Study on microflora of activated sludge and salt and drug resistance of isolated bacteria

Abstract

Bacterial isolation from the standard activated sludge was performed, their physiological characteristics such as salt and drug resistance were examined, and bacterial flora of the satndard activated sludge was determined. A lot of strains were isolatedfromthestandardactivated sludge under loth saline and fresh water conditions, when a sample was incubated for 3 days at 30°C with polypeptone-meat extract agar plate. It was found that total viable cells were 2.6×10⁷ cells/ml under fresh water condition and 9.7×10⁵ cells/ml under saline condition. The strains from typical colonies were idendified taxonomically, they were Acinetobacter sp., Bacillus sp., Corynebacterium sp., Enterobaceriaceae, Flavobacterium sp. and Moraxella sp. Dominant strains were Acinetobacter sp., Corynebacterium sp. and Enterobacteriaceae and they occupied 37, 25 and 15%, respectively, under fresh water condition. Under saline condition Bacillus sp. was dominant and 78%. PY medium was the best one compared with other media such as PPYE, SS and CF for culture medium.
Corynebacterium sp. was able to grow in 2.5M NaCl hypertonic environment, while Bacillus sp. (S2) isolated under salinecondition grew in 3.5M NaCl concentration. The salt resistance in both strains was not specific for Na⁺, optimal concentration for growth of both strains was 0.5M NaCl, optimal pH range was 7-8, temperature, 30-35°C. All of isolated strains had drug resistance to some antibiotics and salt resistant strains showed also stronger drug resistance in saline environment.