A team of researchers from multiple academic institutions in Brazil examined the use of several different potential probiotic strains to act as antimicrobials and control pathogenic bacteria in shrimp. The group published its work in the journal Aquaculture.
“The ongoing study was carried out to evaluate the in vitro antimicrobial activity of Bacillus subtilis and Shewanella algae and to quantify Vibrio spp. load in the gastrointestinal tract of reared juveniles of L. vannamei given feed supplemented with B. subtilis and S. algae,” said the researchers. “Therefore, this work aims to understand the potential of the use of specific probiotic bacterial strains to improve conditions in shrimp farming.”
The research team found that diets supplemented with the Bacillus subtilis IPA-S.51 strain demonstrated a “greater inhibitory frequency” against the pathogenic bacteria. “Moreover, shrimp fed with IPA-S.51 presented greater final weight, weight gain rate and daily weight gain than the Control and [Shewanella algae] IPA-S.252,” they added.
“Overall, our results showed that B. subtilis strain administration significantly improved shrimp growth and could develop in shrimp hepatopancreas and intestine,” the researchers said. “Furthermore, feed supplemented with S. algae and B. subtilis strains could also control Vibrio load in the L. vannamei hepatopancreas.”
Why probiotic trials and use?
Shrimp farming has become a main aquaculture activity for several countries and produces about 3.49m tons of shrimp worth about $15bn annually, the researchers said. The whiteleg shrimp Litopenaeus vannamei is one of the primary species raised in Brazil and several other countries.
However, production of shrimp faces challenge from disease and “deteriorating environmental conditions,” which have caused economic loss, they said. Frequent outbreaks of epidemic diseases like those caused by viruses or the bacteria Vibrio spp. have damaged the industry.
Antibiotics have been used to control pathogens and limit microorganism development, they said. However, pathogenic bacteria have become resistant to the antimicrobials used following antibiotic administration.
“An alternative treatment is the use of probiotics or beneficial bacteria that control pathogens,” said the researchers. “Probiotics for aquaculture are generally defined as a set of live microorganisms which, when consumed in adequate amounts, provide a health benefit to the host by competing with pathogenic bacteria through exclusion and modification of the microbial flora associated with the host and its environment.”
Probiotics also could improve enzymatic digestion and feed use in addition to boosting immune response to pathogens, they said.
The use of Bacillus subtilis has had promising results including improving growth performance, disease management and health, they said. Shewanella algae also has been of interest as a probiotic as it can reduce pathogenicity or inhibit Vibrio harveyi.
Methods and materials
In initial in vitro work, the candidate probiotic strains Bacillus subtilis (IPA-S.51) and Shewanella algae (IPA-S.252 and IPA-S.111) along with a commercial probiotic (CP) were tested for pathogen inhibition, the researchers said.
In the feeding trial, two different trial strains – Bacillus subtilis (IPA-S.51) and Shewanella algae (IPA-S.252) were added to shrimp feeds and given to L. vannamei juveniles for a 45-day period, the researchers said. A commercial probiotic (CP) also was used in a trial diet and a Control group was given the same commercial feed with no bacterial supplement.
Shrimp growth parameters were noted including survival rate, final weight, weight gain rate, specific growth rate (SGR), and daily weight gain, they said.
Samples of shrimp hepatopancreases, intestine and fecal matter were collected weekly to check for total heterotrophic bacteria and thiosulfate bile sucrose (TCBS) qualification, they said. Probiotic type and pH also were determined.
In the in vitro disease challenges, all three trial probiotics demonstrated antimicrobial activity against V. alginolyticus, however, IPA-S.51 had the most zones cleared of bacteria during the last 24h and IPA-2.252 and IPA-S.111 had more during the first 24h, the researchers said. Both CP and IPA-S.51 acted with lower colony forming units (CFU) concentration.
All three also had antimicrobial activity against Vibrio parahaemolyticus, they said.
IPA-S.51 demonstrated effectiveness at a wider range of salinities and the initial pH tested, they said, adding "IPA-S.51 produced a greater inhibitory frequency against V. alginolyticus and V. parahaemolyticus."
“It was observed that the IPA-S.51 and IPA-S.252 probiotic candidates produced an inhibition effect against Vibrio pathogens under different bacterial growth periods, pH and NaCl concentrations,” they said. “Regarding pH and NaCl conditions, the maximum antagonistic levels were in the same range as for optimum shrimp culture.”
During the feeding trial, shrimp receiving feed with IPA-S.51 had a greater final weight, improved weight gain rate and daily weight gain when compared to shrimp getting the non-supplemented control or the other experimental diet, the researchers said.
Shrimp on the control and CP diets had a survival rate of 86.8%, while those on the IPA-S.252 diet reached 75% and those on the IPA-S.51 diet had 100%, they said.
“In the in vivo experiment, the candidate probiotics (IPA-S.51 and IPA-S.252) could control the Vibrio load in the hepatopancreas,” they said. “It is suggested that this load was shifted to the intestine and ultimately eliminated through feces in the IPA-S.51 and IPA-S.252 groups.”
TCBS counts in the shrimp hepatopancreas were higher for IPA-S.51 during weeks 1 and 4, while they were higher for IPA-S252 during weeks 1, 3 and 5, they said. IPA-S.252 saw an increase in TCBS counts in the intestine during weeks 3 and 4, but overall the TCBS quantification increased in week 5 for all diets.
“Overall, in the fifth rearing week, the Vibrio quantification in feces decreased with IPA-S.51, but increased with the Control and IPA-S.252,” they said.
Title: In vitro and in vivo potential probiotic activity of Bacillus subtilis and Shewanella algae for use in Litopenaeus vannamei rearing
Authors: Juliana Interaminense, Joana Vogeley, Carolina Gouveia, Rogério Portela, José Oliveira, Humber Andrade, Sílvio Peixoto, Roberta Soares, Diego Buarque, Ranilson Bezerra