Vibrio cholerae and Its CtxA Toxin: A Comparative Study of the Histopathological and Related Changes in Albino Mice

While V. cholerae primarily causes massive secretory diarrhea due to CT, whether CT in its purified form inflicts the same injurious effect on tissues seen in the presence of the whole bacteria in vivo is unknown. To examine the histopathological changes caused by different clinical V. cholerae isolates and their partially purified enterotoxin in an experimental model of the mouse, and to determine the antimicrobial susceptibility profile of the isolate and ctxA gene carriage.

From 250 clinical samples of 200 stool and 50 rectal samples taken in Baghdad (2022 to 2023), and using culture, biochemical tests, and serotyping methods, V. cholerae was isolated. Antimicrobial susceptibility was determined using the disk diffusion method according to the CLSI 2022. ctxA gene was detected by conventional PCR. In the experiment, 6 weeks old mice received intraperitoneal injections of either partially purified toxin (2 dilutions corresponding to 55 and 45 μg/mL), live V. cholerae (10²-10⁸ CFU/mL), or normal saline (control). After 5 days, the liver, small intestine, and lungs were collected and subjected to histological examination.

V. cholerae was found in 20 of 250 specimens (8%) (18 by stool culture, 2 by rectal swabs). Of these, 8 (40%) were ctxA positive. The most frequent resistances were to ceftriaxone (90%), amoxicillin (90%), tetracycline (85%), gentamicin (80%), while the highest susceptibility was found for ceftazidime (95%), imipenem (90%) and streptomycin (90%). When tested in mice, the purified toxin caused localized injury to mucosa which led to neutrophilic infiltration with patchy ulceration. When the whole bacterium was inoculated, extensive mucosal necrosis and hemorrhage appeared, along with disruption of the intestinal architecture. The livers of mice exposed to either the toxin or the whole bacterium showed inflammatory cell infiltration, congestion of the central vein, patches of necrosis, and vacuolated hepatocytes. The changes in the lungs of both groups were mild (congestion and focal inflammatory infiltrates).

Given the conditions of our experiments, the whole V. cholerae produced extensive intestinal mucosal damage compared to the purified toxin, while similar effects were seen on the liver in both cases with only slight changes in the lung. These findings are of a descriptive nature and would require a quantitative assessment of tissues and a proper statistical analysis to support them.