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Citrobacter species are often present in the stools of children and are generally considered a normal component of the intestinal microflora. Previous reports suggested that they might act as enteric pathogens. Aiming at defining the role of Citrobacter species in inducing diarrhea, we looked for their presence in the stools of 328 children with diarrhea and in 108 controls. Citrobacter strains were isolated from 46 patients (14%) and 7 controls (6.5%) (P less than 0.05). All isolates were tested for heat-stable (ST) and heat-labile (LT) enterotoxin. No LT-producing organisms were found. Three C. freundii strains, all isolated from children with diarrhea, elaborated an enterotoxin detected by the suckling mouse assay. A crude extract was prepared by acetone precipitation and a sequential ultrafiltration technique. The enterotoxin was heat stable, and its estimated molecular weight was between 2,000 and 10,000. Citrobacter enterotoxin was soluble in methanol and stable at acid and neutral pHs but not above pH 8, and its activity was destroyed by treatment with 2-mercaptoethanol. Citrobacter enterotoxin was inactive in the 18-h rabbit ileal loop test. All these characteristics closely resemble STa produced by Escherichia coli. The time course of Citrobacter enterotoxin-induced intestinal secretion in suckling mice was similar to that of E. coli STa. The enterotoxin produced by C. freundii cross-reacted with monoclonal antibodies raised against E. coli STa. These results suggest that C. freundii is capable of inducing diarrhea through the production of an E. coli-like STa, and its presence in the stools of patients with diarrhea should be considered as that of a possible etiologic agent.

To elucidate the pathophysiological changes leading to postantibiotic diarrhoea caused by Clostridium difficile and its cytotoxin, oral ampicillin was given to rabbits, and jejunal, ileal, and caecal segments of those that developed diarrhoea were investigated in vitro. The rabbits that, in response to treatment, harboured Clostridium difficile in their colonic lumen were studied, and the results expressed according to the presence or absence of Clostridium difficile and/or its cytotoxin. Thus, we refer to either CD+ or CD- segments. The influx of glucose, phenylalanine, glycylphenylalanine, and lysine across the brush border of jejunum and ileum of CD+ segments was severely impaired, while only slightly blunted in CD-. No significant change was detected in the influx of glutamic acid in the jejunum of all treated animals and in the CD- ilea. Morphologic damage in ileum and caecum of CD+ was also more evident than in CD-. Transepithelial ion transport across short circuited ileal mucosa (CD+ and CD-) revealed secretory changes in Cl net transport that were more marked in CD-. We conclude that: (1) Clostridium difficile may also colonise the upper intestinal tract, where it induces morphological and functional damage, severely impairing nutrient absorption; and (2) the ileum contributes to the diarrhoea caused by CD even when the micro-organism is confined to the more distal gut by showing moderate impairment of nutrient absorption and marked electrolyte secretion.

We wished to identify, in the in vitro rabbit intestine, the pathogenesis of post-antibiotic non CD-mediated diarrhea. Out of 25rabbits which were given Ampicillin (A) 14 developed diarrhea and were in vestigated. Results: 1)CD and its cytotoxin (absent in all control rabbits)were found in the ileum and/or caecum of 8 rabbits (CD+), while only other enterobacterial species were found in 5(CD-).Clostridium spiroforme was found in one. 2) Ileal and caecal transepithelial ion fluxes were measured in Ussing chambers: secretory charges in Na and Cl transport developed in both segments and were more marked (by about 2μEq/hr.cm2) inCD--. 3)Influx of 5mM Glucose, 1mM Phenylalanine and 2mM Glycyl-Phenylalanine across the brush border of jejunal mucosa was not affected in CD-rabbits, while it was markedly reduced in CD+(respectively, 1.5±.06, .27±.05, .55±.07μmoles/hr.cm2, means ±SE in controlG vs.1.12±.08,.32±.01, .59±.08 in CD-and .51±.06,.09±.01, .15±.03 in CD+). In conclusion: 1) both CD+ and CD-animals show secretory changes in the small and large intestine, more pronounced in CD-; 2)jejunal influx of nutrients is hampered only in CD+ animals. Thus, the pathogenesis of post-antibiotic CD-mediated diarrhea appears essentially invasive, while that not due to CD appears essentially secretory.