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.