possibility of infection. Additional methods of identification may be used to diagnosis C. fetus to the subspecies level. Biochemical methods can identify subspecies of C. fetus, though may be considered unreliable. Campylobacter fetus subspecies fetus (Cff) can grow in 1% glycine and produce H2S, while C. fetus subspecies venerealis (Cfv) cannot. Growth of Cff will not occur in 3.5% NaCl. To increase reliability of identification, molecular methods such as polymerase chain reaction or DNA sequencing may be utilized. Other methods of identification include histology, immunohistochemistry, direct immunofluorescence, agglutination and enzyme-linked immunosorbent assay. Virulence factors Campylobacter spp. in general possess membrane lipopolysaccharide (LPS) with low biological activity compared to other bacteria (i.e. Enterobacteriaceae), subsequently avoiding detection by the host immune system and which may explain why persistent infections can occur. In terms of subspecies, C. fetus subspecies venerealis and C. fetus subspecies fetus have a unique structural component that prevents host-mediated phagocytosis; this "S-layer" is a microcapsule of high molecular weight proteins arranged in a lattice formation. The S-layer prevents complement-mediated bacterial killing by impairing the binding of C3b to the surface of the bacteria. The S-layer is critical in the pathogenicity of C. fetus, as it allows for a significant bacteremic phase for hematogenous dissemination. Additionally, Cfv has long LPS side chains (O-antigens) that may resist complement-mediated bacterial killing. Aside from complement-mediated mechanisms, C. fetus has also evolved variation in its S-layer proteins (SLPs) of the S-layer to subvert the host antibody response. Pathogenesis and disease There are two subspecies of C. fetus that cause reproductive disease in ruminants; C. fetus subspecies fetus and C. fetus subspecies venerealis. These subspecies are associated with abortion in sheep and cattle and infertility in cattle, respectively. C. fetus subspecies fetus is a zoonotic pathogen that has been reported to cause disease in immunocompromised humans. Similar to C. fetus subspecies jejuni, C. fetus subspecies fetus can be acquired via fecal-oral route and resides mostly in the gastrointestinal tract. Other means of transmission include the ingestion of infected fluid or placentas. Infections with Cff appear to be more detrimental in ewes than in cows, spreading readily through a flock resulting in abortion storms. Bovine Campylobacter fetus subspecies venerealis Bovine infectious infertility is a reproductive disease caused by infection of Cfv that leads to early embryonic mortality in cattle. Other names for this disease in cattle include campylobacteriosis, bovine venereal campylobacteriosis (BVC), bovine genital campylobacteriosis. The