Detection of Colistin-Resistant Genes in Gram-Negative Bacilli Isolated From Patients With Covid-19 Publisher

Summary: Are last-line antibiotics losing power in COVID-19 wards? Among bacterial isolates, 41.9% resisted colistin; a study urges continued resistance surveillance. #AntibioticResistance #COVID19

Jahandar R ; Hoveida L ; Rostami S
Source: Archives of Razi Institute Published:2026

Abstract

Introduction: Recent reports have highlighted bacterial coinfections alongside COVID-19, increasing mortality rates. The emergence of high resistance to carbapenems and colistin mediated by mobile genetic elements poses a severe public health concern. Materials & Methods: In this cross-sectional study, 74 gram-negative bacterial isolates were collected from tracheal samples of COVID-19 patients admitted to Al-Zahra Hospital, Isfahan, Iran. Bacterial identification was performed using biochemical tests, and antibiotic susceptibility was determined by the Kirby-Bauer method. Colistin minimum inhibitory concentrations (MICs) were assessed by broth microdilution. The presence of mcr-1, mcr-2, mcr-3, and pmrAB genes was detected via polymerase chain reaction (PCR). Clinical isolates were obtained from COVID-19 patients admitted to the intensive care unit (ICU) (n=23), internal unit (n=23), surgical unit (n=10), and from other units (n=18). Results: The predominant isolates were Acinetobacter spp. (70%), Klebsiella pneumoniae (16%), Pseudomonas aeruginosa (7%), and Escherichia coli (4%). The highest resistance was observed against ampicillin (94.6%), while gentamicin and ceftazidime exhibited the lowest resistance (74.3%). Among all isolates, 31(41.9%) had MICs ≥4, indicating resistance to colistin. Additionally, 20% of the isolates harbored the pmrAB gene, while none possessed mcr-1, mcr-2, or mcr-3 genes. Conclusion: Since colistin is one of the last choices for treating severe infections, the high prevalence of colistin-resistant bacteria in this study, coupled with the detection of pmrAB, underscores the urgent need for continuous surveillance of colistin resistance mechanisms to inform effective clinical management and infection control strategies in COVID-19 patients. Although no horizontal transfer of resistance genes was found in this study, hospital infection control systems should routinely scan Enterobacteriaceae and non-fermentative Gram-negative bacteria, especially Acinetobacter spp., for colistin resistance and its mechanisms of action. © 2026 The Author(s).