Hidden Reservoirs, Emerging Threats: Herbal Medicines Fuel the Spread of Antimicrobial Resistance

Abstract Contaminated herbal medicinal products are increasingly recognized as a potential reservoir for the dissemination of antimicrobial-resistant bacteria within communities. This study provides a systematic characterization of the resistance phenotypes and genotypes of bacteria contaminating herbal medicinal products sold across six Local Council Development Areas of Alimosho Local Government Area, Lagos State, Nigeria. A cross sectional study of 150 herbal products in six Local Council Development Areas of Alimosho Local Government Area, Lagos State, Nigeria was conducted. The bacteria were isolated by using the standard method and susceptibility was determined by Kirby–Bauer disc diffusion following CLSI recommendations. The MAR indices and MDR, MDR and PDR phenotypes were calculated. The resistant isolates were subjected to PCR for tetA, sul1, blaCTX-M, ant(3″)-Ia, qnrA, qnrB, qnrC and qnrS to identify the genotype–phenotype associations and statistical analysis was performed. The total number of bacteria isolated was 520, which included S taphylococcus, Escherichia, Bacillus, Enterobacter, Klebsiella, Citrobacter, Proteus, Pseudomonas, Salmonella and Shigella. A high level of resistance was seen in sulfamethoxazole-trimethoprim (67.7%), imipenem (63.1%), augmentin (60.2%), erythromycin (50.4%), and tetracycline (49.2%) and a high level of sensitivity was shown in ciprofloxacin (96.3%) and gentamicin (88.5%) in the antimicrobial susceptibility test with MDR phenotypes being common and MAR indices > 0.20 in most strains. Molecular analysis revealed the presence of several resistance genes, including sul1 (60.6%), tetA (49.7%), QnrC (24.2%), ant(3")-Ia (21.8%), QnrA (20.6%), blaCTX-M (18.8%), QnrB (7.3%), and QnrS (3.6%). The distribution of genes was significantly different among LCDAs and sample types (p < 0.05); some genes had significant genotype–phenotype associations prior to multiple testing correction. Herbal products sold within Alimosho LGA constitute a significant source of resistant bacteria and transferable resistance genes, potentially contributing to the spread of antimicrobial resistance within the community. Strengthened microbiological and molecular surveillance, alongside more rigorous regulatory control, would meaningfully improve the safety of these products and reduce the risk they pose to public health.