Intranasal immunogenicity of a Delta cya Delta crp-pabA mutant of Salmonella enterica serotype Typhimurium for the horse

Phenotype, Virulence and Immunogenicity of Edwardsiella piscicida Cyclic AMP Receptor Protein (Crp) Mutants in Catfish Host

Edwardsiella piscicida, a facultative aerobic pathogen belonging to the Enterobacteriaceae family, is the etiological agent of edwardsiellosis that causes significant economic loses in the aquaculture industry. cAMP receptor protein (CRP) is one of the most important transcriptional regulators, which can regulate large quantities of operons in different bacteria. Here we characterize the crp gene and report the effect of a crp deletion in E. piscicida. The crp-deficient mutant lost the capacity to utilize maltose, and showed significantly reduced motility due to the lack of flagella synthesis. We further constructed a ΔP_crp mutant to support that the phenotype above was caused by the crp deletion. Evidence obtained in fish serum killing assay and competitive infection assay strongly indicated that the inactivation of crp impaired the ability of E. piscicida to evade host immune clearance. More importantly, the virulence of the crp mutant was attenuated in both zebrafish and channel catfish, with reductions in mortality rates. In the end, we found that crp mutant could confer immune protection against E. piscicida infection to zebrafish and channel catfish, indicating its potential as a live attenuated vaccine.

Phenotype of Aeromonas salmonicida sp. salmonicida cyclic adenosine 3',5'-monophosphate receptor protein (Crp) mutants and its virulence in rainbow trout (Oncorhynchus mykiss)

Precise deletion of genes related to virulence can be used as a strategy to produce attenuated bacterial vaccines. Here, we study the deletion of the cyclic-3',5'-adenosine monophosphate (cAMP) receptor protein (Crp) in Aeromonas salmonicida, the aetiologic agent of furunculosis in marine and freshwater fish. The Crp protein is a conserved global regulator, controlling physiology processes, like sugar utilization. Deletion of the crp gene has been utilized in live attenuated vaccines for mammals, birds and warm water fish. Here, we characterized the crp gene and reported the effect of a crp deletion in A. salmonicida virulent and non-virulent isolates. We found that A. salmonicida Δcrp was not able to utilize maltose and other sugars, and its generation time was similar to the wild type. A. salmonicida ∆crp showed a higher ability of cell invasion compared to the wild type. Fish challenges showed that A. salmonicida ∆crp is ~6 times attenuated in Oncorhynchus mykiss and conferred protective immunity against the intraperitoneal challenge with A. salmonicida wild type. We concluded that deletion of A. salmonicida crp influences sugar utilization, cell invasion and virulence. Deletion of crp in A. salmonicida could be considered as part of an effective strategy to develop immersion live attenuated vaccines against furunculosis.

Identification of the crp gene in avian Pasteurella multocida and evaluation of the effects of crp deletion on its phenotype, virulence and immunogenicity

Background

Pasteurella multocida (P. multocida) is an important veterinary pathogen that can cause severe diseases in a wide range of mammals and birds. The global regulator crp gene has been found to regulate the virulence of some bacteria, and crp mutants have been demonstrated to be effective attenuated vaccines against Salmonella enterica and Yersinia enterocolitica. Here, we first characterized the crp gene in P. multocida, and we report the effects of a crp deletion.

Results

The P. multocida crp mutant exhibited a similar lipopolysaccharide and outer membrane protein profile but displayed defective growth and serum complement resistance in vitro compared with the parent strain. Furthermore, crp deletion decreased virulence but did not result in full attenuation. The 50 % lethal dose (LD₅₀) of the Δcrp mutant was 85-fold higher than that of the parent strain for intranasal infection. Transcriptome sequencing analysis showed that 92 genes were up-regulated and 94 genes were down-regulated in the absence of the crp gene. Finally, we found that intranasal immunization with the Δcrp mutant triggered both systematic and mucosal antibody responses and conferred 60 % protection against virulent P. multocida challenge in ducks.

Conclusion

The deletion of the crp gene has an inhibitory effect on bacterial growth and bacterial resistance to serum complement in vitro. The P. multocida crp mutant was attenuated and conferred moderate protection in ducks. This work affords a platform for analyzing the function of crp and aiding the formulation of a novel vaccine against P. multocida.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0739-y) contains supplementary material, which is available to authorized users.

Phenotype, virulence and immunogenicity of Edwardsiella ictaluri cyclic adenosine 3',5'-monophosphate receptor protein (Crp) mutants in catfish host

Edwardsiella ictaluri is an Enterobacteriaceae that causes lethal enteric septicemia in catfish. Being a mucosal facultative intracellular pathogen, this bacterium is an excellent candidate to develop immersion-oral live attenuated vaccines for the catfish aquaculture industry. Deletion of the cyclic 3',5'-adenosine monophosphate (cAMP) receptor protein (crp) gene in several Enterobacteriaceae has been utilized in live attenuated vaccines for mammals and birds. Here we characterize the crp gene and report the effect of a crp deletion in E. ictaluri. The E. ictaluri crp gene and encoded protein are similar to other Enterobacteriaceae family members, complementing Salmonella enterica Δcrp mutants in a cAMP-dependent fashion. The E. ictaluri Δcrp-10 in-frame deletion mutant demonstrated growth defects, loss of maltose utilization, and lack of flagella synthesis. We found that the E. ictaluri Δcrp-10 mutant was attenuated, colonized lymphoid tissues, and conferred immune protection against E. ictaluri infection to zebrafish (Danio rerio) and catfish (Ictalurus punctatus). Evaluation of the IgM titers indicated that bath immunization with the E. ictaluri Δcrp-10 mutant triggered systemic and skin immune responses in catfish. We propose that deletion of the crp gene in E. ictaluri is an effective strategy to develop immersion live attenuated antibiotic-sensitive vaccines for the catfish aquaculture industry.

IgA in the horse: cloning of equine polymeric Ig receptor and J chain and characterization of recombinant forms of equine IgA

As in other mammals, immunoglobulin A (IgA) in the horse has a key role in immune defense. To better dissect equine IgA function, we isolated complementary DNA (cDNA) clones for equine J chain and polymeric Ig receptor (pIgR). When coexpressed with equine IgA, equine J chain promoted efficient IgA polymerization. A truncated version of equine pIgR, equivalent to secretory component, bound with nanomolar affinity to recombinant equine and human dimeric IgA but not with monomeric IgA from either species. Searches of the equine genome localized equine J chain and pIgR to chromosomes 3 and 5, respectively, with J chain and pIgR coding sequence distributed across 4 and 11 exons, respectively. Comparisons of transcriptional regulatory sequences suggest that horse and human pIgR expression is controlled through common regulatory mechanisms that are less conserved in rodents. These studies pave the way for full dissection of equine IgA function and open up possibilities for immune-based treatment of equine diseases.

Mutations in the Salmonella enterica serovar Choleraesuis cAMP-receptor protein gene lead to functional defects in the SPI-1 Type III secretion system

Salmonella enterica serovar Choleraesuis (Salmonella Choleraesuis) causes a lethal systemic infection (salmonellosis) in swine. Live attenuated Salmonella Choleraesuis vaccines are effective in preventing the disease, and isolates of Salmonella Choleraesuis with mutations in the cAMP-receptor protein (CRP) gene (Salmonella Choleraesuis ∆crp) are the most widely used, although the basis of the attenuation remains unclear. The objective of this study was to determine if the attenuated phenotype of Salmonella Choleraesuis ∆crp was due to alterations in susceptibility to gastrointestinal factors such as pH and bile salts, ability to colonize or invade the intestine, or cytotoxicity for macrophages. Compared with the parental strain, the survival rate of Salmonella Choleraesuis ∆crp at low pH or in the presence of bile salts was higher, while the ability of the mutant to invade intestinal epithelia was significantly decreased. In examining the role of CRP on the secretory function of the Salmonella pathogenicity island 1 (SPI-1) encoded type III secretion system (T3SS), it was shown that Salmonella Choleraesuis ∆crp was unable to secrete the SPI-1 T3SS effector proteins, SopB and SipB, which play a role in Salmonella intestinal invasiveness and macrophage cytotoxicity, respectively. In addition, caspase-1 dependent cytotoxicity for macrophages was significantly reduced in Salmonella Choleraesuis ∆crp. Collectively, this study demonstrates that the CRP affects the secretory function of SPI-1 T3SS and the resulting ability to invade the host intestinal epithelium, which is a critical element in the pathogenesis of Salmonella Choleraesuis.

Development of an indirect enzyme-linked immunosorbent assay for detecting equine serum antibodies to the lipopolysaccharide of Salmonella abortusequi

An indirect enzyme-linked immunosorbent assay (IELISA) was developed for the detection of equine serum antibodies to lipopolysaccharide of Salmonella enterica subsp. enterica serovar Abortusequi (LPS), a causative organism of Equine Paratyphoid. The data presented demonstrates that horses immunized with S. abortusequi LPS developed antibodies detectable by the IELISA. By comparison, the tube agglutination test (TAT) did not detect antibody to S. abortusequi LPS as consistently as the IELISA. The data suggests that the IELISA may be a more suitable test for the detection of serum antibodies to S. abortusequi than the TAT.

Cloning and characterization of equine CD89 and identification of the CD89 gene in chimpanzees and rhesus macaques

Immunoglobulin A (IgA) is the major antibody class present in external secretions of mammals. At the vulnerable mucosal surfaces, IgA provides a crucial first-line defence by neutralizing pathogens. Primates also have a substantial level of IgA in serum and although not well understood, the biological role of this IgA depends, at least partly, on its ability to interact with specific receptors (FcalphaRs) on the surface of leucocytes. The human FcalphaR, CD89, was the first IgA Fc receptor to be identified and binding of IgA-coated particles to CD89 triggers numerous cellular effector functions, including phagocytosis, antibody-dependent cellular cytotoxicity, and release of inflammatory mediators, all of which may play an important role in both systemic and mucosal immunity. For many years humans were the only species known to express CD89, however, it has recently been cloned from cows and rats. Here, we describe the identification of the CD89 gene in three additional species: horses, chimpanzees, and Rhesus macaques. Equine CD89 was identified at the cDNA level, whereas the chimpanzee and Rhesus macaque genes were identified from the available draft genomic sequence. Interestingly, when compared with humans and other primates, horses, cows and rats have a relatively low concentration of serum IgA, so the role of CD89 in these species is of particular interest. The identification and characterization of CD89 in different species will contribute to a greater understanding of the biological role of IgA and CD89 in mucosal and systemic immunity throughout evolution.

Advances in equine immunology: Havemeyer workshop reports from Santa Fe, New Mexico, and Hortobagy, Hungary

The horse has been human kind's most important partner throughout history. Similarly, in the field of immunology, many critical scientific advances have depended on the horse. Equine immunology today is an active and important field of study, with a focus on control of many common infectious diseases and immunopathologic conditions of broad comparative interest. In 2001 two major equine immunology workshops were held, in Santa Fe, USA, and in Hortobagy, Hungary, with major sponsorship from the Havemeyer Foundation. This report summarizes the scientific themes and foci of those meetings.