Opportunistic pathogenic bacteria Pseudomonas, Aeromonas and Staphylococcus in the water of a Lake D ugie Wigierskie in the presence of cormorants (Phalocrocorax Carbo)

Counts of Pseudomonas aeruginosa, Aeromonas hydrophila and bacteria of the genus Staphylococcus were assayed in the water of D ugie Wigierskie Lake, which are situated in Wigry National Park and is settled by a colony of about 1,000 black cormorants. The studies were conducted at monthly intervals in spring, summer and autumn of 1999-2001. Water was sampled at 8 sites located in the lake's littoral zone (sites 4, 5 and 6), profundal zone (sites 1, 2, 3) and in the vicinity of a water inflow from Muliczne Lake as well as an outflow to Okr g e Lake (sites 7 and 8, respectively). In total, 176 water samples were assayed. Counts of Pseudomonas aeruginosa in the water of D ugie Wigierskie Lake were very small, even in 50 cm3 capacity water samples; frequently, no presence of these bacteria was determined (particularly in the year 2001). Aeromonas hydrophila was determined in higher numbers from June to September. Staphyloccocus spp. appeared in higher counts in spring and summer. As a rule, more bacteria were found in the water sampled at the sites located in the south-eastern part of the lake (sites 2); they were quite frequently determined near the inflow from Muliczne Lake (site 7) and around the areas inhabited by cormorants (sites 4, 5 and 6). Among the bacteria which belong to the genus Staphylococcus, coagulase-negative strains S. caprae, S. capitis and S. sciuri were most numerous, whereas coagulase-positive S. aureus cells were detected only occasionally in spring and early autumn.