Bacteria associated with early life stages of the great scallop, Pecten maximus: impact on larval survival

Abstract

International audienceA bacteriological study was carried out at a scallop (Pecten maximus) hatchery near Bergen, western Norway following a severe increase in mortality rates during the larval stages of the scallops. No larvae survived to settling, except for those in groups treated prophylactically with chloramphenicol. In order to identify pathogenic strains of bacteria, we performed a challenge test on 10- to 16-day-old larvae using isolated bacterial strains from the hatchery. Infection with six of these strains produced mortalities that were not statistically different from that resulting from infection with the known pathogen Vibrio pectenicida. However, about 5% of the strains tested in the challenge experiment produced higher motility rates than found in the unchallenged control group, indicating a possible probiotic effect. On the basis of 16S rDNA analysis on these strains, the phylogenetic tree indicated two groups of apparent pathogens: (1) one strain, LT13, grouped together with Alteromonas/Pseudoalteromonas; (2) a cluster of strains grouped together with Vibrio splendidus (LT06, LT21, LT73, PMV18 and PMV19). Strain LT13 was isolated from cultures of the microalga Chaetoceros calcitrans used for feed, while the other strains were isolated from larval cultures. Transmission electron microscopy showed intracellular bacteria that resembled bacteria in the groups Chlamydiaceae and Rickettsiaceae

Isolation and characterization of a virulent Vibrio sp. bacterium from clams (Meretrix meretrix) with mass mortality

“…Paillard (2004) has pointed out that infection of bivalve may imply colonization, multiplication, invasion or persistence of the bacteria on or within the host. To Pecten maximus, V. pectenicida was identified as being responsible for mortality outbreaks in hatcheries in France and reported to be present in the stomach, velum fold (Lambert et al, 1998) and gut epithelium of the infected individuals (Torkildsen et al, 2005). In this study, more MM5 were observed in hepatopancreas, which is consistent with the result of TEM, suggesting that hepatopancreas was the susceptible tissue comparing to other tissues.…”

Identification and characterization of the pathogenic effect of a Vibrio parahaemolyticus-related bacterium isolated from clam Meretrix meretrix with mass mortality

“…In recent years, V. parahaemolyticus has been recognized as a pathogen of scallop P. maximus (Torkildsen et al, 2005), abalone Haliotis diversicolor supertexta (Cai et al, 2006) and shrimp Penaeus monodon Fabricius (Ruangpan and Kitao, 1991). As mentioned above, the sea water temperature at the time when the mortality of clam, M. meretrix happened in Jiangsu Province of China was suitable for the growth and proliferation of V. parahaemolyticus (Kaneko and Colwell, 1973).…”

Physiological and biochemical changes associated with massive mortality events occurring in larvae of American oyster (Crassostrea virginica)

“…These results illustrated the progressive action of the antibiotic on the bacterial community. The improvement of larval survival following chloramphenicol treatment has been previously measured in bivalve hatcheries (Nicolas et al 1996;Gomez-Leon et al 2005;Torkildsen et al 2005). It was suggested in these previous researches that protective effect was probably due to capacity of chloramphenicol to decrease the bacterial load in larval tanks, limiting the proliferation of opportunistic pathogens and thus avoiding the occurrence of massive mortality; However, the use of antibiotic favour the selection of resistant bacteria which represent some risks for health and environment.…”