Luminescent vibrios are amongst the most important pathogens in aquaculture, affecting almost all types of cultured organisms. Vibrio campbellii is one of these most important pathogens. In this study, the effects of feeding mnn9 yeast cell wall mutant and wild type yeast strain were investigated in the digestive tract of brine shrimp nauplii, Artemia franciscana, after experimental infection with V. campbellii (LMG 21363). Gnotobiotic A. franciscana nauplii were fed daily with dead Aeromonas hydrophila LVS3, and with either wild type strain of baker's yeast, Saccharomyces cerevisiae, or mutant strain mnn9, of which the cell wall contains elevated chitin and glucan and lower mannose levels. After three days of feeding, some nauplii were challenged with V. campbellii. Mean survival (%), individual length (mm) and total length (mm) at one day and two days after challenge were significantly higher in the group fed mnn9 than in the group fed wild type yeast (81 ± 1.50 and 63 ± 0.49, 1.56 ± 0.07 and 1.13 ± 0.02, 38.21 ± 3.11 and 21.26 ± 0.81 respectively for one day and 50 ± 2.37 and 20 ± 1.41, 2.33 ± 0.01 and 1.24 ± 0.04, 34.97 ± 5.56 and 7.45 ± 1.63 for two days after challenge). Histological examination revealed that the luminal diameter and enterocyte height of both mid- and hindgut were larger in the mnn9-fed group. Colonization of the gut lumen by V. campbellii could be observed by transmission electron microscopy for the group of nauplii fed with wild type yeast. Furthermore, it was observed that V. campbellii caused damage to the gut epithelium including shortening and disappearance of the microvilli, destruction of the apical cell membrane and cell lysis in the nauplii fed wild type yeast. The gut epithelium remained intact in challenged nauplii fed mnn9 yeast. The morphological findings of the present study further substantiate previous studies reporting a protective effect of this yeast cell wall mutant. |
