In vitro effects of Clostridium difficile toxins on hepatocytes

Clostridium difficile in foods and animals: history and measures to reduce exposure

Many articles have summarized the changing epidemiology of Clostridium difficile infections (CDI) in humans, but the emerging presence of C. difficile in foods and animals and possible measures to reduce human exposure to this important pathogen have been infrequently addressed. CDIs have traditionally been assumed to be restricted to health-care settings. However, recent molecular studies indicate that this is no longer the case; animals and foods might be involved in the changing epidemiology of CDIs in humans; and genome sequencing is disproving person-to-person transmission in hospitals. Although zoonotic and foodborne transmission have not been confirmed, it is evident that susceptible people can be inadvertently exposed to C. difficile from foods, animals, or their environment. Strains of epidemic clones present in humans are common in companion and food animals, raw meats, poultry products, vegetables, and ready-to-eat foods, including salads. In order to develop science-based prevention strategies, it is critical to understand how C. difficile reaches foods and humans. This review contextualizes the current understanding of CDIs in humans, animals, and foods. Based on available information, we propose a list of educational measures that could reduce the exposure of susceptible people to C. difficile. Enhanced educational efforts and behavior change targeting medical and non-medical personnel are needed.

Epidemiology, pathogenesis, and management of Clostridium difficile infection

Clostridium difficile infection is an important health problem worldwide and leads to increased morbidity and mortality, particularly among the elderly population. Antibiotics, especially those with a broad spectrum, often trigger the infection; hence the use of unnecessary antibiotics should be avoided. Mild to moderate cases respond to metronidazole or vancomycin. Severe cases may require bowel resection. Chronic relapsing cases require a prolonged course of antibiotics, immunoglobulin, probiotics, and, occasionally, feces enema. This review provides a comprehensive update on pathogenesis and management of Clostridium difficile infection for health professionals all over the world.

Identification of Clostridium difficile toxin B cardiotoxicity using a zebrafish embryo model of intoxication

Clostridium difficile toxin B (TcdB) has been studied extensively by using cell-free systems and tissue culture, but, like many bacterial toxins, the in vivo targets of TcdB are unknown and have been difficult to elucidate with traditional animal models. In the current study, the transparent Danio rerio (zebrafish) embryo was used as a model for imaging of in vivo TcdB localization and organ-specific damage in real time. At 24 h after treatment, TcdB was found to localize at the pericardial region, and zebrafish exhibited the first signs of cardiovascular damage, including a 90% reduction in systemic blood flow and a 20% reduction in heart rate. Within 72 h of exposure to TcdB, the ventricle chamber of the heart became deformed and was unable to contract or pump blood, and the fish exhibited extensive pericardial edema. In line with the observed defects in ventricle contraction, TcdB was found to directly disrupt coordinated contractility and rhythmicity in primary cardiomyocytes. Furthermore, using a caspase-3 inhibitor, we were able to block TcdB-related cardiovascular damage and prevent zebrafish death. These findings present an insight into the in vivo targets of TcdB, as well as demonstrate the strength of the zebrafish embryo as a tractable model for identification of in vivo targets of bacterial toxins and evaluation of novel candidate therapeutics.

Clostridium difficile infection in allogeneic stem cell transplant recipients is associated with severe graft-versus-host disease and non-relapse mortality

We retrospectively evaluated 75 allogeneic stem cell transplant recipients to ascertain the incidence, risk factors and outcome of infection with Clostridium difficile. Ten patients (13%) had Clostridium difficile infection at a median of 38 days (range day -6 to day +72) following the transplant. There was no difference in the duration or severity of diarrhoea in patients with Clostridium difficile infection compared to the uninfected patients and no relationship to the prior antibiotic or chemotherapy usage, age, gender, underlying disease, donor type, CMV serostatus, total body irradiation or time to engraftment. The incidence of viral infections was increased in patients infected with Clostridium difficile (7/10 vs 15/65, P = 0.005, odds ratio 7.7), but the strongest association was with GVHD >grade 2 (5/10 vs 6/65 uninfected patients, P = 0.004, odds ratio 9.8). Patients infected with Clostridium difficile also suffered a higher non-relapse mortality with 7/10 patients succumbing to either GVHD or infections, compared to 19/65 patients in the uninfected group (P = 0.02, odds ratio 5.6). Thus Clostridium difficile infections in our study had a strong association with GVHD and increased non-relapse mortality. It is possible that Clostridium difficile toxin might predispose to increased severity of GVHD leading to an adverse outcome.

Clostridium difficile toxin: cytoskeletal changes and lactate dehydrogenase release in hepatocytes

BACKGROUND

We have found that Clostridium difficile toxins can evoke hepatocyte acute-phase protein synthesis, and that this effect is dependent on a functioning interleukin-1 (IL-1) receptor. The present study was undertaken to determine if C. difficile toxicity, as determined by actin rearrangement and lactate dehydrogenase (LDH) release, also requires a functioning IL-1 receptor.

METHODS

Primary hepatocyte cultures were prepared from normal mice, knockout mice deficient in the IL-1-converting enzyme (ICE), and knockout mice deficient in the IL-1 p80 receptor. Hepatocytes were treated for 24 h with C. difficile culture extract, purified C. difficile toxin A, or purified C. difficile toxin B. The actin cytoskeleton was examined using confocal microscopy, and LDH release was measured by spectrophotometric analysis.

RESULTS

C. difficile culture extract, toxin A, and toxin B induced collapse of the actin cytoskeleton in hepatocytes from normal mice. Hepatocytes from both the ICE-deficient mice and the IL-1 p80 receptor-deficient mice demonstrated similar responses to both toxins. These toxins also induced significant LDH release in a concentration-dependent fashion in the normal hepatocytes and the ICE-deficient hepatocytes. However, no significant increase in LDH release was observed in hepatocytes from IL-1 p80 receptor-deficient mice.

CONCLUSIONS

C. difficile toxins induce actin cytoskeletal collapse independent of IL-1 or the IL-1 receptor. In contrast, toxin-stimulated LDH release was dependent on the presence of the IL-1 receptor. Thus, separate pathways appear to mediate toxic effects as manifested by actin rearrangement and LDH release.