Generation of a superoxide dismutase (SOD)-deficient mutant of Campylobacter coli: evidence for the significance of SOD in Campylobacter survival and colonization.

The microaerophilic nature of Campylobacter species implies an inherent sensitivity towards oxygen and its reduction products, particularly the superoxide anion. The deleterious effects of exposure to superoxide radicals are counteracted by the activity of superoxide dismutase (SOD). We have shown previously that Campylobacter coli possesses an iron cofactored SOD. The sodB gene of C. coli UA585 was insertionally inactivated by the site-specific insertion of a tetO cassette. Organisms harboring the inactivated gene failed to produce a biologically functional form of the enzyme. While the ability of this mutant to grow in aerobic conditions was unchanged relative to the parental strain, its survival was severely compromised when nongrowing cells were exposed to air. Accordingly, the SOD-deficient mutant was unable to survive for prolonged periods in model foods. Furthermore, inactivation of the sodB gene decreased the colonization potential in an experimental infection of 1-day-old chicks. In contrast, strain CK100, which is deficient in catalase activity, showed the same survival and colonization characteristics as the parental strain. These results indicate that SOD, but not catalase, is an important determinant in the ability of C. coli to survive aerobically and for optimal colonization within the chicken gut.

Targeted and random mutagenesis of the Campylobacter coli chromosome with integrational plasmid vectors.

A number of integrational vectors were developed for use as genetic tools in the food-borne pathogen Campylobacter coli. Integration of the plasmids occurred following genetic recombination via a Campbell-like mechanism. For an integrative plasmid containing a DNA fragment internal to the C. coli catalase gene, the insertion was mutagenic and led to a catalase-deficient phenotype. A procedure for generating random mutations in the C. coli chromosome, with these suicide-plasmids, was developed. In addition, the construction and utility of an integrable plasmid for generating transcriptional fusions to a cat reporter gene is described.

The direct application of the polymerase chain reaction to DNA extracted from foods.

Two methods for the successful extraction of DNA from foods are described. The rapid lysis method uses a proteinase K buffer system to lyse cells and solubilize food samples. DNA is then precipitated using isopropanol. The second method achieves cell lysis using toluene and mutanolysin, and solubilization using guanidium thiocyanate. Following protein removal with organic solvents DNA is precipitated with isopropanol. Both methods enabled the polymerase chain reaction to be applied directly to DNA extracted from samples of cheese, coleslaw and raw chicken and allowed the direct rapid, sensitive and specific detection of Yersinia enterocolitica, Aerococcus viridans and Listeria monocytogenes in these foods.

Use of the polymerase chain reaction and 16S rRNA sequences for the rapid detection of Brochothrix spp. in foods.

Oligonucleotide primers were designed against rRNA sequences to give a DNA-based PCR assay for the rapid identification/detection of Brochothrix spp. The PCR products could be confirmed by hybridization to an internal oligonucleotide probe. The method successfully and sensitively detected/identified these organisms in pure cultures but was of limited value as a detection method because the detection sensitivity, in relation to conventional plate counts, varied and the assay sensitivity was reduced in the presence of staphylococci. Furthermore, sensitivity was also lost when the assay was applied directly to meat samples. However, a separation step using a lectin (from Agaricus bisporus) immobilized on magnetic beads prior to the PCR assay, allowed the direct detection of low numbers (> 10(2) cfu g-1) of Brochothrix in meat samples within a working day.

Rapid identification of Aerococcus viridans using the polymerase chain reaction and an oligonucleotide probe.

A polymerase chain reaction/oligonucleotide probe method was developed for the specific identification of the Gram-positive bacterium Aerococcus viridans. Primers for the enzymatic amplification reaction were designed from specific sequences within the 16S rRNA. The method was also highly sensitive and 10 cfu of A. viridans could be detected in 5 h although the reliability of detection was poor in mixed cultures with Escherichia coli.

Location of post-translational cleavage events within F and HN glycoproteins of Newcastle disease virus.

The biologically active form of the fusion glycoprotein F from Newcastle disease virus (NDV) comprises two polypeptides, F1 and F2 (derived from a precursor polypeptide F0 by a post translational cleavage event), which are covalently linked together (F1,2) by disulphide bonds. This feature was exploited in a two-dimensional SDS-polyacrylamide gel electrophoretic analysis to orientate the position of the cleavage event within F0. Separation of proteins from NDV-infected CEF in the first dimension in the absence of reducing agent resolved F1,2 protein from all NDV-induced proteins other than F0. Reduction of the first dimension gel with 2-mercaptoethanol, followed by electrophoresis in the second dimension, resolved F1 (55K), F2 (12.5K) and F0 (64K) proteins. The only polypeptides other than F1 and F2 which fell below the diagonal, indicating the positions of the polypeptides from infected cells, were two minor glycoproteins designated HN1 (51.5K) and HN2 (27.5K) which took up positions vertically beneath the major haemagglutinin-neuraminidase glycoprotein HN (75K). Dual isotope labelling experiments with NDV-infected chick embryo fibroblasts, which had previously received a salt shock to effect synchronization of polypeptide initiation upon release of salt shock, revealed the following orientations within the parent molecules: NH2-F2-F1-COOH and NH2-HN1-HN2-COOH. The existence of intermolecular disulphide bonds, orientation and relative lengths of the two NDV HN fragments is analogous to the HA1 and HA2 proteins of influenza virus haemagglutinin.