REMOVAL OF BURKHOLDERIA-CEPACIA BIOFILMS WITH OXIDANTS

Iodine is used to disinfect the water system aboard US space shuttles and is the anticipated biocide for the international space station. Wa ter quality on spacecraft must be maintained at the highest possible l evels for the safety of the crew. Furthermore, the treatment process u sed to maintain the quality of water on spacecraft must be robust and operate for long periods with minimal crew intervention. Biofilms are recalcitrant and pose a major threat with regard to chronic contaminat ion of spacecraft water systems, We measured the effectiveness of oxid izing biocides on the removal and regrowth of Burkholderia (Pseudomona s) cepacia biofilms. B. cepacia, isolated from the water distribution system of the space shuttle Discovery was grown in continuous culture to produce a bacterial contamination source for biofilm formation and removal studies, A 10(7) CFU . ml(-1) B. cepacia suspension, in distil led water, was used to form biofilms on 3000 mu m(2) glass surfaces. R ates of attachment were measured directly with image analysis and were found to be 7.8, 15.2, and 22.8 attachment events . h(-1) for flow ra tes of 20.7, 15.2, and 9.8 ml . min(-1), respectively. After 18 h of f ormation, the B. cepacia biofilms were challenged with oxidants (ozone , chlorine, and iodine) and the rates of biofilm removal determined by image analysis. Fifty percent of the biofilm material was removed in the first hour of continuous treatment with 24 mg . l(-1) chlorine or 2 mg . l(-1) ozone. Iodine (48 mg . l(-1)) did not remove any measurab le cellular material after 6 h continuous contact. After this first re moval of biofilms by the oxidants. the surface was allowed to refoul a nd was again treated with the biocide. Iodine was the only compound th at was unable to remove cellular debris from either primary or seconda ry biofilms. Moreover, treating primary biofilms with iodine increased the rate of formation of secondary biofilms, from 4.4 to 5.8 attachme nt events . h(-1). Ail the oxidants tested inactivated the B. cepacia associated with both primary and secondary biofilms. The amount of bio cide needed to inactivate 50% of planktonic B. cepacia in 10 min at 25 degrees C was 8.4, 0.5, and 0.2 mg . l(-1) for iodine, chlorine, and ozone, respectively. The data suggest that iodine may not be the best chemical for treating of biofilms when removal of cellular material is required.