John Gerard S. Abando1 and Jayzon G. Bitacura2*
The excessive use of oxytetracycline for the cost-efficient production of swine can increase the development of antibiotic resistance among pathogenic bacteria. This study was conducted to isolate and identify putative cultivable heterotrophic bacteria from pig feces and evaluate their resistance to oxytetracycline. Composite fecal samples were serially diluted and plated using Tryptic Soy Agar (TSA). Distinct colonies were selected and grown on TSA plates and the pure cultures were subjected to limited screening for morphological and physiological characteristics. Representative isolates were then identified and subjected to oxytetracycline susceptibility assay through the disk diffusion method. Thirteen out of 15 selected colonies from TSA plates were successfully cultured and grouped into eight based on the isolates’ morphological and physiological characteristics. Of the eight representative isolates, three were identified as putative Escherichia coli, two were Staphylococcus aureus strains, Staphylococcus vitulinus, Bacillus cereus and Proteus mirabilis. Furthermore, S. vitulinus and S. aureus strains exhibited susceptibility to oxytetracycline. Meanwhile, isolates, P. mirabilis and the three strains of E. coli showed the highest resistance while B. cereus showed the least. These oxytetracycline-resistant isolates can be used as test organisms to determine the antibacterial effect of novel bioactive compounds or as potential sources of oxytetracycline resistance genes that could be used as selection markers in transgenic experiments.
Keywords: oxytetracycline resistance, swine fecal bacteria, Proteus mirabilis, Escherichia coli, Bacillus cereus