Emergence of Colistin Resistance Among Carbapenem-Resistant MDR <i>Pseudomonas aeruginosa</i> Isolates from Northeast Iran: Determination of MIC Values

Abstract

Background: A major treatment problem is multidrug-resistant (MDR) Pseudomonas aeruginosa, which is often connected to several nosocomial infections. Treating infections brought on by MDR strains with colistin is considered last-line monotherapy. Recent years have shown a concerning rise in colistin resistance, but little is known about its frequency, especially in specific areas. Methods: Clinical isolates of P. aeruginosa were gathered from hospitalized individuals at Hashemi Nejad Hospital in Mashhad, Iran, over a one-year time frame. Isolates designated as MDR underwent confirmatory testing involving ecfX gene-targeted polymerase chain reaction (PCR) and antibiotic susceptibility tests. Then, using the broth microdilution technique, colistin susceptibility was evaluated; minimum inhibitory concentrations (MICs) were calculated following Clinical and Laboratory Standards Institute (CLSI) recommendations. This was a descriptive cross-sectional study. Results: The study comprised 48 MDR isolates altogether from confirmatory tests. All 48 isolates showed 100% resistance to piperacillin-tazobactam, ceftazidime, cefepime, levofloxacin, meropenem, and imipenem, hence verifying their categorization as both MDR and carbapenem-resistant. Based on MIC values ≥ 4 µg/mL per CLSI criteria, colistin susceptibility tests indicated 9 isolates (18.75%) were colistin-resistant. Conclusions: The results draw attention to the growing colistin resistance in MDR P. aeruginosa isolates, hence stressing the critical requirement of ongoing monitoring and improved antimicrobial stewardship initiatives to reduce the spread of resistance and maintain the efficacy of last-resort antibiotics.