Isolation of Vibrio alginolyticus and Vibrio splendidus from Aquacultured Carpet Shell Clam ( Ruditapes decussatus ) Larvae Associated with Mass Mortalities

Abstract

Two episodes of mortality of cultured carpet shell clams (Ruditapes decussatus) associated with bacterial infections were recorded during 2001 and 2002 in a commercial hatchery located in Spain. Vibrio alginolyticus was isolated as the primary organism from moribund clam larvae that were obtained during the two separate events. Vibrio splendidus biovar II, in addition to V. alginolyticus, was isolated as a result of a mixed Vibrio infection from moribund clam larvae obtained from the second mortality event. The larval mortality rates for these events were 62 and 73%, respectively. Mortality was also detected in spat. To our knowledge, this is the fist time that these bacterial species have been associated with larval and juvenile carpet shell clam mortality. The bacterial strains were identified by morphological and biochemical techniques and also by PCR and sequencing of a conserved region of the 16S rRNA gene. In both cases bacteria isolated in pure culture were inoculated into spat of carpet shell clams by intravalvar injection and by immersion. The mortality was attributed to the inoculated strains, since the bacteria were obtained in pure culture from the soft tissues of experimentally infected clams. V. alginolyticus TA15 and V. splendidus biovar II strain TA2 caused similar histological lesions that affected mainly the mantle, the velum, and the connective tissue of infected organisms. The general enzymatic activity of both live cells and extracellular products (ECPs), as evaluated by the API ZYM system, revealed that whole bacterial cells showed greater enzymatic activity than ECPs and that the activity of most enzymes ceased after heat treatment (100°C for 10 min). Both strain TA15 and strain TA2 produced hydroxamate siderophores, although the activity was greater in strain TA15. ECPs from both bacterial species at high concentrations, as well as viable bacteria, caused significant reductions in hemocyte survival after 4 h of incubation, whereas no significant differences in viability were observed during incubation with heat-killed bacteria.Culture of carpet shell clams (Ruditapes decussatus) is a traditional activity that has great economical importance in Spain, particularly in Galicia (northwest region of Spain). Therefore, losses in production of this clam species would seriously affect the economy of this region.Globally, clam production is often affected by vibriosis, which leads to high mortality rates mainly in nursery cultures of juvenile bivalves (20,35). In Spain serious mass mortalities associated with Vibrio tapetis infections have been reported previously (15, 21). V. tapetis causes brown ring disease in Ruditapes species, which is characterized by the appearance of brown conchioline deposits that have variable distributions and variable thicknesses on the inner shell of diseased clams (41, 42).Susceptibility of other cultured bivalve species to infections caused by bacteria belonging to the genus Vibrio has been found in several scallop species, including Aequipecten irradians (52), Euvo...

Role of Alkaline Serine Protease, Asp, in Vibrio alginolyticus Virulence and Regulation of Its Expression by LuxO-LuxR Regulatory System

“…Studies on the pathogenicity of various isolates of V. alginolyticus suggested that some extracellular enzymes with strong proteolytic activities could be important virulent factors [1,2,11], and alkaline serine protease from the extracellular products (ECP) of V. alginolyticus was reported to be lethal to fish but the detailed information about its DNA sequence and protein structure was unknown [14]. By searching the whole genome of V. alginolyticus 12G01, we found that two alkaline serine proteases existed in the genome, and they were totally different from each other (16% identity at the amino acid level).…”

Prevalence of Biofilm Formation and Wide Distribution of Virulence Associated Genes among Vibrio spp. Strains Isolated from the Monastir Lagoon, Tunisia

“…V. alginolyticus is recognized as one of the major causative agent of vibriosis in cultured fish and shellfish in Mediterranean coastal environment (Gomez-Leon et al, 2005;Sonia and Lipton, 2012). Other studies reported that this specie is considered as an important human opportunistic pathogen usually associated with otitis This copy is for personal use only -distribution prohibited.…”

Finding immune gene expression differences induced by marine bacterial pathogens in the Deep-sea hydrothermal vent mussel <i>Bathymodiolus azoricus</i>

“…Although the pathologies caused by Vibrio in bivalves have been described since the 1960s (Paillard et al, 2004) to this day, some of these species, such as V. alginolyticus, V. splendidus, V. anguillarum, are still being reported in case studies. V. alginolyticus and V. splendidus cause histological lesions that affect mainly the mantle, the velum, and the connective tissue of infected organisms (Gómez-León et al, 2005). Even though Vibrio anguillarum is the most studied aetiological agent of vibriosis, other members of the genus Vibrio have been implicated in epizootics of cultured and wild marine fish and shellfish (Toranzo and Barja, 1990).…”