The Journal of Medical Microbiology, Vol 28, Issue 1 9-14, Copyright © 1989 by Society for General Microbiology
Aggregation by fragilis and non-fragilis Bacteroides strains in vitro
M. Blake, O. D. Rotstein, M. Llano, M. J. Girotti and G. Reid
Urology Research, Toronto General Hospital, University of Toronto, Ontario, Canada.
Bacteroides fragilis is associated with the formation of intra-abdominal
abscesses, whereas other Bacteroides species are rarely involved. Since
bacterial clumping may contribute to the survival of bacteria in the face
of host defence mechanisms, the hypothesis has been put forward that
differences in aggregation between fragilis and non-fragilis strains of
Bacteroides may account for their differences in survival in vivo. All
seven B. fragilis strains tested formed aggregates within 4 h, but strains
not associated with intra-abdominal sepsis--B. vulgatus, B.
thetaiotaomicron and B. distasonis--did not form aggregates in vitro.
Aggregation occurred at 37 degrees C, but not at 4 degrees C or 20 degrees
C. Treatment with pronase partially inhibited aggregation. Periodate
treatment killed the cells and caused them to form clumps which were
distinguishable from the control aggregates. Heat-killed B. fragilis cells
formed similar distinct clumps, but cells killed by glutaraldehyde and
formaldehyde did so to a lesser degree. No inhibition was found upon
addition of carbohydrates, ethylenediaminetetraacetic acid or after
treatment with trypsin. These results demonstrate that aggregate formation
occurs with B. fragilis strains alone, and that surface proteins probably
mediate this interaction.
