Passive immunization has been suggested as a method to prevent coloniz
ation of teeth by mutans streptococci. However, the mechanism of actio
n of antibodies, both polyclonal and monoclonal, is not clear. In this
study we investigated the effect of polyclonal antibodies (pAbs) and
a monoclonal antibody (OMVU10) on the chain length and growth of Strep
tococcus sobrinus. During growth in broth S. sobrinus formed significa
ntly longer chains in the presence of pAbs in comparison to pre-immune
serum (p<0.01), but pAbs did not influence the growth rate of S. sobr
inus in broth. OMVU10 did not influence the growth rate nor the chain
length. In order to study the effect of the antibodies on adhesion and
growth on a surface, S. sobrinus was grown on hydroxyapatite discs in
the presence of two other bacteria, Streptococcus oralis and Actinomy
ces viscosus. No effect of the antibodies was found on the total culti
vable count of the three bacteria after growth on hydroxyapatite discs
. However, the morphology of the S. sobrinus microcolonies was differe
nt after growth in the presence of both pAbs and OMVU10. The colonies
were less dense and chains of S. sobrinus could be seen using a confoc
al laser microscope. After growth in the presence of the control antib
odies, the colonies were dense and no long chains could be observed. I
t was concluded that pAbs influenced the chain length, in broth and on
hydroxyapatite discs, and the colony morphology of S. sobrinus on hyd
roxyapatite discs, whereas OMVU10 influenced the colony morphology of
S. sobrinus on hydroxyapatite discs.