One hundred and Fifty six samples of Nile tilapia (Oreochromis niloticus),
(53 samples from diseased and 103 samples from apparently healthy),
were collected from different farms in different locality in Kafr Elsheikh
Governorate,the samples were analysed for the prevalence of
Aeromonas hydrophila over a period of nine months from first of
December 2007 to end of Agusts 2008. and for their anti-microbial
resistance using the disk diffusion method. Moreover the bacteria were
tested for their pathogen city for fish and hemolytic activity,
The prevalence of Aeromonas hydrophila among Oreochromis niloticus
were 6(35.3%).There was a clear seasonality, as one isolates (1.3%)
were recovered in the winter months while five isolates (6.4%) recovered
in summer.
Despite the high level of homogeneity observed in strains of Aeromonas
hydrophila in biochemical patterns, they displayed different degrees
of virulence for Tilapia fish; were 16.7% strong virulent, 50% virulent
,16.7% weak virulent and 16.7% avirulent by subcutaneous injection
of Aeromonas hydrophila isolates .
All strains of Aeromonas hydrophila showed hemolytic activity on blood
agar except one avirulant strains showing non hemolytic activity. There
is slight correlation was found between hemolytic activity and degree
of virulence of the strains,also the isolates were tested against 13
antimicrobial agents and the result were , all the isolates were found
100% resistant to Penicillin, Streptomycin, Polymyxin B,95% for
Ampicillin and 70% for Ciprofloxacin.All strains 100% sensitive to
Amikacin, Gentamicin, Nalidixic acid, Kanamycin, Neomycin, Tetracycline,
and 90%Chloramphenicol.