Notably, all of the control (PBS-inoculated) chickens died within 7 days post-challenge, whereas none of the AESN1331-inoculated chickens died. The clinical and lesion scores (in heart and liver) of the AESN1331 group were significantly lower than those of the control group. The challenge strain was detected in the hearts and this website livers of all of the dead control chickens, but
only in a subset (20%–50%) of AESN1331-inoculated birds. We constructed and characterized an APEC O78 strain carrying a deletion of the crp gene. The mutant bacterium, AESN1331, had the following favorable characteristics: (i) low pathogenicity for chickens and embryonated eggs; (ii) protection against colibacillosis caused by the avian E. coli O78 wild-type strain, and (iii) ease of inoculation by various routes. Thus, AESN1331 is a suitable candidate for a live vaccine against avian colibacillosis. Our previous study also demonstrated that hemolytic APEC strains produce β-hemolysin, which is encoded
by a gene whose expression is dependent on crp gene function (36). In the present study, we showed that the LD50 value was higher for AESN1331 than for the parent strain and that the in vivo survival time of AESN1331 was clearly shortened. The mutant in this study was phenotypically different from the parent in other respects, including loss of some abilities such as hemolytic activity, adsorption of Congo red, tryptophan deaminase activity, indole production, and utilization of multiple sugars. stiripentol As with virulence factor production, these abilities are presumably directly Selleck GSK1120212 or indirectly governed by the crp gene product. Peighambari et al. showed that a ΔcyaΔcrp mutant of an APEC O78 strain was not immunogenic against airsacculitis induced by homologous experimental challenge (23, 24). In contrast, a ΔcyaΔcrp mutant of Salmonella Typhimurium provided laying hens with marked protection against colonization and invasion by S. Typhimurium and S. Enteritidis
(42). Our crp deletion mutant of APEC O78 was an effective live vaccine against septicemia caused by experimental challenge with a APEC O78 strain. There appears to be a fine line between reduced virulence and immunogenicity; the behavior of a mutant presumably varies with the species, serovar, strain, and infection model. We postulate that cya crp double mutants of APEC are too attenuated for growth to serve as live vaccines. It seems that direct testing is the only way to assess the immunization potential of various attenuated mutants. Gene reversions are extremely rare in large fragment (351 bp nucleotide) deletion, though calculation of probability indicates the possibility of reversion of our single mutant is higher than that of double mutant. The survival time of our mutant in the field was too short for acquisition of a functional crp gene from exogenous source to be possible.