Determination of Colistin Resistance in Clinical Isolates from Healthcare Facilities in Mthatha and Surrounding Areas

<b>Background</b>: Antimicrobial resistance (AMR) is a global threat in the public healthcare sector. The emergence of carbapenem-resistant <i>Enterobacterales</i> (CRE) has become a serious public health threat in South Africa. The spread of CRE has led to the use of colistin for treating severe infections. Colistin is a cationic, lipopeptide antibacterial agent that is effective against most Gram-negative bacteria through its disruption of the bacterial cell membrane. This study aims to determine the colistin resistance (MIC) and mobile colistin resistance (<i>mcr-1</i>) gene in clinical isolates from healthcare facilities in Mthatha and its surrounding areas. <b>Methods</b>: Fifty-three CRE isolates were collected from health facilities between January 2019 and June 2021 and stored in skim milk 10% and 5% inositol broth. The carbapenemase confirmatory test involved a RESIST-4 O.K.N.V assay (Coris BioConcept, Gembloux, Belgium), which was conducted following manufacturer protocol. Broth microdilution was performed according to the ISO standard method (20776-1) using A ComAspTM colistin 0.25-16 μg/mL MIC Broth. Conventional polymerase reaction (PCR) was performed for the detection of <i>mcr-1</i>. <b>Results</b>: <i>N</i> = 53 (100%) isolates were used. A total of 53% were defined as <i>Klebsiella pneumoniae</i>, Escherichia coli constituted 8%, <i>Enterobacter cloacae</i> 8%, <i>Serratia marcescens</i> 8%, <i>Serratia fonticola</i> 2%, <i>Enterobacter aerogenes</i> 2%, <i>Klebsiella oxytoca</i> 2%, <i>Citrobacter koseri</i> 2%, and <i>Citrobacter freundii</i> 2%. The specimens were from the following wards: Pediatric and Neonatal 38%, Medical 30%, Gynecology, Labour, and Maternity 11%, OPD and A&E 11%, ENT 4%, and Others-Male TB ward, Trauma, and adult ICU 6%. In total, 13% of the isolates were resistant and 86% were sensitive to colistin. The common CRE genes detected were OXA-48 at 47%, NDM at 13%, VIM at 1%, and a combination of OXA-48 and NDM at 5%. Of the isolates, 66% were positive for the production of carbapenamase. In this study, we found that all <i>N</i> = 53 (100%) isolates did not have the mobile colistin resistance gene (<i>mcr-1</i>). <b>Conclusions</b>: Antimicrobial resistance is associated with the emergence of carbapenemases genes. Increasing resistance to colistin in clinical settings can lead to difficulties in treating CRE infections, which may lead to clinical failure. In our study, 13% of isolates were phenotypically resistant to colistin.