Prevalence of Antibiotics and Cr, Cd, Cu Metals Co-resistant Coliforms in Refuse Dumpsites and Air of Surrounding Buildings in a Nigerian Urban Setting

Abstract

Prevalence of co-resistance to antibiotics and Cr⁶⁺, Cd²⁺, and Cu²⁺ among coliforms from dumpsites and surrounding buildings’ indoor and outdoor air was investigated in Warri town, in the Niger Delta region of Nigeria. A total of 1,465 coliforms were isolated with McConkey and Eosin Methylene Blue Agar, and 38.8% had multiple antibiotics resistance (MAR) index ≥ 0.3 based on nine antibiotics. The prevalence of coliform bacteria with a MAR index of ≥ 0.3 varied (20.0 - 69.2%) and was lower in indoor and outdoor air farther away from the dumpsites. All dumpsite isolates were resistant to Cr and Cd but not to Cu, while resistance varied (48.5 - 100%) among indoor and outdoor air isolates. Plasmid-encoded resistance was indicated when the mean MAR (0.48 ± 0.04 - 0.5 ± 0.04) and multiple heavy metal resistance (MHMR) indexes (0.66 ± 0.00) declined to 0.11 ± 0.01 - 0.36 ± 0.03 and 0.33 ± 0.00, respectively, after curing. The differences in MAR indexes of isolates from the four dumpsite locations and between indoor and outdoor air isolates were only significant (P < 0.05) after curing, unlike the MHMR index, where there was no significant difference before and after curing. The prevalence of metals and antibiotics co-resistance, which was based on the concomitant reduction in MAR and MHMR indexes after curing, was higher in isolates from dumpsites than in indoor and outdoor air (32.1 - 38.1 vs 0.0 - 16.8%). The role of plasmid-encoded genes in the co-resistance phenomenon was therefore indicated. Dumpsites as selective pressure spots for the emergence of resistance genes in bacteria should be of public health concern in countries characterised by indiscriminate dumping of wastes, as this can result in potential spread to houses via bioaerosols.