A CARAB MUTANT OF AVIAN PATHOGENIC ESCHERICHIA-COLI SEROGROUP O2 IS ATTENUATED AND EFFECTIVE AS A LIVE ORAL VACCINE AGAINST COLIBACILLOSIS IN TURKEYS

Colibacillosis is a serious and economically important disease of the respiratory tract of chickens and turkeys. The serogroups of Escherich ia coil commonly associated with colibacillosis in poultry are 01, 02, and 078. Although previous attempts to develop a vaccine have not bee n very successful, vaccination is still considered the most effective way of controlling the disease. Therefore, our laboratory has been inv olved in the development of an attenuated live vaccine that will be ef fective in the prevention of colibacillosis. The carAB operon coding f or carbamoyl-phosphate synthetase, an essential enzyme in arginine and pyrimidine metabolism, was selected for study. Generalized transducti on was used to transfer a Tn10-generated mutation from a laboratory st rain to virulent avian field isolates of E. coli. Molecular techniques were used to determine the point of Tn10 insertion within the carAB o peron. The insertion mutants were then cured of the tetracycline resis tance gene of the transposon to select for antibiotic-sensitive and st able carAB mutants. The degree of attenuation obtained by the mutation was determined in day-old chickens. Typically, when 100-fold the 50% lethal dose (for the wild type) was given, no more than 50% mortality in the day-old chickens was observed. The deletion mutant of serotype 02 was also found to be avirulent in turkeys rendered susceptible to i nfection with hemorrhagic enteritis virus A. Turkey poults vaccinated orally at 4 weeks old with either the wild-type E. coli EC317 strain o r its carAB mutant EC751 were completely protected from infection foll owing challenge with the homologous wild-type strain. Our data indicat e that carAB mutants of virulent avian strains of E. coil will be effe ctive and safe as live oral vaccines for prevention of colibacillosis in poultry.