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Differentiation between vaccinal and field strains of E. coli using phenotype and genotype characterization

Fatma El-Zahraa Gamal; Fatma Gadallah; Moustafa Zaghloul; Ekram Salama; Selim Salama; Afaf Khedr.

Abstract
Background: E. coli infection is considered as an important bacterial problem associated with significant economic losses and usually associated with a variety of disease conditions, including acute septicaemia, haemorrhagic enteritis, pericariditis, salpingitis and complicated air saculitis. These considerations suggest that control of E. coli by vaccination could be of great value especially live vaccine that based on defined mutations that impair and non-revering virulence.
Material and Methods: Wild type O78 strain, Live O78 aroA gene deleted vaccine and Live O78 crp gene deleted vaccine were used to accomplish this study. Phenotypic characterization was adopted by studying the cultural, biochemical and serological properties. Also genotypic characterization was studied for 16S rRNA, aroA and crp genes.
Results: Growth pattern on different media differed among the used strains as the wild type and Δ aroA mutant were nearly similar while the Δ crp mutant strain was greatly differed. Biochemically the difference between the wild-type and Δ aroA mutant was inability of mutant strain to produce argenine dihydrase (ADH) and fermentation of saccharose. On the other hand the Δ crp mutant failed to produce ADH and to ferment any of the carbohydrates except glucose. A successful amplification of the 16S rRNA gene at 585 bp was detected with the all tested strains while was 1206 bp with only wild type and Δ crp mutant strain when aroA gene primers were used. Regarding crp genes, the amplified products was at 1029 bp with the wild and Δ aroA mutant but not with Δ crp mutant strains.
Conclusion: Findings of this study prove the use of methods based on molecular techniques like PCR to differentiate between different types of E. coli either wild or vaccinal mutant type strains. Also it may help in exclusion or proving the return back to virulence of the mutant vaccinal strains.

Key words: E. coli O78;chickens;phenotypic characterization;genotypic characterization;wild and vaccinal mutant strains


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