Single species and two species biofilms comprising
Streptococcus sanquis
and
Actinomyces naeslundii
were established in order to determine the susceptibility to
chlorhexidine of the bacteria growing in biofilms compared to
planktonic growth, and when growing in single species
biofilms compared to mixed biofilms. The MIC of the bacteria to
chlorhexidine was determined by a broth dilution method. Single and two
species biofilms were established in a flow model in a modified Robbins
device and subsequently exposed to chlorhexidine for 48 h at concentrations
from 10 to 2000 mg/ml. Further, two species biofilms were exposed to 1000
mg/ml of chlorhexidine in 10 min pulses two or six times a day. The biofilm
cell number was determined by viable counting at different time intervals.
Two species biofilms were established faster than single species biofilms,
but after establishment
A. naeslundii was suppressed by
S.
sanguis. When lower concentrations of chlorhexidine were added,
however,
A. naeslundii also remained in the biofilm. Resistance of
S. sanguis and
A. naeslundii to
chlorhexidine increased
considerably when growing in biofilms and }100 mg/ml was needed to
eliminate growth of the bacteria. Somewhat different patterns of
susceptibility were observed in single species compared to two species
biofilms. Thus, the results of this study indicate that the susceptibility
of bacteria to antimicrobial agents is influenced by biofilm growth as well
as by bacterial interactions in mixed bacterial communities.
