Hydrogen peroxide-mediated antagonism against serratia marcescens by Streptococcus mitis

The alpha-hemolytic Streptococcus mitis strain no. 17-1, isolated from the oral cavity of an healthy female adult, antagonized the growth of all 24 test strains of Serratia marcescens examined; furthermore, this strain inhibited the growth of various strains of Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes, S. agalactiae, S. pneumoniae, Haemophilus influenzae, Listeria monocytogenes, and Corynebacterium diphtheriae. However, strans of Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, and Pseudomonas aeruginosa proved refractory. The mechanism of microbial antagonism was due to production and release of hydrogen peroxide under aerobic atmospheric conditions, which was neutralized through incorporation of bovine liver catalase into the solid assay medium.