<i>&gt;Growing bacterial colonies of botulism might be inherently riskier than day-to-day contact with sick people. Growing bacterial colonies of what&#x27;s on your toothbrush just ain&#x27;t.</i><p>The difference between petri dishes with what was often a specified bacteria&#x2F;mold and the bacteria from a person&#x27;s mouth should be self-evident.<p>As brandmeyer pointed out, the girl may have had bacteria while showing no sign of having an illness (example given was strep throat). Having a small amount of the bacteria and then <i>raising a colony of it</i> could pose some risk of getting others sick.