Aeromonas hydrophila is a valuable indicator of the quality of water polluted by sewage and pathogens that pose a risk for humans and cold-blooded animals, including fi sh. The main aim of this research was to evaluate anthropogenic pollution of river water based on genetic diversity of 82 A. hydrophila strains by means of RAPD, semi-random AP-PCR (ISJ) and the rep-BOX conservative repeats test. Genetic diversity of A. hydrophila was HT = 0.28 (SD = 0.02) for all DNA markers (RAPD, semi random and rep-BOX). None of the analyzed electrophoretic patterns was identical, implying that there were many sources of strain transmission. The presence of genes for aerolysin (aerA), hemolysin (ahh1) and the cytotoxic enzyme complex (AHCYTOGEN) was verifi ed for all tested strains, and drug resistance patterns for tetracycline, enrofl oxacin and erythromycin were determined. The most diverse A. hydrophila strains isolated from river water were susceptible to enrofl oxacine (HS = 0.27), whereas less diverse strains were susceptible to erythromycin (HS = 0.24). The presence of the multidrug resistance marker (ISJ4-25; 1100 bp locus) in the examined strains (resistant to three analyzed drugs) indicates that intensive fi sh cultivation affects the microbiological quality of river water.

Studies were carried out in the summer seasons of l 995-1999 (from June to September) on the quantitative and qualitative composition of Enterobacteriaceae bacteria (including Escherichia coli and Salmonella sp.), and potentially pathogenic bacteria Aeromonas hydrophila, Pseudomonas aeruginosa and Staphylococcus sp. in the water of 8 bathing sites of the Lake Wigry. Aeromonas hydrophila occurred in the all samples of studied water and was the most numerous in water sampled from sites of increased trophic levels. Irrespective of the site and time of sampling Pseudomonas aeruginosa was rarely isolated. In the total of 160 samples of water analysed Salmonella sp.. Escherichia coli and Staphyloccocus aureus were determined in 32 (22.6%), 68 (42.4%) and 90 (55%) samples, respectively. Pathogenic bacteria of the genus Salmonella sp. and potentially pathogenic Staphylococcus aureus and Aeromonas hydrophila identified in the analysed offshore waters (also when Escherichia coli were absent) suggest that the use of the Lake Wigry waters for swimming, falling into account faecal bacterial counts, may not be sufficient to fully reflect safety conditions for bathers. The results of the research suggest that the evaluation of the Lake Wigry surface waters for recreational use should include the frequency of the occurrence of Salmonella sp., Staphylococcus aureus, Aeromonas hydrophila and Pseudomonas aeruginosa. These three species, which arc not directly linked to faecal contamination, can cause various diseases of the skin, nasal and oral cavities, eyes, internal car and other problems in people swimming in contaminated water.