Higher normalized concentrations of tetracycline resistance found in ballast and harbor water compared to ocean water

Abstract Although ballast water is a known vector for the global transport of microorganisms, the Ballast Water Management Convention only sets limits for indicator organisms and does not consider antibiotic resistance genes (ARGs). Herein, we examined the concentration of indicator organisms and prevalence of three ARGs (sul1, tet (M), and vanA) in a total of 53 ballast, 21 harbor, and 8 ocean samples collected in Singapore, China, South Africa, and California. E. coli was found in significantly higher concentrations in ballast samples obtained in Singapore and China compared to South Africa (Singapore, p = 0.040) and California (Singapore, p