Evaluation of cycloserine-cefoxitin-fructose agar and cycloserine-cefoxitin-fructose broth for recovery of Clostridium difficile from environmental sites

Development of a rapid-viability PCR method for detection of Clostridioides difficile spores from environmental samples

Clostridioides difficile is a common pathogen that is well known to survive for extended periods of time on environmental healthcare surfaces from fecal contamination. During epidemiological investigations of healthcare-associated infections, it is important to be able to detect whether or not there are viable spores of C. difficile on surfaces. Current methods to detect C. difficile can take up to 7 days for culture and in the case of detection by PCR, viability of the spores cannot be ascertained. Prevention of C. difficile infection in healthcare settings includes adequate cleaning and disinfection of environmental surfaces which increases the likelihood of detecting dead organisms from an environmental sample during an investigation. In this study, we were able to adapt a rapid-viability PCR (RV-PCR) method, first developed for detection of viable Bacillus anthracis spores, for the detection of viable C. difficile spores. RV-PCR uses the change in cycle threshold after incubation to confirm the presence of live organisms. Using this modified method we were able to detect viable C. difficile after 22 h of anaerobic incubation in Cycloserine Cefoxitin Fructose Broth (CCFB). This method also used bead beating combined with the Maxwell 16 Casework kit for DNA extraction and purification and a real-time duplex PCR assay for toxin B and cdd3 genes to confirm the identity of the C. difficile spores. Spiked environmental sponge-wipes with and without added organic load were tested to determine the limit of detection (LOD). The LOD from spiked environmental sponge-wipe samples was 10⁴ spores/mL but after incubation initial spore levels of 10¹ spores/mL were detected. Use of this method would greatly decrease the amount of time required to detect viable C. difficile spores; incubation of samples is only required for germination (22 h or less) instead of colony formation, which can take up to 7 days. In addition, PCR can then quickly confirm or deny the identity of the organism at the same time it would confirm viability. The presence of viable C. difficile spores could be detected at very low levels within 28 h total compared to the 2 to 10-day process that would be needed for culture, identification and toxin detection.

Comparison of culture based methods for the isolation of Clostridium difficile from stool samples in a research setting

Effective isolation of Clostridium difficile from stool samples is important in the research setting, especially where low numbers of spores/vegetative cells may be present within a sample. In this study, three protocols for stool culture were investigated to find a sensitive, cost effective and timely method of C. difficile isolation. For the initial enrichment step, the effectiveness of two different rich media, cycloserine-cefoxitin fructose broth (CCFB) and cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme (CCMB-TAL) were compared. For the comparison of four different, selective solid media; Cycloserine-cefoxitin fructose agar (CCFA), Cycloserine-cefoxitin egg yolk agar (CCEY), ChromID C. difficile and tryptone soy agar (TSA) with 5% sheep's blood with and without preceding broth enrichment were used. As a means to enable differentiation between C. difficile and other fecal flora, the effectiveness of the inclusion of a pH indictor (1% Neutral Red), was also evaluated. The data derived indicated that CCFB is more sensitive than CCMB-TAL, however, the latter had an improved recovery rate. A broth enrichment step had a reduced sensitivity over direct plating. ChromID C. difficile showed the best recovery rate whereas CCEY egg yolk agar was the most sensitive of the four. The addition of 1% Neutral Red did not show sufficient colour change when added to CCEY egg yolk agar to be used as a differential medium. For a low cost, timely and sensitive method of isolating C. difficile from stool samples we recommend direct plating onto CCEY egg yolk agar after heat shock.

Comparison of the Rodac imprint method to selective enrichment broth for recovery of vancomycin-resistant enterococci and drug-resistant Enterobacteriaceae from environmental surfaces

We compared the Rodac imprint technique to selective enrichment broth for detecting vancomycin-resistant enterococci (VRE) and multidrug-resistant Enterobacteriaceae (MDRE) on surfaces. Rodac plates contained tryptic soy agar with 5% sheep blood, vancomycin (6 microg/ml), ceftazidime (2 microg/ml), amphotericin B (2 microg/ml), and clindamycin (1 microg/ml). Two types of broth were used: brain heart infusion (BHI) and BHI plus vancomycin (6 microg/ml) and ceftazidime (2 microg/ml) (BHIVC). Of the 46 surfaces cultured for VRE, 12 (26%) were positive. Of the 12 VRE-positive surfaces, 11 (92%) grew from Rodac, 8 (67%) grew from BHIVC, and 7 (58%) grew from BHI. A larger study is needed for MDRE, as only 4 of 43 surfaces were MDRE positive. The Rodac imprint technique successfully recovered VRE from environmental surfaces.

Value of lysozyme agar incorporation and alkaline thioglycollate exposure for the environmental recovery of Clostridium difficile

Clostridium difficile is an increasingly prevalent nosocomial pathogen. Environmental contamination by spores is believed to be a major factor propagating the spread of C. difficile. Various approaches including the use of bile salts have been described to enhance the recovery of C. difficile from clinical and environmental specimens. We found that lysozyme (5 mg/L) incorporated into a selective medium containing bile salts significantly increased the recovery of C. difficile from swabs of 197 environmental sites (11% versus 24% samples positive, P< 0.01). Furthermore, in a separate series of experiments additional use of cooked meat broth enrichment significantly enhanced the recovery of C. difficile (35% versus 45%, P = 0.009). Conversely, we found that pre-exposure to alkaline thioglycollate did not improve the yield of C. difficile. Lysozyme incorporation markedly increases the recovery of C. difficile from environmental samples probably by stimulation of spore germination. Our findings suggest that previous attempts to determine the level of environmental C. difficile contamination have markedly underestimated the true prevalence of this pathogen.

Nosocomial diarrhoea in the elderly due to enterotoxigenic Clostridium perfringens

To diagnose sporadic diarrhoea due to Clostridium perfringens infection, faecal specimens from elderly patients were examined directly for C.perfringens enterotoxin using reverse passive latex agglutination assay, and then cultured for this organism. C.perfringens isolates from those samples were grouped by slide agglutination and by pulsed-field gel electrophoresis (PFGE). Fifty of the 60 isolates agglutinated with newly raised antiserum WX2 and 38 shared the same genomic PFGE pattern. Characteristics of the epidemics and experimental data suggest that the diarrhoea was caused by a nosocomial spread of C.perfringens, and not by a food-borne outbreak.

Effectiveness of liquid soap vs. chlorhexidine gluconate for the removal of Clostridium difficile from bare hands and gloved hands

OBJECTIVE

To compare liquid soap versus 4% chlorhexidine gluconate in 4% alcohol for the decontamination of bare or gloved hands inoculated with an epidemic strain of Clostridium difficile.

DESIGN

C difficile (6.7 log10 colony-forming units [CFU], 47% spores), was seeded onto bare or latex gloved hands of ten volunteers and allowed to dry. Half the volunteers initially washed with soap and half with chlorhexidine, followed by the other agent 1 week later. Cultures were done with Rodac plates at three sites on the hand: finger/thumbtips, the palmar surfaces of the fingers, and the palm. Statistical comparison was by paired Student's t test.

RESULTS

On bare hands, soap and chlorhexidine did not differ in residual bacterial counts on the finger/thumbtips (log10 CFU, 2.0 and 2.1, P = NS) and fingers (log10 CFU, 2.4 and 2.5, P = NS). Counts were too high on bare palms to quantitate. On gloved hands, soap was more effective than chlorhexidine on fingers (log10 CFU 1.3 and 1.7, P < .01) and palms (log10 CFU 1.5 and 2.0, P < .01), but not finger/thumbtips (log10 CFU 1.6 with each, P = NS). Residual C difficile counts were lower on gloved hands than bare hands (P < 0.01 to < 0.0001).

CONCLUSIONS

The two agents did not differ significantly in residual counts of C difficile on bare hands, but on gloved hands residual counts were lower following soap wash than following chlorhexidine wash. These observations support the use of either soap or chlorhexidine as a handwash for removal of C difficile, but efficacy in the prevention of C difficile transmission must be determined by prospective clinical trials.

Development of a rapid and efficient restriction endonuclease analysis typing system for Clostridium difficile and correlation with other typing systems

A HindIII restriction endonuclease analysis (REA) typing system for total genomic Clostridium difficile DNA including a rapid and efficient method of DNA extraction and a scheme for organizing unique electrophoretic DNA band patterns was developed. REA typing was performed by two extraction methods for 1,965 C. difficile isolates obtained from patients with symptomatic C. difficile disease, asymptomatic patients who were C. difficile culture positive, and environmental surfaces. This isolate collection yielded 206 unique REA types, which were organized into 75 groups. A reference strain representing each unique REA type was chosen for DNA band pattern comparisons, cytotoxin testing, and plasmid analysis. The DNA band patterns utilizing a guanidine thiocyanate-EDTA-Sarkosyl DNA extraction method were 94% reproducible, while the original and sporadically problematic diethyl pyrocarbonate-sodium dodecyl sulfate DNA extraction method was 98% reproducible when readable patterns were obtained. Reference strains from 43 of the 75 groups were cytotoxin positive, 28 groups were cytotoxin negative, and 4 groups included both toxigenic and nontoxigenic strains. Cytotoxicity of isolates with a particular REA type was always consistent with the toxicity of the reference strain for that type. REA typing was able to discriminate strain differences within types identified by the immunoblot (89 isolates), bacteriophage-bacteriocin (44 isolates), and ribotyping (23 isolates) methods. REA typing is a sensitive, discriminating, reproducible, and rapid method for differentiating C. difficile strains and is suitable for large-scale epidemiologic studies.