An assessment of antibiotic resistant bacteria in poultry litter and agricultural soils in Kandy district, Sri Lanka

Abstract

Antibiotic resistant gut flora and nearly large amount of antimicrobials used in feed could end up in poultry litter. Hence, poultry litter could serve as sources of antibiotic resistance determinants to the environment. A study was conducted to assess the abundance of antibiotic resistant bacteria (ARB) in poultry litter and manure samples, and agricultural soils. Sampling was performed in WM3 agro-ecological region in Kandy district, Sri Lanka. Soil from thirteen cultivated and two uncultivated lands were sampled. Poultry litter from layer and broiler farms (four each) and poultry manure from five heaps at agricultural fields in the study area were collected. All samples were analyzed for pH, electrical conductivity, respiration, potentially mineralizable N (PMN), active carbon. Bacteria were enumerated using 0.3% tryptic soy agar supplemented with tetracycline or enrofloxacin each at 0, 1 and 10 ppm in spread plate technique. Selected 20 isolates were characterized for gram staining and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for tetracycline and antibiotic sensitivity towards tetracycline, enrofloxacin and neomycin. The highest and the lowest abundance of culturable bacteria populations were recorded for layer litter (7.42±0.38 log 10 CFU/g) and cultivated soils (6.96±0.34 log 10 CFU/g) respectively. Total Culturable bacteria populations significantly correlated with active C and PMN of soils and manures. In soils, bacteria resistant towards tetracycline and enrofloxacins at 10 ppm ranged from 3.58 to 4.99 log 10 CFU/g and 0.96 to 2.55 log 10 CFU/g respectively. Abundance of bacteria resistant towards tetracycline was higher than enrofloxacin in all samples. MIC and MBC of the isolates ranged from 0.5 to 1024 ppm and 4 to >1024 ppm of tetracycline, respectively. Poultry litter and manure, and soils collected from study area contain bacteria resistant to tetracycline and /or enroflaxacin. Variability in tetracycline and enrofloxacin resistance characters is suggestive of high diversity among ARB.