Several strains, one disease: experimental investigation of Vibrio aestuarianus infection parameters in the Pacific oyster, Crassostrea gigas

Abstract

This study investigated oyster infection dynamics by different strains of Vibrio aestuarianus isolated before and after the apparent re-emergence of this pathogen observed in France in 2011. We conducted experiments to compare minimal infective dose, lethal dose 50 and bacterial shedding for six V. aestuarianus strains. Whatever the strain used, mortality was induced in juvenile oysters by intramuscular injection and reached 90–100% of mortality within 5 days. Moreover, bacterial shedding was comparable among strains and reached its maximum after 20 h (≈10 EXP5 bacteria/mL/animal). Similarly, our first estimations of lethal dose 50 were comparable among strains (minimal infective dose around 0.4 × 10EXP5 bacteria/mL and LD50 around 10EXP5 bacteria/mL) by using seawater containing freshly shed bacteria. These results indicate that, at least with these criteria, despite V. aestuarianus strains genetic diversity, the disease process is similar. The strains isolated after the apparent re-emergence of the bacteria in 2011, do not present a more acute virulence phenotype than the reference strains isolated between 2002 and 2007. Finally, our study provides original and noteworthy data indicating that infected oysters shed bacteria at a level above the threshold of LD50 a few days before they die, meaning that infection is expected to spread in a susceptible population.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-017-0438-1) contains supplementary material, which is available to authorized users.

Oyster Farming, Temperature, and Plankton Influence the Dynamics of Pathogenic Vibrios in the Thau Lagoon

“…Over the past two decades, strains of Vibrio aestuarianus and those of the Splendidus clade have been associated with mortality among farmed oysters ( Soletchnik et al, 1999 ; Gay et al, 2004 ; Lemire et al, 2015 ). Whereas V. aestuarianus is known as a major pathogen to adult oysters ( Travers et al, 2017 ), strains of the Splendidus clade ( Vibrio tasmaniensis and Vibrio crassostreae ) are associated with a multifactorial disease affecting spats and juveniles ( Gay et al, 2004 ; Lemire et al, 2015 ; Bruto et al, 2017 ; de Lorgeril et al, 2018 ), which is triggered by herpes virus OsHV-1 μVar ( Segarra et al, 2010 ; Martenot et al, 2011 ). This disease, referred to as Pacific oyster mortality syndrome, occurs seasonally when seawater temperature reaches 16–24°C ( Pernet et al, 2012 , 2014 ).…”

Experimental infection of Mytilus edulis by two Vibrio splendidus‐related strains: Determination of pathogenicity level of strains and influence of the origin and annual cycle of mussels on their sensitivity

“…By achieving the objective of testing bacterial concentrations consistent with those found in sea water or in mussel tissues (~10 4 CFU animal −1 ; Eiler et al, 2007;Garnier et al, 2007;Pfeffer et al, 2003), as well as high concentrations (~10 7 CFU animal −1 ), different results were observed. Most of the experimental infections performed on mussels (Ben Cheikh, Travers, & Foll, 2017;Ben Cheikh et al, 2016;Parisi et al, 2008;Tanguy et al, 2013) or oysters (Garnier et al, 2007;Gay, Berthe, & Roux, 2004;Travers et al, 2017) were made by injections with high bacterial strain concentrations around 10 7 /10 8 CFU animal −1 which is quite far from those found in the field. On this point, Travers et al (2017) mentioned that defining a strain as virulent through high concentration injections was a debatable issue.…”

“…Most of the experimental infections performed on mussels (Ben Cheikh, Travers, & Foll, 2017;Ben Cheikh et al, 2016;Parisi et al, 2008;Tanguy et al, 2013) or oysters (Garnier et al, 2007;Gay, Berthe, & Roux, 2004;Travers et al, 2017) were made by injections with high bacterial strain concentrations around 10 7 /10 8 CFU animal −1 which is quite far from those found in the field. On this point, Travers et al (2017) mentioned that defining a strain as virulent through high concentration injections was a debatable issue. As for Goudenège et al (2015), they determined three categories of strains as part of their high-throughput bacterial infections: virulent (>50% mortalities at 10 2 CFU animal −1 ), non-virulent (<50% mortalities at 10 7 CFU animal −1 ) and intermediate (i.e.…”

Histopathological and Molecular Study of Pacific Oyster Tissues Provides Insights into V. aestuarianus Infection Related to Oyster Mortality

“…Beside OsHV-1, several Vibrio species have been found to coinfect oysters during mortality episodes, although their role in disease is not yet completely understood and appears controversial [ 15 ]. Several Vibrio strains were isolated from healthy and moribund oysters, and numerous reports indicate V. aestuarianus as the main causative agent in adult oysters, sometimes in synergy with V. splendidus [ 16 , 17 , 18 , 19 ]. Nevertheless, data about V. aestuarianus and oyster interaction in the field are poorly reported in the literature, while most data derives from experimental challenges [ 6 ].…”