Occurrence of Vibrio species, beta-lactam resistant Vibrio species, and indicator bacteria in ballast and port waters of a tropical harbor

Highlights: • Microbial characteristics of ballast water were assessed on six ships. • Ballast water did not always meet D2 Ballast Water Management Convention guidelines. • Non-toxigenic V. cholera, V. parahaemolyticus, and V. vulnificus were detected. • Antibiotic resistant Vibrio spp. were detected in ballast water. • Prioritized screening of high-risk vessels should be implemented. Ballast water discharges are potential sources for the spread of invasive and pathogenic aquatic organisms. Ballast waters from six ships docked in the Port of Singapore were tested to determine if indictor organisms fell within proposed standards for ballast water discharge according to regulation D-2 of the Ballast Water Management Convention (BWMC) guidelines. Vibrio species were cultured on media supplemented with beta-lactam antibiotics to determine the presence of antibiotic resistant Vibrio species in the ballast waters of these vessels. Indicator organisms were quantified using culture media Colilert-18 and Enterolert in ballast waters of six ships docked in a tropical harbor, with uptake from different geographical locations. Of the six ships, one had ballast water originating from the Persian Gulf, another from the East China Sea, and four from the South China Sea. Two of the six ships which carried ballast waters from the East China Sea and the South China Sea did not meet the D-2 stipulated requirements of the Ballast Water Management Convention for indicator organisms with Enterococci values more than three times higher than the acceptable limit of < 100 CFU/100 mL. Using the most-probable-number-PCR (MPN-PCR) method for Vibrio species detection, non-toxigenic species of V. cholerae (2 MPN/100 mL), Vibrio vulnificus (> 110 MPN/100 mL), and Vibrio parahaemolyticus (2 to > 110 MPN/100 mL) were detected in at least one of six ballast water samples. Using thiosulfate-citrate-bile salts-sucrose agar (TCBS) supplemented with beta-lactam antibiotics (meropenem, ceftazidime), 11 different Vibrio species, exhibiting resistance to beta-lactam antibiotics were isolated; with Vibrio campbellii (44%) and Vibrio alginolyticus (15%) the most detected antibiotic resistant Vibrio species. A practical approach of prioritized screening of high-risk vessels should be conducted to ensure that the water quality meets D-2 standards prior to discharge.