Secretory IgA, Salivary Peroxidase, and Catalase-Mediated Microbicidal Activity during Hydrogen Peroxide Catabolism in Viridans Streptococci: Pathogen Coaggregation

Viridans streptococcican kill methicillin-resistant Staphylococcus aureus(MRSA) through the production of hydrogen peroxide (H 2 O 2 ). However, several hundred viridans streptococcicells are necessary to kill 1 cfu of MRSA. We analyzed the potency of bactericidal and fungicidal effector molecules induced by catabolism of H 2 O 2 in the oral cavity. Secretory IgA(SIgA) and an unidentified salivary component bound Streptococcus sanguinis, a viridans streprococcus, and MRSA into coaggregates. In these coaggregates, salivary peroxidase and the MRSA catalase produced singlet molecular oxygen ( 1 O 2 ) from H 2 O 2 produced by viridans streptococci. SIgA converted 1 O 2 into ozone, which has potent bactericidal and fungicidal activity. We calculated that <10 cfu of Streptococcus sanguiniswere necessary to kill 1 cfu of MRSA in the coaggregate. SIgA, Aspergillus niger catalase, and H 2 O 2 in saliva killed Candida albicans, which is highly resistant to reagent H 2 O 2 . Together with indigenous bacteria and innate immunity, SIgA potentially constitutes a novel system that may sustain oral homeostasis.