RESEARCH OF THE MICROBIAL CONTAMINATION OF A LAKE IN THE CITY OF SOFIA WITH REGARD TO ASSESSMENT OF ITS ENVIRONMENTAL SAFETY

Abstract

Microbiological studies were performed on ten samples from a water body in a metropolitan district with a view to evaluating its epidemiological safety. The amounts of microorganisms from the main groups that include pathogenic species, were determined using microscopical, cultural and biochemical methods. The quantities of Gram–negative aerobic and facultative–anaerobic bacteria (5.50x10 2±6.43 – 5.74x10 2±8.87 CFU/ml) and staphylococci (0.42x10 2±0.84 – 5.62x10 2±1.07 CFU/ml) prevailed. The sanitary indicative species Escherichia coli was abundant, especially in the surface water layers (2.92x10 2±5.54 CFU/ml). Pseudomonas species were less (0.30x10 2±0.51 CFU/ml) and found only in the surface layer. Clostridia were isolated from 40% of surface water samples and 80% of bottom samples, but the sanitary indicative species C. perfringens was not detected. The isolated microorganisms were in greater quantities in the surface water layer, but the differences were statistically significant only for staphylococci. Fungi and clostridia were established in greater quantity at the bottom of the lake.