Parents/carers collected the initial samples from the twins by following detailed instructions given in Fig. S8 . The samples were cultured within 7–10 days of reception to check for Streptococcus mutans. This was undertaken to check viability of the samples collected by the parents/carers.
Samples were plated on agar selective for Streptococcus mutans (TSYC20B) which was incubated for 72 h at 37 °C in an atmosphere of 95% nitrogen and 5% carbon dioxide. Following incubation S mutans was identified by characteristic colony morphology under a dissecting microscope. A sub-sample of positive colonies was confirmed by carbohydrate fermentation patterns. Each sample was assessed independently. After three contiguous positive cultures for S mutans it was assumed that S mutans had been acquired. The samples were then placed in black semi-solid transport media VMG II50 (link) and stored at 80 °C.
Samples were plated on agar selective for Streptococcus mutans (TSYC20B) which was incubated for 72 h at 37 °C in an atmosphere of 95% nitrogen and 5% carbon dioxide. Following incubation S mutans was identified by characteristic colony morphology under a dissecting microscope. A sub-sample of positive colonies was confirmed by carbohydrate fermentation patterns. Each sample was assessed independently. After three contiguous positive cultures for S mutans it was assumed that S mutans had been acquired. The samples were then placed in black semi-solid transport media VMG II50 (link) and stored at 80 °C.
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