Department of Pathology UCD-School of Medicine



Self Assessment Exercises VII

Return to Microbiology



The curved gram-negative bacilli include the Campylobacters, Helicobacter species, and the Vibrios; the oxidase fermenters include Aeromonas and Plesiomonas. The Campylobacters, particularly Campylobacter jejuni, are common agents human diarrhea, primarily acquired from contact with infected animals, particularly chickens and turkeys. Ingestion of raw milk, partially cooked poultry, or contaminated water are common sources for human infections. The bacterial cells of the closely related Helicobacter species, particularly Helicobacter pylori, are found in the mucus-secreting epithelial cells of the stomach where such infection is associated with chronic antral gastritis, also serves as a major factor in the pathogenesis of peptic ulcer disease, and is likely also linked to gastric adenocarcinoma. Vibrio cholera is the agent of epidemic and pandemic cholera in humans. Several other non-cholera species may be encountered, the most important of which is Vibrio vulnificus, a particularly virulent species causing wound infections associated with skin contact with contaminated seawater, and often fatal septicemia following consumption of contaminated seafood, particularly raw oysters.


Aeromonas species and Plesiomonas species, with their natural habitat in fresh and seawater, can also cause wound infections at sites of lacerations from water sports or other penetrating injuries, and gastroenteritis and diarrhea from ingestion of contaminated water. The key to laboratory recognition is the recovery of isolates that appear as non-lactose fermenters on blood and MacConkey agar, except they are oxidase positive.


The following exercises will focus on the laboratory recovery and identification of this group of bacterial species.




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