Genotypic Diversity and Multidrug Resistance Profiles of AmpC-Producing Escherichia coli and Klebsiella pneumoniae in Abakaliki, Nigeria

Background: This study investigated the genotypic diversity and multidrug resistance profiles of plasmid-mediated AmpC (pAmpC)-producing Escherichia coli and Klebsiella pneumoniae isolated from clinical samples at AE-FUTHA, Nigeria. Methods: A total of 200 clinical samples (140 urine and 60 wound swabs) were collected from patients at AE-FUTHA. Phenotypic detection of AmpC β-lactamases was performed using the cefoxitin-cloxacillin double-disk synergy test (CC-DDST). All phenotypically confirmed AmpC-producing isolates were subjected to antimicrobial susceptibility testing using the Kirby-Bauer disk diffusion method against 10 antibiotics from seven classes. Multiplex PCR was used to detect six pAmpC gene families (blaFOX, blaEBC, blaDHA, blaCIT, blaACC, and blaMOX) in all phenotypic AmpC producers. Results: A total of 72 bacterial isolates comprising 51 (70.8%) E. coli and 21 (29.2%) K. pneumoniae were recovered. Phenotypic AmpC production was detected in 67 (93.1%) isolates, with a significantly higher prevalence in K. pneumoniae (100%) compared to E. coli (90.2%) (p=0.04). All 67 AmpC-producing isolates (100%) exhibited multidrug resistance (MDR) with MAR indices ranging from 0.3-0.7. High-level resistance was observed to β-lactams: and the β-lactam/β-lactamase inhibitor combination (100%). Resistance to the monobactam aztreonam was 95.5%, while the folate pathway inhibitor trimethoprim-sulfamethoxazole showed 98.5% resistance. The carbapenem imipenem remained highly effective (97.0% susceptibility), followed by the aminoglycoside amikacin (89.6%) and the fluoroquinolone ofloxacin (82.1%). The blaFOX gene was present in 100% of E. coli but only 52.4% of K. pneumoniae isolates (p<0.001). Co-carriage of all six pAmpC gene families was observed in 52.4% of K. pneumoniae and 100% of E. coli isolates. Significant associations were found between sample source and blaFOX carriage in K. pneumoniae (p=0.002). Conclusion: This study reveals a remarkably high prevalence of genotypically diverse pAmpC genes with alarming MDR profiles among clinical E. coli and K. pneumoniae isolates in Abakaliki, Nigeria. The universal co-carriage of five pAmpC gene families and species-specific distribution of blaFOX highlight the complex molecular epidemiology of resistance in this setting. The sustained efficacy of carbapenems, amikacin, and ofloxacin provides therapeutic options, but urgent antimicrobial stewardship and infection control measures are required to prevent further spread of these resistance determinants.