Campylobacter jejuni is a non-sporeforming, Gram-negative rod with a curved- to S- shaped morphology. Many strains display motility, which is associated with the presence of a flagellum at one or both of the polar ends of this bacterium.
Members of the Campylobacter genus are microaerophilic; i.e., they grow at lower-than- atmospheric oxygen concentrations. Most grow optimally at oxygen concentrations from 3% to 5%. Thus, these bacteria generally are fairly fragile in the ambient environment and somewhat difficult to culture in the laboratory. Additional conditions to which C. jejuni are susceptible include drying, heating, freezing, disinfectants, and acidic conditions.
Other Campylobacter species, such as C. coli and C. fetus, also cause foodborne diseases in humans; however, more than 80% of Campylobacter infections are caused by C. jejuni. C. coli and C. jejuni cause similar disease symptoms. C. fetus infections often are associated with animal contact or consumption of contaminated foods and beverages and are especially problematic for fetuses and neonates, in whom the mortality rate may be up to 70%.
Campylobacter genomes are relatively unstable; several mechanisms that may lead to this genetic instability have been proposed, including bacteriophage activity, DNA recombination and transformation. There are several typing methods, such as pulsed-field gel electrophoresis, PCR-based typing, ribotyping and genomotyping, for assessing the genetic diversity of C. jejuni. A list of Campylobacter genomes that have been sequenced is available under the National Center for Biotechnology Information web link.
• Mortality: Approximately 99 deaths in the United States, per year, are estimated to be due to campylobacteriosis.
• Infective dose: In general, the minimum number of ingested Campylobacter cells that can cause infection is thought to be about 10,000. However, in trials, as few as 500 ingested Campylobacter cells led to disease in volunteers. Differences in infectious dose likely can be attributed to several factors, such as the type of contaminated food consumed and the general health of the exposed person.
• Onset: The incubation period, from time of exposure to onset of symptoms, generally is 2 to 5 days.
• Disease / complications: The disease caused by C. jejuni infections is called campylobacteriosis. The most common manifestation of campylobacteriosis is self- limiting gastroenteritis, termed “Campylobacter enteritis,” without need for antimicrobial therapy. When antimicrobial therapy is indicated, erythromycin or ciprofloxacin are most commonly prescribed. A small percentage of patients develop complications that may be severe. These include bacteremia and infection of various organ systems, such as meningitis, hepatitis, cholecystitis, and pancreatitis. An estimated 1.5 cases of bacteremia occur for every 1,000 case of gastroenteritis. Infections also may lead, although rarely, to miscarriage or neonatal sepsis. Autoimmune disorders are another potential long-term complication associated with campylobacteriosis; for example, Guillain-Barré syndrome (GBS). One case of GBS is estimated to develop per 2,000 C. jejuni infections, typically 2 to 3 weeks post infection. Not all cases of GBS appear to be associated with campylobacteriosis, but it is the factor most commonly identified prior to development of GBS. Various studies have shown that up to 40% of GBS patients first had Campylobacter infection. It is believed that antigens present on C. jejuni are similar to those in certain nervous tissues in humans, leading to the autoimmune reaction. Reactive arthritis is another potential long-term autoimmune complication. It can be triggered by various kinds of infections and occurs in about 2% of C. jejuni gastroenteritis cases. Hemolytic uremic syndrome and recurrent colitis following C. jejuni infection also have been documented.
• Symptoms: Fever, diarrhea, abdominal cramps, and vomiting are the major symptoms. The stool may be watery or sticky and may contain blood (sometimes occult – not discernible to the naked eye) and fecal leukocytes (white cells). Other symptoms often present include abdominal pain, nausea, headache, and muscle pain.
• Duration: Most cases of campylobacteriosis are self-limiting. The disease typically lasts from 2 to 10 days.
• Route of entry: Oral.
• Pathway: The mechanisms of pathogenesis by C. jejuni are not well understood and usually vary based on the virulence genes present in a particular strain. In general, C. jejuni cause infections by invading and colonizing the human gastrointestinal tract.
Motility appears to be an important factor in C. jejuni pathogenesis, enabling the bacterium to invade the human intestinal mucosa. The mechanisms by which cellular invasion by C. jejuni cause the observed symptoms remain a mystery. In genome- sequencing studies, researchers were not able to identify the presence of toxin genes that likely contribute to diarrhea and other common symptoms.
Campylobacter species are believed to be the third leading cause of domestically acquired bacterial foodborne illness in the United States, with an estimated 845,024 cases occurring annually, according to the Centers for Disease Control and Prevention (CDC). According to data from FoodNet, the incidence of cases of campylobacteriosis reported to the CDC in 2008 was 12.68 per 100,000 individuals, which is a decrease of 32% over the last decade. For each reported case of campylobacteriosis, it is estimated that 30 cases are unreported.
Major food sources linked to C. jejuni infections include improperly handled or undercooked poultry products, unpasteurized (“raw”) milk and cheeses made from unpasteurized milk, and contaminated water. Campylobacter infection in humans has been linked to handling and eating raw or undercooked meat and poultry, whether fresh or frozen. Avoiding cross contamination of uncooked items from raw meat and poultry products, thorough cooking, pasteurization of milk and dairy products, and water disinfection are effective ways to limit food- and water-borne exposure to Campylobacter. Reduction of risk from contaminated poultry products can be achieved through good hygienic practices by manufacturers and consumers.
Campylobacter is part of the natural gut microflora of most food-producing animals, such as chickens, turkeys, swine, cattle, and sheep. Typically, each contaminated poultry carcass can carry 100 to 100,000 Campylobacter cells. Given the fact that up to 500 Campylobacter cells can cause infection, poultry products pose a significant risk for consumers who mishandle fresh or processed poultry during preparation or who undercook it.
C. jejuni has been found in a variety of other foods, such as vegetables and seafood, and in non- food animal species. C. jejuni also occurs in nonchlorinated water, such as that found in ponds and streams.
Special incubation conditions are required for isolation and growth of C. jejuni cells, since the organism is microaerophilic. Samples from stool or rectal swabs are inoculated directly onto selective media, or they can be enriched to increase recovery. To limit growth of competing organisms, media used for cultivation usually are supplemented with blood and antimicrobial agents. The cultures are incubated at 42oC, under microaerophilic conditions (5% oxygen and 5% to 10% carbon dioxide), for optimal recovery.
6. Target Populations
Children younger than 5 years old and young adults 15 to 29 years old are the populations in whom C. jejuni gastroenteritis most commonly is detected. The highest incidence of infection is among infants 6 to 12 months old. C. jejuni bacteremia may also affect pregnant women, leading to infection of the fetus, which can lead to miscarriage or stillbirth. The incidence of infection is estimated to be 40-fold greater in people with HIV/AIDS, compared with others in the same age group.
7. Food Analysis
Isolation of C. jejuni from food is difficult, because the bacteria are usually present in very low numbers. For isolation from most food products, samples are rinsed and the rinsate is collected and subjected to pre-enrichment and enrichment steps, followed by isolation of C. jejuni from the agar medium. For more information about isolation of Campylobacter from food and water, see FDA’s Bacteriological Analytical Manual.
8. Examples of Outbreaks
For an update on recent outbreaks related to Campylobacter, please visit the CDC’s Morbidity and Mortality Weekly Report and enter Campylobacter in the search field.
The following reports are available on the surveillance of foodborne outbreaks in the U.S.: CDC annual report, CDC report #1, CDC report #2, and FoodNet report.
9. Other Resources
The following web links provide more information about Campylobacter and its prevention and control:
• U.S. Department of Agriculture – Q&A from Food Safety and Inspection Services
• CDC – Disease Listing
• CDC – Emerging Infectious Diseases review
• Several federal surveillance and monitoring programs in the U.S. report the incidences of Campylobacter infections and their resistance to antimicrobial drugs; for example, FoodNet, PulseNet, and National Antimicrobial Resistance Monitoring System. Additional resources include:
- National Center for Biotechnology Information (taxonomy)
- World Health Organization
- FDA report on risk assessment