No abstract

Drinking water should be safe for health and free from amounts of pathogenic microorganisms and parasites posing a threat to human health. In recent years, particular attention has been paid to the threat associated with the operation of hot water installations, potentially providing favourable conditions for the development of bacteria of genera Legionella and Escherichia. Such bacteria are commonly found in the natural environment, but should not reach the consumers' taps. In this experiment, hot water samples were collected from six public buildings, and the detection of pathogenic microorganisms, namely Legionella spp., Legionella pneumophila, and Escherichia coli bacteria, was performed by means of qPCR analysis. The sequences specific for these bacteria were quantified with TaqMan probes in total DNA extracts of the hot tap water samples. Bacteria of the Legionella spp. type were detected at five sampling sites in the range from 4.52 to 15.59 genomes/mL of hot tap water. Legionella pneumophila was detected at four sampling sites in the range from 0.98 to 11.99 genomes/mL. E. coli was recorded at four sites, but in quantities around 0.00 genomes/mL (less than one genome/mL). This preliminary research points to the need to use molecular techniques as an additional source of information in standard water analyses to obtain shorter detection time and more accurate results.

Although antibiotic-resistant bacteria (ARB) have been isolated from tap water worldwide, the knowledge of their resistance patterns is still scarce. Both horizontal and vertical gene transfer has been suggested to contribute to the resistance spread among tap water bacteria. In this study, ARB were isolated from finished water collected at two independent water treatment plants (WTPs) and tap water collected at several point-of-use taps during summer and winter sampling campaigns. A total of 24 strains were identified to genus or species level and subjected to antibiotic and disinfectant susceptibility testing. The investigated tap water ARB belonged to phyla Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes. The majority of the isolates proved multidrug resistant and resistant to chemical disinfectant. Neither seasonal nor WTP-dependent variabilities in antibiotic or disinfectant resistance were found. Antibiotics most effective against the investigated isolates included imipenem, tetracyclines, erythromycin, and least effective – aztreonam, cefotaxime, amoxicillin, and ceftazidime. The most resistant strains originate from Afipia sp. and Methylobacterium sp. Comparing resistance patterns of isolated tap water ARB with literature reports concerning the same genera or species confirms intra-genus or even intra-specific variabilities of environmental bacteria. Neither species-specific nor acquired resistance can be excluded.