Brain heart infusion broth

The bacteriological cultivation for E. coli was performed in accordance with standard procedures [34 ]. Briefly, each rectal swab was directly cultured on sterile MacConkey agar (Mast group Ltd, Merseyside, UK) and incubated at 37 °C for 24 h. Four lactose-fermenting colonies from each sample were separately sub-cultured and biochemically confirmed using tryptophan broth for indole test, methyl red for MVP test and citrate agar for citrate utilization test. The biochemically confirmed E. coli (indole positive, MR positive, VP negative and citrate negative) were stored in brain heart infusion broth (Mast group Ltd, Merseyside, UK) with 20 % glycerol at - 20 °C until needed for DNA extraction.

Streptococcus mutans ATCC 25175 obtained from American Type Culture Collection was used in the study. The strain was grown on brain heart infusion broth (Mast Group, Bootle, UK) with 2% sucrose (BHIS) until, unless mentioned otherwise. For longer storage and preservation, the strain was stored in 20% glycerol at −80 ℃.