Molecular analysis of florfenicol-resistant bacteria isolated from drinking water distribution systems in Southwestern Nigeria

Objectives: Use of chloramphenicol or its veterinary analogue florfenicol can selectively favour antibiotic-resistant bacteria. Understanding how resistance is mobilised and disseminated among pathogens is vital in knowing how different bacterial taxa might serve as reservoirs of these genes for pathogenic bacteria. Methods: Bacterial isolates (n = 30) were selected on the basis of multidrug resistance and resistance to florfenicol from among 296 bacteria originally isolated from drinking water distribution systems in Southwestern Nigeria. Bacterial identification, minimum inhibitory concentration (MIC) determination for florfenicol, PCR detection of florfenicol resistance genes (floR fexA and cfx) and sequence analysis were employed to characterise the isolates. Results: According to sequence data (16S rDNA, v2-v3 region), 30 strains were selected, including-Pseudomonas spp. (43.3%), Serratia spp. (13.3%), Proteus spp. (26.7%), Acinetobacter spp. (13.3%) and Providencia rettgeri (3.3%). MICs ranged between >16 mu g/mL and >1024 mu g/mL. floR was the only resistance gene detected (11/30; 36.7%). The majority offloR-positive isolates (8/11; 72.7%) were Proteus spp. All floR sequences shared 100% identity and 1-2 synonymous substitutions relative to other published sequences. Conclusions: floR-positive strains in this study were originally selected randomly without antibiotics. Finding floR in four genera without selective enrichment is consistent with widespread distribution of this resistance trait in drinking water systems in Nigeria. Further work is needed to determine whether human and veterinary antibiotic use practices in Nigeria are contributing to proliferation of this important antibiotic resistance trait and to determine whether the presence offloR-producing strains is compromising human and animal health. (C) 2020 The Authors. Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.