Vaccination against some E. coli Serotypes Isolated from DiseasedBroiler Chickens with Chronic Respiratory Disease (CRD)

Broiler chickens are frequently infected with Escherichia coli (E.coli), which often results in disease and high economic losses. Poultry of all ages are susceptible to infections with E.coli, but the most affected are birds of 4-5 weeks. In our study Serotypes O78 and O187 were chosen as they were the most prevalent isolated serotypes from diseased broiler chicken with respiratory affections specially CRD, one hundred chicks of different ages, sex and breeds (cobb, native, sasso) were used in this study. The samples were collected from privately owned poultry farms at EL Mina, Fayoum, Giza and Beni-Suef governorates, all sampled chicks showed clinical signs characteristic for E. coli affections including respiratory distress with or without diarrhea, Swabs from internal organs of 60 diseased chicks were subjected to bacterial examination. Out of 53 oxidase negative strains, 40 E. coli isolates were recovered, other Enterobacteriaceae including, Proteus vulgaris and Pseudomonas aeruginosa. Out of 40 E.coli isolates, E. coli O78 was the most predominant serotype isolated (23) with an incidence of 57.5 % followed by E. coli O187 (12) isolates with an incidence of 30 % and E. coli O115 (5) isolates at percentage of 12.5%, The pre-prepared vaccine against E.coli serotype O used in this study was designed vaccine as it contains an E. coli strain that has been genetically-modified by the deletion of the aroA gene responsible for the biosynthesis of amino acids in the virulent E. coli parent strain (The GMO is named aroA- PTA-5094). The aroA gene-deleted vaccine can trigger a protective immunity in poultry against infection and disease from wild, virulent E. coli bacteria found in the environment. However, because the aroA gene is deleted, the live vaccine bacterium becomes a-virulent and unable to form a self-sustaining population since the vaccine strain has lost the capability to synthesize the amino acids necessary for its survival. The E. coli vaccine dosages were calculated according to a titer of 5.0x106 cfu per dose, one hundred one day old chicks were divided into 5 groups each one 20chicks,group 1, control negative and groups 4 and 5 control positive for serotype O78 and serotype O178 ,while group 2 vaccinated at one day and challenged with E.coli O78 at age of 25 day old, also group 3 vaccinated at 5 day old and challenged with E.coli O178 at age of 25 day old, Two findings, the average lesion scores of air sacs in the groups 4 and 5,four and 3 birds died in the positive control at two days post challenge with E. coli O78 and O178 respectively. The birds were found to have acute, severe septicemia and E. coli could be isolated from the livers. The mortality and morbidity rates of the birds vaccinated with E. coli aroA-live vaccine was great better significant difference from the positive control group showing no mortalities and low pathological picture. There were significant differences in the FCR among the 3 groups significantly less than those of the positive control groups; the body weight was higher in vaccinated groups. Our conclusion, vaccination improves health and FCR and ABW of broiler chicks