Difficile Genes Research Articles

Clostridioides difficile Infection in Chronic Kidney Disease/End-Stage Renal Disease.

Clostridioides difficile infection (CDI) is a major health-care burden and increasingly seen in patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD). Increased antibiotic use, alteration in host defenses, and gastric acid suppression are some of the etiologies for increased risk of CDI in these populations. Patients with CKD/ESRD have a higher risk of initial episode, recurrence, and development of severe CDI than those without CKD or ESRD. Diagnosis and management of CDI in patients with CKD/ESRD are similar to that in the general population. The mortality, length of stay, and health-care costs are higher in patients with CDI and CKD/ESRD. Antimicrobial stewardship with reduction in antibiotic use along with infection-control measures such as contact isolation and hand hygiene with soap and water is essential in the control and prevention of CDI in patients with CKD/ESRD.

Incidence and Outbreak of Healthcare-Onset Healthcare-Associated Clostridioides difficile Infections Among Intensive Care Patients in a Large Teaching Hospital in China.

Background: Clostridioides difficile infection (CDI) is an important cause of morbidity and mortality among hospitalized patients. In China, however, hospital staff do not routinely test for CDI, leading to under-diagnosis and poor patient outcomes. Locally generated CDI data can help assess the magnitude of the problem and strengthen approaches for CDI prevention and control.Methods: We prospectively monitored hospital-onset hospital-associated (HOHA) CDI in four intensive care units (ICUs) from June 2013 to September 2014 in a large teaching hospital in China. We collected clinical information from all ICU patients with ≥ 3 episodes of diarrhea occurring within a 24-h period at least 48 h following admission (suspect case definition). Stool specimens were collected from all suspect cases of CDI and cultured for C. difficile. Polymerase chain reaction (PCR) was used to detect toxin genes from positive isolates; multi-locus sequence typing (MLST) was used for typing and identifying novel strains. We estimated the incidence rate as the number of HOHA CDI cases per 10,000 patient days; 95% confidence intervals were generated to assess rate differences between the four ICUs.Results: A total of 593 hospital-onset diarrhea patients met the suspect case definition during the study period. Of these, 47 patients (8%) were positive for C. difficile and toxin genes. The HOHA-CDI incidence rate was 14.1 cases per 10,000 patient days (95% CI: 10.5–18.6). Six patients with HOHA CDI died. ST54 (n = 14, 20%) was the most common type of HOHA-CDI strain circulating in the hospital during the study period and was linked to a temporal cluster (outbreak) involving two (NICU and GICU) of the four ICUs.Conclusion: HOHA-CDI occurs among ICU patients at this teaching hospital, supporting the importance of routine testing for CDI. Information on strain distribution can help detect CDI outbreaks. Detection of ST54 strain in a temporal cluster suggests possible gaps in infection control practices that should be investigated and addressed as needed.

Simultaneous detection and characterization of toxigenic Clostridium difficile directly from clinical stool specimens.

We employed a multiplex polymerase chain reaction (PCR) coupled with capillary electrophoresis (mPCR-CE) targeting six Clostridium difficile genes, including tpi, tcdA, tcdB, cdtA, cdtB, and a deletion in tcdC for simultaneous detection and characterization of toxigenic C. difficile directly from fecal specimens. The mPCR-CE had a limit of detection of 10 colony-forming units per reaction with no cross-reactions with other related bacterial genes. Clinical validation was performed on 354 consecutively collected stool specimens from patients with suspected C. difficile infection and 45 isolates. The results were compared with a reference standard combined with BD MAX Cdiff, real-time cell analysis assay (RTCA), and mPCR-CE. The toxigenic C. difficile species were detected in 36 isolates and 45 stool specimens by the mPCR-CE, which provided a positive rate of 20.3% (81/399). The mPCR-CE had a specificity of 97.2% and a sensitivity of 96.0%, which was higher than RTCA (x2 = 5.67, P = 0.017) but lower than BD MAX Cdiff (P = 0.245). Among the 45 strains, 44 (97.8%) were determined as nonribotype 027 by the mPCR-CE, which was fully agreed with PCR ribotyping. Even though ribotypes 017 (n = 8, 17.8%), 001 (n = 6, 13.3%), and 012 (n = 7, 15.6%) were predominant in this region, ribotype 027 was an important genotype monitored routinely. The mPCR-CE provided an alternative diagnosis tool for the simultaneous detection of toxigenic C. difficile in stool and potentially differentiated between RT027 and non-RT027.

Carvacrol reduces Clostridium difficile sporulation and spore outgrowth in vitro.

Clostridium difficile is an anaerobic spore-forming pathogen that causes a serious toxin-mediated enteric disease in humans. Therapeutic agents that are capable of reducing C. difficile spore production could significantly minimize the transmission and relapse of C. difficile infections. This study investigated the efficacy of a food-grade, plant-derived compound, carvacrol (CR), in reducing C. difficile spore production, germination and spore outgrowth. Two hyper-virulent C. difficile isolates (ATCC BAA 1870 and 1805) were grown with or without a sub-inhibitory concentration (SIC) of CR. Total viable counts and heat-resistant spore counts were determined at different time intervals. Moreover, spores and vegetative cells were visualized using phase-contrast microscopy. To determine the effect of CR on C. difficile germination and spore outgrowth, C. difficile spores were seeded in germination medium with or without the SIC and MIC of CR, and spore germination and spore outgrowth were measured by recording optical density at 600 nm. The effect of CR on C. difficile sporulation genes was also investigated using real-time qPCR. Carvacrol significantly reduced sporulation in C. difficile and down-regulated critical genes involved in spore production (P<0.05). The SIC or MIC of CR did not inhibit C. difficile spore germination; however, the MIC of CR completely inhibited spore outgrowth. The results suggest that CR could potentially be used to control C. difficile by reducing spore production and outgrowth.

Detection of Clostridium difficile and toxin genes in samples of modified atmosphere packaged (MAP) minced and cubed beef meat

In this study it is intended to find out the prevalence of Clostridium difficile in modified atmosphere packaged (MAP) minced (n:50) and cubed beef meat samples (n :50); determine the toxin from the isolates and detect the antibiotic susceptibility against metronidazole, vancomycin and clindamycin. C. difficile isolates have been isolated from two (4%) of 50 minced beef meat samples; one (2%) of 50 cubed beef meat samples. All three isolates were confirmed by PCR as C. difficile by the detection of tpi gene. Three out of 5 C. difficile isolates showed toxigenic character, two of them were carried type B (tcdB) toxin genes, one of them harbored type A (tcdA) toxin gene. When antibiotic resistance profile was phenotypically analyzed, only C. difficile type A (tcdA) was found resistant against clindamycin. All isolates were found sensitive to vancomycin and metronidazole. The result of this study demonstrated that C. difficile strains detected in samples of modified atmosphere packaged (MAP) beef meat could be a potential problem to public health

Detection of Clostridium Difficile from Faecal Specimens of Hospitalized Patients at Theodor Bilharz Research Institute

Background: C. difficile is the leading cause of healthcare-associated diarrhea in Western countries. Objectives: To investigate the prevalence of C. difficile colonization among hospital inpatients at TBRI, its role in antibiotic-associated diarrhea; and developing an algorithm that can provide a specific, cost-effective approach to detect toxigenic C. difficile. Methodology: 87 faecal specimens obtained from 54 patients with abdominal pain and diarrhea (group A) and 33 patients with no gastrointestinal symptoms (group B) were included. All specimens subjected to screening by anaerobic culture on CCFA, GDH detection by EIA and real time PCR for genes of C. difficile; toxin production was also tested for by EIA for C. difficile toxins and real time PCR for detection of C. difficile toxins genes. Results: Using PCR, the prevalence of C. difficile was 21.8% (19 out of 87 specimens). Out of the 19 C. difficile positive specimens, 17(90%) harboured non-toxigenic organism and only 2 specimens (10%) harbour toxigenic C. difficile. By culture, sensitivity was 26.3% and specificity was 83.8%. Combining results of both culture and EIA for GDH has improved the specificity to 94.1%. Sensitivity of 100% and specificity of 87.1% were recorded when EIA for toxins was compared to PCR. Conclusions: C. difficile colonization is common among our inpatients. The high prevalence of non-toxigenic C. difficile colonization may have a protective role against infection with toxigenic strains. The use of EIA for GDH for screening for presence of C. difficile in faecal specimens followed by real-time PCR for presence of toxins genes in the samples provides a convenient, rapid and specific strategy for diagnosis of CDI.

A comparison of Clostridium difficile diagnostic methods for identification of local strains in a South African centre

Accurate diagnosis of Clostridium difficile infection is essential for disease management. A clinical and molecular analysis of C. difficile isolated from symptomatic patients at Groote Schuur Hospital, South Africa, was conducted to establish the most suitable clinical test for the diagnosis and characterization of locally prevalent strains. C. difficile was detected in stool samples using enzyme-based immunoassays (EIA) and nucleic acid amplification methods, and their performance was compared with that of C. difficile isolation using direct selective culture combined with specific PCR to detect the C. difficile tpi gene, toxin A and B genes and binary toxin genes. Toxigenic isolates were characterized further by ribotyping. Selective culture isolated 32 C. difficile strains from 145 patients (22 %). Of these, the most prevalent (50 %) were of ribotype 017 (toxin A- B+) while 15.6 % were ribotype 001 (toxin A+B+). No ribotype 027 strains or binary toxin genes (cdtA and cdtB) were detected. The test sensitivities and specificities, respectively, of four commercial clinical diagnostic methods were as follows: ImmunoCard Toxins A & B (40 % and 99.1 %), VIDAS C. difficile Toxin A & B (50 % and 99.1 %), GenoType CDiff (86.7 % and 88.3 %) and Xpert C. difficile (90 % and 97.3 %). Ribotype 001 and 017 strains had a 100 % detection rate by Xpert C. difficile, 100 % and 93.3 % by GenoType CDiff, 75 % and 53.3 % by ImmunoCard and 75 % and 60 % by VIDAS, respectively. The overall poor performance of EIA suggests that a change to PCR-based testing would assist diagnosis and ensure reliable detection of locally prevalent C. difficile 017 strains.

Single fluorophore melting curve analysis for detection of hypervirulent Clostridium difficile

This study demonstrates a novel detection assay able to identify and subtype strains of Clostridium difficile. Primers carefully designed for melting curve analysis amplify DNA from three C. difficile genes, tcdB, tcdC and cdtB, during quantitative (q)PCR. The tcdB gene allows for confirmation of organism presence, whilst the tcdC and cdtB genes allow for differentiation of virulence status, as deletions in the tcdC gene and the concurrent presence of the cdtB gene, which produces binary toxin, are associated with hypervirulence. Following qPCR, subtyping is then achieved by automated, inline melting curve analysis using only a single intercalating dye and verified by microchip electrophoresis. This assay represents a novel means of distinguishing between toxigenic and hypervirulent C. difficile strains NAP1/027/BI and 078 ribotype, which are highly prevalent hypervirulent strains in humans. This methodology can help rapidly detect and identify C. difficile strains that impose a significant health and economic burden in hospitals and other healthcare settings.

Clostridium difficile secreted Pro-Pro endopeptidase PPEP-1 (ZMP1/CD2830) modulates adhesion through cleavage of the collagen binding protein CD2831

The Clostridium difficile cd2830 gene product is a secreted metalloprotease, named Pro-Pro endopeptidase (PPEP-1). PPEP-1 cleaves C. difficile cell surface proteins (e.g. CD2831). Here, we confirmed that PPEP-1 has a unique preference for prolines surrounding the scissile bond. Moreover, we show that it exhibits a high preference for an asparagine at the P2 position and hydrophobic residues at the P3 position. Using a PPEP-1 knockout C. difficile strain, we demonstrate that the removal of the collagen binding protein CD2831 is fully attributable to PPEP-1 activity. The PPEP-1 knockout strain demonstrated higher affinity for collagen type I with attenuated virulence in hamsters.

Virulence genes and clinical features of Clostridium difficile-associated diarrhea in children

Clostridium difficile is an obligate anaerobic Gram-positive bacillus, it can cause Clostridium difficile-associated diarrhea (CDAD). This study aimed to investigate the virulence genes and clinical features of CDAD in children by gene detection. From May 2012 to January 2013, the 121 inpatients in Beijing Children's Hospital who suffered from diarrhea after antibiotics treatment were detected for Clostridium difficile virulence genes including the five genes for pathogenic loci (tcdA, tcdB, tcdC, tcdD, tcdE) and the genes for binary toxin CDT (cdtA and cdtB) using polymerase chain reaction (PCR) in order to research the clinical features of CDAD, and analyze target products by sequencing. In the 121 children with diarrhea, 60 (49.6%) were toxin B-positive,including 12 toxin A-positive and toxin B-positive (A+B+), 48 toxin A-negative but toxin B-positive (A-B+). The toxin A-positive but toxin B-negative (A+B-) specimens or binary toxin (cdtA and cdtB)-positive specimens were not detected. Of 60 tcdB-positive specimens, tcdC, tcdD and tcdE positive specimens were 24 (40%), 25 (42%), 24 (40%), respectively. The sequencing results of tcdA, tcdB, tcdC, tcdD, and tcdE gene were consistent with the reference sequence. In the 60 children with CDAD, infants (≤3 years) accounted for 62% (37/60). The duration of diarrhea was 3-77 days, and 42 (70%) cases had acute diarrhea; 39 (65%) patients had fever, 40 (67%) had anemia, 36 (60%) had abnormal white blood cell count, 30 (50%) had hypoalbuminemia, 25 (42%) had elevated C-reactive protein (CRP). The level of CRP in positive group was significantly higher compared to the negative group (45.0(16.0,89.0) mg/L vs. 19.0(14.5,41.5) mg/L, Z=-2.008, P=0.045). The level of plasma albumin in positive group was significantly lower compared to the negative group (35.3(29.7,39.8) g/L vs. 38.5(33.9,41.5) g/L, Z=-2.610, P=0.009). There were no significant differences in gender, age, duration of diarrhea, hospital staytime, time of using antibiotics and laboratory test between A+B+ group and A-B+ group (all P>0.05). The main virulence genotype of Clostridium difficile was toxin A-negative but toxin B-positive in this research. The clinical features of CDAD in children were acute diarrhea with fever. Laboratory examination showed that white blood cell count was abnormal, CRP was increased, hemoglobin and plasma albumin were reduced.

Mo1868 Role of Rpon (σ54) in the Regulation of Clostridium difficile Gene Expression and Growth

Mo1868 Role of Rpon (σ54) in the Regulation of Clostridium difficile Gene Expression and Growth

An alkaline phosphatase reporter for use in Clostridium difficile

Clostridium difficile is an anaerobic, Gram-positive pathogen that causes severe gastrointestinal disease in humans and other mammals. C. difficile is notoriously difficult to work with and, until recently, few tools were available for genetic manipulation and molecular analyses. Despite the recent advances in the field, there is no simple or cost-effective technique for measuring gene transcription in C. difficile other than direct transcriptional analyses (e.g., quantitative real-time PCR and RNA-seq), which are time-consuming, expensive and difficult to scale-up. We describe the development of an in vivo reporter assay that can provide qualitative and quantitative measurements of C. difficile gene expression. Using the Enterococcus faecalis alkaline phosphatase gene, phoZ, we measured expression of C. difficile genes using a colorimetric alkaline phosphatase assay. We show that inducible alkaline phosphatase activity correlates directly with native gene expression. The ability to analyze gene expression using a standard reporter is an important and critically needed tool to study gene regulation and design genetic screens for C. difficile and other anaerobic clostridia.

Functional genomics reveals that Clostridium difficileSpo0A coordinates sporulation, virulence and metabolism

BackgroundClostridium difficile is an anaerobic, Gram-positive bacterium that can reside as a commensal within the intestinal microbiota of healthy individuals or cause life-threatening antibiotic-associated diarrhea in immunocompromised hosts. C. difficile can also form highly resistant spores that are excreted facilitating host-to-host transmission. The C. difficile spo0A gene encodes a highly conserved transcriptional regulator of sporulation that is required for relapsing disease and transmission in mice.ResultsHere we describe a genome-wide approach using a combined transcriptomic and proteomic analysis to identify Spo0A regulated genes. Our results validate Spo0A as a positive regulator of putative and novel sporulation genes as well as components of the mature spore proteome. We also show that Spo0A regulates a number of virulence-associated factors such as flagella and metabolic pathways including glucose fermentation leading to butyrate production.ConclusionsThe C. difficile spo0A gene is a global transcriptional regulator that controls diverse sporulation, virulence and metabolic phenotypes coordinating pathogen adaptation to a wide range of host interactions. Additionally, the rich breadth of functional data allowed us to significantly update the annotation of the C. difficile 630 reference genome which will facilitate basic and applied research on this emerging pathogen.

What Does the Talking?: Quorum Sensing Signalling Genes Discovered in a Bacteriophage Genome

The transfer of novel genetic material into the genomes of bacterial viruses (phages) has been widely documented in several host-phage systems. Bacterial genes are incorporated into the phage genome and, if retained, subsequently evolve within them. The expression of these phage genes can subvert or bolster bacterial processes, including altering bacterial pathogenicity. The phage phiCDHM1 infects Clostridium difficile, a pathogenic bacterium that causes nosocomial infections and is associated with antibiotic treatment. Genome sequencing and annotation of phiCDHM1 shows that despite being closely related to other C. difficile myoviruses, it has several genes that have not been previously reported in any phage genomes. Notably, these include three homologs of bacterial genes from the accessory gene regulator (agr) quorum sensing (QS) system. These are; a pre-peptide (AgrD) of an autoinducing peptide (AIP), an enzyme which processes the pre-peptide (AgrB) and a histidine kinase (AgrC) that detects the AIP to activate a response regulator. Phylogenetic analysis of the phage and C. difficile agr genes revealed that there are three types of agr loci in this species. We propose that the phage genes belonging to a third type, agr3, and have been horizontally transferred from the host. AgrB and AgrC are transcribed during the infection of two different strains. In addition, the phage agrC appears not to be confined to the phiCDHM1 genome as it was detected in genetically distinct C. difficile strains. The discovery of QS gene homologs in a phage genome presents a novel way in which phages could influence their bacterial hosts, or neighbouring bacterial populations. This is the first time that these QS genes have been reported in a phage genome and their distribution both in C. difficile and phage genomes suggests that the agr3 locus undergoes horizontal gene transfer within this species.

Evaluation of the Diagnostic Performance of the XpertClostridium difficileAssay and Its Comparison With the Toxin A/B Enzyme-Linked Fluorescent Assay and In-House Real-Time PCR Assay Used for the Detection of ToxigenicC. difficile

Clostridium difficile genes or toxin can be detected using several laboratory techniques. In this study, we compared the performance of the Xpert C. difficile assay with that of a toxin A/B enzyme-linked fluorescent immunoassay (ELFA) and an in-house real-time PCR assay for the tcdB gene. From April 2011 through January 2012, 138 soft or liquid stool samples from 138 adult patients at Paik Hospital were tested using the toxin A/B ELFA, in-house real-time PCR assay, and Xpert C. difficile assay to detect toxigenic C. difficile. Specimens were considered true positives if results were positive in both the in-house real-time PCR for tcdB gene and Xpert C. difficile assays. Sensitivity of the toxin A/B ELFA, in-house tcdB gene real-time PCR, and Xpert C. difficile assay were 67.6%, 97.3%, and 100.0%, respectively. The specificity of the in-house tcdB gene real-time PCR assay was 100%, while the specificity was 98.0% for the other two methods. The turnaround time (TAT) was 50 min for the Xpert C. difficile assay, 75 min for the toxin A/B ELFA, and 160 min for the in-house real-time PCR assay. The Xpert C. difficile assay and the in-house real-time PCR assay had higher sensitivity than the toxin A/B ELFA; however, the specificities of the three assays were similar. Considering its rapid TAT and high sensitivity, use of the Xpert C. difficile assay is highly recommended for rapid and accurate diagnosis of C. difficile infection.

An Unusual Case of Clostridium difficile Infection in Trinidad and Tobago

Clostridium difficile infection (CDI) is the leading cause of healthcare-associated diarrhea. Psuedomembraneous colitis is a major complication of CDI and its outbreaks with increased severity and mortality has been reported. In this study we report the first fatal case of a toxin A and B gene positive strain of C. difficile associated with pseudomembraneous colitis in a patient from Trinidad and Tobago. Patients admitted to tertiary hospitals with history of diarrhea were investigated and reviewed. A fatal case of a 47-year old Trinidadian of African descent who presented with diarrheal stool at a public hospital in Trinidad and Tobago was reviewed and is being reported. The identified patient had his stool sample analyzed using conventional and molecular microbiology procedures to identify the C. difficile bacteria, toxins and genes. The antimicrobial susceptibility profile was also determined using agar dilutions according to CLSI guidelines.This patient’s stool sample was positive for Clostridium difficile toxin and the enzyme glutamate dehydrogenase which were demonstrated using the Quick Check Complete® kit. The antimicrobial susceptibility test produced an unusual profile - being resistant to meropenem, ampicillin, ceftriaxone, cefotaxime and ciprofloxacin. PCR analysis demonstrated that the strain produced a 1266bp and 204bp DNA fragment corresponding to the toxin A and B gene respectively, based on the primers used. This organism was noted to be responsible for the development of psuedomembranous colitis that led to the demise of this patient. Surveillance work need to be instituted as well as antibiotics stewardship so as to prevent any more case of inflammatory bowel diseases prevalence in our country.

Study of the frequency of Clostridium difficile tcdA, tcdB, cdtA and cdtB genes in feces of Calves in south west of Iran.

BackgroundClostridium difficile (C. difficile) is a gram-positive, toxin-producing bacillus which is an intestinal pathogen in both humans and animals and causes a range of digestive disorders including inflammation of the bowel, abdominal pain, fever and diarrhea. C. difficile toxins include enterotoxin (Toxin A), cytotoxin (Toxin B) and a binary toxin. Two large protein toxins A and B are encoded by separate genes, tcdA and tcdB. Clostridium difficile infection (CDI) mainly caused by the activity of the genes tcdA and tcdB. The binary toxin is encoded by the genes cdtA and cdtB. The binary toxin caused increased adherence of bacteria to intestinal epithelium. The aim of the present study was isolation of C. difficile from feces of calves, and study of the frequency of C. difficile virulence genes.Methods150 samples of fresh feces from calves were collected and C. difficile was isolated from feces of calves using bacterial culture methods. DNA was extracted by a genomic DNA purification kit. Then PCR method was used for definitive diagnosis of C. difficile. Multiplex PCR method performed for identification of tcdA, tcdB, cdtA and cdtB genes. In the final stage antimicrobial resistance determining was carried out by standard Bauer-Kirby disk diffusion method.ResultsC. difficile was isolated from 90 samples (60%). The tcdA was observed in 8 isolates (8.8%), tcdB in 16 isolates (17.7%), cdtA in 8 isolates (8.8%) and cdtB in 14 isolates (15.5%). Only 1 isolated (1.1%) was containing all four genes tcdA, tcdB, cdtA and cdtB, 2 isolates (2.2%) only had both tcdA and tcdB genes, and there was no sample positive only for both cdtA and cdtB. The highest rate of drug resistance was against clindamycin (100%) and the highest rate of drug sensitivity was against ciprofloxacin (50%).ConclusionThe results showed high incidence of C. difficile and also high antibiotic resistance of this bacterium, but frequency of strains containing virulence genes (tcdA, tcdB, cdtA and cdtB) was low.

Regulation of toxin production in the pathogenic clostridia

The genus Clostridium comprises a large, heterogeneous group of obligate anaerobic, Gram-positive spore forming bacilli. Members of this genus are ubiquitous in the environment and although most species are considered saprophytic, several are pathogenic to both humans and animals. These bacteria cause a variety of diseases including neuroparalysis, gas gangrene, necrotic enteritis, food poisoning, toxic shock syndrome and pseudomembraneous colitis, which in most cases arise as a consequence of the production of potent exotoxins. Treatment options are often limited, underscoring the need for new treatment strategies and novel therapeutics. Understanding the fundamental mechanisms and signals that control toxin production in the pathogenic clostridia may lead to the identification of novel therapeutic targets that can be exploited in the development of new antimicrobial agents.

Correlation between virulence gene expression and proton pump inhibitors and ambient pH in Clostridium difficile: results of an in vitro study.

Proton pump inhibitors (PPIs) are associated with the development of Clostridium difficile infection in humans. Though it is assumed that PPIs mediate this effect through gastric acid suppression, there has been little investigation into whether PPIs, or ambient pH, might directly affect the expression of C. difficile toxin genes. In the present study, C. difficile ribotypes 001, 027 and 078 obtained from human subjects were grown under anaerobic conditions prepared at pHs of 5, 7.3 and 9. Matched trios were exposed to 100 µM and 200 µM of omeprazole along with PPI untreated controls. Custom designed reverse transcription quantitative PCR hydrolysis probes were used to assess C. difficile gene expression for toxins A (tcdA), B (tcdB) and binary toxin (cdtB), as well as their positive regulators (tcdR and cdtR), using rrsA, which encodes 16S rRNA, as a constitutively expressed reference gene. tcdC and codY, negative regulators of toxin expression, were also assessed. Basic pH resulted in greater expression of tcdA, and with PPI exposure a 120-fold higher expression was noted with ribotype 001. tcdB and cdtB expressions were much less responsive to pH or PPIs, though a clear response to acidic pH and PPI exposure was observed in ribotype 027. tcdC and codY expressions were largely unaffected, except with ribotype 027; low pH and PPIs resulted in their greater expression, though to a lesser degree than with toxin genes and their positive regulators. Non-neutral pH and PPI exposure appear to have an effect on C. difficile, one that has a net effect towards toxin gene expression.

Metabolic engineering of Escherichia coli for biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from glucose

The Escherichia coli XL1-blue strain was metabolically engineered to synthesize poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] through 2-ketobutyrate, which is generated via citramalate pathway, as a precursor for propionyl-CoA. Two different metabolic pathways were examined for the synthesis of propionyl-CoA from 2-ketobutyrate. The first pathway is composed of the Dickeya dadantii 3937 2-ketobutyrate oxidase or the E. coli pyruvate oxidase mutant (PoxB L253F V380A) for the conversion of 2-ketobutyrate into propionate and the Ralstonia eutropha propionyl-CoA synthetase (PrpE) or the E. coli acetyl-CoA:acetoacetyl-CoA transferase for further conversion of propionate into propionyl-CoA. The second pathway employs pyruvate formate lyase encoded by the E. coli tdcE gene or the Clostridium difficile pflB gene for the direct conversion of 2-ketobutyrate into propionyl-CoA. As the direct conversion of 2-ketobutyrate into propionyl-CoA could not support the efficient production of P(3HB-co-3HV) from glucose, the first metabolic pathway was further examined. When the recombinant E. coli XL1-blue strain equipped with citramalate pathway expressing the E. coli poxB L253F V380A gene and R. eutropha prpE gene together with the R. eutropha PHA biosynthesis genes was cultured in a chemically defined medium containing 20 g/L of glucose as a sole carbon source, P(3HB-co-2.3 mol% 3HV) was produced up to the polymer content of 61.7 wt.%. Moreover, the 3HV monomer fraction in P(3HB-co-3HV) could be increased up to 5.5 mol% by additional deletion of the prpC and scpC genes, which are responsible for the metabolism of propionyl-CoA in host strains.