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Campylobacter
Campylobacters cause both diarrheal and systemic diseases, and are among the
most widespread causes of infection in the world. Campylobacter infection of
domesticated animals also is widespread. C jejuni is the prototype organism in the
group and is a very common cause of diarrhea in humans.
Campylobacter jejuni
C jejuni has emerged as common human pathogen, causing mainly enteritis and
occasionally systemic infection. These bacteria are at least as common as
salmonellae and shigellae as a cause of diarrhea; an estimated 2 million cases
occur in the United States each year.
Morphology and Identification
Typical Organisms
C jejuni are Gram-negative rods with comma, S, or “gull wing” shapes. They
are motile, with a single polar flagellum, and do not form spores.
Culture
The culture characteristics are most important in the isolation and identification
of C jejuni. Selective media are needed, and incubation must be in an atmosphere
with reduced O
2
(5% O
2
) with added CO
2
(10% CO
2
). A relatively simple way to
produce the incubation atmosphere is to place the plates in an anaerobe incubation
jar without the catalyst and to produce the gas with a commercially available gas-
generating pack or by gas exchange. Incubation of primary plates for isolation of
C jejuni should be at 42°C. Although C jejuni grows well at 36–37°C, incubation
at 42°C prevents growth of most of the other bacteria present in feces, thus
simplifying the identification of C jejuni. Several selective media are in
widespread use. Skirrow’s medium contains vancomycin, polymyxin B, and
trimethoprim to inhibit growth of other bacteria, but this medium may be less
Microbiology
Medical bacteriology
Dr. Zainab D. Degaim
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sensitive than other commercial products that contain charcoal, other inhibitory
compounds, and cephalosporin antibiotics. The selective media are suitable
for isolation of C jejuni at 42°C. The colonies tend to be colorless or gray. They
may be watery and spreading or round and convex, and both colony types may
appear on one agar plate.
Growth Characteristics
Because of the selective media and incubation conditions for growth, an
abbreviated set of tests is usually all that is necessary for identification. C jejuni
are positive for both oxidase and catalase. Campylobacters do not oxidize or
ferment carbohydrates.
Gram-stained smears show typical morphology. Nitrate reduction, hydrogen
sulfide production, hippurate tests, and antimicrobial susceptibilities can be used
for further identification of species.
Antigenic Structure and Toxins
The campylobacters have lipopolysaccharides with endotoxic activity.
Cytopathic extracellular toxins and enterotoxins have been found, but the
significance of the toxins in human disease is not well defined.
Pathogenesis and Pathology
The infection is acquired by the oral route from food, drink, or contact with
infected animals or animal products, especially poultry. C jejuni is susceptible to
gastric acid, and ingestion of about 10
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organisms is usually necessary to produce
infection. This inoculum is similar to that required for Salmonella and Shigella
infection but less than that for Vibrio infection. The organisms multiply in the
small intestine, invade the epithelium, and produce inflammation that results in the
appearance of red and white blood cells in the stools. Occasionally, the
bloodstream is invaded, and a clinical picture of enteric fever develops. Localized
tissue invasion coupled with the toxic activity appears to be responsible for the
enteritis.
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Clinical Findings
Clinical manifestations are acute onset of crampy abdominal pain, profuse
diarrhea that may be grossly bloody, headache, malaise, and fever. Usually the
illness is self-limited to a period of 5–8 days, but occasionally it continues longer.
C jejuni isolates are usually susceptible to erythromycin, and therapy shortens the
duration of fecal shedding of bacteria. Most cases resolve without antimicrobial
therapy; however, in about 5–10% of patients, symptoms may recur. Certain
serotypes of C jejuni have been associated with postdiarrheal Guillain-Barre
syndrome, a form of ascending paralytic disease. Reactive arthritis and Reiter’s
syndrome may also follow acute Campylobacter diarrhea.
Diagnostic Laboratory Tests
A. Specimens
Diarrheal stool is the usual specimen. C jejuni may occasionally be recovered
from blood cultures usually from immunocompromised or elderly patients. Other
extra-intestinal infections are uncommon.
B. Smears
Gram-stained smears of stool may show the typical “gull wing”–shaped rods.
Dark-field or phase contrast microscopy may show the typical darting motility of
the organisms.
C. Culture
Culture on the selective media described earlier is the definitive test to
diagnose C jejuni enteritis. If another species of Campylobacter is suspected,
medium without a cephalosporin should be used and incubated at 36–37°C.
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Gram stain of Campylobacter jejuni showing “comma”- or “gull wing”–shaped gram-
negative bacilli (arrows). Campylobacters stain faintly and can be difficult to visualize.