Control of bacterial contamination in microfiltered water dispensers (MWDs) by disinfection

Three microfiltered water dispensers (MWDs) for domestic use were bacteriologically monitored over a period of 1 year to evaluate their hygienic status and to compare the ability of two disinfectants (peracetic acid and hydrogen peroxide) to ensure adequate bacteriological quality of the dispensed water. s end, two dispensers were purposely contaminated with a strain of Pseudomonas aeruginosa of environmental origin. l of 324 samples of input and output water were analyzed. Heterotrophic plate count (HPC) bacteria at 22 °C and 36 °C, total coliforms (CT), Escherichia coli (EC), enterococci (ENT), P. aeruginosa and Staphylococcus aureus were enumerated. hout the study period, the supply water was always of excellent bacteriological quality. All water samples taken from the MWDs complied with the legal requirements for drinking water: CT, EC, ENT and S. aureus were all consistently absent. P. aeruginosa was never isolated from the uncontaminated dispenser. However, an increase in HPCs up to levels of 103–104 cfu/mL was found in the dispensed water. the present operative conditions, hydrogen peroxide was seen to be more effective than peracetic acid in controlling bacterial contamination in the water circuits. Periodic disinfection with hydrogen peroxide made it possible to obtain water with HPC levels conforming to Italian regulations for drinking water (≤ 100 cfu/mL) as well as to the levels recommended by the American Dental Association (ADA) (≤ 200 cfu/mL). Furthermore, in the contaminated circuits, H2O2 disinfection led to a reduction in the concentrations of P. aeruginosa to only a few colony forming units/100 mL or to a complete, albeit temporary, disappearance of the microorganism. clusion, hydrogen peroxide at 3% can be proposed as a suitable product for periodic disinfection of domestic MWDs, taking into consideration also its low cost and easy availability.