Hemolytic bacteria in water from the dental air-water syringe

Abstract

Purpose: The purpose of this pilot study was to determine whether aquatic bacteria expressing hemolysis, a classical virulence factor of pathogenic bacteria, could be found in water flowing from the dental air-water syringe (AWS).

Methods: Water samples were collected from the AWS in each of five dental operatories, and a control sample was collected from the cold-water tap in the sink adjacent to one of the dental operatories. Water samples were plated on NWRI agar to enumerate aquatic heterotrophic bacteria and on Tryptic Soy Blood (TSB) agar to enumerate hemolytic bacteria. After incubation, plates were counted to determine total colony-forming units per mL of AWS water. In addition, TSB plates were examined for hemolytic colonies, which were counted if present.

Results: AWS water samples contained an average of 9.4 x 10(4) colony-forming units cfu/mL on NWRI agar, and 1.3 x 10(4) cfu/mL on TSB agar. The control sample from the cold-water tap contained 2.5 x 102 and 50 cfu/mL on NWRI and TSB agars, respectively. Four out of five AWS water samples contained hemolytic bacteria, with an average hemolytic count of 3.2 x 10(3) hemolytic cfu/mL on TSB agar. No hemolytic bacteria were detected from tap water. Most hemolytic organisms exhibited alpha-hemolysis although beta-hemolytic colonies were seen.

Conclusions: AWS water can contain hemolytic bacteria--such bacteria express a virulence factor and therefore may be regarded as potential pathogens. According to a Medline search conducted April 23, 2002, this is the first report of hemolytic bacteria from dental unit water.