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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
Microbiology department
Medical bacteriology
Dr. Zainab D. Degaim
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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 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
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.
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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.
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 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.
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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.