Survival of Acinetobacter baumannii in natural water media

Acinetobacter baumannii is an emerging opportunistic pathogen associated mainly with hospital infections. Since there is insufficient data regarding the successfulness of A. baumannii in the natural environment, the aim of this investigation was to examine the survival rates of A. baumannii in different types of natural water media. Multi-drug resistant (MDR) environmental isolates were cultivated on CHROMagar Acinetobacter at 42°C/24h. Bacterial suspension was inoculated into bottles containing the 100 mL of sterile spring water, seawater and effluent water from the secondary type of municipal wastewater treatment plant, and incubated at 20°C with stirring (150 rpm) during 28 days. Number of bacteria was followed by cultivation on Nutrient agar plates at 42°C/24h, from which the survival rates were calculated. In effluent water the successful multiplication of A. baumannii was evident (124% survival rate after 28 days), while in natural spring water and seawater no multiplication occurred. The survival rate in spring water was constant (100%) with a slight decrease (94%) after 21 days and 89% after 28 days, while in seawater the survival rate was constant for the first 2 days (100%), and decreased to 64% after 28 days. The chemical oxygen demand of effluent was considerably higher (24 mgO2/L) than the spring (3 mgO2/L) and seawater (4 mgO2/L). These findings indicate that MDR isolates of A. baumannii successfully persist in the natural water media and that the survival rates are dependent on the availability of nutrients.