A loophole in soap dispensers mediates contamination with Gram-negative bacteria

Liquid soap dispensers are widely used in domestic and clinical settings. In previous studies, the risk of bacterial contamination of refillable systems was pointed out and a bacterial contamination rate of 25%, with values of up to 10⁸  colony-forming units/mL (CFU/mL), was reported. However, the route of contamination remains elusive. To address this point, we determined the microbial contamination of refillable standard pump dispensers and nonrefillable press-dispenser systems. Following the collection of 104 liquid soap dispensers from hotel rooms across Germany, bacterial counts were determined. Isolates of samples containing nonfastidious Gram-negative^(lac-) bacteria were further analyzed by the Vitek 2 system for the determination of species. 70.2% of the refillable pump dispensers (mean total bacterial count = 2.2 × 10⁵  CFU/mL) but only 10.6% of the nonrefillable press dispensers, were contaminated (mean total bacterial count = 1.5 × 10¹  CFU/mL). Of samples containing nonfastidious Gram-negative^(lac-) bacteria, Pluralibacter gergoviae was present in 41.7%, Pseudomonads (Pseudomonas aeruginosa and Pseudomonas putida) in 25%, Serratia marcescens in 16.7%, and Klebsiella oxytoca and Pasteurella testudinis in 8.3%. After the initial assessment, we contaminated different dispensing systems with P. aeruginosa/P. gergoviae, to reveal the route of contamination and identied the pressure release of standard pump dispensers as the loophole for microbial contamination.