Research Of Molecular Epidemiology Of Aeromonas Hydrophila Isolated From Crucian Carp In Sheyang Slattern

Recently, with the increment of the rearing densities, the diseases of Crucian carp are more and more serious, especially bacterial septicemia diseases. This epidemic disease infect the biggest fish age range, the most widely endemic areas, the longest epidemic season and resulted in huge economical losses to Crucian carp aquaculture industry. In this research, the investigation on epidemiology of bacterial septicemia diseases of Crucian carp was carried out in Jiangsu Province between 2009 - 2010. The pathogenic bacterial strains were isolated and identified, and were typed by ERIC-PCR technique. The research about the distribution of toxic gene and immunogenicity of the pathogenic bacterial strains were also accomplished. Then the relationship of ERIC-PCR genotype, distribution of toxic gene and immunogenicity of the strains were discussed.1. The investigation of epidemiology of bacterial septicemia diseases of Crucian carp and the Isolation and identification of pathogenic bacterial strains. The investigation on epidemiology of bacterial septicemia diseases of Crucian carp was carried out in sheyang slattern in Jiangsu Province between 2009 - 2010. Bacterial septicemia breaks out from the end of May when water temperature was 20℃, extending to the end of September, the peak period is between July to August. It outbreaks when temperature of water was 29℃-33℃. The infected the Crucian carp which were 0.2-0.4kg. According to different duration, disease can be divided into chronic type and acute type. There were 17 pathogenic bacterial strains were isolated from infected Bacterial septicemia Crucian carp .By means of ATB expression identification and 16SrDNA sequence analysis, 17 strains was identified as Aeromonas hydrophila. The results of drugs showed that strains were highly resistant to Amoxicillin, doxycycline, florfenicol, oxytetracycline, and resistant to Levofloxacin, enrofloxacin, roxithromycin, neomycin, gentamicin, sulfamethoxazole, sulfamethazine, polymyxin in different degree.2. Development and application of ERIC-PCR for epidemiological survey of Aeromonas hydrophila isolates from Crucian carp.With the aim of investigating the epidemiological characteristics of Aeromonas hydrophila from Crucian carp, ERIC-PCR method was chosen to genotype the 24 strains of Aeromonas hydrophila which included 17 strains isolated from sheyang slattern, 6 strains isolated from Zhejiang, Jiangxi, Guangdong, Shanghai, and ATCC7966. The experimental results showed that the tested Aeromonas hydrophila strains exhibited 3 special genotypes, including A, B, C. Among 17 strains isolated from sheyang slattern, genotype B was the main genotype, which consisted of 14 strains, while 3 strains were contained genotype A. Genotypes of the strains which isolated from the same area may be different. In addition, the strains whose genotypes were A or B also distributed in Zhejiang, Jiangxi, Guangdong .3. Detection of virulence genes of Aeromonas hydrophila and the relationship which their ERIC-PCR genetic types The 5 kinds of virulence genes such as aer, hly, ahp, alt, act of the 17 Aeromonas hydrophila strains which isolated from sheyang slattern were detected in the experiments. The positive rate of 5 kinds of virulence genes by Multiplex PCR amplification, act 17/17, hly 16/17, ahp 16/17, aer 16/17, act 13/17. The most distribution contains 5kinds of virulence genes in Aeromonas hydrophila reaching to 70.5%, This show that the majority of Aeromonas hydrophila contained all of these 5 kinds of virulence genes. The pathogenicity of strains carrying 5 virulence genes showed more lethal capacity to the strains carrying virulence gene less. In addition, the genetic type of the strains carrying 5 virulence genes was B type, while the strains whose genetic type were A were carrying virulence gene less.4. Detection of the relationship of the immunogenicity and the ERIC-PCR genetic types of the strains. In this part, the 17 Aeromonas hydrophila strains were inactivated by 0.2%formalin and its whole cell vaccine was made to immune Crucian carp with injection. After immunization 28d, their agglutination titer of serum antibody and cross antibody titer were tested. The experimental results showed that the cross antibody titer the strains which including the same genetic type is significant higher than those including the different genetic type. It indicated that there might be some correlation between the genotype and the immunogenicity of Aeromonas hydrophila strains.