Abstract
Objective: Municipal solid waste (MSW) landfills recently emerged as potential reservoirs of antibiotic resistance. However, little is known about the potentials of unsanitary landfill sites which are common in developing countries as reservoir of antibiotic resistance. In this study, we investigated the antibiotic resistance pattern and presence of selected resistance genes in bacteria from three MSW landfills in Ibadan, southwestern Nigeria.
Methodology: Fifty six antibiotic- and metal-resistant bacteria isolated from leachate and leachate-contaminated surface and groundwater collected from three MSW landfills in Ibadan, Southwestern Nigeria, were searched for sulfonamides, florfenicol and beta-lactams resistance genes and integrons by PCR.
Results: None of the 27 β-lactamase genes tested was detected in the isolates. sul1, sul2 and floR were however detected in 12 (21.4%), 2 (3.6%) and 12 (21.4%) bacteria species identified as Alcaligenes faecalis, Advenella kashmirensis, Brevundimonas spp. and Ralstonia pickettii. The 12 bacteria carrying sul1/floR gene combination were also positive for class 1 integron. Analysis of the gene cassettes in the variable regions of the class 1 integrons (>1.5kb) of the 12 intl1-positive isolates revealed the presence of aadB and unknown genes. The deduced amino acid sequence of the unknown portion of the gene cassettes shared 42-65% identity with sequences of Class D β-lactamase and OXA-2-like protein in the GenBank.
Conclusions: Findings of this study suggest that the landfill ecosystem is a potential site for the evolution of novel resistance genes and are hence important reservoir of antibiotic resistant bacteria. J Microbiol Infect Dis 2019; 9(1): 34-42.

Key words: Landfill leachate, antibiotic resistance, sul genes, floR, aadB, class D β-lactamase