Sidika Hackbusch

• Vibrio spp. are ubiquitous bacteria, common to estuaries and coasts. V.parahaemolyticus, V.vulnificus and V.cholerae are the main water-related pathogenic species, able to cause serious gastroenteritis, wound infections or septicaemia. Infection cases have become more frequent in northern temperate waters, attributed to climate change related events. Little is known about pathogenic Vibrio spp. in the German Bight. Occurrence, abundance and pathogenicity of V.parahaemolyticus, V.vulnificus and V.cholerae were investigated in a salinity gradient of the German Bight over 14 months. Seasonal patterns with increased abundances during summer were detected, while extended periods of warm seawater coincided with prolonged Vibrio spp. occurrences in the German Bight. Temperature and nitrite were the significant factors explaining variations in Vibrio spp. abundances. This study revealed that environmental human pathogenic Vibrio spp. comprise multiple virulence-associated genes in the German Bight, especially in estuarine regions. Pathogen growth potentials of clinically relevant V.vulnificus and V.cholerae strains were investigated in the German Bight to determine the extent of in vitro growth in a broad range of physico-chemical conditions of surface waters originating from a salinity gradient. Those strains, despite revealing different growth patterns, are capable of growth in most seawater samples under ambient physicochemical conditions. Growth kinetics showed strong temperature dependency when grown in seawater, while no salinity dependency was detected. Potentially pathogenic V.parahaemolyticus was detected on marine microplastics for the first time, evidencing that microplastics can serve as additional surfaces for attachment and function as vectors for the enrichment and dispersal. Given the future predictions of climate variability, a species-specific monitoring and risk assessment regarding potentially pathogenic Vibrio spp. in the German Bight is crucial.