Occurrence Of Colistin Resistance Genes Among Clinical Isolates Escherichia Coli In Najaf

Abstract

Background: The last resort against both the infections with carbapenem resistant Enterobacteriaceae regards the polymyxins and the colistin. In the recent past, the transmissible colistin resistance has been reported in Enterobacteriaceae through the m.c.r-genes.

OBJECTIVE

The aim of the present study is to evaluate the frequency of plasmid mediated colistin resistance genes among E. coli isolates obtained from clinical isolates in Najaf hospitals

Subjects and Methods: Cross-section study was conducted between November 2024 to February 2025 at Al-Najaf hospitals. The study population consist 150 clinical specimens were gathered from individuals who were either admitted to or visited hospitals, and the specimens immediately transported to the microbiology laboratory. All Gram-negative isolates in the current study had been identified by depending on morphological characteristic, examination by light microscope, and biochemical studies in accordance to the normal procedure guided by Mac.Faddin and Hart. The disk diffusion procedure was used which is based on recommendations made by international Clinical Laboratory Standards Institute regarding antibiotics susceptibility (CLSI, 2024). For this purpose, twenty-six different antibiotics disks of 10 classes were used. Colistin broth disk elution test as recommended by CLSI (2023) on polymyxin cut points isolates having a MIC of ≥ 4 μg/ml is considered colistin resistant and colistin Kirby Bauer were done to assess phenotypic colistin resistance. The E. coli and K. pneumonia isolates exhibited resistance to colistin were examined for the presences of plasmid mediated mcr-1 to mcr-8 genes. Extended spectrum beta-lactamase (ESBL), AmpC beta lactamase and carbapenemase were inialy detected by the phenotypic methods. bla genes (bla _CTX-M, bla_SHV, bla_OXA, and bla_IMP) were detected by PCR technique.

RESULTS

A total of 150 isolate were collected during the study period, from main hospital in Najaf, these isolates were from clinical specimens which included urine (47, 53%), burn wound (8, 66%), seminal fluid (4,50%), sputum (5, 62.5%), and wound abscesses(8, 80%). Bacterial isolates obtained from clinical specimens, 72(48%) were recognized as E. coli. Antibiotic resistance among isolates diverse from 11.1% for colistin to 100% for ampicillin, amoxicillin and amoxicillin-clavulanic. 48 (66.6%)  E.coli isolates were identified as MDR and 24(33.3%) isolates considered as XDR. Initial screening of ESBL indicated that all isolates were putatively assigned as ESBL producers. (70.8%) E. coli isolates were AmpC β-lactamase producers. Genotype bla gene positive ESBL for E. coli isolates 11 (15.2%) have blaOXA, 12 (16.6%) blaCTX-M isolates have and 15(20.8%) have blaSHV, the frequency of carbapenemase-encoding genes among the isolates, blaIMP was negative for all isolates.

Among screening all phenotype colistin resistance isolates 8 E. coli, the frequencies of plasmid mediated colistin resistance mcr genes. No isolates were positive for plasmid encoded colistin resistance gene mcr1, mcr-2, mcr-3, mcr-4, mcr-5, mcr-7, mcr-8, while all the eight-colistin resistant isolates harbored the plasmid mediated colistin resistance gene mcr-6.

CONCLUSION

Results revealed that the prevalence of colistin resistance E. coli isolates in  Al-Najaf hospital is concerning; further limiting potential therapeutic options. This is the first report of plasmid encoded colistin resistance E.coli  isolate that carries mcr-6 in Al-Najaf hospital

Background: Antibiotic resistance has emerged as a significant global public health issue, driven by the rapid adaptation of microorganisms to commonly prescribed antibiotics(Mondal et al., 2024). These genes can be rapidly disseminated among the strains because they exist on the mobile genetic elements (Gröndahl‐Yli‐Hannuksela et al., 2018). The case of superbugs with extended-spectrum beta-lactamases, AmpC beta lactamases, or Metallo-beta lactamases has minimized treatment options (Shad., 2018). Carbapenems are a type of beta-lactam antibiotics with a wide spectrum of action on numerous aero- and anaerobic bacteria, Gram-positive and Gram-negative bacteria, and are utilized in the management of serious infections that are life-threatening and unresponsive to the conventional antibiotic therapy (Wanger et al., 2017). Carbapenems are widely utilized in the infections that are caused by multidrug resistant strains of the Enterobacteriaceae and they were being taken as the last resort antibiotics to treat the multidrug resistant Gram-negative bacteria (Chiu et al., 2018, Armin et al., 2023).Polymyxins such as colistin are believed to be the final resort of antibiotics to cure infections caused by carbapenem resistant Enterobacteriacea (CRE). In 2012 the World Health Organization reclassified colistin as critically important to human medicine (Newton-Foot et al., 2017).The mechanism of action of colistin utilizes the interaction with the outer-side of the bacteria to remove the divalent cations on negative phosphate groups of the Lipid A of the lipopolysaccharide membrane resulting in cell lysis (Olaitan et al., 2014).Colistin resistance has previously only been regarded as a consequence of chromosomal mutation in the genes that encode either the P.m.r.A/Pmr.B and PhoP/PhoQ signalling systems or the negative regulator MgrB. These mutations lead to an alteration of the Lipid A molecule (Olaitan et al., 2014). In the recent past, resistance by the polymyxins that is transferable through the m.c.r- genes has been observed. The location of these m.c.r- genes was found on the plasmid and this increases the fear that the resistance might be conveyed into Gram-negative bacteria. Mcr-1 gene was initially detected in Escherichia coli and Klebsiella pneumoniae in China(Srijan et al., 2018), and then the existence of mcr-1 gene was also detected in other bacteria in countries around the globe e.g. United States, European Union, Turkey, South Africa, Malaysia, Greece, Italy, Algeria, Tunisia and Kuwait(Wang et al., 2018).The first study carried out in Egypt in 2016 reported the presence of mcr-1 gene in E. coli strain taken from an intensive care unit (ICU) patient(Elnahriry et al., 2016).  In 2016, the mcr-2 plasmid-mediated colistin resistance was detected in E. coli first in Belgium from pigs and then from patients (Xavier et al., 2016).