Adhesion of Streptococcus agalactiae to the Mucus of Tilapia（Oreochromis niloticus）

Key words: 
• Streptococcus agalactiae /
• tilapia /
• pathogen /
• adhesion

Abstract: Bacterial adhesion is the first step of pathogenic infection. In order to explore the adhesion of pathogen Streptococcus agalactiae to the mucus of tilapia（ Oreochromis niloticus）,the effects of the mucus sources（ from skin,gill or intestines）,incubation time,incubation temperature,p H,and salinity on the bacterial adhesion were investigated using the indirect ELISA method. The results show that the adhesion of S. agalactiae to the mucus of tilapia was sensitive to incubation time,incubation temperature and p H,but not to salinity. When the incubation time was upto 120 min and the incubation temperature was 35 ℃,S. agalactiae produced maximum adhesion in the intestinal tract mucus( 4. 052 × 10⁷ cfu ·m L^-1),then in the skin mucus( 6. 480 ×10⁶ cfu ·m L^-1) and the least in the gill mucus( 2. 825 ×10⁶ cfu·m L^-1). When the incubation time was less than 180 min,the adhesion was positively correlated with the incubation time. When the incubation time was 180 min or longer,the adhesion reached saturation at 5 × 10⁸ cfu·m L^-1. S. agalactiae had a maximum adhesion to the mucus of the skin,gill and intestinal tract at p H 5. 0,7. 0 and 8. 0,respectively. These results will help us further understand the infection mechanism of pathogenic S. agalactiae in tilapia.