IMPACT OF SOIL AMENDED WITH PIG MANURES ON THE ABUNDANCE OF ANTIBIOTIC RESISTANT BACTERIA AND THEIR ASSOCIATED GENES

Abstract

The unregulated antibiotic administration in animal husbandry and insufficient supervision on the source of manure has contributed to the spread of antibiotic resistant bacteria (ARB) and their resistant genes to both clinical and environmental bacteria. This research focus on the impact of agricultural soil amended with pig manures on the abundance of antibiotic resistant bacteria and their resistance genes. Uncultivable soil sample for 5 years and pig manure were collected from three different farms within Akure metropolis (FUTA, Adofure and Oda town). Soil amended with pig manure samples at different ratio (4:1, 4:2 and 4:3) under microcosm experiment was plated on Luria-Bertani (LB) agar incorporated with commercial antibiotics. The emerged isolates regarded as ARB were presumptively identified using conventional cultural methods. Identities of the ARB isolates were authenticated using 16S rRNA gene sequence analysis. The antibiotic-resistance genes (ARGs) and mobile genetic element (MGEs) in the genome of ARB were detected by standard molecular tools (Polymerase Chain Reaction). In this study, genera Pseudomonas, Escherichia, Providencia, Salmonella, Bacillus, Alcaligenes and Paenalcaligenes were the cultivable ARB/MARB. A total of 15 antibiotic resistant genes (ARGs) frequently used in clinical or veterinary settings and two (2) mobile genetic elements (Class 1 and Class 2 integrons) were detected. Tetracycline resistant gene was widely distributed with prevalence of 50%, while aminoglycoside and quinolone resistant genes had 13 and 16%, respectively. Other classes of antibiotic resistant genes had 5% prevalence among the 18 ARB isolates. The results of this study shows that 17 ARB isolates carries more than two or more ARGs in their genome. Class 1 integron MGEs was detected among all the 18 ARB isolates with prevalence of 90-100%, while Class 2 integron was detected among 11 ARB isolates. The two classes of integron were found among 10 ARB isolates. The detected ARGs were suspected to

have three different resistance mechanisms: antibiotic deactivation, efflux pumps, and cellular protection. The results highlight a much higher risk of ARGs spreading through pig manure to human pathogens, causing untreatable infection in humans.