Comparison of Resistance to Microbial Contamination of Conventional and Modified Water Dispensers

Abstract

Water dispensers with traditional, open reservoirs were tested comparatively against modified, closed reservoirs and modified caps to determine their failure to resist contamination from exterior surfaces of water bottles and aerosols. Bottle rims and caps were surface inoculated with Escherichia coli (SLR 51), Staphylococcus aureus (SLR 717), and Pseudomonas fluorescens (ATCC 13525) at levels approximating 1 × 107 to 1 × 108 cells for a high level and 1 × 103 cells for a low level. The bottles contained 2,000 ml of water. After mounting the bottles on the appropriate water dispenser type, all water was withdrawn from the units 24 h later. Levels of test organisms recovered ranged from 5.0 × 103 to 4.5 × 105 CFU/ml for the high inoculum and 0.39 to 0.84 CFU/ml for the low inoculum in the traditional water dispensing unit. No test organisms (detection limit <0.01 CFU/ml) were recovered from the modified water dispenser for either high or low inoculum level when the unit was sanitized between trials. Test microorganisms were recovered at levels of ≈ 0.06 CFU/ml to ≈0.8 CFU/ml after 3–5 repetitions of very high level (3 × 108 CFU/ml) inoculation with E. coli and S. aureus without sanitization between trials. An aerosol of 2.02 × 109 CFU E. coli per ml was generated in a chamber directly over the water dispensers without bottles mounted for one trial. The modified water dispenser reduced aerosol contamination by 100- to 1,000-fold.