Abstract
In this study, the protective efficacy of an E. coli live attenuated vaccine was compared to the preventive administration of lectin preparation before the challenge. Two hundred broiler chicks were divided into eight equal groups. The first group was used as a negative control group. Three groups were vaccinated at day 1 with the avian colibacillosis live vaccine of which one group served as a vaccinated nonchallenged group. Another two groups were treated with lectin product (0.5 mL/L drinking water) for three days before the challenge. The last two groups served as challenge control for either E. coli O78 or O125 strains. The challenge was conducted at three weeks of age with either homologous O78 or heterologous O125 E. coli strains, using 0.5 mL/bird of each avian pathogenic E. coli (APEC) strain (~108 colony forming units “CFU”/mL)/subcutaneously. The bodyweight and feed conversion ratios (FCR) were calculated for four weeks. Clinical signs and gross and histopathological lesions were scored at two and seven days post inoculation (dpi). The heart and liver of euthanized chickens at 2 dpi were removed aseptically and homogenized to evaluate pathogenic E. coli colonization. Results showed that live avian colibacillosis vaccine reduced mortalities and APEC colonization in the homologous challenge group but not in the heterologous challenge group. Lectin-treated groups showed 20% and 16% mortality after challenge with E. coli O78 and O125, respectively, and both groups showed performance parameters, clinical signs, and histopathological lesion scores comparable to the negative control group, with variable E. coli colonization of heart and liver. The study demonstrated the efficacy of live attenuated avian colibacillosis vaccine against homologous but not heterologous APEC challenge in broiler chickens. The lectin-containing products can be used as a preventive medication to reduce the clinical impacts of colibacillosis regardless of the challenge strain. Standardization of the evaluation parameters for APEC vaccines is recommended.
Highlights
Escherichia coli (E. coli) is a Gram-negative, rod-shaped, facultative anaerobic bacterium of the Enterobacteriaceae family [1]
Avian pathogenic E. coli (APEC) strains of different serotypes are associated with avian colibacillosis [3]
We explored the protective efficacy of a live attenuated E. coli vaccine against homologous and heterologous APEC challenge with APEC O78 and O125 in comparison to a commercially available lectin preparation administered via drinking water before the challenge
Summary
Escherichia coli (E. coli) is a Gram-negative, rod-shaped, facultative anaerobic bacterium of the Enterobacteriaceae family [1]. Avian pathogenic E. coli (APEC) strains of different serotypes are associated with avian colibacillosis [3]. Antigenic diversity among APEC in Egypt differs according to geographic region, and different serotypes, such as O78 , O157 , O125 , O126 , and O132 , are involved [4,5,6]. The virulence of APEC is attributed to the detection of various virulence gene patterns including detection of 8–13 virulence genes in highly pathogenic E. coli isolates or 5–8 virulence genes in intermediate pathogenicity [7]. In Egypt, several virulence genes were studied that differed based on the geographic area. Few in vivo studies found that pathogenic strains consistently harbor the virulence gene pattern of fimH, fimA, papC, iutA, and tsh that was associated with lethality in one-day-old chicks [6]
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