Oligocene waters are widely recognized as excellent sources of drinking water. Due to the belief in their good quality, the water from Oligocene intakes in Warsaw, Poland, is made available to users without prior treatment or disinfection. The present study aimed at assessing possible microbiological risks associated with the use of this water. The occurrence of microbiological contaminants in selected intakes was evaluated, in addition to an assessment of possible changes in the microbiological quality of the water under typical storage conditions. The possibility of antibiotic resistance in bacteria isolated from Oligocene water samples was also investigated, as was their sensitivity to selected disinfectants. A small number of bacteria-27.0 ± 60.8 CFU/cm3 and 3.0 ± 3.0 CFU/cm3-were found in Oligocene water intakes for psychrophilic and mesophilic bacteria, respectively. Fecal bacteria were not detected. Bacteria present in Oligocene waters showed the ability to multiply intensively during standard water storage; this was especially true for mesophilic bacteria in water stored at room temperature. In some samples, bacterial counts reached 103-104 CFU/cm3 after 48 h. Almost all bacterial isolates were resistant to the commonly used antibiotics: ampicillin, vancomycin and rifampicin. The bacteria were also insensitive to some disinfectants.
Keywords: Oligocene waters; antibiotic resistance; microbiological hazard; microorganisms.