الفهرس 
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Abstract
This study aimed to isolation of Aeromonas species from tilapia and Mugil fishes with emphasis to
detection of pathogenic strains moreover, developing a live attenuated bacterial vaccine against
pathogenic A. veronii isolated strain, which can be applied safely in aquaculture as a future
preventative method for the disease outbreak. Out of 150 fish samples (70 Oreochromis niloticus
and 80 Mugil sehelii) collected from private farm in Shandora, Suez Governorate 108 isolates
(64.3%) isolates were detected positive by cultural method. The isolates of fish samples were
biochemically identified as A. veronii which was the most dominant species with total prevalence
56.25% followed by A. hydrophila with 44.44%. according to the antibiotic resistance pattern,
48.3% of examined isolates exhibited multi drug resistance (MDR) to five or more antimicrobial
classes and 48.3% of examined isolates exhibited extensive drug resistance (XDR) to eleven or more
antimicrobial classes. PCR assay of 29 representatives, biochemically confirmed Aeromonas spp.
isolates were genetically confirmed belonging to genus Aeromonas based on 16S rRNA gene
sequence. Virulence gene properties showed that of aer A was detected in 51.7% of isolates, hly A
was detected in 6.89%, ser was detected in 31.03%, ahp was detected in 31.03%, alt and act were
detected in 13.8% and 10.34%, nuc was detected in 20.69% and omp II was detected in 11.11%
with a specific band at 431bp, 592 bp, 211 bp, 911 bp, 442bp, 232 bp, 504 bp and 1001 bp
respectively. The result also revealed that Lip, Epr (CAI), GCAT and Laf B couldn’t be detected in
any isolates. While antibiotic resistance genes which encoded as (blaTEM, blaSHV, ampC, sul1, and
aadA1) were detected in 16.50% at 516 bp, 83.33% at 392 bp., 27.78% at 550 bp. 61.11% at 433bp
and 33.33% at 484 bp. The challenge experiment revealed that all isolates caused mortality in Nile
tilapia, range from 73.33% to 100% mortality. Mass vaccination of tilapia by immersion using
MAV1 S+R vaccine has increased the resistance against both A. veronii and A. hydrophila infection
and provided the required protection levels (RPS 100%).