Characterization of extracellular virulence properties and biofilm-formation capacity of Vibrio species recovered from ready-to-eat (RTE) shrimps

In this study, we evaluated the virulence factor production, biofilm-forming ability and cell surface properties of ready-to-eat shrimps associated vibrios strains. A total of 1440 ready-to-eat (RTE) shrimp samples were purchased from open markets in southern Nigeria, from November 2016 to October 2017. Biofilm formation was carried out using the microtitre plate method. Cell-to-cell adhesion of Vibrio species was assessed via surface hydrophobicity using the bacterial adherence to hydrocarbons (BATH) and salting aggregation technique, autoaggregation and coaggregation assay. The virulence potential of the identified 120 Vibrio strains includes haemolysis 107 (89.17%), lipase 106 (88.33%), protease 108 (90%), gelatinase 111 (92.5%), the presence of surface-layer (S-layer) 109 (90.8%) and DNA degrading activity 107 (89.17%). Biofilm formation at 30 °C tryptone soy broth in dynamic conditions revealed total biofilm producers for the Vibrio species as follows: V. parahaemolyticus (95.65%), V. vulnificus (92.86%), V. fluvialis (91.67%), V. alginolyticus (87.5%), V. cholerae (100%), V. mimicus (90%), V. harveyi (66.7%), and other Vibrio spp. (84%). A total of 50 biofilm producing vibrios using BATH technique include 49 (98%) hydrophilic and 1 (2%) moderately hydrophobic. Using the modified salting aggregation technique, 50 (100%) was characterized as hydrophilic. Autoaggregation index for the 12 biofilms producing Vibrio strains ranged from 11.6 to 41.3%, while the autoaggregation index for the 12 test bacteria ranged from 26.2 to 71.3%. Coaggregation between the 12 test bacteria with the 12 Vibrio strains ranged from 9.3 to 78.5%. However most vibrios in this study were hydrophilic, their hydrophilic potential is important for their capability to autoaggregate and coaggregate. Findings on the specific process by which virulent Vibrio spp. form biofilm and adhere to shrimp surface as attached plankton may assist in monitoring epidemics of the pathogen.