C. jejuni has emerged as a common human pathogen, causing mainly gastroenteritis and occasionally systemic infections. This organism is the most common cause of bacterial gastro enteritis in the United States; according to the CDC surveil lance data, an estimated 2 million cases occur in the United States each year.

Morphology and Identification

 A. Typical Organisms

C. jejuni and other campylobacters are curved, comma-, or S-shaped, Gram-negative, non-spore-forming rods; they have also been described as having “sea gull wing” shapes (Figure 1). Campylobacters are motile, with a single polar flagellum at one or both ends, but some organisms may lack flagella all together.

Fig1. Gram-stain of C. jejuni showing “comma”- or “gull wing”-shaped Gram-negative bacilli (arrows). Campylobacters stain faintly and can be difficult to visualize. Original magnification × 1000.

 B. Culture

Campylobacter species, including C. jejuni, multiply at a slower rate when compared to other Gram-negative, enteric bacteria; therefore, selective media, containing various anti biotics (eg, Campy-Blood agar and Skirrow’s media) are needed for isolation of campylobacters from stool specimens. Campylobacter species require a microaerobic atmosphere, containing reduced O2 (5–7%) and increased 10% CO2 for incubation and optimal growth. 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. Furthermore, most campylobacters grow best at 42°C, although growth can be seen on agar media with incubation between 36°C and 42°C. Incubation of primary plates for isolation of C. jejuni should always be at 42°C. Several selective agar media are in widespread use for isolation of campylobacters; 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, as well as cephalosporin antibiotics. These selective media are suitable for isolation of C. jejuni and C. coli at 42°C. However, C. upsaliensis, while growing at 42°C, is not recovered on selective media, and C. fetus shows variable growth at 42°C, and may not be recovered at that temperature. The colonies of Campylobacter species may have different appearances; generally, 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. Hemolysis on blood-containing agar media is not observed.

C. Growth Characteristics

 Because of the selective media and incubation conditions for growth, an abbreviated set of tests is usually all that is necessary for further identification of campylobacters. C. jejuni as well as C. coli 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 hydrolysis tests, and antimicrobial susceptibilities can be used for further identification of species. A positive hippurate hydrolysis test distinguishes C. jejuni from the other Campylobacter 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 10⁴ 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.

 Clinical Findings

 C. jejuni and C. coli most commonly cause gastroenteritis, while C. fetus causes bacteremia and extraintestinal infections in pregnant women and in immunocompromised patients. Less frequently, C. upsaliensis, a thermotolerant Campylobacter species, is isolated in humans as the cause of diarrhea and/or bacteremia; the organism is also associated with canine and feline gastroenteritis. Clinical manifestations of C. jejuni gas troenteritis 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 for longer times. C. jejuni isolates are usually susceptible to macrolides (eg, erythromycin), and therapy shortens the duration of fecal shedding of bacteria. While most cases resolve without antimicrobial therapy, symptoms may recur in about 5–10% of patients, and antimicrobial therapy may be necessary to resolve the infection. Certain serotypes of C. jejuni and C. upsaliensis have been associated with postdiarrheal Guillain-Barré 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 preferred specimen when attempting to isolate campylobacters in patients with gastrointestinal ill ness. Rectal swabs may also be acceptable specimens. C. jejuni and C. fetus may occasionally be recovered from blood cultures usually from immunocompromised or elderly patients.

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 as described earlier is the definitive test to diagnose C. jejuni enteritis. If C. fetus or another species of Campylobacter is suspected, an agar medium without cephalosporins should be used and incubation at 36–37°C is necessary.

Epidemiology and Control

Campylobacter species are the cause of zoonotic infections, worldwide. These organisms are usually commensal bacteria in the gastrointestinal tracts of various wild or domesticated animals: common reservoir hosts for C. jejuni include poultry, cattle, and sheep; C. coli is usually found in pigs, sheep, and birds; C. fetus has been isolated from sheep, cattle, and poultry; and C. upsaliensis is most commonly isolated from domesticated pet dogs. Most human infections result typically from consumption of contaminated food and/or water. Since commercially raised poultry is nearly always colonized with C. jejuni, slaughterhouse procedures are known to amplify contamination of chicken and turkey meats that are commonly sold in stores and supermarkets in the United States and other developed countries. Consumption of under cooked (commercial) poultry meats has a strong association with C. jejuni gastroenteritis. In some cases, consumption of unpasteurized (raw) milk had been identified as the source of the infection. As with other enteric pathogens, fecal-oral person-to-person transmission of C. jejuni has been reported; however, this mode of transmission appears to occur less frequent compared to acquisition of the organism via contaminated food and water. In contrast, C. upsaliensis is most commonly acquired by close contact with domesticated (pet) dogs that are either ill with diarrheal disease or may just shed the organisms intermittently.

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