24-09-2017, 05:06 AM
25-09-2017, 10:19 AM
In the present study a method for detecting the effects of antibiotics in soil microbial communities was optimized. The influence of measurement time and nutrient status on contamination - induced community tolerance (PICT) was investigated using sulfonamide sulfacloropyridazine (SCS) as a composite model. The development of tolerance in soil microcosms that were exposed to SCP under different conditions was compared to background tolerance in SCP-unexposed microcosms. Tolerance of bacterial extracts from soil microcosms was determined in Biolog® multiple well plates as the sensitivity to SCP of a number of physiological processes. Background tolerance was not affected by soil nutrient amendments, but an influence of inoculum density on microtiter plates was observed. However, the background tolerance variance was low, which favors the use of community tolerance measures for selective detection of a toxic impact. In line with the assumptions of the PICT concept, soil modification with SCP led to an increase in community tolerance. This development of tolerance was increased with further soil amendment with fresh pork suspension, and less by the addition of alfalfa meal. Tolerance increases were observed after exposure to SCP soil for only 7 days, possibly because the nutrient supply facilitates the rapid adaptation of the soil microbial community. However, a further increase in exposure time caused variable changes in the tolerance observed. The detection of prolonged tolerance in the microtiter plates (11 days) allowed a clearer differentiation between the different treatments of the soil, since it better solved the values of EC50 of processes with a high tolerance to the bacteriostatic antimicrobial compounds. In order to detect the effects of antibiotics in soil microbial communities, it is therefore recommended to use nutrient amendments (possibly fresh pork slurry), to standardize the exposure time to the soil and to extend the period of measurement of the Biolog plate for more than 7 days.