Gram-negative bacteria in water distribution systems of hospitals.

A total of 67 samples of tap water were collected from faucets and showerheads in 6 hospitals located in the Lublin province (eastern Poland). The samples were examined for the presence and species composition of Legionella, Gram-negative bacteria belonging to family Enterobacteriaceae (GNB-E) and Gram-negative bacteria not belonging to family Enterobacteriaceae (GNB-NE), by filtering through cellulose filters and culture on respectively GVPC, EMB and tryptic soya agar media. On average, Legionella was isolated from 65.7% of the water samples taken in hospitals. Strains of the Legionella pneumophila types 2-14 predominated, forming 74.6% of total Legionella isolates. Legionella pneumophila type 1 strains constituted 13.5% of the total count, while other species of Legionella (referred to as Legionella spp.) formed 11.9% of the total. The concentrations of Legionella in positive water samples ranged from 3-350 cfu/100 ml. GNB-E were not found in the examined water samples. GNB-NE were isolated from 79.1% of the water samples taken in hospitals in the concentrations 11-300 cfu/100 ml. Species of the family Pseudomonadaceae predominated among GNB-NE strains isolated from the examined water samples, forming on average 71.5% of the total count. Altogether, 20 GNB-NE species were identified in the examined samples, out of which 12 were potentially pathogenic. In conclusion, Gram-negative flora of water samples taken in the examined hospitals complies with potable water sanitary standards by the lack of Enterobacteriaceae species, but creates a moderate health risk because of mediocre concentrations of Legionella and the presence of potentially pathogenic non-enterobacterial species.