Attachment, Growth and Persistence of Cronobacter on Granular Activated Carbon Filters

Introduction: Several Cronobacter outbreaks have implicated contaminated drinking water.  This prompted us to assess whether activated carbon water filters commonly used in homes could serve as a potential source of Cronobacter.  Past research has suggested that such filters can serve as potential source of bacteria in the home environment if used in conjunction with water with excess organic loads. Accordingly, the attachment, growth and persistence of Cronobacter in granular activated carbon (GAC) filter was investigated to assess the impact of GAC on the microbial quality of the water produced. 

Purpose: This study tested the hypothesis that GAC filters could serve as a reservoir for Cronobacter by trapping low levels of nutrient upon which the organism could grow.

Methods: A simulated water filter system was installed by filling glass tubes with sterile GAC, followed by sterile water with a dilute carbon source (peptone) flowing through the column at a rate of 1 liter/day. Carbon columns were inoculated with 10⁴ CFU of Cronobacter on the surface, and the effluent monitored for Cronobacter levels.  During a second phase, commercial faucet filters will be distributed to households for 4-month use. Used filters were backwashed with sterile peptone water, and analyzed for Cronobacter, total aerobic plate count, coliform bacteria and Enterobacteriaceae.

Results: Cronobacter colonized the simulated GAC and grew when provided minimal levels of nutrients, shedding up to 10⁷ CFU/ml in the effluent water after 2 days. Most Cronobacter colonized on the upper part of the column. Backwashed used filters used in home settings yielded presumptive Cronobacter spp., Escherichia coli, Pseudomonas and other waterborne bacteria.

Significance: Cronobacter and other bacteria are able to colonize on granular activated carbon filter, penetrate the treatment barrier and release into water effluent, introducing a safety risk of waterborne pathogens, and potentially contaminating the kitchen environment. These results suggest that the use of these filters should be considered a potential source of Cronobacter and other foodborne pathogens under certain circumstances.