Convergence of Resistance Gene Determinants in Uropathogenic Pseudomonas aeruginosa and Acinetobacter baumannii from a Nigerian Tertiary Hospital

Abstract

Background: Urinary tract infections (UTIs) caused by multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii represent a growing therapeutic challenge in Nigerian healthcare settings. The convergence of extended-spectrum β-lactamase (ESBL) genes with tetracycline and fluoroquinolone resistance determinants complicates treatment and facilitates extensively drug-resistant phenotypes. Objective: This study aimed to determine the prevalence, phenotypic resistance profiles, and co-carriage of blaCTX-M, tetA, and qepA resistance genes among uropathogenic P. aeruginosa and A.baumannii isolated from female UTI patients in a tertiary hospital in Enugu, Nigeria. Methods: A total of 250 mid-stream urine samples were collected from female patients with clinically diagnosed UTIs between February and October 2025. Bacterial identification employed standard microbiological and biochemical methods. Phenotypic ESBL production was determined by the Double Disc Synergy Test (DDST). Antibiotic susceptibility testing was performed using the Kirby-Bauer disc diffusion method and interpreted according to CLSI guidelines. Multiple Antibiotic Resistance (MAR) index was calculated. Molecular detection of blaCTX-M, tetA, and qepA genes was conducted using conventional PCR. Statistical associations between gene carriage and phenotypic resistance were analyzed using Fisher's exact test and logistic regression, with significance set at p < 0.05. Results: Among 250 urine samples, 152 (60.8%) yielded bacterial growth, with P. aeruginosa accounting for 98 (39.2%) and A. baumannii for 54 (21.6%) isolates. Phenotypic ESBL production was confirmed in 89 (58.6%) of the 152 isolates: 56 (57.1%) of P. aeruginosa and 33 (61.1%) of A. baumannii. Antibiotic susceptibility testing revealed alarmingly high resistance rates: 100% resistance to cefotaxime, ceftazidime, and tetracycline among ESBL-positive isolates. Resistance to ciprofloxacin was observed in 73.2% of P. aeruginosa and 81.8% of A. baumannii ESBL-positive isolates, while levofloxacin resistance was 100% and 63.6%, respectively. Imipenem retained efficacy, with susceptibility rates of 67.9% for P. aeruginosa and 90.9% for A. baumannii. MAR indices exceeded 0.2 in all ESBL-positive isolates, ranging from 0.47 to 0.94. Genotypic analysis of 20 selected ESBL-positive isolates (10 each of P. aeruginosa and A. baumannii) revealed blaCTX-M in 20 (100%), tetA in 20(100%), and qepA in 13(65%). Co-carriage of all three genes was observed in 65% (13/20) of isolates, with significant convergence in the 32-38 years age group. A strong association was found between tetA carriage and phenotypic tetracycline resistance (OR = 28.5, 95% CI: 4.2-192.7, p < 0.001), and between qepA carriage and levofloxacin resistance (OR = 3.21, 95% CI: 1.08-9.54, p = 0.042). blaCTX-M + tetA co-carriage was an independent predictor of multidrug resistance (adjusted OR = 7.82, 95% CI: 1.95-31.36, p = 0.004). Conclusion: This study reveals a critical convergence of blaCTX-M, tetA, and qepA resistance determinants in uropathogenic P. aeruginosa and A. baumannii from Enugu, Nigeria. The 100 % detection of CTX-M and tetA genes, coupled with qepA in two-thirds of ESBL-positive isolates, underscores an urgent need for enhanced antimicrobial stewardship, molecular surveillance, and revised empirical treatment guidelines for UTIs in Nigerian tertiary hospitals.