**5.1 Hydrogen peroxide (H2O2)**

Hydrogen peroxide is produced by most *lactobacilli* in the presence of oxygen. *lactobacilli* possess oxidases that reduce oxygen to hydrogen peroxide, oxidizing substrates such as pyruvate or NADH [41]. Since they do not produce catalases, H2O2 does not suffer auto-degradation. H2O2 has a broad-spectrum planktonic bacteria, but the effect decreases dramatically on biofilm. It appears that *Lactobacilli* do not produce effective concentrations of H2O2 against fungi [42], unlike other bacteria [39].

## **5.2 Bacteriocins**

Lactic acid bacteria produce bacteriocins, proteinaceous antimicrobial substances with molecular weights of several thousand daltons or more. Bacteriocins can be divided into five classes according to their primary structure, molecular composition, and physical and functional properties [43, 44]. However,

bacteriocins produced by lactic acid bacteria against *S. mutans* and *P. gingivalis* are not yet known. Bacteriocin L23 produced by *Lactobacillus fermentum* L23 [44], plantaricin produced by *L. plantarum* [45], and pentocin TV35b produced by *L. pentosus* [46] appear to be effective against the yeast form of *Candida*. Bacteriocins effective for the hyphal forms of *Candida* have not yet been identified [47, 48].
