Current update on the antibiotic resistance profile and the emergence of colistin resistance in Enterobacter isolates from hospital-acquired infections

Abstract

Introduction: Bacterial pathogens are becoming a growing concern as antibiotic resistance among Gram-negative bacteria rises globally. The gram-negative, facultative anaerobic, rod-shaped bacteria belonging to the Enterobacteriaceae family, Enterobacter is a nosocomial pathogen, having ubiquitous distribution in natural environments, including sewage and dairy products. These bacteria increasingly exhibit a multidrug resistance phenotype, thus becoming resilient to available treatment therapies. The fact mentioned above has resulted in them being included in the “ESKAPE” group of opportunistic pathogens, which represents a group for which no effective therapeutic options would be available in a given scenario. So, this study aimed to identify antibiotic resistance patterns in Enterobacter species collected from the bacteriological section of the Institute of Medical Sciences, Banaras Hindu University, Varanasi. Materials and Methods: Fifty-one isolates were collected from clinical samples, including urine, pus, blood, cerebrospinal fluid, sputum, and stool. All isolates were phenotypically identified using VITEK-2 automated systems (ID GNB cards). Additionally, the isolates were genotypically characterised with species-specific primers via PCR, and whole genome sequencing was performed for two isolates, followed by antimicrobial susceptibility testing using the Kirby-Bauer disc diffusion method. Concurrently, broth dilution methods were used to determine the minimum inhibitory concentration (MIC) according to CLSI 2020 guidelines. The Multiple Antibiotic Resistance Index (MARI) was calculated by dividing the number of drugs to which the bacterial isolate is resistant by the total number of antibiotics used in the experiment. Results: The highest resistance rates were observed against levofloxacin (94 %), ciprofloxacin, and ampicillin, with 92 % (47/51) of isolates demonstrating resistance. Cefazolin also exhibited a high resistance rate, with 82 % (42/51) of resistant isolates. Notably, 96.07 % of isolates showed a multiple antibiotic resistance (MAR) index greater than 0.2, indicating a significant burden of multidrug-resistant Gram-negative bacteria. In contrast, 21.56 % had an index greater than 1.0, indicating resistance to all antibiotics tested. Conclusion: This paper highlights the latest information regarding drug resistance patterns in Enterobacter isolates. The last resort for treating gram-negative bacteria is increasingly losing its effectiveness due to the emergence of colistin-resistant strains. Therefore, alternative therapies, such as phage treatment or other antimicrobial agents, must be developed to combat these superbugs. © 2025 The Authors