Adrian L. M. Hodgson

Construction and characterization of a Mycobacterium-Escherichia coli shuttle vector

We have constructed a set of novel Mycobacterium-Escherichia coli shuttle vectors using either a kanamycin- or hygromycin-resistance gene and the replication region from a Corynebacterium plasmid. Important features of these new vectors (pEP2 and pEP3) are that they are small, contain multiple cloning sites, and replicate to high copy number in various Mycobacterium species and E. coli. These vectors are unusual in that plasmid replication in gram-negative and gram-positive bacteria appears to be controlled from a single region. These plasmids will be useful for the genetic analysis of Mycobacterium and gene expression in this genus, particularly Mycobacterium bovis BCG.

Efficacy of an ovine caseous lymphadenitis vaccine formulated using a genetically inactive form of the Corynebacterium pseudotuberculosis phospholipase D

Caseous lymphadenitis (CLA) is an economically significant disease of sheep caused by the gram-positive bacterium Corynebacterium pseudotuberculosis. CLA vaccines are currently formulated using formalin inactivated culture supernatants that are rich in the C. pseudotuberculosis phospholipase D (PLD) exotoxin. One alternative to chemical detoxification is to inactivate the PLD genetically. This procedure not only provides a means to remove an onerous chemical treatment step but also the opportunity to increase gene expression, therefore improve protein yields. Using site-specific mutagenesis the C. pseudotuberculosis PLD was inactivated by substituting a serine residue at histidine 20 within the enzyme active site. CLA vaccine formulated using genetically inactivated PLD protected 44% of sheep against C. pseudotuberculosis challenge compared with 95% protection offered by the formalin inactivated preparation. Since there was no apparent difference in immune response mounted by vaccinated sheep the reason for this variation in vaccine efficacy remains unclear. Although genetic inactivation can be a convenient means to produce toxoid vaccines its use to develop a new CLA vaccine provided no net benefit over the conventional formulation.

Caseous lymphadenitis vaccine development: site-specific inactivation of the Corynebacterium pseudotuberculosis phospholipase D gene

Vaccines for ovine caseous lymphadenitis (CLA) are currently formulated using partially purified, formalin inactivated phospholipase D (PLD) derived from Corynebacterium pseudotuberculosis culture supernatants. Chemical treatment has been a common and effective way of inactivating bacterial toxins for use in toxoid vaccines. Genetic inactivation of toxin genes using site-specific mutagenesis has the potential to improve this process by providing a safer and more cost-effective product. In the present study amino acid substitutions at the putative catalytic site and metal binding domain of the PLD protein had a profound affect upon PLD activity and secretion from C. pseudotuberculosis. Two mutated PLD analogues that were secreted to a level of 40% compared to the wild-type and retained minimal activity showed promise for development as recombinant CLA vaccines. Further work will be required to establish their suitability for commercialization.

Phylogenetic relationship of Fusobacterium necrophorum A, AB, and B biotypes based upon 16S rRNA gene sequence analysis

The 16S rRNA genes from virulent (AB) and benign (B) biotype strains of Fusobacterium necrophorum, the causative agent of ovine foot abscess, were cloned and sequenced. Notwithstanding the distinct phenotypic differences between the AB and B biotypes, a phylogenetic analysis in which the 16S rRNA gene sequences were used revealed the close relationship of these taxa. Comparison of the virulent and benign biotypes of F. necrophorum may therefore be a legitimate way to identify key virulence factors useful in vaccine development.

Putative functional domain within ORF2 on the Mycobacterium insertion sequences IS900 and IS902.

Repeated DNA sequences have been identified in a range of mycobacterial species and have been implicated in the increased virulence of some of these species, namely, Mycobacierium paratuberculosis and M. avium subsp. silvaticum. Here we present a case to suggest that the insertion sequences IS900 and IS902 encode a protein from a putative gene positioned on the complementary strand to their transposase genes. Based on amino acid homology analyses, this open reading frame (ORF2) could encode a transport protein. The ORF2 protein thus IS900 and IS902, may have a role in the increased pathogenicity of M. paratuberculosis and M. avium subsp. silvaticum from an M. avium background.

Foreign gene expression in Corynebacterium pseudotuberculosis : development of a live vaccine vector

A defined phospholipase D mutant of Corynebacterium pseudotuberculosis, designated Toxminus, was used as a live vector to express and deliver a range of candidate vaccine antigens to sheep. Expression levels of the foreign genes in Toxminus were evaluated when directed from a number of different promoters, both constitutively expressed and inducible, as fusions with expressed genes including a signal sequence, and from chromosomal and episomal loci. In general expression levels were low and it appeared that some of the recombinant proteins were tolerated by C. pseudotuberculosis Toxminus better than others. Gene expression was however sufficiently high for three of the genes to elicit antibody responses specific to the recombinant protein following a single dose of the live Toxminus vector vaccine. This work suggests that C. pseudotuberculosis Toxminus has potential for development as a live veterinary vaccine vector.

Cloning and manipulation of the Corynebacterium pseudotuberculosis recA gene for live vaccine vector development

Corynebacterium pseudotuberculosis is an intracellular bacterial pathogen causing a chronic abscessing disease in sheep and goats called caseous lymphadenitis. We are developing this bacterial species as a live vector system to deliver vaccine antigens to the animal immune system. Foreign genes expressed in bacterial hosts can be unstable so we undertook to delete the C. pseudotuberculosis chromosomal recA gene to determine whether a recA- background would reduce the frequency of recombination in cloned DNA. Homologous DNA recombination within an isogenic recA- C. pseudotuberculosis was 10-12-fold lower than that in the recA+ parental strain. Importantly, the recA mutation had no detectable affect upon the virulence of C. pseudotuberculosis in a mouse model. Taken together these results suggest that a recA- background may be useful in the further development of C. pseudotuberculosis as a vaccine vector.

NUCLEOTIDE SEQUENCE OF THE REPLICATION REGION FROM THE MYCOBACTERIUM-ESCHERICHIA COLI SHUTTLE VECTOR PEP2

The replication region derived from the Corynebacterium diphtheriae-Escherichia coli plasmid pNG2 was sequenced. This 1.85-kb segment contains a single origin of DNA replication, one major open reading frame and shares no sequence homology with previously described plasmids.

Conventional and Contemporary Bacterial Veterinary Vaccines

The aim of this chapter is to review some of the conventional and contemporary methods used to vaccinate production animals against bacterial diseases. We confine our discussion to those veterinary diseases where recombinant DNA technology is beginning to play a part in vaccine development. The general objective of vaccinology is to achieve increasingly efficacious vaccines. An emerging trend toward this target is to identify those antigens capable of eliciting protective immunity then to present them to the animal in the optimal fashion. This concept has led first to the purification and presentation of single or mixed antigens, then to the production of recombinant antigens. Here we review the progress in bacterial veterinary vaccine development, from the use of simple bacterin preparations through to live delivery of recombinant antigens.