Risk factors and outcomes of Clostridioides difficile infection in patients with colorectal cancer: critical perspective in management

A healthy gut microbiome includes many bacterial species that help maintain gut homeostasis (Fig. 1A). Altered intestinal microbiota has been identified as a critical factor CRC development and progression (Fig. 1B) [47]. There is growing evidence about the dysbiotic state of the microbiota in patients with CRC, specified with an increase in the abundance of Proteobacteria and a decrease in the abundance of Firmicutes, Bacteroidetes, and Actinobacteria. Particularly, an increased abundance of different bacterial species, such as Fusobacterium nucleatum, Escherichia coli, Enterococcus faecalis, enterotoxigenic Bacteroides fragilis, Streptococcus bovis, Gemella species, Parvimonas, Peptostreptococcus anaerobius, Anaerobutyricum hallii, C. difficile, and Heliobacter pylori has been reported in the gut microbiota of CRC patients [48, 49]. In addition, there is evidence that supports the carcinogenic role of some of these bacteria, such as enterotoxigenic B. fragilis, E. coli producing colibactin, F. nucleatum, and toxigenic C. difficile [50‐54]. Conversely, decreased abundance of different bacterial species, such as Bifidobacterium, Roseburia, and Clostridium butyricum, has also been reported in patients with CRC [55]. Furthermore, changes in microbial metabolites, such as bile salt hydrolases (BSH), short-chain fatty acids (SCFAs), amino acids, and lipopolysaccharides, can affect CRC progression and impact on diarrhea development in CRC patients [56].

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Notably, gut microbiota dysbiotic state and dysregulation of microbial metabolites in CRC patients facilitate C. difficile colonization and provide an environment conducive to CDI occurrence. In fact, alteration in gut microbiota composition, including an increase in the abundance of Proteobacteria (especially Enterobacteriaceae] and a decrease in the abundance of Firmicutes (especially Lachnospiraceae and Ruminococcaceae), Bacteroidetes (especially Bacteroides), and Actinobacteria (especially Bifidobacterium), are risk factors for C. difficile colonization [57‐59], which can also be found in the microbiota composition of patients with CRC. Therefore, dysbiosis in the gut microbiota composition is a crucial factor for CDI development in patients with CRC.

Colorectal surgery is considered the primary treatment for CRC. It has been documented that colectomy and gastric or esophageal surgery, as well as ileostomy closure after rectal cancer, may increase the risk of CDI in hospitalized patients [37, 60]. Previous studies have demonstrated that the rate of CDI in patients undergoing colorectal surgery is nearly three times greater than in non-surgical patients [38, 61, 62], and CDI might be more common in CRC patients undergoing colorectal resection [24, 38]. In addition, the intestinal microbiota composition significantly differs between pre- and post-surgery CRC patients. In two recent studies, a decreased abundance of Bacteroidetes and Firmicutes and an increased abundance of Proteobacteria and Fusobacteriota have been observed in post-operative compared to pre-operative CRC patients [12, 63, 64]. At the genus level, an increased abundance of Escherichia, Klebsiella, Shigella, and Faecalibacterium has been observed in CRC patients undergoing radical surgery compared to pre-operative patients, as well as a decreased abundance of Streptococcus and Lactobacillus [12, 65]. These observations suggest that gut dysbiosis induced by surgery may facilitate gut colonization by C. difficile; therefore, managing CDI in post-operative CRC patients is paramount.

Different chemotherapeutic drugs are recommended for the treatment of CRC. The three major regimens of chemotherapy for advanced CRC include: the FOLFOX regimen (folinic acid in combination with 5-fluorouracil (5-Fu), oxaliplatin), the FOLFIRI regimen (5-Fu in combination with irinotecan), and the CapeOx regimen (capecitabine in combination with oxaliplatin) [11]. The use of chemotherapy can cause various side effects in patients. It has been observed that 40% of patients undergoing standard-dose chemotherapy and 60–100% of patients undergoing high-dose chemotherapy experience malnutrition caused by intestinal mucositis, nausea, abdominal pain, vomiting, and diarrhea [66, 67]. In addition, chemotherapeutic regimens, such as FOLFOX, antimetabolites, alkylating agents, and platinum complexes, can activate toll-like receptor (TLR) signaling pathways and subsequently elevate inflammatory cytokines and reduce mucosal regeneration [7]. Alteration of the gut microbiota is a crucial side effect of chemotherapy [68]. This method can directly or indirectly exert high-impact side effects on the microbiota composition, such as malnutrition, hepatotoxicity, gastrointestinal toxicity, and mucositis [68, 69]. Clinical studies have demonstrated that the intestinal microbiota shift may be peculiar for the different chemotherapy regimens used, although it is generally characterized by a decrease in the Firmicutes (e.g., Ruminococcus, Blautia and Lachnospira) and Actinobacteria (e.g., Bifidobacterium) abundance, and an increased abundance in Proteobacteria (e.g., Staphylococcus, Enterobacter and Escherichia) [11, 68, 70, 71]. Pathological changes in the gut microbiota, such as intestinal mucositis and severe diarrhea, have also been reported in patients receiving systemic chemotherapy [11, 72, 73].

Although antibiotic therapy is commonly cited as the primary risk factor for CDI, chemotherapy can also contribute to CDI development in the absence of antibiotics [74, 75]. Several studies have demonstrated that side effects induced by chemotherapy have adverse consequences and reduce colonization resistance against C. difficile and other enteric pathogens in cancer patients [76‐78]. Altered gut microbiota in patients who have undergone chemotherapy is an important factor associated with an increased incidence of CDI in patients with CRC [79]. The low diversity of the microbiota composition in patients under chemotherapy provides a conductive environment for C. difficile colonization and CDI development [7, 79]. In addition, chemotherapeutic agents, such as 5-Fu and methotrexate, can induce PMC formation, which is a characteristic manifestation of CDI development [80, 81]. Kamthan et al. demonstrated that the incidence of C. difficile-associated diarrhea (CDAD) in patients receiving chemotherapy without any antimicrobial therapy was approximately 5.7% [82]. Zheng et al. found that patients with metastatic lymph nodes, receiving adjuvant chemotherapy, experienced higher C. difficile colonization rates (22.3%) compared with patients with not metastatic lymph nodes that not receiving adjuvant chemotherapy (10.8%), supporting that chemotherapy may increase the rate of CDI in patients [83]. Notably, potent anti-diarrheal agents, such as octreotide, are not recommended for patients experiencing chemotherapy-induced diarrhea with fever or bloody stool due to concerns about infectious colitis. In fact, these drugs may increase the cytotoxic effects of the C. difficile toxin, leading to clinical deterioration [84]. Furthermore, it has been documented that the chemotherapeutic paclitaxel may induce intestinal inflammation and exert antimicrobial activity on enteric bacteria, providing a niche for C. difficile overgrowth [84]. In addition, prior antibiotic use may exacerbate paclitaxel-induced diarrhea [84], promoting dysbiosis and boosting the destructive effect of paclitaxel, which may induce severe CDI. However, the importance of paclitaxel as a risk factor for C. difficile-associated colitis remains unclear. Further research is required to clarify the interplay between the types of chemotherapeutic drugs used and the incidence of CDI.

Antibiotic therapy is a significant risk factor for CDI development, especially with broad-spectrum antibiotics such as cephalosporin, clindamycin, fluoroquinolones, and penicillin. Broad-spectrum antibiotics alter the gut microbiome, dysregulate bile acid metabolism and bacterial metabolites, and provide ideal conditions for C. difficile germination and outgrowth [18, 85, 86]. In addition, recent insights have indicated that the excessive use of broad-spectrum antibiotics can lead to the emergence of antibiotic-resistant bacterial strains, such as Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii, due to horizontal gene transfer by mobile genetic elements like plasmids and transposons [87‐91]. The emergence of these strains requires the use of more potent antibiotics, which in turn leads to a heightened risk for CDI. In addition, the increased abundance of these bacteria may boost dysbiosis [92, 93] and consequently facilitate C. difficile colonization.

Antibiotics may be administered to patients with CRC for different purposes, such as managing sepsis or surgical infections and enhancing chemotherapy results [94, 95]. The use of antibiotics, such as prophylaxis, in patients with CRC who have undergone surgery for tumor removal is considered a standard of care for reducing surgical site infection and overall mortality and improving surgical outcomes [96]. Nonetheless, a higher risk of CDI following prolonged consumption of antibiotic prophylaxis has been reported [97]. Notably, the use of single-dose metronidazole has been suggested as an effective treatment for reducing post-operative diarrhea and CDI in patients who underwent ileostomy reversal surgery [98]. However, preclinical and clinical studies have demonstrated that both metronidazole and vancomycin affect the microbiome, bile acid metabolism, and host physiology [86, 99, 100].

Several studies have suggested that combining antibiotics with chemotherapy could be a potential therapeutic option to improve treatment efficacy. Imai et al. demonstrated that combining antibiotics with oxaliplatin enhanced the treatment effectiveness in advanced CRC patients [94]. Oxaliplatin treatment does not affect the diversity of the gut microbiota but causes a significant increase in the gram-negative microbiota at the genus level [101].

The administration of antibiotics like moxifloxacin or azithromycin in conjunction with chemotherapy could increase the efficacy of treatment [102, 103] but can negatively impact the gut microbiota of cancer patients and may cause intestinal overgrowth of pathogenic strains, including toxigenic C. difficile strains [104, 105]. In addition, the use of both chemotherapeutic drugs and antibiotics may contribute to an increase in drug-resistant strains of the microbiota, raising concerns about a higher infection rate [106]. Nonetheless, prophylaxis is still recommended for post-operative cancer patients due to its effectiveness in clinical studies [107].

Current epidemiological research has shown that age > 50 years is a significant risk factor for CRC [108]. Furthermore, elderly individuals (> 65 years) have an increased risk of acquiring C. difficile, probably because of more usage of PPIs, antibiotics, hospitalization, and exposure to healthcare-associated infections [109, 110]. In addition, these patients may experience a higher risk of morbidity and mortality due to CDI compared with younger individuals [109, 111].

Age-related alterations in physiology and immunity could be involved in the alteration of the gut microbiota diversity, which is strongly associated with CDI [112, 113]. Several studies have reported changes in the gut microbiota related to age [114‐116]. In particular, elderly hospitalized patients often exhibit decreased microbial diversity in their intestinal microflora, characterized by a decrease in the abundance of Bacteroidaceae, Lachnospiraceae, Ruminococcacae, Bifidobacterium, Lactobacillus, and Faecalibacterium, and an increase in the abundance of Enterococcaceae and Enterobacteriaceae [117, 118], which may compromise the gut environment for C. difficile growth. Interestingly, Yoem et al. have demonstrated that an age ≥ 60 represents a risk factor for C. difficile-associated colitis among post-operative CRC patients [62], highlighting the importance of an appropriate CDI management in elderly patients with CRC.

Prolonged hospitalization is another risk factor for increased CDI rates. Previous studies have indicated that the rate of CDI among certain hospitalized cancer patients is approximately twofold higher than that in general hospital patients because of longer hospital stays and extensive antibiotic consumption [119, 120]. Additionally, a higher rate of surgical procedures leads to longer hospital stays for recovery and subsequently contributes to an increase in the rate of CDI. Calu et al. observed that the incidence of CDI development in CRC patients with an age of > 60 years and hospitalization was lengthened by about 53.8% [38]. In contrast, Fang et al. found that cancer patients ≥ 50 years old, with less than 10 days of hospitalization, had a C. difficile-positive rate of about 12.7%, while cancer patients ≤ 50 years old, with at least 10 days of hospitalization, exhibited a high rate of C. difficile-positive cases, reaching up to 35% [121]. These data suggest that patients with CRC experiencing longer hospitalization may be more susceptible to C. difficile acquisition, regardless of age. A systematic review demonstrated that, in general populations, older age was significantly associated with CDI incidence in hospitalized patients and was a likely risk factor for mortality. However, in specific populations, such as patients with cancer, age was often not related to CDI risk [111], indicating the higher importance of hospitalization than aging for CDI development. However, further evidence is required to clarify this aspect.

Bile salts play a pivotal role in the C. difficile life cycle. The bile salt cholate and the conjugated bile salts glycocholate and taurocholate trigger the germination of C. difficile spores, promoting CDI [122, 123]. Bile acid profiles may be affected by the components of the gut microbiota [19]. The primary bile acids, such as cholic acid (CA) and chenodeoxycholic acid (CDCA), are typically conjugated to glycine or taurine and mostly (~ 95%) recycled in the liver, whereas the remaining enter the colon and are deconjugated and converted into secondary bile acids by the bacterial microbiota [124]. Among the gut microbiota components, the Firmicutes phylum, specifically the Lachnospiraceae and Ruminococcaceae families, has a positive correlation with secondary bile acids and plays an important role in bile acid metabolism, whereas members from the Enterobacteriaceae and Lactobacillaceae families have a negative correlation with secondary bile acids [125, 126]. Bacterial species with 7α-dehydroxylating activity, such as Clostridium scindens, can transform unconjugated primary bile acids into secondary bile acids, including deoxycholic acid (DCA) and lithocholic acid (LCA) [124]. In addition, B. fragilis, Bacteroides vulgatus, Clostridium perfringens, Lactobacillus, Bifidobacterium and Listeria monocytognes can also affect bile acid metabolism by producing BSH, which can conjugate both primary and secondary bile acids [127]. The use of broad-spectrum antibiotics decreases the microbiota diversity, resulting in reduced conversion of primary bile acids to secondary bile acids, with a subsequent increase in C. difficile growth and spore germination [122].

Bile acids may have a crucial impact on CRC initiation [128, 129]. High concentrations of bile acids damage the colonic epithelial cells and trigger the production of reactive oxygen species, leading to genetic instability and cancer stem cell-like formation [129]. Primary and secondary bile acids can interact with specific receptors, such as the Farnesoid X Receptor (FXR), which can activate signaling pathways related to inflammation and tumorigenesis. A pervious study found an increased level of secondary bile acid-producing bacteria in high-risk populations for CRC [130]. Cong et al. demonstrated that the gut microbiota could act as a negative regulator for CD8 + T cell effector function by altering the concentration of DCA. They reported that Bacteria harboring secondary bile acid biosynthetic genes, such as C. scindens, suppressed the CD8 + T cells effector function and promoted tumor growth in mice [131], demonstrating the key role of gut microbiota in bile acid metabolism and cancer development [132]. In addition, previous studies have reported that gut microbiota-mediated bile acid metabolism can affect the tumor microenvironment by affecting T helper cells and regulatory T cells (Treg cells) [133, 134]. There is evidence of the involvement of bile acids in CRC progression by activating the epidermal growth factor receptor (EGFR) pathway, resulting in cell proliferation, p53 inhibition, invasion, and angiogenesis [135, 136]. In addition, some conditions, such as bile acid diarrhea (BAD), due to overproduction of bile acids or dysfunction or resection of the terminal ileum, increase colon concentrations of dihydroxy bile acids, triggering peristalsis and watery diarrhea, with an increased overall risk of cancer [137]. All these data suggest that bile acid metabolism dysregulation in patients with CRC may favor CDI development.

C. difficile transmission from person to person occurs via the oral-fecal route [20]. Symptomatic CDI patients are the main source of transmission, causing widespread contamination of the environment near the patients [148]. CDI prevention is a critical point for patients with cancer because this infection significantly increases the risk of mortality, prolonged hospitalization, and diarrhea, which is the most common symptom of CDI and leads to dose reductions in chemotherapeutic or radiotherapeutic regimens [28, 29]. There are several well-established guidelines to prevent CDI, most of which focus on preventing the transmission of C. difficile spores and reducing the susceptibility of patients to CDI [149]. Based on the CDC guidelines, practicing good hand hygiene is the best way to prevent the spread of C. difficile from one person to another [150]. The guidelines strongly recommend isolation of patients with CDI in private rooms [149]. In addition, regularly cleaning and disinfecting equipment and the environment of patients with CDI can kill the C. difficile spores and help reduce the risk of CDI [150]. Another approach is the implementation of a detection system that helps in the immediate diagnosis of C. difficile and is considered as an alert system to prevent CDI transmission [149]. The guidelines also propose several recommendations for reducing the susceptibility of patients to CDI, such as reduction of the unnecessary use of antibiotics and PPIs and administration of probiotics to increase in the diversity of the gut microbiota. Opioids and antimotility agents are recommended to be stopped in cancer patients with CDI because they may contribute to toxic megacolon [151, 152]. Furthermore, when CDI is associated with chemotherapy, switching to an alternative regimen usually leads to symptomatic improvement within 72 h [153]. Further studies are needed to determine a comprehensive protocol for the prevention of C. difficile in patients with CRC.

Currently, several methods with different sensitivity and specificity are recommended for CDI diagnosis, including toxigenic culture (TC), cell cytotoxicity neutralization assay (CCNA), enzyme immunoassays (EIA) for TcdA and TcdB, glutamate dehydrogenase (GDH), and nucleic acid amplification tests (NAATs) [43]. C. difficile culture techniques are highly sensitive but relatively slow. EIAs and NAATs are high-specificity tests for detecting TcdA/B but they have low sensitivity. GDH is a sensitive test for C. difficile detection but does not differentiate between toxigenic and non-toxigenic strains [154‐156]. In general, and in particular, for oncologic patients, there are recommendations to use a diagnostic algorithm that combines more tests: a two-step algorithm, with the highly sensitive test used first, followed by confirmation using a highly specific test, or a three-step algorithm, that adds a NAAT test as a final step in unclear results [154, 157, 158].

Interestingly, Kamboj et al. found that the selection of diagnostic tests is extremely important for CDI diagnosis in cancer patients. In fact, the introduction of molecular-based testing methods for CDI in the Cleveland Clinic (Ohio) and Memorial Sloan Kettering Cancer Center (MSKCC) (New York) resulted in the duplication of the CDI rates in these patients [119]. In addition, immune checkpoint inhibitors (ICIs), a revolutionary cancer therapy that enhances antiantitumor activity by blocking negative regulators of T-cell function, are associated with immune-mediated diarrhea and colitis (IMDC) [159]. Therefore, due to overlapping symptoms, it may be difficult to interpret C. difficile-positive stool in the context of IMDC, leading to a potential underestimation of this infection. Accordingly, molecular-based testing methods in combination with a highly sensitive test can be recommended for CDI diagnosis in CRC patients. In addition, cytotoxicity assays can be used to detect the C. difficile toxins in fecal samples and monitor active disease.

According to the SHEA/IDSA guidelines, severe CDI is defined as a white blood cell (WBC) count > 15,000 cells/µL or a serum creatinine level ≥ 1.5 mg/dl [158]. These criteria have some limitations for cancer patients, who are usually neutropenic and have higher creatinine levels than the non-cancer population [74, 160]. For these reasons, several authors have proposed scales for severity markers in cancer patients. Zar et al. have proposed that CDI may be considered severe if cancer patients present with two or more of the following characteristics: age > 60 years, temperature ≥ 38.3 °C, an albumin level < 2.5 mg/dL, or a peripheral WBC ≥ 15,000 cells/µL within 48 h of hospitalization, endoscopic evidence of pseudomembranous colitis, or being in the intensive care unit (ICU) [161]. Differently, Belmares et al. have suggested that CDI may be considered severe if cancer patients show three or more of the following points: temperature ≥ 38.0°C, ileus (either clinically or radiographically), systolic BP < 100 mmH, leukocytosis with WBC ≥ 15,000/µL (one point)/WBC > 30,000/µL (two points), and abdominal CT scan one abnormal finding (one point)/≥ two abnormal findings (two points) [162]. Since these two detailed scales are expensive, including colonoscopy and CT scan, respectively, Yoon et al. have predicted CDI mortality in cancer patients considering severe neutropenia (absolute neutrophil count ≤ 500/µL) as associated with a worse outcome [163]. A prospective cohort study including 553 patients reported no statistically significant difference in 30-day all-cause mortality between cancer patients and those without cancer and concomitant CDI [164]. Notably, Yepez Guevara et al. demonstrated that cancer patients may experience more severe CDI episodes due to infection with virulent ribotypes, such as 027 [165]. Furthermore, cancer patients with CDI may experience an increased risk of treatment failure or recurrence compared with non-cancerous patients due to immunosuppression [45, 166]. Data on CDI recurrence (rCDI) rates among cancer patients remain scarce and are limited because of the small sample size and inadequate analysis of recurrent risk factors. A recent observational population-based cohort study comparing rCDI rates between patients with and without a cancer diagnosis found an increased risk of mortality in patients with cancer or a history of cancer as a secondary outcome [167]. Scappaticci et al. estimated the recurrence rate in hematology patients to be approximately 41% [141]. However, further studies considering large numbers of patients are needed to determine the rate of rCDI in patients with cancer.

There is discordant evidence of CDI severity in CRC patients. Some authors have reported more severe clinical symptoms of CDI in CRC patients than in healthy controls, as well as higher rates of complications, such as extended pre-operative hospital stay, admission to ICU, increased readmission rate, and mortality, compared with non-CDI patients [25, 168]. In contrast, Polpichai et al. found that CDI in CRC patients was associated with a longer length of hospitalization, increased incidence of peritonitis, bowel perforation, paralytic ileus, and colectomy, but was also associated with a lower risk of mortality, sepsis, septic shock, acute kidney injury, and mechanical ventilation, compared with patients without CRC [168]. These data may be partially due to the treating physicians’ vigilance on early diagnosis and treatment of CDI in patients with CRC, which may contribute to the observed decreased mortality and end-organ damage in these patients, and surgical intervention that may contribute to better outcomes as well.

Treatment plays a vital role in managing CDI in patients with CRC. Antibiotic therapy during the early stages of infection may prevent CDI progression and gut injury development. Nevertheless, the use of broad-spectrum antibiotics can disrupt the gut microbiota, leading to a higher risk of recurrent CDI and potentially affecting cancer progression [50, 51]. Hence, the use of approaches that cause minimal damage to the microbiome composition and restore gut microbiota diversity may provide long-term efficacy for controlling infection or even help treat CRC. So far different approaches have been introduced for CDI, which exhibit high effectiveness and specificity with minimal side effects compared with standard therapies (Table 2). In recent years, most studies have focused on the application of specific antibiotics, antibody therapy, probiotics, and FMT [39, 42, 169‐171], as detailed in the following sections.