Studying the antibiotic-resistant patterns of bacteria isolated from commercially available chicken manure samples

Abstract

Chicken manure is widely applied as a fertilizer in agricultural fields in Sri Lanka. However, the extensive usage of antibiotics in the chicken farming industry may carry a risk of having soil contaminated with antibiotic residues and antibiotic-resistant bacteria. This may increase the potential threat to public health due to the mobilization of antibiotic resistance within bacterial populations. In this study, antibiotic-resistant bacteria were isolated from commercially available chicken manure samples, and the antibiotic-resistant profiles of these isolates were studied. Two chicken manure samples obtained from Kosgama and Beruwala were used to isolate a total of 20 antibiotic resistant bacteria using nutrient agar supplemented with ampicillin (50 μgmL-1), tetracycline (30 μgmL-1) and kanamycin (30 μgmL-1) separately. Antibiotic resistance of selected isolates was determined using a standard well diffusion assay with 3 different concentrations (100, 150 and 200 μgmL-1) of each of the antibiotic used. The multidrug-resistant isolates, exhibiting resistance to the highest concentrations of all three antibiotics tested, were selected for further analysis. These isolates were subsequently exposed to higher concentrations of ampicillin, tetracycline, and kanamycin (200, 250, and 300 μgmL-1), as well as chloramphenicol, erythromycin, and rifampicin (100 and 150 μgmL-1). Out of the antibiotic-resistant bacterial isolates, 50% were resistant to 2 or more antibiotics tested, while 20% of the isolates were resistant to all 3 antibiotics at 200 μgmL-1 concentration. Among the selected multidrug-resistant isolates (S1AmpC4, S1KanC2, S1TetC3 and S1TetC4), S1AmpC4 exhibited resistance to ampicillin (300 μgmL-1), kanamycin (300 μgmL-1) and chloramphenicol (150 μgmL-1). S1TetC3 exhibited resistance to ampicillin (300 μgmL-1), tetracycline (300 μgmL-1), kanamycin (300 μgmL-1) and erythromycin (150 μgmL-1) and S1TetC4 exhibited resistance to ampicillin (300 μgmL-1), tetracycline (300 μgmL-1) and erythromycin (150 μgmL-1). Isolate S1AmpC4, S1TetC3, S1TetC4 were resistant to four out of six antibiotics used. The results of this study suggest that the application of untreated chicken manure to the soil can facilitate the mobility of antibiotic resistance through the ecosystem via these multidrug-resistant bacteria.