Alarming colistin and carbapenem resistance in Klebsiella pneumoniae: molecular insights from Tehran hospitals, Iran.

OBJECTIVE

An alert has been issued regarding the widespread emergence of multidrug-resistant (MDR) and carbapenem-resistant Klebsiella pneumoniae (CRKP) in hospital settings. A total of 150 consecutive, non-duplicate K. pneumoniae isolates were obtained from patients admitted to tertiary care hospitals in Tehran between April 2023 and December 2024. These isolates were cultured from various clinical specimens, including sputum, urine, blood, wounds, bronchoalveolar lavage, and tracheal swabs. Antimicrobial susceptibility testing was performed using both disk diffusion and microdilution methods according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Additionally, combined disk diffusion test (CDDT), modified carbapenem inactivation method (mCIM), and EDTA-modified carbapenem inactivation method (eCIM) tests were used to confirm the production of extended-spectrum β-lactamases (ESBLs), carbapenemases, and metallo-β-lactamases (MBLs), respectively. Biofilm production was assessed using the microtiter plate method with crystal violet staining. Molecular detection of ESBL genes (blaTEM, blaSHV, blaCTX-M, blaGES, blaPER, blaVEB), carbapenemase/MBL genes (blaNDM, blaVIM, blaIMP, blaKPC, blaOXA-48), and colistin resistance genes (mcr-1 to mcr-4) was performed by PCR sequencing.

RESULTS

Colistin showed the highest efficacy, with susceptibility rates of 83.3%. Notably, 25 isolates (16.7%) were colistin-resistant and 115 (76.7%) were carbapenem-resistant. Phenotypic analysis identified 87 (57.3%) isolates as ESBL producers, 93 (62%) as carbapenemase producers, and 79 (52.7%) as MBL producers. Biofilm production levels were categorized as strong (44 isolates, 29.3%), moderate (56, 37.3%), and weak (50, 33.3%). The spectrum of detected resistance genes included blaTEM (117, 78%), blaSHV (74, 49.3%), blaCTX-M (121, 80.7%), blaNDM (71, 47.3%), blaOXA-48 (44, 29.3%) and blaVIM (4, 2.7%), whereas blaGES, blaPER, blaVEB, blaIMP, blaKPC, and mcr-1 to mcr-4 genes were not detected in any isolates. These findings underscore the critical need for comprehensive surveillance and stringent infection control measures to prevent the spread of resistant K. pneumoniae strains in healthcare facilities.