In vitro survival of Bacteroides intermedius in five transport media, alone or in the presence of Streptococcus sanguis.

The survival rate of Bacteroides intermedius was first tested in monoculture, and Streptococcus sanguis was then added in 5 different transport media; 2 nonnutritious media, the viability-preserving medium of the University of Göteborg No. IV (VMG IV), reduced transport fluid (RTF), and 3 nutritious media, thioglycolate medium (TG), peptone yeast extract medium (PY) and PY medium with 1% glucose (PYG). All manipulations were carried out in an anaerobic chamber. After a given transport time (6 or 24 h) aliquots were spread on plates containing solid PY medium by means of an automated spiral system device, thus permitting counts after incubation. The slight variations in the counts of B. intermedius in monoculture, not exceeding 0.5 log10 in the 5 media tested, indicated its good survival capability, i.e. at least 24 h. By contrast, when S. sanguis was added, it was only possible to use nutritious media such as PY or TG for 6 h. In the glocose-containing media (PYG, TG), the multiplication of rapidly glucose-fermenting microorganisms such as streptococci influenced the B. intermedius survival rate. Therefore, the transport time for oral microbiological samples needs to be reduced as much as possible. The use of excessively rich media (particularly media containing a high level of glucose) should be avoided.