Fermented condiments remain the key constituents of diets throughout the world especially in Africa and Asia. The process of fermentation of these condiments involves different types of microorganisms which interact with each other and mode of interaction need to be understood. Iru and ogiri-egusi were purchased from retail markets in Oyo State, Southwest Nigeria. Microorganisms were isolated, characterised and co - cultured for fermentation of the condiments. Bacteria obtained were 168; 100 Gram-positive bacteria, 30 Gram-negative and 38 Lactic acid bacteria. Bacillus species comprising B. subtilis, B. pumilus, B. licheniformis and B. megaterium had the highest frequency of occurrence of 72% while Staphylococcus epidermidis and some lactic acid bacteria were consistently present. B. subtilis had the highest growth rate at 60 h when used singly both in iru and ogiri-egusi. Co - culturing B. subtilis and S. epidermidis in iru and ogiri-egusi showed an increase in growth rate of 46 and 23% respectively while addition of L. plantarum gave a decrease of 33% in growth thus depressing the growth of B. subtilis. The factors at play by the lactic acid bacteria during the interaction were presumed to be due to production of acids and metabolites which have effect on the proteolytic Bacillus species. Knowledge of the key roles of the organisms studied facilitates the development of starter cultures using mixed cultures. © All Rights Reserved.