In vitro antagonistic effect and in vivo protective efficacy of Gram-positive probiotics versus Gram-negative bacterial pathogens in finfish and shellfish

Abstract

It is well established that Gram-positive probiotic bacteria are efficacious as a preventive tool for control of disease outbreaks in aquaculture. Secretion of bioactive compounds such as bacteriocins, siderophores, enzymes, and antibiotics by Gram-positive probiotics can adversely affect potential pathogenic of Gram-negative bacteria in the intestine of aquatic animals providing a barrier against attachment and colonization of disease agents in the gastrointestinal (GI) tract. More than 50 species of Gram-positive bacteria [mostly Bacillus and lactic acid bacteria (LAB)], originally isolated from GI tract of aquatic animals have been examined as potential probiotics in about 40 commercial finfish and shellfish species. These putative probiotics are thought to interact with or antagonize Gram negative pathogens in the GI tract. Members of genera Vibrio and Aeromonas are the most important pathogens of aquatic animals, and Gram-positive probiotics can inhibit their growth in vitro. There are, however, minimum data showing minimum inhibitory concentration of Gram-positive probiotics against these pathogenic Gram-negatives. Moreover, incorporation of Gram-positive probiotics into aquafeeds can also improve host immune-physiological functions and enhance disease resistance. There are, however, a lack of knowledge correlating the in vitro antagonist data with the in vivo protective efficacies of selected Gram-positive probiotics. The probiotic dosage optimization is, therefore missed in the most studied works. In addition, scarce data are available to demonstrate behavioral growth of Gram-positive probiotics such as synergistic or antagonistic effects. The present review addressed in vitro antagonistic effects and in vivo clinical efficacy of putative Gram-positive probiotics administration versus Gram-negative pathogens in finfish and shellfish and discussed the current gaps and future research works required.