Vibrio, Campylobacter, and Helicobacter are Gram-negative rods that are all widely distributed in nature. The vibrios are found in marine and surface waters. The campylobacters are found in many species of animals, including many domesticated animals. Vibrio cholerae produces an enterotoxin that causes cholera, a profuse watery diarrhea that can rapidly lead to dehydration and death. Campylobacter jejuni is a common cause of enteritis in humans. Helicobacter pylori is associated with gastritis and duodenal ulcer disease.
Vibrios are among the most common bacteria in surface waters worldwide. They are curved aerobic rods and are motile, possessing a polar flagellum. V cholerae serogroups O1 and O139 cause cholera in humans, and other vibrios may cause skin and soft tissue infections, sepsis, or enteritis. The medically important vibrios are listed in Table 17-1.
TABLE 17-1The Medically Important Vibrios ||Download (.pdf) TABLE 17-1 The Medically Important Vibrios
|Organism ||Human Disease |
|Vibrio cholerae serogroups O1 and O139 ||Epidemic and pandemic cholera |
|Vibrio cholerae serogroups non-O1/non-O139 ||Cholera-like diarrhea; mild diarrhea; rarely, extraintestinal infection |
|Vibrio parahaemolyticus ||Gastroenteritis, wound infections, septicemia |
|Vibrio vulnificus ||Gastroenteritis, wound infections, septicemia |
The epidemiology of cholera closely parallels the recognition of V cholerae transmission in water and the development of sanitary water systems.
Morphology and Identification
Upon first isolation, V cholerae is a comma-shaped, curved rod 2–4 μm long (Figure 17-1). It is actively motile by means of a polar flagellum. On prolonged cultivation, vibrios may become straight rods that resemble the Gram-negative enteric bacteria.
Gram stain of Vibrio cholerae. Often they are comma shaped or slightly curved (arrows) and 1 × 2 to 4 μm. Original magnification ×1000.
V cholerae produces convex, smooth, round colonies that are opaque and granular in transmitted light. V cholerae and most other vibrios grow well at 37°C on many kinds of media, including defined media containing mineral salts and asparagine as sources of carbon and nitrogen. V cholerae grows well on thiosulfate-citrate-bile-sucrose (TCBS) agar, a media selective for vibrios, on which it produces yellow colonies (sucrose fermented) that are readily visible against the dark-green background of the agar (Figure 17-2). Vibrios are oxidase positive, which differentiates them from enteric Gram-negative bacteria. Characteristically, vibrios grow at a very high pH (8.5–9.5) and are rapidly killed by acid. Cultures containing fermentable carbohydrates therefore quickly become sterile.
Colonies of Vibrio cholerae growing on thiosulfate, citrate, bile salts, and sucrose agar. The glistening yellow colonies are 2–3 mm in diameter and are surrounded by a ...