Clostridium difficile

Transcription

1 Clostridium difficile By Karla Givens Means of Transmission and Usual Reservoirs Clostridium difficile or C. diff., is transmitted by oral contact with feces containing bacterial spores. Reservoirs include patients, healthcare workers, surfaces, equipment, or other objects that have become contaminated.1 Once inside the human body, conditions are favorable enough to form back into its vegetative state, where the bacterium can grow, divide, and produce toxins.3 While prevalence is higher in hospital settings as one of the top nosocomial infections, community incidences are on the rise.2 Approximately 3% of adults and 70% of babies carry the bacteria in the large intestine without any negative side effects.3 Etiologic Agent, Its General Characteristics and Key Tests for Identification As a member of the Domain Bacteria and Kingdom Eubacteria, Clostridium difficile, is a unicellular prokaryote containing peptidoglycan in the cell wall.4 The bacterium is rod shaped with flagella evenly projecting around the surface, which allow it to move in a tumbling or forward motion.3 A gram- positive stain further classifies it in the Phylum Firmicutes, and then into the Class Clostridia because of its anaerobic properties. It is funneled into the Order Clostridiales with all others from Class Clostridia except those that live in extreme environments such as hot springs.4 It s ability to form endospores along with specific 16S rrna gene sequences place the bacteria in the Family Clostridiaceae, while it s inability to reduce sulfate to sulfide places it in the Genus Clostridium.4 Clostridium difficile is unique to others in its class because it generates two exotoxins, toxin A and toxin B.4 These exotoxins of the species are the etiological agent for antibiotic- associated diarrhea (AAD), pseudomembranous colitis (PMC), toxic megacolon, perforations of the colon, sepsis, and in rare cases death.1 It also generates ATP via amino acid fermentation.4 The heterotroph needs six amino acids for fermentative metabolism: leucine, isoleucine, proline, tryptophan, valine, and glycine.3

2 Several tests are available for identification. Stool cultures can be obtained and tested for the bacterium, but may also need to be further examined by testing isolates in toxigenic cultures in the incidence of a false- positive result with a nontoxigenic strain. These tests often take longer periods of time to complete, and must be done before the toxin degrades at room temperature, which can produce false- negative results. Due to the limitations of stool cultures, other non- culture tests are often used. 1 Molcular tests involving PCR assays test for the gene encoding only toxin B, not toxin A. However, it is highly accurate. The quickest test available involves testing for the Clostridium difficile antigen, specifically glutamate dehydrogenase, 5 using latex agglutination or immunochromatographic assays. These tests are non- specific making them primarily useful in combination with other tests. 1 Tissue culture cytotoxicitiy assays can detect toxin B only, but are considered less sensitive and not as readily available compared to toxogenic culture or PCR. Another toxin test, enzyme immunoassay, can detect either toxin A, B, or both. While these tests are quick, they are often insensitive compared to others. 1 In rare cases, a sigmoidoscopy or colonoscopy may be used to view the colon for immflamation or pseudomembranes to confirm diagnosis. 2 Historical Information The Greek word Clostridium translates to kloster or spindle, much like the rod- shaped of the bacterium. The species name, difficile, was given due to its complicated nature when culturing in the lab. 4 Hall and O Toole first isolated Clostridium difficile in 1935 from the stool of a healthy infant and named it Bacillus difficile. And although psuedomembranous colitis was first described in 1893, it was not until 1978 that George and his team associated C. diff. with this disease and attributed it to most cases of antibiotic- associated diarrhea (AAD). 5 Signs and Symptoms of The Disease The most common symptom of infection is watery diarrhea and can also included things such as fever, nausea, dehydration, decrease in appetite, and abdominal pain. 1 Severe cases may exhibit blood or pus in stool, swollen abdomen, kidney failure, increased white blood cell count, toxic megacolon, bowl perforation, or even death. 2 The infection often occurs in those taking antibiotics, over 65, those that have a severe underlying medical disorder, and those staying in a health care facility. 1 Microbial Virulence Mechanisms The main virulence factors for C. difficile are its toxins, Toxins A (TcdA) and B (TcdB). The Tcd toxins bind to host receptors and are transferred into the cytoplasm where they become

3 active. 6 They inactive GTP binding proteins such as RhoA, Rac1, and Cdc42, which results in disturbances in signaling cascades, a halt of cell cycle progression, and cytoskeletal integrity damage (see table below 10 ). Studies suggest that TcdB is the major toxin for virulence. 6 In addition, there exists genes for a binary toxins and high-grade fluoroquinolone resistance. 6 While in spore form, the bacteria can withstand severe conditions and are resistant to antibiotics. They are able to stay in the digestive track and cause reinfection at anytime, but usually following an extended period of antibiotic treatment. In addition, other factors such as fimbriae may contribute to the bacteria s ability to attach itself to the gut wall. 5 Control or Treatment for The Disease Although antibiotics can be used to treat a variety of things, they also destroy good bacteria in the gut, allowing C. diff. to take over and cause infection. That being said, it is important to only take antibiotics when needed. An antibiotic such as metronidazole, vancomycin, or fidaxomicin may be taken oral for approximately 10 days to treat severe infections. Reinfection occurs in about 20% of patients. This can be treated by fecal transplant from a healthy person, although the long term safety has not been documented. 1 As a last resort, surgery can be performed to remove infected areas of the colon. 2 Below is a table reflecting treatment therapy. 10

4 Prevention Hospital personnel follow strict infection-control guidelines in order to help prevent the spread of C. difficile. These guidelines include hand washing with soap and water before and after leaving any room, wearing disposable gloves and gowns when near an infected patient, efficient disinfection of surfaces with bleach, and avoidance of antibiotics unless necessary. 2 9

5 In addition, biotherapeutic approaches such as consuming probiotics like the yeast, Saccharomyces boulardii, in conjunction with antibiotics may prevent recurrent C. difficile infections. 1 Both Sanofi and Pfizer are undergoing clinical trials for vaccines to prevent C. diff infection. Pfizer reported last August that the vaccine received fast track status for the US FDA. 7 A recent study reported that hamsters that were infected with non- toxigenic strains of the bacteria did not develop infection when infected with historic epidemic strains. 8 Current Cases or Outbreaks Clostridium difficile is an ongoing epidemic. The Center for Disease Control states that at about 250,000 people require hospital care for Clostridium difficile infections and at least 14,000 people die each year. The threat to public health is considered urgent. 9 The distribution of ribotypes can be observed in the table below. The pathogen has been established in North America and Europe, but is just now emerging in Asia. 10 References

6 1. Clostridium difficile Infection. Center for Disease Control and Prevention. Updated February 25, 2015 [cited March 9, 2015]. Available from 2. C. difficile infection. Mayo Clinic. July 13, 2013 [ cited March 9, 2015]. Available from conditions/c- difficile/basics/causes/con General Characteristics of Clostridium difficile University of Wisconsin- La Crosse. Updated April 2009 [cited March 9, 2015]. Available from 4. Classification of Clostridium difficile. University of Wisconsin- La Crosse. Updated April 2009 [cited March 9, 2015]. Available from 5. Heinlen, Latisha and Ballard, Jimmy D. Clostridium difficile Infection. National Center for Biotechnology Information, U.S. National Library of Medicine. September 1, 2011 [cited March 9, 2015]. Available from 6. Dubberke, Erik, Haslam, David et. al. The Ecology and Pathobiology of Clostridium difficile Infections: An Interdisciplinary Challenge. Zoonoses Public Health Feb; 58(1): 4-20 [cited March 20, 2015]. Available from 7. Pfizer s C. difficile Vaccine in Phase II gets US FDA Fast Track Status. C Diff Foundation. August 28, 2014 [cited March 20, 2015]. Available from diffificle- vaccine- clinical- study/ 8. Bug vs. Bug: Benign C. Difficile strains keep fatal strains at bay. American Society for Microbiology. ScienceDaily. October [cited March 20, 2015]. < 9. Antibiotic Resistant Threats in the United States, Centers for Disease Control and Prevention [cited March 20, 2015]. Available from threats pdf 10. Burke, Kristin and Lamont, Thomas. Clostridium difficile Infection: A Worldwide Disease. Gut Liver Jan; 8(1): 1 6. [cited March 20, 2015]. Available from