Isolation and Identification of Probiotic Bacteria for the Management of Epizootic Shell Disease

Grace Underwood, University of Rhode Island


Epizootic shell disease (ESD) is an emerging disease in the American lobster (Homarus americanus) characterized by lesions on the carapace. The diseased appearance of the carapace due to the lesions has had significant negative impact upon the lobster fisheries in New York, Connecticut, Rhode Island, and Massachusetts, since fishers are not able to sell affected lobsters to the more lucrative live market. ESD lesions are different from other shell diseases found in the American lobster populations because they are due to a poly-microbial infection that degrades the epicuticle layer, while the pillars of the chitin matrix remain intact in the lesions. ESD was first described in the 1980’s has increased in prevalence Southern New England. In inshore waters, ESD was estimated to affect 10-40% of the lobsters with 50-80% of the ovigerous females affected by ESD. Additionally, ESD has expanded to lobster populations outside the original geographic range. New or consistent disease observations have been seen in Maine at low levels of disease prevalence. The increase in ESD has generated concern for the health of the lobsters and the economic status of the fishery. ^ It has been shown that probiotics are an effective way to prevent infectious diseases in a variety of animals, including fish and shellfish by inhibition or exclusion of the pathogenic bacteria. The goal of this research was to isolate commensal, potential probiotic, bacteria from the shells of healthy looking lobsters and characterize their ability to reduce or eliminate the ESD-causing organisms. Twenty-four out of 217 isolates were characterized as potential probiotic organisms. Isolates that exhibited inhibitory activity against Thalassobius sp. 131.1 or Aquimarina macrocephali 132.4 (formerly known as Aquimarina homaria) and strong biofilm formation were tested to determine their effect on Thalassobius sp. 131.1 growth and biofilm formation. Isolates were characterized as potential probiotic organisms if they had inhibitory activity against one or both the ESD pathogens. Inhibitory activity was determined by a zone of inhibition test. While twenty-four isolates exhibited activity against at least one of the target organisms, only two potential probiotic organisms, Bacillus sp. 06-YP001, and Pseudoalteromonas sp. 10B-YPO11, had inhibitory activity against both pathogens. Biofilm formation on polystyrene, sterilized lobster shell fragments or glass coverslips was variable in strength across isolates. Sequencing of the 16S rRNA gene was used to identify the genus of the selected potential probiotic organisms; 19 of 24 isolates were identified as Pseudoalteromonas. From the results of the biofilm assays and gene sequencing five isolates were selected for the competition assays to test the ability of these isolates to inhibit Thalassobius sp. 131.1 growth and biofilm formation. The competition assays demonstrated that four isolates, L. maritima 06-YPC210, Bacillus sp. 06-YP001, Pseudoalteromonas sp. 03-YP014, Pseudoalteromonas sp. 08-YPC21, and Phaeobacter inhibens S4Sm were effective in reducing the growth of Thalassobius sp. I31.1. These results demonstrate that potential probiotic organisms can be isolated from the host (lobsters) and used to reduce growth and biofilm formation of the targeted pathogens (ESD). Looking at the interactions of the pathogens of ESD and the potential probiotics could help elucidate the cause and development of ESD.^

Subject Area


Recommended Citation

Grace Underwood, "Isolation and Identification of Probiotic Bacteria for the Management of Epizootic Shell Disease" (2018). Dissertations and Master's Theses (Campus Access). Paper AAI10751689.