Modified multiple antibiotic resistance analysis for the nonpoint source tracking of fecal pollution

Abstract

Although Multiple Antibiotic Resistance Analysis (MARA) has been adopted for the source tracking of bacterial contamination in natural waters, the accuracy and experimental cost of MARA still have the potential to be improved. Therefore, a process of modified MARA using turbidity was developed, and its feasibility and reliability were evaluated for Fecal Streptococci (FS) in this study. The experimental results are as follows. The development of turbidity via the aesculin hydrolysis by FS could occur in 2–3 hours, and the turbidity of the stock solutions and the number of FS had a proportionate relationship (R2 = 0.991). Thus, the modified MARA could exclude several incubation steps as well as reduce experimental errors by inoculating the same amount of the bacteria into the culture media mixed with antibiotics. The Average Rates of Correct Classification (ARCCs) of the established database based on the modified MARA technique for two-way division and three-way division showed much higher ARCCs (89%) than those of previous studies (61~84%), implying that the modified MARA technique had relatively higher reproducibility than conventional MARA. Also, reliability of the modified MARA was verified by source tracking of stream samples that could be predicted and the real source tracking was carried out by applying the modified MARA in the stream (upstream, midstream, and downstream), which showed reasonable prediction results. The results conclusively demonstrated the modified MARA to be more efficient tool/phenotypic method than conventional MARA for source tracking of fecal contamination in water.