Bacteriological and clinical studies in infantile diarrhoea: II. Doubtful pathogens: Enterobacteriaceae, Pseudomonas, Alcaligens and Aeromonas

Clinical and microbiological features of Aeromonas hydrophila-associated diarrhea

The prevalence of Aeromonas hydrophila in stool specimens from patients with diarrhea was studied during 18 months. A. hydrophila was found in 1.1% of patients with diarrhea and in none of 533 control patients (P less than 0.02). Cases were detected 1.5 times more often during the summer months than the winter months, and most occurred in children less than 2 years of age. Clinical features included fever greater than 38 degrees C (55%), abdominal cramps (35%), vomiting (25%), and duration of illness greater than 10 days (50%). Detection of A. hydrophila in stools was facilitated by the use of sheep blood agar with 15 micrograms of ampicillin per ml which was flooded with oxidase reagent after growth. A cytotoxin was produced by 62% of the isolates, and the cytotoxic strains showed positive results in a hemolysin assay and a lysine decarboxylase reaction.

Aeromonas hydrophila toxins - intestinal fluid accumulation and mucosal injury in animal models

Strains of Aeromonas hydrophila were earlier shown to produce a heat-labile enterotoxin and two cytolytic toxins, alpha- and beta-haemolysin. These investigations have been extended. When separated from the cytolysins, the enterotoxin elicited fluid accumulation in rabbit intestinal loops. The electrolyte and albumin content of the fluid was similar to that of cholera toxin. The enterotoxin was non-injurious to the mucosa. Purified hemolysins did not give a positive loop test. They produced hemorrhagic enteritis with leakage of small amounts of hemorrhagic fluid. In electrolyte and albumin content this fluid differed from the fluid elicited by the enterotoxin. Prostaglandin inhibitors did not reduce the diarrheal response to Aeromonas enterotoxin. The cAMP inhibitor chlorpromazine reduced the fluid accumulation in rat and mice intestinal loops by 60%. Cholera toxin and Aeromonas enterotoxin may have a common pathway in the elicitation of intestinal fluid accumulation. By passage in intestinal loops, strains of A. hydrophila could regain lost enterotoxicity. Experimental diarrhea could not be induced in rabbits and rats with various enterotoxigenic strains of Aeromonas.