Journal o f General Microbio/ogy (1983), 129, 439445. Printed in Great Britain
The Influence of Ionic Strength, pH and a Protein Layer on the Interaction
between Streptococcus mutans and Glass Surfaces
By A. ABBOTT,t P. R. RUTTERS AND R. C. W. BERKELEY*
Department o f Microbiology, University of Bristol, Medical School, University Walk,
Bristol BS8 ITD, U.K.
(Received 15 July 1982)
The initial interaction between Streptococcus mutans and hard surfaces has been investigated
using a rotating disc technique. The deposition to clean and BSA-coated glass of two strains of S.
mutans, FA-1 (serotype b) and KPSK2 (serotype c), which exhibit different surface properties,
was studied. Organisms were harvested from cultures grown in a chemostat at a dilution rate of
0.06 h-l and suspended in NaCl solutions of defined ionic strengths and pH values. The
deposition of both strains showed a strong dependence on electrolyte concentration, particularly
at low ionic strengths, which was inversely related to the zeta potentials of the organisms.
Similarly, the ionic strength at which maximum deposition was first noted (critical coagulation
concentration) for the two strains correlated with their relative potentials. Deposition was
insensitive to changes in pH at an electrolyte concentration of 0.05 M. The maximum observed
deposition did not approach values predicted by theory, suggesting that a further barrier to
deposition, other than electrostatic repulsion, might exist. Under all experimental conditions,
some of the deposited bacteria were observed to be oscillating, suggesting that they were held at
a distance from the collector surface. The cells did not, however, appear to be deposited in a
secondary minimum predicted by DLVO theory hence it may be that long-range polymer inter-
actions are also involved in the deposition of these organisms.
Streptococcus mutans is an oral organism found almost exclusively on the teeth and its presence
appears to be correlated with dental caries (Fitzgerald et al., 1960; Krasse, 1966; Bowen, 1969;
Loesche et al., 1975). In the development of caries the deposition and adherence of S. mutans on
to the hard, enamel tooth surface are important processes.
A previous study carried out in this laboratory concerning the initial interaction, referred to as
‘deposition’, between S. mutans and hard surfaces showed a great variability in this property
among a number of strains of the organisms (Abbott et al., 1980). The serotype b strains studied
(FA-1, BHT and OMZ51) showed particularly low deposition tendencies which correlated with
the possession of high negative zeta potential suggesting that, for these strains, electrostatic
repulsion may be important in the initial interaction with the collector.
The present study was designed to establish whether variations in the environmental
conditions under which deposition occurred affected the zeta potentials of S. mutans cells, which
would influence the electrostatic repulsion between the cells and the collector surface, and
whether these variations altered the tendency of the organisms to deposit.
Two strains of S. mutans, FA-1 (a serotype b strain) and KPSK2 (serotype c), were grown in a
continuous culture apparatus under conditions of glucose-limitation, and deposition from
7 Present address: MRC Dental Unit, The Dental School, Lower Maudlin Street, Bristol BSl 2LY, U.K.
2 Present address : Physical Sciences Branch, New Technology Division, BP Research Centre, Chertsey Road,
Sunbury-on-Thames, Middlesex TW 16 7LN, U.K.
0022-1287/83/0001-0696 $02.00 0
Interaction of S. mutans with hard surfaces
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