Antimicrobial resistance of the coral pathogen Vibrio coralliilyticus and Caribbean sister phylotypes isolated from a diseased octocoral.

Vibrio coralliilyticus is a global marine pathogen that has been found to cause disease in several marine organisms, including corals. This study is the first report of the isolation of V. coralliilyticus from a diseased Caribbean octocoral, Pseudopterogorgia americana. Five sister phylotypes were positively identified using 16S rRNA gene sequencing, recA probes specific for V. coralliilyticus, and rep-PCR fingerprinting. The antimicrobial resistance was compared between pathogenic strains of V. coralliilyticus and the Caribbean strains. First, the antimicrobial resistance of V. coralliilyticus-type strain ATCC BAA-450 was determined using an agar-overlay antimicrobial bioassay at 24 degrees C and 27 degrees C, temperatures which are relevant to its known temperature-dependent virulence. From 108 distinct bacteria isolated from P. americana, 12 inhibited the V. coralliilyticus-type strain at 24 degrees C and five at 27 degrees C. Next, the phenotypic comparison of two Caribbean phylotypes and three V. coralliilyticus reference strains against a subset of 30 bacteria demonstrated a similar resistance trend. At both temperatures, the reference strains were inhibited by three bacteria isolates, while the Caribbean strains were inhibited by four to nine bacteria. Additionally, V. coralliilyticus-type strain ATCC BAA-450 and one of the Caribbean strains were inhibited by a higher number of bacteria at 24 degrees C compared with 27 degrees C. Together, these results highlight that V. coralliilyticus strains have antimicrobial resistance to the majority of coral-associated bacteria tested, which may be temperature-dependent in some strains. Furthermore, all V. coralliilyticus strains tested showed multi-drug resistance to a range of 11-16 (out of 26) commercial antibiotics. This study establishes V. coralliilyticus in association with a Caribbean octocoral and demonstrates its resistance to the antimicrobial activity of coral-associated bacteria and to commercial antibiotics.