Survival of Escherichia coli and Acinetobacter junii at various concentrations of sodium chloride

Abstract

The survival of two heterotrophic bacteria in conditions of various concentrations of NaCl was tested. Both bacteria can commonly enter marine environments through sewage or wastewater treatment plant effluents; the Escherichia coli is a common enteric bacterium and Acinetobacter junii is a phosphate-accumulating bacterium inhabiting activated sludge. When cultivated in nutrient rich media (COD 8700 mg O2 L -1 ), both bacteria were multiplying during 72 h at concentrations of NaCl up to 5% for E. coli and 3.5% for A. junii. Total die-off of E. coli was detected at 72 h by NaCl concentration of 20%. Total die-off of A. junii was detected at 72 h by NaCl concentration of 10%. When the same bacteria were cultured in nutrient depleted media (COD 90 mg O2 L -1 ), the multiplication of E. coli stopped at 3.5% of NaCl and higher, but the cells were able to survive for longer period of time at extreme NaCl concentrations of 20 and 30%. The negative influence of NaCl to A. junii was pronounced in conditions of organic matter shortage and rapid die-off was observed at 3.5% of NaCl and higher. Both bacteria seemed to be osmotolerant when cultured in nutrient-rich media, but not in nutrient-depleted media.