The diagnosis of Campylobacter infection is confirmed by dem-onstrating the bacteria by direct examination of feces or isola-tion of the bacteria by culture.
Diarrheic fresh stool is the specimen of choice for enteric infec-tions. Rectal swab may also be used. Other specimens include blood, body fluids, and tissues for diagnosis of extraintestinal infections. In case of delay, feces or rectal swab are transported in Cary–Blair transport medium. Campylobacter spp. survive for 1–2 weeks at 4°C in this medium.
Presumptive diagnosis is made by examination of wet mount of stool by dark-field microscopy or phase contrast microscopy. The bacteria are identified by their characteristic darting motil-ity. Gram staining of the stool shows typical Gram-negative, curved rods with a sensitivity of 50–75%. Fecal leukocytes and erythrocytes can also be detected in Gram-stained smear of the stool in approximately 75% patients with Campylobacter enteritis.
Definitive diagnosis of Campylobacter enteric infection is best done on isolation of the organism by stool culture. Culture of C. jejunifrom stool requires special selective media— Butzler medium, Skirrow’s medium, Preston’s Campylobacter selective medium, and Blaser’s medium (Campy-BAP). The selective media contain antibiotics that inhibit growth of the other fecal bacteria. Fresh stool specimens collected within 24 hours are inoculated directly on their media. But old stool specimens are first enriched in an enrichment medium, such as Preston campylobacter enrichment broth for at least 24 hours at 4°C (cold enrichment) before inoculating on the selective media.
Inoculated media are incubated in 5% O2 and 10% CO2 at 42°C for 48 hours. If C. fetus or other unusual Campylobacter species are suspected, stool specimens are inoculated on media with-out antibiotics and are incubated at 37°C. Other extraintesti-nal specimens, such as blood, body fluids, and tissue, can be inoculated on routine media for isolation of Campylobacter species.
Preliminary identification of colonies is made by typical Gram-staining features, darting motility, and oxidase test. Definitive identification is made by biochemical tests.
Examination by sigmoidoscopy shows widening or proctoco-litis in up to 80% of patients with Campylobacter enteritis. The histopathological changes include fecal mucosal edema and hyperemia with crypt abscess formation.
ELISA is available for demonstration of specific antibodies in the serum, and a high titer of antibodies is usually seen after the symptoms are resolved. Serology may not be useful for rou-tine diagnosis, but is useful for epidemiological studies.