Spread of Multi-drug Resistant Aerosolised Salmonella sp and Escherichiacoli from Dumpsites in Built Environment of Abraka Town, Nigeria

Waste dumpsites are known to be hot spots for the development of multi-drug resistant (MDR) pathogenic microorganisms, which can be dispersed via aerosols. The dispersal of MDR Salmonella sp and E. coli in dumpsite-infested neighbourhoods of Abraka, a university town, was therefore investigated. Eosine Methylene Blue and Bismuth Sulphite agar plates were used to isolate airborne E. coli and Salmonella sp, respectively using settling plate technique. Air sampling was carried out at 3 neighbourhood dumpsites and at intervals of 50m up to 200m away from the dumpsites along the cardinal directions. The isolates were tested for antibiotics resistance using 10 antibiotics and those with multiple antibiotics resistance (MAR) index≥0.3 were considered MDR and subsequently subjected to plasmid curing, and re-tested for antibiotics resistance. The population of both organisms varied with cardinal directions and dumpsites, but generally declined as the distance from dumpsites increased (E. coli, 2.96-1.72 log cfu/m3 ; Salmonella sp, 2.65-0.00 cfu/m3 ). By overall assessment, mean MAR index for E. coli isolates was 0.39±0.01-0.64±0.04 and 0.37±0.02-0.68±0.03 for Salmonella sp isolates. MDR E. coli and Salmonella sp constituted 26.7-45.7 and 0.0-47.1% of the total population, respectively; and were encountered up to 200m away from the dumpsites at all directions although with decreasing numbers. There were significant reductions (P<0.05) in the MAR indexes of both organisms after curing thereby indicating plasmid involvement in the MDR. In conclusion, the aerosolised plasmid-encoded and chromosome-based genes in MDR organisms from dumpsites can be dispersed in neighbourhoods; and plasmids can spread antibiotics resistant genes by horizontal transfer and compound therapeutic options