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The field studies were conducted to determine the effects of three antibiotics tetracycline (TC),
chlortetracycline (CTC) and oxytetracycline (OTC) at three different concentrations (50, 100 and 200 mg
kg-1 soil) on total bacterial population present in two alluvial soils of Aligarh, one irrigated with tube well
water and other by sewage water at four depths (0-15; 15-30; 30-45 and 45-60 cm) for a period of 91
days. Nutrient agar medium was used for the count of bacterial population. The results obtained from
studies revealed that in presence of studied antibiotics significant reduction in the number of bacterial
population occurs up to 21-35 days of application in tube well water irrigated soil and 35-42 days of
application in sewage water irrigated soil and thereafter population of bacteria increased. The
bactericidal activity of antibiotics was in the order CTC> OTC>TC. The results also showed that with
increase of antibiotics concentration and soil depth bacterial population decreased appreciably. A
comparison of results of both studies revealed that bacterial population in sewage irrigated soil was
higher than tube well water irrigated soil. The % reduction of bacterial population in presence of
antibiotics was lesser in sewage irrigated soil than tube well water irrigated soil, suggesting that soil
irrigated by sewage water might have antibiotics resistant bacteria. Soil organic matter was significantly
correlated with soil bacterial population.
Keywords: Antibiotics, Tetracycline, Sewage water, Microorganisms, Bacteria.