Abstract:
Antimicrobial Resistance (AR) in bacteria is currently one of the greatest threats to global health. Antimicrobial resistance research has primarily focused on hospitals, but recent information points to the environment as important platform for the proliferation of AR due to selection pressure from anthropogenic pollutants such as Heavy Metals (HMs). Electronic waste (E-waste) is an important source of environmental contamination with HMs in developing countries, which could lead to proliferation of AR in the bacterial flora of E-waste dumpsites. However, few studies have investigated E-waste dumpsites as reservoir of AR. Therefore, this study was aimed at investigating selected E-waste dumpsites in Lagos and Ibadan, Nigeria as reservoirs of AR.
Fifteen soil (Lagos=9, Ibadan=6) and 24 water (Lagos=15, Ibadan=9) samples from three E-waste dumpsites in Lagos and two in Ibadan were processed for isolation of bacteria using standard methods. The HMs content of the samples were determined using inductively coupled plasma-optical emission spectroscopy. Isolated bacteria were tested for co-resistance to metals and ten antibiotics using spot inoculation and disc-diffusion, respectively. Selected bacteria showing co-resistance to metals and antibiotics were subjected to whole genome sequencing to determine genetic basis of metal and antibiotic resistance. The abundance of selected Antibiotic Resistance Genes (ARGs) (sul1, sul2, dfrA1, tetA, blaCTX-M-1) and mobile genetic element intI1 in the metagenomic DNA of the samples were measured by qPCR to determine the level of E-waste dumpsite contamination with ARGs. Data were analysed using linear regression and Principal Component Analysis (PCA) at α=0.05 to examine the relationship between HMs concentrations and ARG abundance.
Eighty-four metal and antibiotic resistant bacteria identified as Escherichia coli (n=66), Enterobacter (n=10), Citrobacter (n=6), Kluyvera (n=1) and Leclercia (n=1) species were isolated from the soil and water samples. Heavy metals (Cu, Pb, Zn, Fe, Ni, Al, Co, Se and Cd) concentration in the water were beyond permissible limits set for drinking water quality by the Standards Organization of Nigeria. Ninety-four percent of the strains were multidrug resistant. Forty-nine different ARGs conferring resistance to tetracycline, aminoglycosides, trimethoprim, sulphonamides, β-lactams, fosfomycins, phenicols and Macrolide-Lincosamides-Stretogramines were identified. Detected genes were tetA/C/D, strA/B, aadA, aac(6')Ib-cr, dfrA1, blaTEM, blaMIR, blaOXA, blaCMY, blaACT, blaCTX-M-15, sul1/2/3, qnrS1, qnrB, qepA, fosA, catA/B, cmlA1 and mphA. Metal-resistance genes arsB, pcoABDRS, silABCPRS, merA and plasmids of the Col, IncF, IncY, IncR, IncI and IncR groups were identified. The ARG/intI1 abundance (copy number/gram) in soil ranged from 1.09x106_1.23x108 (sul1), 1.48x106_9.53x107 (sul2), 1.33x105_3.19x107 (dfrA1), 1.25x105_1.10x106(tetA),9.90x104_2.08x105(blaCTX-M-1) and 6.73x106_8.76x107 (intI1). Abundance (copy number/100ml) for water samples ranged from 1.07x105_2.61x108 (sul1), 4.75x104_1.47x108 (sul2), 1.73x104_1.12x108 (dfrA1), 8.80x103_1.28x106(tetA),4.69x104_5.67x106(blaCTX-M-1) and 1.05x104_2.61x107(intI1). Linear regression and PCA confirmed positive (0.28≥ r ≤0.78) relationships between HM contamination and ARGs abundance in soil and water samples. A higher correlation (0.60≥ r ≤0.78) occurred between intI1 and HMs, while poor correlations were observed with Co, Se and Cd.
The selected electronic waste dumpsites in Lagos and Ibadan were reservoirs of antimicrobial resistant bacteria with heavy metals playing a role in the proliferation of antimicrobial resistance.
