Fig. 2.

Factors contributing to microbe-microbe interaction. The microbe-microbe interaction confers a stable intestinal environment. Direct and indirect interactions exist due to complex mechanisms of action and microbial factors in health (eubiosis) or disease (dysbiosis). Mechanisms potentially involved in microbe–microbe interaction in the gut include: 1) direct competition between resident and pathogenic bacteria; 2) production of growth inhibitory metabolites such as short chain fatty acids (SCFAs); 3) consumption of luminal oxygen which inhibits the growth of pathogenic bacteria; 4) production of superoxide anion (i.e., by Enterococcus faecalis inhibiting Staphylococcus aureus); 5) secretion of toxins against pathogenic bacteria mediating the type VI secretion system (T6SS) of Gram- negative bacteria; 6) production of antimicrobial peptides (AMPs)