Breastfed children showed increased presence and abundance of the lactic acid bacterium Dolosigranulum ( relative effect size [ RES ] , 2.61 ; P = 0.005 ) and Corynebacterium ( RES , 1.98 ; P = 0.039 ) and decreased abundance of Staphylococcus ( RES , 0.48 ; P 0.03 ) and anaerobic bacteria , such as Prevotella ( RES , 0.25 ; P < 0.001 ) and Veillonella ( RES , 0.33 ; P < 0.001 ) .