Inhibition of Bacillus cereus Growth by Bacteriocin-producing Bacillus subtilis Strains Isolated from Maari, a Baobab Seeds Fermented Condiment, is Substrate Dependent

Introduction: Maari is a spontaneously fermented alkaline fermented condiment made from baobab seeds. Maari fermentations are dominated by Bacillus subtilis contributing to desirable organoleptic properties. Due to the spontaneous fermentation, occasionally Bacillus cereus occurs in high numbers

Purpose: The aim is to select starter-cultures against B. cereus.

Methods: The Influence of substrate on antimicrobial activity was investigated by inoculating separately B. subtilis B3, B122 and B222 in baobab whole seeds, baobab ground seeds and in BHI incorporated with baobab ground seeds. For survival of B. cereus, BHI broth, ground baobab seeds broth and whole baobab seeds were inoculated with each B3, B122 and B222 as mono-cultures and in co-culture with B. cereus NVH391-98. Samples were collected for determination of pH, CFU/ml and antimicrobial activity.

Results: All three strains showed antimicrobial activity against B. cereus NVH391-98 in BHI-broth, whereas no antimicrobial activity was detected in cooked seeds and in ground baobab seeds broth. However, incorporation of ground baobab seeds with to 95-99.5% (w/w) BHI enhanced antimicrobial activity of B. subtilis in a strain dependent manner. Addition of FeCl₃, MgSO₄ and MnSO₄ to baobab ground seeds broth did not cause any antimicrobial activity. B. cereus NVH391-98 grew well in all the 3 substrates in mono-culture. Further, all the 3 B. subtilis strains were able to decrease B. cereus NVH391-98 to levels below detection limit in BHI, while outgrowth of B. cereus NVH391-98 was delayed in baobab ground seeds broth and during cooked baobab seeds fermentations by up to 40 h.

Significance: The present study contributes to the selection of Bacillus strains to be used as starter cultures for controlled production of Maari.