Background and Aim: Avian colibacillosis, which is caused by avian pathogenic Escherichia coli (APEC), is a major bacterial disease that affects birds of all ages worldwide, causing significant economic losses. APEC manifests in several clinical forms, including cellulitis, and its high pathogenicity is attributed to harboring numerous virulence-associated genes (VGs). This study evaluated the pathogenicity of the cellulitis-derived E. coli (O78) strain through molecular identification of genes coding for seven virulence factors and by conducting an in vivo assessment of capability for cellulitis induction in broiler chickens.
Materials and Methods: This study was performed using a previously isolated and identified cellulitis-derived E. coli (O78), which was screened for seven VGs using molecular detection and identification through polymerase chain reaction followed by nucleotide sequencing and phylogenetic analysis. Experimental infection by subcutaneous (SC) inoculation in broilers and its pathogenicity was confirmed in vivo by cellulitis induction. The impact of cellulitis on broiler performance was assessed.
Results: Molecular genotyping proved that the isolate harbored five virulence genes (iroN, iutA, tsh, iss, and papC) and was negative for stx1 and hly genes. The amplified products for iroN, iss, and iutA were subjected to sequencing and phylogenetic analysis, and the results indicate the highest similarity and matching with E. coli submitted to the National Center for Biotechnology Information GenBank. SC inoculation of bacteria in broiler chickens resulted in cellulitis, as indicated by thick red edematous skin with yellowish-white material in the SC tissue at the inoculation site, and the abdominal muscle showed redness and increased vacuolization. Histopathological examination revealed moderate-to-severe caseous inflammatory reaction with a marked accumulation of heterophils and mononuclear cells in the SC fatty tissue. The average feed intake, body weight gain (BWG), and feed conversion ratio (FCR) were lower in infected chickens in comparison with those of the control non-infected chickens.
Conclusion: This study proves that molecular techniques are accurate for pathogenicity determination in virulent bacteria, with the advantages of being rapid, time-saving, and economical. Cellulitis is associated with economic losses that are represented by a lower BWG and FCR.
O NE HUNDRED and sixty, 1-day old broiler chicks were grouped into 4 equal groups, at the 10 th day birds of groups 1-3 were s.c inoculated with 0.5 ml containing y 1.5x 10 8 of S.xylosis, S. sciuri and S.lentus; respectively and group 4 was noninfected control. Clinical signs in infected groups started at 2-3dpi as general signs. Signs disappear in Ciprofloxacillin treated subgroups 24 hr post treatment and lasted to the 7 th day in non treated. Average body weight gain in S.xylosis infected non treated was the highest (813.90 gm), followed by S. scuiri (778.50gm) and 773.75 in S. lentus infected treated. FCR was the highest in control (1.69 treated and 1.74 non treated) followed by S. scuiri infected (1.81 non treated and 1.82 treated) and the lowest 1.94 was in S.lentus infected non treated. S. sciuri was reisolated from intestine and spleen (5 th dpi) and from intestine (7 and 10 dpi). While S.lentuswas reisolated from intestine , liver and spleen (3 rd dpi) ; from intestine and spleen (5 th dpi) and intestine (10 th dpi). Histopathological lesion was recorded in infected group as hemorrhages with sinusoidal dilation, focal areas of vacuolar degeneration , fatty degeneration and shrinkage of hepatocytes in liver, necrotic changes of lymphocytes and vacuolion of corpuscle in spleen. Leucocytic infiltration , degeneration and necrosis of epithelium surface and intraepithelial as well as submucosal leucoytic infiltration were seen in intestine. In conclusion the injected organisms induce mild subclinical disease with recording of histopathological lesions in liver, spleen and intestine. This area needs more investigation to explore pathogenicity of CoNS in chickens.
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