Abstract
Problem statement: Omphalitis is one of the most common causes of mortality in chicks during the first week after hatching. Escherichia coli strains are the most common isolated bacteria from omphalitis cases of chickens. Bacterial colonization in the host cells surfaces is a critical first step in the pathogenesis of avian pathogenic Escherichia coli isolates. Thus the current study was undertaken to determine the presence and prevalence of several adhesin-encoding genes in E. coli isolates from omphalitis of chicks. Approach: One hundred four E. coli isolates were recovered from omphalitis cases and were identified by standard biochemical tests. The omphalitis-derived isolates were examined for the presence of fimbrial and non-fimbrial adhesin-encoding genes by PCR technique. Results: Most (93.26%) of the E. coli isolates exhibited at least one of the examined adhesin-encoding genes. None of the isolates contained the afaI B-C, afa E-VIII and f17A genes. The two most prevalent genes were crl (87.50%) and fimH (77.88%). P (papC) and S (sfa) fimbriae encoding genes were detected in 8 (7.69%) and 5 (4.80%) isolates respectively. Seven combination patterns of the adhesin-encoding genes were detected. In 83 (79.80%) isolates combinations of 2-4 genes were detected. The gene combinations of crl-fimH and fimH-papC were the two most prevalent patterns respectively. Fourteen (13.46%) isolates showed crl gene alone and 7 (6.73%) isolates were negative for examined genes. Conclusion: The current study showed that some of the adhesin-encoding genes are more prevalent in E. coli isolates from omphalitis of chicks but, E. coli isolates may be expressing still unknown adhesins that could have a role in the pathogenicity of omphalitis-derived isolates.
Highlights
Omphalitis is infectious and non-contagious condition of yolk sac which accompanied by unhealed navels in young fowl
Escherichia coli (E. coli) is the most common contaminant of yolk sacs in chickens and about 70% of chicks with omphalitis had this bacterium in their yolk sacs
McPeake et al (2005) and Delicato et al (2003) reported that 100% of Avian Pathogenic E. coli (APEC) isolates were positive for curli encoding genes whereas Amabile de Campos et al (2005) indicated that 16.7 % of E. coli isolates from colisepticemic cases were positive for crl gene
Summary
Omphalitis is infectious and non-contagious condition of yolk sac which accompanied by unhealed navels in young fowl. Bacterial infection of navel area is one of the most common causes of mortality in chicks during the first week after hatching (Pattison et al, 2008). Several bacteria such as Proteus spp., Enterobacter spp., Pseudomonas spp., Klebsiella spp., Staphylococcus spp., Streptococcus spp., Clostridium spp., Bacillus cereus and Enterococcus have been isolated from yolk sac infection of birds (Cortes et al, 2004). It is common to recover low numbers of E. coli from normal yolk sacs (Saif et al, 2008). E. coli is one of the opportunist pathogen responsible for number of disease conditions such as yolk sac infection, air sac disease, perihepatitis, enteritis, omphalitis, coligranuloma, colibacillosis (Ahmad et al, 2009). The role of virulence factors in pathogenesis of APEC isolates have not been fully elucidated but considerable progress has been made recently to establish the mechanisms of pathogenesis (Stehling et al, 2007)
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