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

MM5 was a bacterial strain isolated from moribund clam (Meretrix meretrix) collected from a farm with mass mortality outbreak. Primary genotypic and phenotypic identification including 16S rDNA sequence analysis, multilocus sequence analysis (MLSA) of four housekeeping genes (gapA, ftsZ, mreB and topA) and biochemical tests suggested that strain MM5 was a Vibrio species closest to but different from Vibrio furnissii. Our previous study indicated that MM5 could induce a high mortality of M. meretrix ( Yue et al., 2010). Quantitative challenge test was performed in this study to further evaluate the pathogenic potential of MM5, which showed that at 84 h post-inoculation, the cumulative mortalities of the MM5-injected group were significantly higher than those of control groups (P < 0.05). Cytopathological and histopathological features of the clam infected by MM5 were carried out by transmission electron microscopy (TEM) and Hematoxylin and Eosin (H&E) staining, respectively. Cytopathologically, foci of MM5 were found in hepatocytes of the clam infected by MM5. In addition, cytopathological lesion was detected in foot of infected clam. Histopathologically, MM5 was detected in different tissues of infected clam, including hepatopancreas, mantle and gill. Challenge test combined with pathological features indicated that MM5 was virulent to M. meretrix.

Phylogenetic analysis by MLSA of four housekeeping genes (gapA, ftsZ, mreB and topA) indicated that MM5 has the closest relationship with Vibrio furnissii and Vibrio fluvialis in the Cholerae clade. By means of TEM, foci of MM5 were found in hepatocytes of challenged clam.Figure optionsDownload as PowerPoint slideResearch highlights
► A Vibrio species MM5 was isolated and identified from clam Meretrix meretrix with mass mortality.
► MM5 is able to induce significantly increase in mortality of clams.
► MM5 was detected in different tissues of MM5-infected M. meretrix by TEM and H&E staining.
► MM5 is a potential pathogen to M. meretrix.