Bacteriophages against pathogenic vibrios in Delaware Bay oysters (Crassostrea virginica) during a period of high levels of pathogenic vibrio parahaemolyticus

Authors: Richards, Gary; CHINTAPENTA, LATHADIVI - Delaware State University; Watson, Michael; ABBOTT, AMANDA - Delaware State University; OZBAY, GULNIHAL - Delaware State University; Uknalis, Joseph; OYELADE, ABOLADE - New Jersey Department Of Environmental Protection; PARVEEN, SALINA - University Of Maryland Eastern Shore (UMES)

Submitted to: Food and Environmental Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2019
Publication Date: 1/31/2019
Citation: Richards, G.P., Chintapenta, L.K., Watson, M.A., Abbott, A.G., Ozbay, G., Uknalis, J., Oyelade, A., Parveen, S. 2019. Bacteriophages against pathogenic vibrios in Delaware Bay oysters (Crassostrea virginica) during a period of high levels of pathogenic vibrio parahaemolyticus. Food and Environmental Virology. https://doi.org/10.1007/s12560-019-09365-5.
DOI: https://doi.org/10.1007/s12560-019-09365-5

Interpretive Summary: Bacteriophages (phages for short) are bacterial viruses capable of infecting and killing bacteria, including pathogenic vibrios. We conducted a 6-month survey of oysters from three sites in the Delaware Bay for phages against several vibrios, including the human pathogens Vibrio parahaemolyticus and V. vulnificus. These bacteria cause the greatest number of shellfish-borne bacterial illnesses and deaths in the United States. The levels of total and pathogenic V. parahaemolyticus as well as pathogenic strains of V. vulnificus were identified along with the presence of phages against these pathogens. One site contained an extremely high abundance of total and pathogenic V. parahaemolyticus while another site had only low levels. V. vulnificus were also intermittently high at two of the three sites. Phages were detected at all sites against V. parahaemolyticus, but no phages against V. vulnificus were detected during the entire study. Isolated phages generally did not infect other species of Vibrio. Electron microscopy identified the phages to be of at least two distinct types: small spherical phages and phages containing a head and tail structure. It is believed that V. parahaemolyticus phages will reduce the levels of pathogenic V. parahaemolyticus in oysters and their environment. It is not clear why no phages were identified against pathogenic V. vulnificus.

Technical Abstract: Eastern oysters (Crassostrea virginica) from three locations along the Delaware Bay were surveyed monthly from May to October 2017 for levels of total Vibrio parahaemolyticus, pathogenic strains of V. parahaemolyticus and Vibrio vulnificus, and for strain-specific bacteriophages against vibrios (vibriophages). The objectives were to determine a) whether vibriophages against known strains or serotypes of clinical and environmental vibrios were detectable in oysters from the Delaware Bay and b) whether vibriophage presence or absence corresponded with Vibrio abundances in oysters. Host cells for phage assays included pathogenic V. parahaemolyticus serotypes O3:K6, O1:KUT (untypable) and O1:K1, as well as clinical and environmental strains of V. vulnificus. Vibriophages against some, but not all, pathogenic V. parahaemolyticus serotypes were readily detected in Delaware Bay oysters. In July, abundances of total and pathogenic V. parahaemolyticus at one site spiked to levels exceeding regulatory guidelines. Phages against three V. parahaemolyticus host serotypes were detected in these same oysters, but also in oysters with low V. parahaemolyticus levels. Serotype-specific vibriophage presence or absence did not correspond with abundances of total or pathogenic V. parahaemolyticus. Vibriophages were not detected against three V. vulnificus host strains, even though V. vulnificus were readily detectable in oyster tissues. Selected phage isolates against V. parahaemolyticus showed high host specificity. Transmission electron micrographs revealed that most isolates were ~60-nm diameter, non-tailed phages. In conclusion, vibriophages were detected against pandemic V. parahaemolyticus O3:K6 and O1:KUT, suggesting that phage monitoring in specific host cells may be a useful technique to assess public health risks from oyster consumption.