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Cells of the Gram-negative bacteria Campylobacter fetus are covered by monomolecular arrays of surface layer proteins (SLPs) critical for both persistence in their natural hosts and for virulence. For C. fetus cells, expression of SLPs essentially eliminates C3b binding and their antigenic variation thwarts host immunological defences. Each cell possesses multiple partially homologous and highly conserved SLP gene cassettes, tightly clustered in the genome, that encode SLPs of 97-149 kDa. These attach non-covalently via a conserved N-terminus to the cell wall lipopolysaccharide. Recent studies indicate that C. fetus reassorts a single promoter, controlling SLP expression, and one, or more, complete open reading frame strictly by DNA inversion, and that rearrangement is independent of the distance between sites of inversion. In contrast to previously reported programmed DNA inversion systems, inversion in C. fetus is recA-dependent. These rearrangements permit variation in protein expression from the family of SLP genes and suggest an expanding paradigm of programmed DNA rearrangements among microorganisms.

Campylobacter fetus utilizes paracrystalline surface (S-) layer proteins that confer complement resistance and that undergo antigenic variation to facilitate persistent mucosal colonization in ungulates. C. fetus possesses multiple homologues of sapA, each of which encode full-length S-layer proteins. Disruption of sapA by a gene targeting method (insertion of kanamycin (km) resistance) caused the loss of C. fetus cells bearing full-length S-layer proteins and their replacement by cells bearing a 50 kDa truncated protein that was not exported to the cell surface. After incubation of the mutants with serum, the survival rate was approximately 2 x 10(-2). Immunoblots of survivors showed that phenotypic reversion involving high-level production of full-length (98, 127 or 149 kDa) S-layer proteins had occurred. Revertants were serum resistant but caused approximately 10-fold less bacteraemia in orally challenged mice than did the wild-type strain. Southern hybridizations of the revertants showed rearrangement of sapA homologues and retention of the km marker. These results indicate that there exists high-frequency generation of C. fetus sapA antigenic variants, and that intracellular mechanisms acting at the level of DNA reciprocal recombination play key roles in this phenomenon.

On Mueller Hinton (MH) agar, Campylobacter jejuni showed 20.0 and 30.9 mm zones of inhibition surrounding discs impregnated with 2.5 and 20 micrograms CdCl2 respectively. The minimal inhibitory concentration (MIC) ranged from 0.64 to 3.2 micrograms CdCl2/ml of MH agar for four C. jejuni strains. In the presence of 23 micrograms FeSO4/ml of MH the MIC increased to a range of 1.5-5.4 micrograms CdCl2/ml of MH. Moreover, the numbers of colonies present on MH supplemented with FeSO4 were greater than on MH without iron. The growth response of C. jejuni in the presence of 0.025% (w/v) FeSO4 in MH broth was increased about 10,000 fold in three of four strains when compared with the growth in unsupplemented MH broth. Zones of inhibition surrounding 20 micrograms discs of CdCl, were 50.6 and 24.4 mm on MH and Campy-BAP media respectively, with cells grown on MH. These results suggest that the blood-containing medium 'neutralized' the biocidal influence of the CdCl2. In comparison, C. jejuni inoculum from fluid thioglycollate (FT) medium showed smaller zones of inhibition. These decreased from 34.9 mm on MH agar to 19.6 mm on Campy-BAP agar, suggesting that components in the FT growth medium ameliorated the toxic influence of CdCl2. Atomic absorption spectroscopy analysis indicated mean values (mg/100 g dry weight) of selected metals bound by C. jejuni as: Cu, 10.4; Mg, 146; Na, 2385; Fe, 45.1; Zn, 13.0; and K, 172.