Vibrio vulnificus is a member of the Vibrio genus of the Vibrionaceae family of gram negative, motile, curved bacillary bacteria (1,3). Initially called lactose-positive Vibrio by Hollis in 1976, V. vulnificus is associated with disease in people who ingest contaminated seafood (classically, raw oysters) or are exposed to seawater (2). Immunocompetent individuals develop vomiting, diarrhea, and abdominal pain, and are also at risk for wound infections. Immunocompromised patients and those with chronic liver disease are at markedly increased risk of developing severe septicemia with hemorrhagic skin bullae. The organism accesses the blood stream by invading the intestinal mucosa (1-3). Even with early diagnosis and aggressive therapy, Vibrio sepsis is fatal in approximately 50% of cases. The generally recommended antibiotic regimen consists of doxycycline (100mg PO/IV twice a day for 7-14 days) in addition to a third-generation cephalosporin (ceftazidime 1-2g IV/IM every 8 hours) (2).
Vibrios will grow easily on most isolation media, but as a halophilic organism, growth is enhanced by addition of 1% NaCl. On blood-agar based plates, colonies appear smooth, convex, and gray-white. Gram stain reveals gram negative straight or curved bacilli with lateral flagella. Several Vibrio species can be differentiated based on their ability to ferment the sucrose in TCBS (thiosulfate, citrate, bile, sucrose) medium. Because V. cholerae and V. alginolyticus will ferment sucrose, they produce yellow-colored colonies on TCBS medium. Colonies of V. parahaemolyticus and V. vulnificus produce a blue-green color because they do not ferment sucrose. As these organisms are facultative anaerobes capable of aerobic and fermentative metabolism and growth and reaction in carbohydrate test media, they are classified with the fermenters. Biochemical differentiation of the clinically significant Vibrio species into groups is shown in Table 1 (3).
To prevent infection by V. vulnificus, one should avoid exposure of open wounds or broken skin to warm salt water and properly and thoroughly cook all shellfish. Even oysters legally harvested can be contaminated, as the organism is part of the natural marine flora (2). Although this disease is unusual, V. vulnificus infections have increased in incidence by 41% between 1996 and 2005 (1). The CDC received reports of 900 infections in the Gulf Coast states between 1998 and 2006. Most cases do occur in this region; however, Vibrio infection should still be kept in mind as oysters are shipped widely. In 2007, this infection became nationally notifiable (2).
Campylobacter jejuni is a microaerophilic (requiring decreased O2) and capnophilic (requiring increased CO2) gram-negative curved bacillus with a polar flagellum. It was first described in 1931 by Jones and colleagues as an agent of bovine dysentery that appeared similar to another member of the Vibrio genus. C. jejuni subspecies jejuni is a major human pathogen that is ubiquitous in domestic animals including house pets and fowl (3). Disease is estimated to affect over 2.4 million persons per year. Infection by ingestion of or exposure to unpasteurized milk, under-cooked poultry, and contaminated water causes enteritis within 2-5 days of exposure. Most infected individuals suffer from cramping and abdominal pain, diarrhea that may be bloody, and nausea and vomiting; subclinical asymptomatic infections are also possible. Although death from infection is uncommon, Campylobacter septicemia does occur in immune-compromised individuals. (3,4). Relative to Salmonella and Shigella infections, infection with Campylobacter is less acute but more likely to recur without therapy (5). If initiated early in the course of disease, treatment with erythromycin or a flouroquinolone may shorten the duration of symptoms (4). Although most Campylobacter infections resolve spontaneously in 10 days at most, the organism can be shed in the stool for 2-4 weeks (3,4). Also, there are rare post-infectious complications like reactive arthritis, urticaria, and erythema nodosum. Guillain Barré syndrome, an acute demyelinating process affecting the peripheral nervous system, complicates as many as one in every 1,000 reported Campylobacter illnesses (4,5). The CDC further estimates that as many as 40% of Guillain Barré cases may be triggered by this infection (4). There is no correlation between severity of disease and risk of developing Guillain Barré; the syndrome can follow even asymptomatic infections (3).
Laboratory isolation of Campylobacter requires the use of selective Campy media containing Vancomycin, Trimethoprim, Polymyxin B, Cephalothin, and Amphotericin B in a sheep blood agar base incubated at an elevated temperature of 42° C in an atmosphere containing 5% oxygen, 10% CO2, and 85% nitrogen. Non-hemolytic, flat, gray, dry or moist, round or irregularly shaped colonies on selective media under the appropriate conditions constitutes presumptive identification as a thermophilic Campylobacter. Occasionally, another thermophilic organism like Pseudomonas aeruginosa may break through on the selective media, but the colony morphology should help in differentiation. Gram-stained Campylobacter organisms from colonies 24-48 hours old demonstrate a particularly characteristic gram-negative S-shaped, curved, or gull-wing morphology; older cultures appear more coccoid. As these organisms are very faintly-staining, the time alotted for Safranin counter-stain should be extended (3). Biochemical tests can further confirm and differentiate the Campylobacters. Rapid catalase and cytochrome oxidase tests suggest C. jejuni, C. coli, and C. lari (3). Although the biologic significance of the enzyme is unclear, it is important to note that only the two subspecies of C. jejuni possess the enzyme hippuricase (hippurate hydrolase) and can hydrolyze sodium hippurate to benzoic acid and glycine (3, 7).
Chicken flocks are commonly asymptomatically infected by Campylobacter, which spreads easily via infected feces or water, and the organism is transferred to the meat at the time of slaughter. Most human cases of disease arise from direct ingestion of or cross-contamination of other foodstuffs by raw poultry. Even fewer than 500 Campylobacter organisms, or a single drop of juice from raw chicken meat, can cause human illness. Infection can also be acquired through contact with stool of a sick house pet. Outbreaks are uncommon, but are typically related to unpasteurized milk or contaminated water. Person to person spread is unusual. Prevention of infection is best achieved by thorough cooking of chicken, carefully cleaning hands and all kitchen surfaces or utensils that come into contact with raw chicken, and frequent hand-washing when in the company of others with diarrhea (4).
Comments on Campylobacter and Vibrio Co-Infection:
A brief search of the PubMed database returned no obvious cases of co-infection by these two organisms. This patient's history of eating raw oysters is classic for Vibrio infection. A PubMed search for 'Campylobacter' and 'oysters' did turn up reports of contamination of the shellfish by Campylobacter species coli, lari, and jejuni (8-10). There are several possible explanations in this case. The patient's recent history may include some other food exposure more classic for Campylobacter, he may have had a pre-existing sub-clinical infection with the organism, or both organisms were acquired through the ingestion of raw oysters.
Contributed by Hannah Kastenbaum, MD and William Pasculle, ScD