Clostridioides difficile infection: history, epidemiology, risk factors, prevention, clinical manifestations, treatment, and future options.

SUMMARYClostridioides difficile infection (CDI) is one of the major issues in nosocomial infections. This bacterium is constantly evolving and poses complex challenges for clinicians, often encountered in real-life scenarios. In the face of CDI, we are increasingly equipped with new therapeutic strategies, such as monoclonal antibodies and live biotherapeutic products, which need to be thoroughly understood to fully harness their benefits. Moreover, interesting options are currently under study for the future, including bacteriophages, vaccines, and antibiotic inhibitors. Surveillance and prevention strategies continue to play a pivotal role in limiting the spread of the infection. In this review, we aim to provide the reader with a comprehensive overview of epidemiological aspects, predisposing factors, clinical manifestations, diagnostic tools, and current and future prophylactic and therapeutic options for C. difficile infection.

"Inhibitory immune checkpoints predict 7-day, in-hospital and 1-year mortality of internal medicine patients admitted with bacterial sepsis".

BACKGROUND: Sepsis is a life-threatening syndrome with complex pathophysiology and great clinical heterogeneity which complicates the delivery of personalized therapies. Our goals were to demonstrate that some biomarkers identified as regulatory immune checkpoints in preclinical studies could 1)improve sepsis prognostication based on clinical variables and 2)guide the stratification of septic patients in subgroups with shared characteristics of immune response or survival outcomes. METHODS: We assayed the soluble counterparts of 12 biomarkers of immune response in 113 internal medicine patients with bacterial sepsis. RESULTS: IL-1 receptor-associated kinase M (IRAK-M) exhibited the highest hazard ratios (HRs) for increased 7-day (1.94 [1.17-3.20]) and 30-day mortality (1.61 [1.14-2.28]). HRs of IRAK-M and Galectin-1 for predicting 1-year mortality were 1.52 (1.20-1.92) and 1.64 (1.13-2.36), respectively. A prognostic model including IRAK-M, Galectin-1, and clinical variables (Charlson Comorbidty Index, multiple source of sepsis, and SOFA score) had high discrimination for death at 7 days and 30 days (area under the curve 0.90 [0.82-0.99]) and 0.86 [0.79-0.94], respectively). Patients with elevated serum levels of IRAK-M and Galectin-1 had clinical traits of immune suppression and low survival rates. None of the 12 biomarkers were independent predictors of 2-year mortality. CONCLUSIONS: Two inhibitory immune checkpoint biomarkers (IRAK-M and Galectin-1) helped identify 3 distinct sepsis phenotypes with distinct prognoses. These biomarkers shed light on the interplay between immune dysfunction and prognosis in patients with bacterial sepsis and may prove to be useful prognostic markers, therapeutic targets, and biochemical markers for targeted enrollment in targeted therapeutic trials.

Human Campylobacter spp. infections in Italy.

PURPOSE: Campylobacter is a frequent cause of enteric infections with common antimicrobial resistance issues. The most recent reports of campylobacteriosis in Italy include data from 2013 to 2016. We aimed to provide national epidemiological and microbiological data on human Campylobacter infections in Italy during the period 2017-2021. METHODS: Data was collected from 19 Hospitals in 13 Italian Regions. Bacterial identification was performed by mass spectrometry. Antibiograms were determined with Etest or Kirby-Bauer (EUCAST criteria). RESULTS: In total, 5419 isolations of Campylobacter spp. were performed. The most common species were C. jejuni (n = 4535, 83.7%), followed by C. coli (n = 732, 13.5%) and C. fetus (n = 34, 0.6%). The mean age of patients was 34.61 years and 57.1% were males. Outpatients accounted for 54% of the cases detected. Campylobacter were isolated from faeces in 97.3% of cases and in 2.7% from blood. C. fetus was mostly isolated from blood (88.2% of cases). We tested for antimicrobial susceptibility 4627 isolates (85.4%). Resistance to ciprofloxacin and tetracyclines was 75.5% and 54.8%, respectively; resistance to erythromycin was 4.8%; clarithromycin 2% and azithromycin 2%. 50% of C. jejuni and C. coli were resistant to ≥ 2 antibiotics. Over the study period, resistance to ciprofloxacin and tetracyclines significantly decreased (p < 0.005), while resistance to macrolides remained stable. CONCLUSION: Campylobacter resistance to fluoroquinolones and tetracyclines in Italy is decreasing but is still high, while macrolides retain good activity.

Predicting sepsis at emergency department triage: Implementing clinical and laboratory markers within the first nursing assessment to enhance diagnostic accuracy.

BACKGROUND: Early identification of sepsis in the emergency department (ED) triage is both valuable and challenging. Numerous studies have endeavored to pinpoint clinical and biochemical criteria to assist clinicians in the prompt diagnosis of sepsis, but few studies have assessed the efficacy of these criteria in the ED triage setting. The aim of the study was to explore the accuracy of clinical and laboratory markers evaluated at the triage level in identifying patients with sepsis. METHODS: A prospective study was conducted in a large academic urban hospital, implementing a triage protocol aimed at early identification of septic patients based on clinical and laboratory markers. A multidisciplinary panel of experts reviewed cases to ensure accurate identification of septic patients. Variables analyzed included: Charlson comorbidity index, mean arterial pressure (MAP), partial pressure of carbon dioxide (PetCO2), white cell count, eosinophil count, C-reactive protein to albumin ratio, procalcitonin, and lactate. RESULTS: A total of 235 patients were included. Multivariable analysis identified procalcitonin ≥1 ng/mL (OR 5.2; p < 0.001); CRP-to-albumin ratio ≥32 (OR 6.6; p < 0.001); PetCO2 ≤ 28 mmHg (OR 2.7; p = 0.031), and MAP <85 mmHg (OR 7.5; p < 0.001) as independent predictors for sepsis. MAP ≥85 mmHg, CRP/albumin ratio <32, and procalcitonin <1 ng/mL demonstrated negative predictive values for sepsis of 90%, 89%, and 88%, respectively. CONCLUSIONS: Our study underscores the significance of procalcitonin and mean arterial pressure, while introducing CRP/albumin ratio and PetCO2 as important variables to consider in the very initial assessment of patients with suspected sepsis in the ED. CLINICAL RELEVANCE: Early identification of sepsis since the emergency department (ED) triage is challenging Implementing the ED triage protocol with simple clinical and laboratory markers allows to recognize patients with sepsis with a very good discriminatory power (AUC 0.88).

A subanalysis of Clostridium perfringens bloodstream infections from a 5-year retrospective nationwide survey (ITANAEROBY).

C: perfringens bloodstream infections (BSIs) can be associated with high mortality rates. We performed a subanalysis of all C. perfringens BSIs enrolled during a multicentric retrospective observational study (ITANAEROBY). Data were collected from January 2016 to December 2020. C. perfringens BSIs were 134 (134/1960, 6.8%). The highest resistance rate was observed for clindamycin (26/120, 21.6%), penicillin (11/71, 15.4%) and metronidazole (14/131, 10.7%). In conclusion, C. perfringens reduced susceptible phenotype to first-line therapy.

Lamivudine, Doravirine, and Cabotegravir Downregulate the Expression of Human Endogenous Retroviruses (HERVs), Inhibit Cell Growth, and Reduce Invasive Capability in Melanoma Cell Lines.

This study explores the impact of antiretroviral administration on the expression of human endogenous retroviruses (HERVs), cell growth, and invasive capability of human melanoma cell lines in culture. We investigated three antiretrovirals-lamivudine, doravirine, and cabotegravir-in A375, FO-1, and SK-Mel-28, BRAF-mutated, and in MeWo, P53-mutated, melanoma cell lines. The findings indicate a general capability of these drugs to downregulate the expression of HERV-K Pol and Env genes and hinder cell viability, mobility, and colony formation capacity of melanoma cells. The antiretroviral drugs also demonstrate selectivity against malignant cells, sparing normal human epithelial melanocytes. The study reveals that the integrase inhibitor cabotegravir is particularly effective in inhibiting cell growth and invasion across different cell lines in comparison with lamivudine and doravirine, which are inhibitors of the viral reverse transcriptase enzyme. The investigation further delves into the molecular mechanisms underlying the observed effects, highlighting the potential induction of ferroptosis, apoptosis, and alterations in cell cycle regulatory proteins. Our findings showed cytostatic effects principally revealed in A375, and SK-Mel-28 cell lines through a downregulation of retinoblastoma protein phosphorylation and/or cyclin D1 expression. Signs of ferroptosis were detected in both A375 cells and FO-1 cells by a decrease in glutathione peroxidase 4 and ferritin expression, as well as by an increase in transferrin protein levels. Apoptosis was also detected in FO-1 and SK-Mel-28, but only with cabotegravir treatment. Moreover, we explored the expression and activity of the stimulator of interferon genes (STING) protein and its correlation with programmed death-ligand 1 (PD-L1) expression. Both the STING activity and PD-L1 expression were decreased, suggesting that the antiretroviral treatments may counteract the detrimental effects of PD-L1 expression activation through the STING/interferon pathway triggered by HERV-K. Finally, this study underscores the potential therapeutic significance of cabotegravir in melanoma treatment. The findings also raise the prospect of using antiretroviral drugs to downregulate PD-L1 expression, potentially enhancing the therapeutic responses of immune checkpoint inhibitors.

Endemic Systemic Mycoses in Italy: A Systematic Review of Literature and a Practical Update.

Endemic systemic mycoses such as blastomycosis, coccidioidomycosis, histoplasmosis, talaromycosis, paracoccidioidomycosis are emerging as an important cause of morbidity and mortality worldwide. We conducted a systematic review on endemic systemic mycoses reported in Italy from 1914 to nowadays. We found out: 105 cases of histoplasmosis, 15 of paracoccidioidomycosis, 10 of coccidioidomycosis, 10 of blastomycosis and 3 of talaromycosis. Most cases have been reported in returning travelers and expatriates or immigrants. Thirtytwo patients did not have a story of traveling to an endemic area. Fortysix subjects had HIV/AIDS. Immunosuppression was the major risk factor for getting these infections and for severe outcomes. We provided an overview on microbiological characteristics and clinical management principles of systemic endemic mycoses with a focus on the cases reported in Italy.

Potential of outpatient steroid therapy in elderly patients with early COVID-19.

Corticosteroids lower mortality in hospitalized patients with COVID-19 pneumonia requiring oxygen support. In this observational retrospective study (September 2020-June 2021), we explored the association between receiving home corticosteroids without oxygen supply and 30-day mortality in hospitalized patients with COVID-19 pneumonia. Among a total of 794 COVID-19 pneumonia patients, 763 were included into the study (males 68%; mean age 65 ±12 years), of whom 197 (26%) received home corticosteroids (mean daily prednisone equivalent-dose 40 mg ± 12 mg; range 10-50 mg; median 50 mg; IQR 25-50 mg; for 4 days). The overall 30-day mortality of the study population was 12%. The risk of death-adjusted for age, comorbidities, administration of remdesivir and respiratory failure severity-was lower (HR 0.405; p = 0.024) in patients receiving home corticosteroids. After stratifying the study population by age categories, home corticosteroids were associated with an adjusted decrease in mortality risk in patients > 77 years (HR 0.346; p = 0.040). Home corticosteroids may lower the 30-day mortality in elderly COVID-19 patients.

Anaerobic bloodstream infections in Italy (ITANAEROBY): A 5-year retrospective nationwide survey.

INTRODUCTION: A lack of updated data on the burden and profile of anaerobic bloodstream infections (ABIs) exists. We assessed the incidence of ABIs and trends in antimicrobial resistance in anaerobes isolated from blood in Italy. MATERIAL AND METHODS: We conducted a retrospective study on 17 Italian hospitals (2016-2020). Anaerobes isolated from blood culture and their in vitro susceptibility profiles (EUCAST-interpreted) were registered and analyzed. RESULTS: A total of 1960 ABIs were identified. The mean age of ABIs patients was 68.6 ± 18.5 years, 57.6% were males. The overall incidence rate of ABIs was 1.01 per 10.000 patient-days. Forty-seven% of ABIs occurred in medical wards, 17% in ICUs, 14% in surgical wards, 7% in hemato-oncology, 14% in outpatients. The three most common anti-anaerobic tested drugs were metronidazole (92%), clindamycin (89%) and amoxicillin/clavulanate (83%). The three most common isolated anaerobes were Bacteroides fragilis (n = 529), Cutibacterium acnes (n = 262) and Clostridium perfringens (n = 134). The lowest resistance rate (1.5%) was to carbapenems, whereas the highest rate (51%) was to penicillin. Clindamycin resistance was >20% for Bacteroides spp., Prevotella spp. and Clostridium spp. Metronidazole resistance was 9.2% after excluding C. acnes and Actinomyces spp. Bacteroides spp. showed an increased prevalence of clindamycin resistance through the study period: 19% in 2016, 33% in 2020 (p ≤ 0.001). CONCLUSIONS: Our data provide a comprehensive overview of the epidemiology of ABIs in Italy, filling a gap that has existed since 1995. Caution is needed when clindamycin is used as empirical anti-anaerobic drug.

Painful thoracic swelling in a refugee teenager.

A 14-year-old refugee, escaping from a Middle East war zone, was admitted with a 3-month history of chest pain and a 2-week history of sternal swelling. The patient had no previous medical history, but reported having been beaten by a policeman at a border at the beginning of his journey. He did not have the following symptoms: cough, wheezing fever, weight loss and sweating. When he was admitted to the hospital, he was afebrile; blood pressure was 120/70 mm Hg, pulse 95 beats per minute and oxygen saturation 97% while breathing ambient air. On physical examination, there was a 10 cm fluctuating swelling in the sternal region. The lesion was reddish, warm, tender and painful (figure 1). Digital clubbing was also noticed. The remaining examination was normal. White blood cell count was 9000 cells per mm3, haemoglobin 145 g/L, erythrocyte sedimentation rate and C reactive protein were normal as well as renal and liver function tests. ECG was regular.

Neck circumference as reliable predictor of mechanical ventilation support in adult inpatients with COVID-19: A multicentric prospective evaluation.

AIMS: COVID-19 is especially severe for elderly subjects with cardiometabolic and respiratory comorbidities. Neck circumference (NC) has been shown to be strongly related to cardiometabolic and respiratory illnesses even after adjustment for body mass index (BMI). We performed a prospective study to investigate the potential of NC to predict the need for invasive mechanical ventilation (IMV) in adult COVID-19 inpatients. MATERIALS AND METHODS: We prospectively and consecutively enrolled COVID-19 adult patients admitted to dedicated medical wards of two Italian hospitals from 25 March to 7 April 2020. On admission, clinical, biochemical and anthropometric data, including BMI and NC were collected. As primary outcome measure, the maximum respiratory support received was evaluated. Follow-up time was 30 days from hospital admission. RESULTS: We enrolled 132 subjects (55.0-75.8 years, 32% female). During the study period, 26 (19.7%) patients underwent IMV. In multivariable logistic regression analyses, after adjusting for age, sex, diabetes, hypertension and COPD, NC resulted independently and significantly associated with IMV risk (adjusted OR 1.260-per 1 cm increase 95% CI:1.120-1.417; P < .001), with a stronger association in the subgroup with BMI ≤30 Kg/m2 (adjusted OR 1.526; 95% CI:1.243-1.874; P < .001). NC showed a good discrimination power in predicting patients requiring IMV (AUC 0.783; 95% CI:0.684-0.882; P < .001). In particular, NC > 40.5 cm (>37.5 for females and >42.5 for males) showed a higher and earlier IMV risk compared to subjects with lower NC (Log-rank test: P < .001). CONCLUSIONS: NC is an easy to measure parameter able to predict the need for IMV in adult COVID-19 inpatients.

Fosfomycin in continuous or prolonged infusion for systemic bacterial infections: a systematic review of its dosing regimen proposal from in vitro, in vivo and clinical studies.

Fosfomycin (FOS) administered intravenously has been recently rediscovered for the treatment of systemic infections due to multidrug-resistant bacteria. Its pharmacokinetic properties suggest a time-dependent dosing schedule with more clinical benefits from prolonged (PI) or continuous infusion (CI) than from intermittent infusion. We revised literature concerning PI and CI FOS to identify the best dosing regimen based on current evidence. We performed a MEDLINE/PubMed search. Ninety-one studies and their pertinent references were screened. Seventeen studies were included in the present review. The activity of FOS against Gram-negative and Gram-positive bacteria was evaluated in fourteen and five studies, respectively. Six studies evaluated FOS activity in combination with another antibiotic. Daily dosing of 12, 16, 18 or 24 g, administered with different schedules, were investigated. These regimens resulted active against the tested isolates in most cases. Emergence of resistant isolates has been shown to be preventable through the coadministration of another active antibiotic. FOS is a promising option to treat systemic infections caused by multidrug-resistant bacteria. Coadministration with another active molecule is required to prevent the emergence of resistant bacterial strains. The results of our review suggest that a therapeutic regimen including a loading dose of FOS 8 g followed by a daily dose of 16 g or 24 g CI could be the best therapeutic approach for patients with normal renal function. The dosing regimens in patients with renal insufficiency and CI or PI superiority compared with intermittent infusion in clinical settings should be further investigated.

Dengue: Status of current and under-development vaccines.

Dengue is an emerging mosquito-borne viral infection with increasing reports of outbreaks. The clinical picture ranges from a benign febrile illness through to severe and potentially fatal manifestations. No specific anti-viral treatment exists, and therapy only consists of supportive care. During the last three decades, several attempts to develop an effective vaccine have been made. The first dengue vaccine to obtain licensure was Dengvaxia, which was authorized in 2015 and is currently available in over 20 countries. Its use has been approved with strict limitations regarding age and serostatus of the recipients, highlighting the necessity for a more safe and efficacious vaccine. At present several vaccine, candidates are undergoing clinical and pre-clinical trials. The most advanced candidates are TDV and TDV 003/005, two live-attenuated vaccines, but another 15 vaccines are under development, introducing novel immunization strategies to the traditional dengue vaccine scenario. This work reviews the current research status on dengue vaccines.

Determination of pentraxin 3 levels in cerebrospinal fluid during central nervous system infections.

Pentraxin 3 (PTX3) is an acute phase protein; its plasmatic levels significantly rise during severe infections. Data on PTX3 levels in cerebrospinal fluid (CSF) of patients with central nervous system (CNS) infections are lacking. We aimed (a) to assess the diagnostic potential of measuring CSF PTX3 levels in patients with CNS infections and (b) to establish CSF PTX3 cutoffs to distinguish between bacterial and aseptic meningoencephalitis (ROC curve). PTX3 levels were measured in CSF from 19 patients admitted to Trieste Hospital, Italy, with CNS infection. A diagnosis of bacterial infection and aseptic meningoencephalitis was made in 7 (37%) and 12 (63%) patients, respectively. Subjects with bacterial infections showed significantly higher PTX3 levels (13.5 vs 1.27 ng/mL in aseptic meningoencephalitis, p = 0.010). We identified two different CSF PTX3 levels cutoffs. (1) The best cutoff to maximise Youden's J was 9.6 ng/mL with a sensitivity, specificity, positive predictive value and negative predictive value (NPV) of 71.4%, 91.4%, 83.3%, 84.6%, respectively. (2) The cutoff with higher NPV (100%) was 3.6 ng/mL; a diagnosis of bacterial infections was obtained in 0% patients with CSF PTX3 levels < 3.6 ng/mL vs 58% of those with CSF PTX3 levels ≥ 3.6 ng/mL (p = 0.017). CSF PTX3 levels are higher in bacterial meningitis than aseptic meningoencephalitis. A cutoff of 3.6 ng/mL of CSF PTX3 has a high NPV and can be used to exclude bacterial CNS infections.

Clinical Features and Mortality of Nosocomial Candidemia in Very Old Patients: A Multicentre Italian Study.

INTRODUCTION: Being elderly is a well-known risk factor for candidemia, but few data are available on the prognostic impact of candidemia in the very old (VO) subjects, as defined as people aged ≥75 years. OBJECTIVE: The aim of this study was to assess risk factors for nosocomial candidemia in two groups of candidemia patients, consisting of VO patients (≥75 years) and adult and old (AO) patients (18-74 years). In addition, risk factors for death (30-day mortality) were analysed separately in the two groups. METHODS: We included all consecutive candidemia episodes from January 2011 to December 2013 occurring in six referral hospitals in north-eastern Italy. RESULTS: A total of 683 nosocomial candidemia episodes occurred. Of those, 293 (42.9%) episodes were in VO and 390 (57.1%) in AO patients. Hospitalization in medical wards, chronic renal failure, urinary catheter, and peripheral parenteral nutrition (PPN) were more common in VO than in AO patients. In the former patient group, adequate antifungal therapy (73.2%) and central venous catheter (CVC) removal (67.6%) occurred less frequently than in AO patients (82.5 and 80%, p < 0.002 and p < 0.004, respectively). Thirty-day mortality was higher in VO compared to AO patients (47.8 vs. 23.6%, p < 0.0001). In AO patients, independent risk factors for death were age (OR 1.04, 95% CI 1.00-1.09, p = 0.038), recent history of chemotherapy (OR 22.01, 95% CI 3.12-155.20, p = 0.002), and severity of sepsis (OR 40.68, 95% CI 7.42-223.10, p < 0.001); CVC removal was associated with higher probability of survival (OR 0.10, 95% CI 0.03-0.33, p < 0.001). In VO patients, independent risk factors for death were PPN (OR 3.5, 95% CI 1.17-10.47, p = 0.025) and hospitalization in medical wards (OR 2.58, 95% CI 1.02-6.53, p = 0.046), while CVC removal was associated with improved survival (OR 0.40, 95% CI 0.16-1.00, p = 0.050). CONCLUSION: Thirty-day mortality was high among VO patients and was associated with inadequate management of candidemia, especially in medical wards.

Mycobacterium chimaera infections: An update.

Mycobacterium chimaera is a non-tuberculous mycobacterium belonging to the Mycobacterium avium complex, described for the first time in 2004. It acts as an opportunistic pathogen, with infections, usually respiratory illnesses, occurring more frequently in immunocompromised patients or in patients with underlying respiratory diseases. During the last decade Mycobacterium chimaera disseminated infections following cardiothoracic surgery, especially open-heart surgery, have been increasingly reported worldwide. From a pathogenic standpoint, Mycobacterium chimaera is acquired during cardiopulmonary bypass via bioaerosols emitted from contaminated heater-cooler units water systems. Due to non-specific symptoms and long latency, postoperative Mycobacterium chimaera infections may not be promptly diagnosed and treated, and may become life-threatening. The indication for revision surgery needs to be carefully evaluated on a case-by-case basis, and antibiotic therapy should be based on drug susceptibility testing results. Our review aims to provide an updated account of microbiological characteristics, clinical presentation, diagnosis, and management of Mycobacterium chimaera infections, with a special focus on those developing after cardiothoracic surgery.

Management of abdominal aortic prosthetic graft and endograft infections. A multidisciplinary update.

Abdominal aortic graft infections (AGIs) occur in 1-5% of aortic prosthetic placements. It can result in limb amputation, pseudo-aneurysm formation, septic emboli, aorto-enteric fistulae, septic shock and death. The most frequently involved pathogens are methicillin-susceptible Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci, followed by Enterobacteriaceae and uncommon bacteria. In case of gut involvement the presence of fungi has to be considered. Computed tomography angiography is actually the gold standard diagnostic imaging but magnetic resonance is a valid alternative. Nuclear medicine imaging is commonly used to improve sensitivity and specificity. Signs and symptoms are often aspecific and blood cultures can be negative, requiring alternative ways to detect the microorganism responsible for infection, such as 16S rRNA gene sequencing and molecular rapid diagnostic tests. Curative surgical intervention is the first choice approach, with in-situ reconstruction providing by far the best outcome and xenopericardial bovine patch as a promising option. For patients unable to undergo major surgery, the outcome of conservative approach remains uncertain but usually provides for life-long suppressive therapy. However, in selected cases an attempt of stopping antibiotic treatment after 3-6 months can be done. Given the difficulty in their management, we performed a review of AGIs, in order to raise awareness on clinical presentation, current available diagnostic tools, prophylaxis, surgical and anti-infective treatment of AGIs.

Human Serum Albumin Is an Essential Component of the Host Defense Mechanism Against Clostridium difficile Intoxication.

Background: The pathogenic effects of Clostridium difficile are primarily attributable to the production of the large protein toxins (C difficile toxins [Tcd]) A (TcdA) and B (TcdB). These toxins monoglucosylate Rho GTPases in the cytosol of host cells, causing destruction of the actin cytoskeleton with cytotoxic effects. Low human serum albumin (HSA) levels indicate a higher risk of acquiring and developing a severe C difficile infection (CDI) and are associated with recurrent and fatal disease. Methods: We used a combined approach based on docking simulation and biochemical analyses that were performed in vitro on purified proteins and in human epithelial colorectal adenocarcinoma cells (Caco-2), and in vivo on stem cell-derived human intestinal organoids and zebrafish embryos. Results: Our results show that HSA specifically binds via its domain II to TcdA and TcdB and thereby induces their autoproteolytic cleavage at physiological concentrations. This process impairs toxin internalization into the host cells and reduces the toxin-dependent glucosylation of Rho proteins. Conclusions: Our data provide evidence for a specific HSA-dependent self-defense mechanism against C difficile toxins and provide an explanation for the clinical correlation between CDI severity and hypoalbuminemia.