The Study On The Virulence Genes And The Effect Of Environmental Factors On The Expressions Of These Genes In Aeromonas Spp.

This paper consists of two parts: (I) These effects of temperature and pH on the expression of four virulence factors: hemolysin (AHH), aerolysin (AerA), outer membrane proteins (OMP) and adhesion (Aha), from Aeromonas hydrophila and on its pathogenicity were studied. The results showed that the expression of these virulence factors from A.hydrophila was affected by temperature and pH in the media. All four virulence factors were highly expressed in A.hydrophila when grown at 15℃, 25℃ and 37℃ determined by RT-PCR. At 4℃, both AHH and AerA were still expressed, but neither OMP nor Aha was. All four virulence factors tested in the present study were expressed in bacterial cells when grown at pH5.0 and pH7.0. Only AHH expression was detected at pH9.0. These results were supported by the results from the challenge experiments with crucian carp. In addition, the study showed that the pathogenicity of the bacteria was affected by the body temperature of fish. (II) we have studied the distribution of virulence factors in 78 strains of Aeromonas hydrophila and antimicrobial susceptibility testa of the 64 strains. Of the eight virulence factor, AerA have the highest frequence up to 73 %, we can't detect S-Layer protein (SL) and extracellular serine protease (ahpA) in all the 78 strains of Aeromonas hydrophila. In the 64 strains, Aeromonas hydrophila have high level resistant to Bacitracin and Ampicillin, but up to 73 % are sensitive to twelve drugs including Ciprofloxacin.