Extract from the fermented soybean product Natto inhibits Vibrio biofilm formation and reduces shrimp mortality from Vibrio harveyi infection

• Published in: Fish & shellfish immunology 2018-01, Vol.72, p.348-355
• Main Authors: Yatip, Pattanan, Nitin Chandra Teja, D., Flegel, Timothy W., Soowannayan, Chumporn
• Format: Article
• Language: English
• Subjects: Bacillus subtilis; Biofilm; Natto; Shrimp; Vibrio harveyi; Vibriosis
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2017.11.008

Many bacteria, including Vibrio pathogens of shrimp, need to colonize and/or form biofilms in hosts or the environment to cause disease. Thus, one possible control strategy for shrimp Vibriosis is biofilm inhibition. With this objective, an extract from the Japanese fermented soybean product, Natto was tested with the luminescent shrimp pathogen Vibrio harveyi (VH) for its ability to inhibit or degrade biofilm and to interfere with cell growth in broth. Natto is a traditional fermentation product of Bacillus subtilis var Natto (BSN1). Using 96 well microtiter plates coated with 0.4% chitosan, we found that biofilm formation by VH was inhibited, while growth in parallel broth cultures was not. When an extract from Natto prepared using BSN1 was mixed with feed for the whiteleg shrimp Penaeus vannamei before immersion challenge with V. harveyi at 106 cfu/ml, survival was significantly higher (p≤0.05) than for control shrimp given feed without these additives. Further work done to test whether d-amino acids were involved in biofilm formation as previously reported for B. subtilis, Staphylococus aureus and Pseudomonas aeruginosa gave negative results. In conclusion, we discovered that Natto extract can inhibit Vibrio biofilm formation and that it or BSN1 alone added to shrimp feed can significantly reduce shrimp mortality in immersion challenges with pathogenic VH. This shows some promise for possible application against Vibriosis in shrimp since Natto is generally regarded as safe (GRAS) for human consumption. •Bacillus subtilis Natto (BSN) fermented soybean extracts (BSNE) inhibited Vibrio biofilm formation but not growth.•Tests with specific D-amino acids known to be produced by BSN did not cause inhibition.•BSNE or BSN cells added to shrimp feed greatly reduced mortality of shrimp post larvae challenged with V. harveyi.•Reduced mortality correlated with less severe pathologies in the treated shrimp.•BSNE and BSN show promise for application against shrimp Vibriosis since Natto is generally regarded as safe (GRAS) food.