Novel one-step method for detection and isolation of active-toxin-producing Clostridium difficile strains directly from stool samples

Potential effectiveness of parenteral nemonoxacin in the treatment of Clostridioides difficile infections: in vitro, ex vivo, and mouse studies

Introduction

Antimicrobial therapy plays a crucial role in the management of CDI patients. However, the standard agent for treating CDIs is limited to oral fidaxomicin or vancomycin. For patients made nil by mouth, there is a clinically urgent and essential need to develop an intravenous antibiotic.

Methods

For C. difficile with the lowest MIC of nemonoxacin and vancomycin, the inhibitory effects were tested using the kinetic time-kill assay and ex vivo co-culture model. The effectiveness of nemonoxacin and vancomycin in inhibiting spore germination, the sporicidal activity, and the treatment of mice with CDIs were compared.

Results

For clinical isolates and laboratory strains, lower MICs of nemonoxacin against C. difficile than levofloxacin and ciprofloxacin were observed, even in those harboring point mutations in the quinolone-resistance determining region. Although nemonoxacin failed to suppress spore outgrowth and germination in C. difficile, it exhibited an effective inhibitory effect against C. difficile in the kinetic time-kill assay and the ex vivo co-culture model. Mice receiving intraperitoneal nemonoxacin had less weight loss, higher cecum weight, a longer colon length, and lower expression of the tcdB gene, compared with untreated mice. Notably, there were no significant differences observed in weight loss, cecum weight, colon length, or tcdB gene expression between mice treated with vancomycin and those treated with any dose of nemonoxacin. Similarly, no significant differences were found between mice receiving combination therapy of intraperitoneal nemonoxacin plus oral vancomycin and those treated with intraperitoneal nemonoxacin or oral vancomycin alone.

Discussion

The potential role of nemonoxacin, which can be administered parenterally, for treating CDIs was evidenced through the in vitro, ex vivo, and mouse models.

High-throughput functional trait testing for bacterial pathogens

Functional traits are characteristics that affect the fitness and metabolic function of a microorganism. There is growing interest in using high-throughput methods to characterize bacterial pathogens based on functional virulence traits. Traditional methods that phenotype a single organism for a single virulence trait can be time consuming and labor intensive. Alternatively, machine learning of whole-genome sequences (WGS) has shown some success in predicting virulence. However, relying solely on WGS can miss functional traits, particularly for organisms lacking classical virulence factors. We propose that high-throughput assays for functional virulence trait identification should become a prominent method of characterizing bacterial pathogens on a population scale. This work is critical as we move from compiling lists of bacterial species associated with disease to pathogen-agnostic approaches capable of detecting novel microbes. We discuss six key areas of functional trait testing and how advancing high-throughput methods could provide a greater understanding of pathogens.

Pediatric diarrhea patients living in urban areas have a higher incidence of Clostridioides difficile infection

Clostridioides difficile infection (CDI) is a major cause of antibiotic-associated diarrhea and an unappreciated contributor to child mortality in low- and middle-income countries where the diagnosis may be difficult. There is little information about the prevalence of CDI among infants, children, and adolescents in Africa. Using a cross-sectional design, seventy-six samples were collected from pediatric patients presenting with diarrhea, including infants (≤ 2 years old), children (2-12 years), and adolescents (13 ≤17 years) from three hospitals between January and December 2019. Demographic data, medical history, and prior antibiotic use were recorded. Toxigenic culture and PCR were used to detect and validate the presence of C. difficile in the samples. Data obtained were analyzed using descriptive and inferential statistics. A total of 29 (38.7%), 39 (52.0%) and 7 (9.3%) samples were from infants, children, and adolescents, respectively. The average age of the patients was 4.4 years. Of these samples, 31 (41%) were positive for C. difficile by culture and were verified by PCR amplification of C. difficile-specific genes (tcdA and tcdB). The most positive cases were children (53.3%) and infants (40.0%) with the majority of them residing in urban areas. Forty-nine (66.2%) of the patients had no known antibiotics exposure, whereas 29.0% and 29.7% reported the use of over-the-counter antibiotics at 14 and 90 days, prior to the hospital visit, respectively. CDI is relatively common among children with diarrhea in Northern Nigeria. Therefore, for effective management and treatment, more attention should be given to testing for C. difficile as one of the causative agents of diarrhea.

Emergence of Clinical Clostridioides difficile Isolates With Decreased Susceptibility to Vancomycin

BACKGROUND

Clostridioides difficile infection (CDI) is a leading cause of hospital-associated antibiotic-related diarrhea and deaths worldwide. Vancomycin is one of the few antibiotics recommended for both nonsevere and severe CDI cases. We sought to determine whether vancomycin nonsusceptible C. difficile strains are circulating in the patient population.

METHODS

Stool samples from patients with CDI were collected from 438 and 98 patients at a large university hospital in Houston, Texas, and Nairobi, Kenya, respectively. The stools were examined for the presence of vancomycin and metronidazole nonsusceptible C. difficile using broth dilution culture, Etest (BioMérieux, France), polymerase chain reaction (PCR), whole-genome sequencing, and in vivo testing in a CDI mouse model.

RESULTS

Of the Houston stool samples, 114/438 (26%) had vancomycin nonsusceptible C. difficile isolates and 128/438 (29%) were metronidazole nonsusceptible. Similarly, 66 out of 98 (67%) and 83/98 (85%) of the Nairobi patients harbored vancomycin and metronidazole nonsusceptible isolates, respectively. Vancomycin treatment of a CDI mouse model infected with a vancomycin nonsusceptible isolate failed to eradicate the infection. Whole-genome sequencing analyses did not identify vanA genes, suggesting a different mechanism of resistance.

CONCLUSIONS

C. difficile strains exhibiting reduced susceptibility to vancomycin are currently circulating in patient populations. The spread of strains resistance to vancomycin, a first-line antibiotic for CDI, poses a serious therapeutic challenge. Routine susceptibility testing may be necessary.

Clostridium difficile Modulates the Gut Microbiota by Inducing the Production of Indole, an Interkingdom Signaling and Antimicrobial Molecule

Clostridium (Clostridioides) difficile infection (CDI) is associated with dysbiosis. C. difficile has a characteristic propensity to persist and recur 1 to 4 weeks after treatment, but the mechanism is unknown. We hypothesized that C. difficile may persist by manipulating the intestinal microenvironment, thereby hampering gut microbiota reconstitution following antibiotic-mediated dysbiosis. By screening stools from CDI patients for unique markers, a metabolite identified to be indole by mass spectrometry and Fourier transform infrared spectroscopy was identified. The average fecal indole concentration detected in CDI patients (n = 216; mean, 1,684.0 ± 84.4 µM) was significantly higher than in stools of patients with non-C. difficile diarrhea (n = 204; mean, 762.8 ± 53.8 µM). Certain intestinal bacteria, but not C. difficile, produce indole, a potent antimicrobial antioxidant. Remarkably, C. difficile induced other indole-producing gut microbes to produce increasing amounts of indole. Furthermore, a C. difficile accessory gene regulator 1 quorum sensing system mutant cannot induce indole, but complementation of the mutant strain with the wild-type gene restored its ability to induce indole production. Indole tolerance assays indicated that the amount of indole required to inhibit growth of most gut-protective bacteria was within the range detected in the CDI stools. We think that a high indole level limits the growth of beneficial indole-sensitive bacteria in the colon and alters colonization resistance and this might allow C. difficile to proliferate and persist. Together, these results reveal a unique mechanism of C. difficile persistence and provide insight into complex interactions and chemical warfare among the gut microbiota. IMPORTANCE Clostridium difficile infection is the leading cause of hospital-acquired and antibiotic-associated diarrhea worldwide. C. difficile flourishes in the colon after the diversity of the beneficial and protective gut microbiota have been altered by antibiotic therapy. C. difficile tends to persist, as does dysbiosis, encouraging recurrence a few days to weeks after treatment, and this further complicates treatment options. Here, we show that C. difficile might persist by manipulating the indigenous microbiota to produce indole, a bioactive molecule that inhibits the growth and reconstitution of the protective gut microbiota during infection. This discovery may explain a unique strategy C. difficile uses to control other bacteria in the colon and provide insight into the complex interactions and chemical warfare among the gut microbiota.

Prevalence of Clostridium difficile infections among Kenyan children with diarrhea

BACKGROUND

Diarrhea causes significant morbidity and mortality among children worldwide. Regions most affected by diarrhea include Sub-Saharan Africa and Southeast Asia, where antibiotics are in common use and can make children more vulnerable to Clostridium difficile and pathogens that are not affected by these drugs. Indeed, C. difficile is a major diarrhea-associated pathogen and poses a significant threat to vulnerable and immunocompromised populations. Yet, little is known about the role and epidemiology of C. difficile in diarrhea-associated illness among young children. As a result, C. difficile is often neglected in regions such as Sub-Saharan Africa that are most impacted by childhood diarrhea. The purpose of this study was to establish the frequency of C. difficile in young children (<5 years) with diarrhea.

METHODS

Children presenting with diarrhea at a national hospital in Kenya from 2015 to 2018 were enrolled consecutively. Following informed consent by a parent or legal guardian, stool samples were obtained from the children and demographic data were collected. The stools were examined for the presence of four common pathogens known to cause diarrhea: C. difficile, rotavirus, Cryptosporidium parvum, and Giardia lamblia. C. difficile was verified by toxigenic culture and PCR. The presence of C. parvum and/or G. lamblia was determined using the ImmunoCard STAT! Crypto/Giardia Rapid assay. Rotavirus was detected by ELISA.

RESULTS

The study population comprised 157 children; 62.4% were male and 37.6% were female and their average age was 12.4 months. Of the 157 stool specimens investigated, 37.6% were positive for C. difficile, 33.8% for rotavirus, 5.1% for Cryptosporidium, and 5.1% for Giardia. PCR analysis identified at least one of the C. difficile-specific - genes (tcdA, tcdB, or tcdC). Further, 57.6% of the stools had C. difficile colonies bearing a frame-shift deletion in the tcdC gene, a mutation associated with increased toxin production. The frequency of C. difficile was 32.6% in children ≤12 months old and increased to 46.6% in children 12-24 months old.

CONCLUSIONS

In Kenyan children presenting with diarrhea, C. difficile is more prevalent than rotavirus or Cryptosporidium, two leading causes of childhood diarrhea. These findings underscore the need to better understand the role of C. difficile in children with diarrhea, especially in areas with antibiotic overuse. Understanding C. difficile epidemiology and its relationship to co-infecting pathogens among African children with diarrhea will help in devising ways of reducing diarrhea-associated illness.

High rate of Clostridium difficile among young adults presenting with diarrhea at two hospitals in Kenya

Background:

Clostridium difficile infection (CDI) is the leading cause of antibiotic-associated diarrhea worldwide. As a result, the US Centers for Disease Control and Prevention have designated C. difficile as an urgent threat. Despite the global public health risk posed by CDI, little is known about its epidemiology on the African continent. This article describes the common occurrence of CDI from a cross-section of consecutively seen, randomly enrolled patients presenting with diarrhea at two major hospitals in Kenya.

Methods:

Patients presenting with diarrhea at two major hospitals in Kenya from May to July 2017 were enrolled. After signing the informed consent, stool samples, demographic data, medical history, prior antibiotic use, and HIV status were obtained from the patients. C. difficile was detected and validated by toxigenic culture and PCR.

Results:

The average age of the patients was 35.5 years (range 3–86 years); 59% were male and 41% were female. Out of 105 patient s tools tested, 98 (93.3%) were positive for C. difficile by culture. PCR analysis confirmed C. Difficile-specific genes, tcdA, tcdB, and tcdC, in the strains isolated from the stools. Further, 82.5% of the stools had C. difficile isolates bearing the frame-shift delection associated with hypervirulent strains. Remarkably, 91.9% of the stools that tested positive for C. difficile came from patients under 60 years old, with 64.3% being less than 40 years of age.The majorityof the patients (85%) reported over-the-counter antibiotic use in the last 30 days before the hospital visit.

Conclusions:

Together, the results revealed an unusually high incidence of C. difficile in the stools analyzed, especially among young adults who are thought to be less vulnerable. Comprehensive research is urgently needed to examine the epidemiology, risk factors, pathogenesis, comorbidities, clinical outcomes, antibiotic susceptibility, and genetic makeup of C. difficile strains circulating on the African continent.

A Decade of Development of Chromogenic Culture Media for Clinical Microbiology in an Era of Molecular Diagnostics

In the last 25 years, chromogenic culture media have found widespread application in diagnostic clinical microbiology. In the last decade, the range of media available to clinical laboratories has expanded greatly, allowing specific detection of additional pathogens, including Pseudomonas aeruginosa, group B streptococci, Clostridium difficile, Campylobacter spp., and Yersinia enterocolitica. New media have also been developed to screen for pathogens with acquired antimicrobial resistance, including vancomycin-resistant enterococci, carbapenem-resistant Acinetobacter spp., and Enterobacteriaceae with extended-spectrum β-lactamases and carbapenemases. This review seeks to explore the utility of chromogenic media in clinical microbiology, with particular attention given to media that have been commercialized in the last decade. The impact of laboratory automation and complementary technologies such as matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is also assessed. Finally, the review also seeks to demarcate the role of chromogenic media in an era of molecular diagnostics.

Clostridium difficile

Clostridium difficile infections (CDIs) have emerged as one of the principal threats to the health of hospitalized and immunocompromised patients. The importance of C difficile colonization is increasingly recognized not only as a source for false-positive clinical testing but also as a source of new infections within hospitals and other health care environments. In the last five years, several new treatment strategies that capitalize on the increasing understanding of the altered microbiome and host defenses in patients with CDI have completed clinical trials, including fecal microbiota transplantation. This article highlights the changing epidemiology, laboratory diagnostics, pathogenesis, and treatment of CDI.

Clostridium difficile-associated clinical burden from lack of diagnostic testing in a Chinese tertiary hospital

Despite Clostridium difficile infection (CDI) being a common cause of diarrhoea in hospitals worldwide, diagnostic testing or management guidelines are not available in most hospitals in China. In this prospective two-year study, the incidence of CDI among 276 patients with watery diarrhoea was 23.1%. Lack of diagnostic testing for CDI was associated with improper management in 26.4% of patients, risk of nosocomial transmission from lack of isolation precautions, and risk of community transmission from discharging symptomatic toxigenic C. difficile carriers. Updating practice guidelines in line with the current evidence and implementing diagnostic testing for CDI are recommended in hospitals in China.

Accessory Gene Regulator-1 Locus Is Essential for Virulence and Pathogenesis of Clostridium difficile

Clostridium difficile infection (CDI) is responsible for most of the definable cases of antibiotic- and hospital-associated diarrhea worldwide and is a frequent cause of morbidity and mortality in older patients. C. difficile, a multidrug-resistant anaerobic pathogen, causes disease by producing toxins A and B, which are controlled by an accessory gene regulator (Agr) quorum signaling system. Some C. difficile strains encode two Agr loci in their genomes, designated agr1 and agr2 The agr1 locus is present in all of the C. difficile strains sequenced to date, whereas the agr2 locus is present in a few strains. The functional roles of agr1 and agr2 in C. difficile toxin regulation and pathogenesis were unknown until now. Using allelic exchange, we deleted components of both agr loci and examined the mutants for toxin production and virulence. The results showed that the agr1 mutant cannot produce toxins A and B; toxin production can be restored by complementation with wild-type agr1 Furthermore, the agr1 mutant is able to colonize but unable to cause disease in a murine CDI model. These findings have profound implications for CDI treatment because we have uncovered a promising therapeutic target for the development of nonantibiotic drugs to treat this life-threatening emerging pathogen by targeting the toxins directly responsible for disease.

IMPORTANCE

Within the last decade, the number of cases of C. difficile infections has been increasing exponentially in the United States, resulting in about 4.8 billion U.S. dollars in health care costs annually. As a multidrug-resistant, spore-forming, anaerobic pathogen, C. difficile overpopulates the colon after the gut microbiota has been altered by antibiotic therapy. With increasing resistance to antibiotic treatment of C. difficile infections, patients are experiencing higher costs of health care and a lower quality of life as treatment options decrease. During infection, C. difficile produces toxins A and B, which directly cause disease. As a result, the toxins have become promising nonantibiotic treatment targets. Here, we have identified a pathway responsible for activating the production of the toxins. This important finding opens up a unique therapeutic target for the development of a novel nonantibiotic therapy for C. difficile infections.

Toxin synthesis by Clostridium difficile is regulated through quorum signaling

Clostridium difficile infection (CDI) is dramatically increasing as a cause of antibiotic- and hospital-associated diarrhea worldwide. C. difficile, a multidrug-resistant pathogen, flourishes in the colon after the gut microbiota has been altered by antibiotic therapy. Consequently, it produces toxins A and B that directly cause disease. Despite the enormous public health problem posed by this pathogen, the molecular mechanisms that regulate production of the toxins, which are directly responsible for disease, remained largely unknown until now. Here, we show that C. difficile toxin synthesis is regulated by an accessory gene regulator quorum-signaling system, which is mediated through a small (<1,000-Da) thiolactone that can be detected directly in stools of CDI patients. These findings provide direct evidence of the mechanism of regulation of C. difficile toxin synthesis and offer exciting new avenues both for rapid detection of C. difficile infection and development of quorum-signaling-based non-antibiotic therapies to combat this life-threatening emerging pathogen.

IMPORTANCE

Clostridium difficile infection (CDI) is the most common definable cause of hospital-acquired and antibiotic-associated diarrhea in the United States, with the total cost of treatment estimated between 1 and 4.8 billion U.S. dollars annually. C. difficile, a Gram-positive, spore-forming anaerobe, flourishes in the colon after the gut microbiota has been altered by antibiotic therapy. As a result, there is an urgent need for non-antibiotic CDI treatments that preserve the colonic microbiota. C. difficile produces toxins A and B, which are directly responsible for disease. Here, we report that C. difficile regulates its toxin synthesis by quorum signaling, in which a novel signaling peptide activates transcription of the disease-causing toxin genes. This finding provides new therapeutic targets to be harnessed for novel nonantibiotic therapy for C. difficile infections.

Evaluation of a chromogenic culture medium for the detection of Clostridium difficile

PURPOSE

Clostridium difficile (C. difficile) is an important cause of nosocomial diarrhea. Diagnostic methods for detection of C. difficile infection (CDI) are shifting to molecular techniques, which are faster and more sensitive than conventional methods. Although recent advances in these methods have been made in terms of their cost-benefit, ease of use, and turnaround time, anaerobic culture remains an important method for detection of CDI.

MATERIALS AND METHODS

In efforts to evaluate a novel chromogenic medium for the detection of C. difficile (chromID CD agar), 289 fecal specimens were analyzed using two other culture media of blood agar and cycloserine-cefoxitin-fructose-egg yolk agar while enzyme immunosorbent assay and polymerase chain reaction-based assay were used for toxin detection.

RESULTS

ChromID showed the highest detection rate among the three culture media. Both positive rate and sensitivity were higher from chromID than other culture media. ChromID was better at detecting toxin producing C. difficile at 24 h and showed the highest detection rate at both 24 h and 48 h.

CONCLUSION

Simultaneous use of toxin assay and anaerobic culture has been considered as the most accurate and sensitive diagnostic approach of CDI. Utilization of a more rapid and sensitive chromogenic medium will aid in the dianogsis of CDI.

Colonic immunopathogenesis of Clostridium difficile infections

There are major gaps in our understanding of the immunopathogenesis of Clostridium difficile infections (CDIs). In this study, 36 different biomarkers were examined in the stools of CDI and non-CDI patients using the Proteome Profiler human cytokine array assay and quantitative enzyme-linked immunosorbent assay. Diarrheal stools from patients with CDI (CDI-positive diarrheal stools) showed higher relative amounts of the following inflammatory markers than the diarrheal stools from CDI-negative patients (CDI-negative diarrheal stools): C5a, CD40L, granulocyte colony-stimulating factor, I-309, interleukin-13 (IL-13), IL-16, IL-27, monocyte chemoattractant protein 1, tumor necrosis factor alpha, and IL-8. IL-8 and IL-23 were present in a larger number of CDI-positive diarrheal stools than CDI-negative diarrheal stools. Th1 and Th2 cytokines were not significantly different between the CDI-positive and CDI-negative diarrheal stools. Lactoferrin and calprotectin concentrations were also higher in the CDI-positive diarrheal stools. Our results demonstrate that CDI elicits a proinflammatory host response, and we report for the first time that IL-23 is a major marker in CDI-positive diarrheal stools. IL-23 may explain the lack of a robust immunological response exhibited by a proportion of CDI patients and may relate to recurrence; the IL-23 levels induced during CDI in these patients may be inadequate to sustain the cellular immunity conferred by this cytokine in promoting the induction and proliferation of effector memory T cells.

Bile salt inhibition of host cell damage by Clostridium difficile toxins

Virulent Clostridium difficile strains produce toxin A and/or toxin B that are the etiological agents of diarrhea and pseudomembranous colitis. Treatment of C. difficile infections (CDI) has been hampered by resistance to multiple antibiotics, sporulation, emergence of strains with increased virulence, recurrence of the infection, and the lack of drugs that preserve or restore the colonic bacterial flora. As a result, there is new interest in non-antibiotic CDI treatments. The human conjugated bile salt taurocholate was previously shown in our laboratory to inhibit C. difficile toxin A and B activities in an in vitro assay. Here we demonstrate for the first time in an ex vivo assay that taurocholate can protect Caco-2 colonic epithelial cells from the damaging effects of the C. difficile toxins. Using caspase-3 and lactate dehydrogenase assays, we have demonstrated that taurocholate reduced the extent of toxin B-induced apoptosis and cell membrane damage. Confluent Caco-2 cells cultured with toxin B induced elevated caspase-3 activity. Remarkably, addition of 5 mM taurocholate reduced caspase-3 activity in cells treated with 2, 4, 6, and 12 µg/ml of toxin B by 99%, 78%, 64%, and 60%, respectively. Furthermore, spent culture medium from Caco-2 cells incubated with both toxin B and taurocholate exhibited significantly decreased lactate dehydrogenase activity compared to spent culture medium from cells incubated with toxin B only. Our results suggest that the mechanism of taurocholate-mediated inhibition functions at the level of toxin activity since taurocholate did not affect C. difficile growth and toxin production. These findings open up a new avenue for the development of non-antibiotic therapeutics for CDI treatment.

Evaluation of the chromogenic agar chromID C. difficile

Three selective media (chromID C. difficile agar, taurocholate cycloserine cefoxitin agar [TCCA; homemade], and CLO medium) were compared from 406 stool samples of patients suspected of having Clostridium difficile infection. The sensitivities of chromID C. difficile agar at 24 h and 48 h, CLO medium, and TCCA were 74.1%, 87%, 85.2%, and 70.4%, respectively.

Clostridium difficile

Clostridium difficile has re-emerged as a major hospital-acquired infection since 2001. Despite development of polymerase chain reaction-based testing, no single clinical diagnostic test has emerged with sufficient sensitivity, specificity, and turnaround time to be entirely reliable for disease diagnosis. The importance of C difficile acquired outside the hospital environment remains an unknown factor and awaits further epidemiologic investigation. This article discusses the changing epidemiology, clinical presentation, and pathogenesis of C difficile infection and highlights the ongoing challenges of laboratory diagnosis, treatment, and disease relapse.