Niki F. Foster

Asymptomatic Clostridium difficile colonization: epidemiology and clinical implications

BackgroundThe epidemiology of Clostridium difficile infection (CDI) has changed over the past decades with the emergence of highly virulent strains. The role of asymptomatic C. difficile colonization as part of the clinical spectrum of CDI is complex because many risk factors are common to both disease and asymptomatic states. In this article, we review the role of asymptomatic C. difficile colonization in the progression to symptomatic CDI, describe the epidemiology of asymptomatic C. difficile colonization, assess the effectiveness of screening and intensive infection control practices for patients at risk of asymptomatic C. difficile colonization, and discuss the implications for clinical practice.MethodsA narrative review was performed in PubMed for articles published from January 1980 to February 2015 using search terms ‘Clostridium difficile’ and ‘colonization’ or ‘colonisation’ or ‘carriage’.ResultsThere is no clear definition for asymptomatic CDI and the terms carriage and colonization are often used interchangeably. The prevalence of asymptomatic C. difficile colonization varies depending on a number of host, pathogen, and environmental factors; current estimates of asymptomatic colonization may be underestimated as stool culture is not practical in a clinical setting.ConclusionsAsymptomatic C. difficile colonization presents challenging concepts in the overall picture of this disease and its management. Individuals who are colonized by the organism may acquire protection from progression to disease, however they also have the potential to contribute to transmission in healthcare settings.

Comparison of Rapid, Automated Ribotyping and DNA Macrorestriction Analysis of Burkholderia pseudomallei

ABSTRACT An automated ribotyping device (RiboPrinter) was used to determine the ribotypes of a collection of Burkholderia pseudomallei isolates. In a preliminary evaluation with the restriction enzymes BamHI and EcoRI, the protocol with EcoRI was more discriminating. The reproducibilities of the ribotypes obtained with EcoRI (EcoRI ribotypes) were determined by testing three levels of bacterial loads. The performance of the manufacturers software was assessed by comparing the machine-optimized ribotypes with the type determined from the original gel image analyzed with Bionumerics software. The library of B. pseudomallei EcoRI ribotypes was then compared with the ribotypes obtained by DNA macrorestriction analysis of XbaI digests by pulsed-field gel electrophoresis. The typeability of B. pseudomallei by EcoRI ribotyping was 100%, and the discrimination index was 0.94. The slightly greater discrimination provided by DNA macrorestriction analysis (0.96) was achieved at the expense of a significantly longer processing time of 6 days, although the method was only half the cost of automated ribotyping. Typeability by macrorestriction analysis was lower (97%) unless a thiourea step was added to neutralize the action of Tris-dependent endonucleases. The digital record of B. pseudomallei isolates analyzed thus far provides a useful resource for future epidemiological studies and will help shorten the response time in the event of a further melioidosis outbreak or the deliberate release of B. pseudomallei as a biohazard.

Epidemiology of Clostridium difficile infection in two tertiary-care hospitals in Perth, Western Australia: a cross-sectional study

The epidemiology of Clostridium difficile infection (CDI) has changed over time and between countries. It is therefore essential to monitor the characteristics of patients at risk of infection and the circulating strains to recognize local and global trends, and improve patient management. From December 2011 to May 2012 we conducted a prospective, observational epidemiological study of patients with laboratory-confirmed CDI at two tertiary teaching hospitals in Perth, Western Australia to determine CDI incidence and risk factors in an Australian setting. The incidence of CDI varied from 5.2 to 8.1 cases/10 000 occupied bed days (OBDs) at one hospital and from 3.9 to 16.3/10 000 OBDs at the second hospital. In total, 80 patients with laboratory-confirmed CDI met eligibility criteria and consented to be in the study. More than half (53.8%) had hospital-onset disease, 28.8% had community-onset and healthcare facility-associated disease and 7.5% were community-associated infections according to the definitions used. Severe CDI was observed in 40.0% of these cases but the 30-day mortality rate for all cases was only 2.5%. Besides a shorter length of stay among cases of community-onset CDI, no characteristics were identified that were significantly associated with community-onset or severe CDI. From 70 isolates, 34 different ribotypes were identified. The predominant ribotypes were 014 (24.3%), 020 (5.7%), 056 (5.7%) and 070 (5.7%). Whereas this study suggests that the characteristics of CDI cases in Australia are not markedly different from those in other developed countries, the increase in CDI rate observed emphasizes the importance of surveillance.

Challenges for Standardization of Clostridium difficile Typing Methods

ABSTRACT Typing of Clostridium difficile facilitates understanding of the epidemiology of the infection. Some evaluations have shown that certain strain types (for example, ribotype 027) are more virulent than others and are associated with worse clinical outcomes. Although restriction endonuclease analysis (REA) and pulsed-field gel electrophoresis have been widely used in the past, PCR ribotyping is the current method of choice for typing of C. difficile. However, global standardization of ribotyping results is urgently needed. Whole-genome sequencing of C. difficile has the potential to provide even greater epidemiologic information than ribotyping.

Isolation of Clostridium difficile from faecal specimens--a comparison of chromID C. difficile agar and cycloserine-cefoxitin-fructose agar.

The culture of toxigenic Clostridium difficile from stool specimens is still seen as the gold standard for the laboratory diagnosis of C. difficile infection (CDI). bioMérieux have released ChromID Cdiff chromogenic agar (CDIF) for the isolation and identification of C. difficile in 24 h. In this study, we compared CDIF to pre-reduced cycloserine-cefoxitin-fructose agar with sodium taurocholate (TCCFA) in the examination of glutamate dehydrogenase-positive faecal specimens that were either GeneOhm positive or negative, using direct culture or culture following alcohol shock. Direct culture on CDIF had a sensitivity of 100 % and recovery of 94 % while for TCCFA these were 87 % and 82 %, respectively. For GeneOhm-positive alcohol-shocked faecal samples, sensitivity and recovery on CDIF was similar to direct culture while on TCCFA they were about 10 % higher. For direct culture, there was a significant difference between growth on CDIF at 24 h and TCCFA at 48 h (P = 0.001) and between the two media at 48 h (P<0.001). A total of 142 strains of C. difficile were recovered in pure culture from all GeneOhm-positive samples used in this study and 11 (7.7 %) of these were A(-)B(-)CDT(-) and may represent mixed infections of toxigenic and non-toxigenic C. difficile. The most dominant ribotype was UK 014 (14.7 %) followed by 002 (11.9 %) and 020 (11.9 %), and 36 % of toxigenic isolates, including an A(-)B(+)CDT(-) strain, could not be assigned a UK ribotype. CDIF outperformed pre-reduced TCCFA by negating the need for alcohol shock treatment and by giving a time saving of 24 h in the isolation of C. difficile. CDIF plates were also more selective than TCCFA and C. difficile colonies were easy to identify and subculture prior to strain typing.

Infection with Toxin A-Negative, Toxin B-Negative, Binary Toxin-Positive Clostridium difficile in a Young Patient with Ulcerative Colitis.

ABSTRACT Large clostridial toxin-negative, binary toxin-positive (A− B− CDT+) strains of Clostridium difficile are almost never associated with clinically significant C. difficile infection (CDI), possibly because such strains are not detected by most diagnostic methods. We report the isolation of an A− B− CDT+ ribotype 033 (RT033) strain of C. difficile from a young patient with ulcerative colitis and severe diarrhea.

Evaluation of the Cepheid Xpert C. difficile/Epi and Meridian Bioscience illumigene C. difficile Assays for Detecting Clostridium difficile Ribotype 033 Strains

ABSTRACT Clostridium difficile PCR ribotype 033 (RT033) is found in the gastrointestinal tracts of production animals and, occasionally, humans. The illumigene C. difficile assay (Meridian Bioscience, Inc.) failed to detect any of 52 C. difficile RT033 isolates, while all strains signaled positive for the binary toxin genes but were reported as negative for C. difficile by the Xpert C. difficile/Epi assay (Cepheid).

Improved recovery of Clostridium difficile spores with the incorporation of synthetic taurocholate in cycloserine-cefoxitin-fructose agar (CCFA)

Aim: Culture remains important for the detection and typing of Clostridium difficile. Culture of C. difficile spores can be enhanced on media supplemented with a germinant. Despite this, unsupplemented media continues to be used in some laboratories. The aim of this study was to quantify the effect of the known germinant sodium taurocholate on recovery of C. difficile spores and to determine if the supplement impacts on the recovery of vegetative C. difficile. Methods: The recovery on cycloserine-cefoxitin-fructose agar (CCFA) with and without taurocholate, of spore, vegetative, and total cell fractions of broth cultures of eight C. difficile isolates was compared. Results: Taurocholate in CCFA did not inhibit growth of vegetative C. difficile and significantly increased recovery of spores (p = 0.04). Conclusions: The routine incorporation of taurocholate in CCFA is recommended for improved sensitivity in C. difficile culture from specimens.

Inspiration from old dyes: tris(stilbene) compounds as potent gram-positive antibacterial agents.

Herein we describe the preparation and structure-activity relationship studies on range of stilbene based compounds and their antibacterial activity. Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin-resistant Staphylococcus aureus MRSA (ATCC 33592 and NCTC 10442). Compound 10 was most active against Moraxella catarrhalis with minimum inhibitory concentrations (MICs) of 0.12-0.25 μg mL(-1) and against Staphylococcus spp. with MICs ranging from 2-4 μg mL(-1). The derivative 17 showed increased activity with MICs of 0.06-0.25 μg mL(-1) against M. catarrhalis and 0.12-1 against Staphylococcus spp. This level of activity is similar to that reported for S. aureus for antibiotics, such as vancomycin, with MICs of ≤2.0 μg mL(-1) and clindamycin with MICs of ≤0.5 μg mL(-1). As an indicator of toxicity, 17 was tested for its ability to lyse sheep erythrocytes, and showed low haemolytic activity. Such results highlight the value of tris(stilbene) compounds as antibacterial agents providing suitable properties for further development.

Comparison of ChromID C. difficile agar and cycloserine-cefoxitin-fructose agar for the recovery of Clostridium difficile.

Aim: The rapidly changing epidemiology of Clostridium difficile infection highlights the need for improved and continuing surveillance involving stool culturing to enable molecular tracking. Culture of C. difficile can be difficult and time consuming. In this report ChromID C. difficile agar (CDIF) was compared to cycloserine-cefoxitin-fructose-egg-yolk agar which contained 0.1% sodium taurocholate (TCCFA) as a germinant. Results: All ribotypes of C. difficile tested (n = 90) grew well on CDIF within 24 h and most gave characteristic small irregular black colonies with a raised umbonate profile. Counts from standard suspensions of C. difficile at 24 h (p < 0.005) and 48 h (p = 0.01) were significantly higher on CDIF than on TCCFA. Similar results were achieved after alcohol shock. When temperature shock was used to differentiate vegetative cells and spores, the total number of culturable and vegetative cells on CDIF was significantly higher than on TCCFA (culturable cells, p = 0.003 at 24 h and p = 0.002 at 48 h; vegetative cells, p = 0.0003 at 24 h and p = 0.0002 at 48 h). Conclusions: These data suggest that CDIF is a better medium for the recovery of vegetative C. difficile than TCCFA and equal to TCCFA for spore recovery.