistan. We identified predominant species, quantified resistance patterns, and detected carbapenemase genes using PCR, exclusively on meropenem-resistant isolates. Network analysis highlighted high-centrality contamination hubs across ICUs and HDUs. Acinetobacter baumannii (36.7%) and Klebsiella pneumoniae (33.9%) were predominant, with 58% originating from environmental reservoirs. Meropenem non-susceptibility was 55% (60/109), and colistin non-susceptibility was 68.6% (35/51), based on standardized CLSI testing. ICU isolates exhibited significantly higher meropenem resistance than HDU isolates. Among carbapenem-resistant isolates, blaOXA-48-like (52.8%) and blaNDM (25%) were most prevalent. Network topology revealed ICU1 and HDU2 as high-centrality transmission nodes. These findings highlight pervasive environmental colonization and heightened antimicrobial pressure in ICUs, necessitating reinforced decontamination protocols, antimicrobial stewardship, and continuous molecular surveillance. This study provides the first integrated clinical-environmental surveillance of MDR Gram-negative bacteria in Pakistan, revealing that over half of isolates originated from surfaces and that network-based mapping can pinpoint contamination hubs driving hospital transmission.