BACKGROUND

The relentless evolution of K. pneumoniae ST307 into a "superbug" with dual resistance to last-line antibiotics and hospital disinfectants poses an existential threat to infection control. This study characterizes the molecular epidemiology, resistance profiles, and biocide tolerance of ST307 isolates from Iranian hospitals, highlighting its role in nosocomial outbreaks.

METHODS

A multicenter cross-sectional analysis of 500 K. pneumoniae isolates (2022-2024) utilized CLSI-compliant disk diffusion, broth microdilution, and PCR for resistance genes (bla, blacepA, qacED1). Biocide MICs were correlated with genetic markers.

RESULTS

ST307 accounted for 30% (150/500) of isolates, predominantly from ICUs. Resistance rates included meropenem (60.0%; MIC₅₀ >32 µg/mL), ciprofloxacin (75.3%), and gentamicin (45.3%). Colistin retained efficacy (85.3% susceptibility). Elevated biocide MICs (chlorhexidine ≥ 0.5% [70.0%]; benzalkonium chloride ≥ 0.1% [65.3%]) correlated with cepA (65.3%) and qacED1 (70.0%) positivity (p < 0.01). Carbapenemase genes bla (22.0%) and bla (10.0%) co-occurred with ESBLs.

CONCLUSIONS

ST307's convergence of resistance mechanisms represents a catastrophic failure of current infection control frameworks. Without immediate interventions-such as ICU closures for deep disinfection, restricted colistin/tigecycline use, and genomic surveillance mandates-this clone will dominate Iranian hospitals within 3-5 years.