No abstract

Here construction of an attenuated mutant of an avian pathogenic Escherichia coli serovar O78 using an allelic exchange procedure is described. The mutant AESN1331, which carries a deletion in the crp gene, lost tryptophan deaminase activity and therefore lacked the ability to produce indole. The mutant strain additionally lacked the ability to adsorb Congo red, no longer fermented sugars other than glucose and L‐arabinose, did not harbor four known virulence‐associated genes (iss, tsh, cvaA, papC), and was susceptible to many antimicrobials, with the exception of nalidixic acid. The lethal dose (LD50 value) of the mutant strain on intravenous challenge in chickens was approximately 10‐fold higher than that of the parent strain. Additionally, the mutant strain was rapidly eliminated from chickens, being detected in the respiratory tract only on the first day post‐inoculation by fine spray. Administration of the mutant strain via various routes such as spray and eye drop for chickens, as well as in ovo inoculation for embryonated egg, evoked an effective immune response that protected against a virulent wild‐type E. coli O78 strain. Specifically, after immunization with the mutant strain, chickens challenged intravenously with an E. coli O78 strain exhibited decreases in mortality, clinical scores, organ lesion scores, and recovery of the challenge strain from organs compared to non‐immunized chickens. These findings suggest that AESN1331 is a suitable candidate for a live vaccine strain to protect chickens from colibacillosis caused by avian E. coli O78.

ABSTRACT. The existence of apathogenic strains of Yersinia pseudotuberculosis (Yp) has not so far been reported. Recently, the authors characterized new serogroups and a new subgroup in Yp, that is, O9, O10, O12, O13, O14 and O1c, and the pathogenicity of these new strains was of interest. A total of 137 strains of serogroups O1c, O6, O7, O9, O10, O11, O12, O13 and O14 of Yp were investigated for their pathogenicity in vivo and in vitro. Although catalase activity and the inv gene were detected in all strains except those of groups O13 and O14, only a few strains, from serogroups O6 and O10 caused severe infection in mice. The remaining strains caused no mortality or severe infection even when they grew in limited tissues of infected mice. All the strains of Yp not possessing the virulence plasmid pYV caused no severe infection in mice. It is evident that less pathogenic Yp exists and that not only pathogenic but also less pathogenic Yp organisms exist in the same serogroup. -KEY WORDS: new serogroup, non-pathogenic strain, Yersinia pseudotuberculosis.

Previously, we showed that surface protective antigen (Spa) proteins of Erysipelothrix rhusiopathiae can be classified into three molecular species-SpaA, SpaB, and SpaC-and that SpaC is the most broadly cross-protective antigen among the three Spa proteins. In this study, we examined the ability of the ␣-helical domain, which comprises the N-terminal half of SpaC, to elicit cross-protective immunity in mice and pigs. Mice actively immunized with the full-length protein (rSpaC664) or the ␣-helical domain (rSpaC427), but not the C-terminal domain (rSpaC253), were protected against challenge with E. rhusiopathiae serovars 1a, 2, 6, 19, and 18 expressing heterologous (SpaA or SpaB) and homologous (SpaC) Spas. The ␣-helical domain seemed to provide better protection than rSpaC664, although the differences did not reach statistical significance. Similarly, mice passively immunized with rabbit anti-rSpaC664 or anti-rSpaC427 sera, but not anti-rSpaC253 serum, were protected from challenge with various serovars. Pigs immunized with SpaC427 also developed specific antibodies against Spa proteins and were protected from challenge with the highly virulent heterologous E. rhusiopathiae strain Fujisawa (serovar 1a). Taken together, these results demonstrate for the first time the striking protective efficacy of the ␣-helical domain-mediated immunization in both mice and pigs, thereby highlighting its utility as the most promising candidate for the development of a safe and effective vaccine against erysipelas.

The objectives of this study were to determine the serovar of a collection of Actinobacillus pleuropneumoniae strains within the 3-6-8-15 cross-reacting group and to analyze their phenotypic and genetic properties. Based on the serological tests, forty-seven field strains of Actinobacillus pleuropneumoniae isolated from lungs with pleuropneumonia lesions in Japan and Argentina were found to be serovars belonging to the 3-6-8-15 cross-reacting group. By using a capsule loci-based PCR, twenty-nine (96.7%) and one (3.3%) from Japan were identified as serovars 15 and 8, respectively, whereas seventeen (100%) from Argentina were identified as serovar 8. The findings suggested that serovars 8 and 15 were prevalent within the 3-6-8-15 cross-reacting group, in Argentina and Japan, respectively. Phenotypic analyses revealed that the protein patterns observed on SDS-PAGE and the lipopolysaccharide antigen detected by immunoblotting of the reference and field strains of serovars 8 and 15 were similar to each other. Genetic (16S rDNA, apxIIA, apxIIIA, cps, cpx genes, apx and omlA patterns) analyses revealed that the apxIIA and apxIIIA genes of the field strains of serovars 8 and 15 were similar to those of the reference strains of serovars 3, 4, 6, 8 and 15. The results obtained in the present study may be useful for the development of more effective vaccines against disease caused by A. pleuropneumoniae by including the homologous antigens to the most prevalent serovars in specific geographical areas.