Stool culture is very effective in detecting C. difficile. Unfortunately, non-toxigenic strains will also grow, requiring strains to be tested for toxin production. The greatest disadvantage to culture is the length of time that is needed before results are available, which may be up to four days. However, antibiotic sensitivity testing following culture is useful for strain-typing that would provide necessary epidemiological information during nosocomial outbreaks.Colonies of C. difficile will appear white, flat, and spreading on blood agar (see top image on the right). Cycloserin- cefoxitin-fructose agar(CCFA) is a selective media that is used for isolation of C. difficile. There is however, no distinction between pathogenic and commensal strains, which all produce yellow colonies with a characteristic "ground glass" appearance. as shown in the bottom image on the right. The characteristic odor of "horse manure" aids in identification of C. difficile. Stool samples are directly inoculated onto CCFA and incubated in an anaerobic atmosphere at 37°C for 48 hours. Large, thin, gram-positive bacilli with spores will be observed on a Gram stain of a typical colony, as shown below.
Clostridium are gram-positive or gram-variable, spore-forming, catalase-negative anaerobic bacilli. More than 100 species are currently recognized, though relatively few are encountered in properly collected clinical specimens from humans. There are three types of infection associated with Clostridium species: Non-invasive: Toxin-mediated Invasive: Progressive infection with tissue destruction Purulent disease: Closed space (e.g., in the peritoneal cavity) mixed infection with multiple organisms.Clostridium are well known as the agents of these classic toxin-mediated diseases : DISEASE TOXIN INVOLVED CAUSATIVE ORGANISM Tetanus or "lock jaw" Tetanospasmin Clostridium tetani Myonecrosis/Gas gangrene Exotoxins Clostridium perfringens Botulism (severe food poisoning) Botulin Clostridium botulinum
|Clostridium difficile-associated Diarrhea|
Clostridium difficile-associated diarrhea (CDAD) is a unique hospital infection that occurs almost entirely in patients who have received previous antimicrobial treatment. Anaerobic gut flora are crucial to colonization resistance, so any disruption of the normal colonic flora (through illness, therapeutic procedures or, most commonly, antibiotic use) is essential to the pathogenesis of C. difficile infection. The association of CDAD with antibiotic use is significant. Early attention (1970s) focused on clindamycin but later on (1980s,1990s & continuing today) the cephalosporins, especially third generation, and broad spectrum penicillins (e.g., amoxycillin/ampicillin) were also implicated. The risk of CDAD is increased if C. difficile is resistant to the particular antimicrobial. In the case of clindamycin, C. difficile resistance is variable. Risk of infection due to a clindamycin-resistant strain increases with use of the drug. For the third generation cephalosporins, C. difficile is universally resistant; thus, any toxigenic strain is capable of causing CDAD during cephalosporin use. Other less commonly implicated antibiotics are the macrolides, e.g., erythromycin, azithromycin, clarithromycin. However, prolonged courses of any antibiotics will increase the risk of disease. Even those antibiotics used to treat colitis (metronidazole, for example) have sometimes been reported to cause CDAD.The fluoroquinolones have been in use since the 1980s. Ciprofloxacin was approved in 1987, but it is only in recent years with the emergence of the epidemic strain 027/NAP1/BI, which is resistant to the fluoroquinolones, that this class of drugs has been implicated in Clostridium difficile disease. The fluoroquinolones were initially considered to be low risk but their use has been increasing, both with hospital inpatients and in the community, and fluoroquinolones are now implicated as a risk factor for C. difficile infection. The newer fluoroquinolones, e.g., gatifloxacin, moxifloxacin, have better activity against anaerobes, but poor in vitro activity against C. difficile, thus increasing the likelihood of CDAD. The CDC now recommends that all fluoroquinolones, as a class, be used sparingly as each poses an increased risk for CDAD.