gram positive bacteria including clostridium

overview of one of gram positive bacteria

1. Gram positive

2. Background history. C. difficile was first described in 1935 from the feces of healthy newborns and was initially not thought to be a pathogen. It was named difficile because it grows slowly and is difficult to c ulture . It is a long slender Gram-positive, anaerobic bacillus bearing large, oval, and terminal spores. It is nonhemolytic , saccharolytic , and mild proteolytic .

3. C. difficile is the causative agent of antibiotic-associated diarrhea and colitis. C. difficile produces two antigenically distinct toxins: toxin A and toxin B. Toxin A is an enterotoxin and toxin B is a cytotoxin . Both the toxins contribute to pathogenesis of C. difficile colitis and diarrhea in humans. Both are proteins which bind to specific receptors present in the mucosa of the intestine. The toxins gain entry into cells and catalyze a specific alteration of Rho proteins and glutamyl transpeptidase (GTP)-binding proteins that help in actin polymerization, cytoskeletal architecture, and cell movement.

4. Epidemiology C .  difficile   is  part  of  the  normal  intestinal  flora  in  a  small number   of  healthy  people  and  hospitalized  patients.  In   contrast  with  the  original  belief  that  C.  difficile   disease  is restricted to hospitalized patients, it is now recognized that a significant proportion of individuals with C. difficile disease develops symptomatic disease outside the hospital. For most of these patients, they have a recent history of exposure to a health care facility, where they were presumably exposed to C. difficile , and antibiotic use. The disease develops in people taking antibiotics, because the drugs alter the normal enteric f lora , either permitting overgrowth of these relatively resistant organisms or making the patient more susceptible to exogenous acquisition of C. difficile . The disease occurs if the organisms proliferate in the colon and produce their toxins

5. Pathogenesis •Resistance to certain antibiotics may permit overgrowth or acquisition of C. difficile in patients receiving these drugs for other infections. •Enterotoxin ( toxinA ) promotes fluid secretion and intestinal hemorrhage (similar to choleratoxin ). • Cytotoxin ( toxinB ) damages mucosal membranes by depolymerizing cellular cytoskeleton. •Adhesion factor binds to human colon cells. •Spores are insensitive to oxygen and resistant to many disinfectants, including alcohol based hand cleaners, making their elimination from hospital environments difficult.

6. Laboratory Diagnosis Isolation of the C. difficile in stool culture documents colonization but not disease, so the diagnosis of disease is confirmed by demonstration of the enterotoxin or cytotoxin in a stool specimen from a patient with compatible clinical symptoms or detection of the C. difficile toxin genes directly in clinical specimens by nucleic acid amplification techniques. Commercial assays with high sensitivity and specificity are now available that provide results within a few hours of sample collection .

7. Diagnosis Diagnosis of C. difficile diarrhea is made by demonstration of C. difficile toxin in the feces by stool cytotoxin test and by enzyme-linked immunosorbent assay: ■ The stool cytotoxin test is the test of choice . In this test, diarrheal stool is filtered and then inoculated to Hep-2 and human diploid cell cultures. The demonstration of a cytopathic effect that is neutralized by specific antiserum indicates the presence of the toxin (positive test). Absence of cytopathic effect is considered a negative test. The test has a high sensitivity of 94–100% and a specificity of 99%. NOTE: Disadvantage of the test are that it is expensive and it requires a tissue culture facility.

8. ■ Several enzyme immunoassays with moderate sensitivity (69–87%) and high specificity (99–100%) are now commercially available for rapid detection of the toxin and diagnosis. The latex agglutination test has been employed to detect the presence of glutamate dehydrogenase, produced by C. difficile , for diagnosis of C. difficile diarrhea. The test shows a low sensitivity (48–59%) but a high specificity (95–96%). ■ Stool cultures, however, are not useful due to the presence of nontoxigenic strains of C. difficile in feces.

9. T reatment No treatment is necessary for asymptomatic carriers. Stoppage of the use of causative antibiotics may be the only treatment necessary for those with mild antibiotic-associated diarrhea without fever, abdominal pain, or leukocytosis. This approach allows for reconstitution of the normal colonic microflora and significantly reduces the risk of relapse. Patients with more severe diarrhea or colitis require treatment with antibiotics . Metronidazole is the drug of choice . Vancomycin and bacitracin are also effective. More than 95% of patients respond to 10 days of treatment with oral vancomycin , or oral or intravenous metronidazole.