Improvement of Clostridium difficile isolation by heat-shock and typing of the isolated strains by SDS-PAGE

Effect of Multiple Rounds of Enrichment on Metabolite Accumulation and Microbiota Composition of Pit Mud for Baijiu Fermentation

Pit mud (PM) is the main component of Baijiu (traditional Chinese liquor), and its microorganisms are the primary sources of the aroma of Chinese strong-flavor Baijiu (SFB). Enrichment plays an important role in the selection of functional microorganisms in PM. Herein, the PM of SFB was submitted to six rounds of enrichment using clostridial growth medium (CGM), and changes in the metabolite accumulation and microbiota composition were evaluated. Based on the metabolite production and microbiota composition, the enrichment rounds were classified as the acclimation stage (round 2), main fermentation stage (rounds 3 and 4), and late fermentation stage (rounds 5 and 6). Species within the genus Clostridium dominated in the acclimation stage (65.84-74.51%). In the main fermentation stage, the dominant microbial groups were producers of butyric acid, acetic acid, and caproic acid, which included Clostridium (45.99-74.80%), Caproicibacter (1.45-17.02%), and potential new species within the order of Oscillataceae (14.26-29.10%). In the late stage of enrichment, Pediococcus dominated (45.96-79.44%). Thus, the main fermentation stage can be considered optimal for the isolation of acid-producing bacteria from PM. The findings discussed herein support the development and application of functional bacteria by bioaugmentation, and contribute to improving the quality of PM and SFB production.

Evaluation of 3 automated real-time PCR (Xpert C. difficile assay, BD MAX Cdiff, and IMDx C. difficile for Abbott m2000 assay) for detecting Clostridium difficile toxin gene compared to toxigenic culture in stool specimens

We evaluated the performance of the 3 automated systems (Cepheid Xpert, BD MAX, and IMDx C. difficile for Abbott m2000) detecting Clostridium difficile toxin gene compared to toxigenic culture. Of the 254 stool specimens tested, 87 (48 slight, 35 moderate, and 4 heavy growth) were toxigenic culture positive. The overall sensitivities and specificities were 82.8% and 98.8% for Xpert, 81.6% and 95.8% for BD MAX, and 62.1% and 99.4% for IMDx, respectively. The specificity was significantly higher in IMDx than BD MAX (P= 0.03). All stool samples underwent toxin A/B enzyme immunoassay testing, and of the 254 samples, only 29 samples were positive and 2 of them were toxigenic culture negative. Considering the rapidity and high specificity of the real-time PCR assays compared to the toxigenic culture, they can be used as the first test method for C. difficile infection/colonization.

Performance of chromID Clostridium difficile agar compared with BBL C. difficile selective agar for detection of C. difficile in stool specimens

We evaluated the performance of a new chromogenic medium for detection of Clostridium difficile, chromID C. difficile agar (CDIF; bioMérieux, France), by comparison with BBL C. difficile Selective Agar (CDSA; Becton Dickinson and Company, USA). After heat pre-treatment (80℃, 5 min), 185 diarrheal stool samples were inoculated onto the two media types and incubated anaerobically for 24 hr and 48 hr for CDIF and for 48 hr and 72 hr for CDSA. All typical colonies on each medium were examined by Gram staining, and the gram-positive rods confirmed to contain the tpi gene by PCR were identified as C. difficile. C. difficile was recovered from 36 samples by using a combination of the two media. The sensitivity with CDIF 48 hr was highest (100%) and was significantly higher than that with CDIF 24 hr (58.3%; P<0.001), because samples with a low burden of C. difficile tended to require prolonged incubation up to 48 hr (P<0.001). The specificity of CDIF 24 hr and CDIF 48 hr (99.3% and 90.6%, respectively) was significantly higher than that of CDSA 48 hr and CDSA 72 hr (72.5% and 67.1%, respectively; P<0.001). CDIF was effective for detecting C. difficile in heat-pretreated stool specimens, thus reducing unnecessary testing for toxin production in non-C. difficile isolates and turnaround time.

Biology of Clostridium difficile: implications for epidemiology and diagnosis

Clostridium difficile is an anaerobic, spore-forming, gram-positive rod that causes a spectrum of antibiotic-associated colitis through the elaboration of two large clostridial toxins and other virulence factors. Since its discovery in 1978 as the agent responsible for pseudomembranous colitis, the organism has continued to evolve into an adaptable, aggressive, hypervirulent strain. Advances in molecular methods and improved animal models have facilitated an understanding of how this organism survives in the environment, adapts to the gastrointestinal tract of animals and humans, and accomplishes its unique pathogenesis. The advances in microbiology have been accompanied by some important clinical observations including increased rates of C. difficile infection, increased virulence, and multiple outbreaks. The major new risk is fluoroquinolone use; there is also an association with proton pump inhibitors and increased recognition of cases in outpatients, pediatric patients, and patients without recent antibiotic use. The combination of more aggressive strains with mobile genomes in a setting of an expanded pool of individuals at risk has refocused attention on and challenged assumptions regarding diagnostic gold standards. Future research is likely to build upon the advancements in phylogenetics to create novel strategies for diagnosis, treatment, and prevention.

Clostridium difficile infection

The spore-forming anaerobe Clostridium difficile has become a serious enteropathogen. Changes in the composition of natural intestinal flora, mainly due to antibiotic therapy, permit its colonization of, and multiplication in, the colon. The disease is caused by (entero)toxin A and (cyto)toxin B, and infection ranges from asymptomatic carrier state and mild diarrhea to pseudomembranous colitis. The clinical diagnosis is made by observing inflammatory, sometimes bloody, diarrhea and by the colonoscopic detection of epithelial necrosis, ulceration, and, in the advanced state, pseudomembrane formation. The laboratory supports the diagnosis by detecting toxin A and/or B by an enzyme-linked immunoassay with high specificity, but sometimes less sensitivity than with the cytotoxin assay in tissue culture cells. Fecal leukocytes or fecal lactoferrin may be found. Culture for the isolation and identification of toxigenic C. difficile is time consuming but necessary for epidemiological studies. Polymerase chain reaction (PCR) tests have been tested for detection of the toxin B gene directly in stool. Therapy consists of stopping all systemic antibiotic treatment and the use of oral metronidazole or vancomycin. There may be more relapses after vancomycin therapy, and the increasing vancomycin resistance of Enterococcus is worrisome. Prevention, especially of nosocomial spread, requires isolation and enforced handwashing. For epidemiological studies, the bacteria can be typed by molecular DNA analyses, including PCR, protein electrophoresis, and immunological tests.