“Hypervirulent” C. difficileFurthermore, a new strain is on the loose. C. difficile makes a toxin that destroys the lining of the colon, and the new strain produces 20 to 30 times as much of this toxin as older strains, Guglielmo says. The new, “hypervirulent” strain is much more likely to be associated with more severe disease, sometimes requiring surgical intervention. Both the normal strains and the hypervirulent strain are becoming more common on the East Coast and in Canada, Guglielmo says. While he was conducting rounds as an attending hospital pharmacist recently, Guglielmo encountered a patient who had been receiving chemotherapy as an outpatient and who had just been admitted to the hospital with diarrhea originally thought to be due to the chemotherapy. Despite a relatively normal abdominal exam, the patient had a high white blood cell count, suggesting a serious infection. The patient was treated immediately, without waiting for results of tests to detect C. difficile infection. He died the next day, before the positive test results came back.
This micrograph depicts Gram-positive C. difficile bacteria from a stool sample culture obtained using a .1µm filter.
Credit: Janice Haney Carr, Centers for Disease Control and Prevention
Antibiotics that Pose Infection Risk Differ Among Bacterial StrainsWith C. difficile, antibiotics are a double-edged sword. Some antibiotics increase risk of infection. But when C. difficile infection already has taken hold, other antibiotics are needed to combat it. A standard treatment for milder infections is metronidazole taken in pill form. More serious infections, including those triggered by the hypervirulent strain, require more aggressive treatment, Guglielmo says. Research has confirmed that the antibiotic of choice for potentially life-threatening infections should now be vancomysin, also taken orally, he says. Vancomycin concentrates in the gut, ground zero for C. difficile infection. Oral metronidazole acts in the gut, too, but it also is systemically absorbed into the bloodstream. “For severe infection, the treatment is the same, but the outcomes are far more problematic with the hypervirulent strain,” Guglielmo says. The antibiotics thought to increase risk for hypervirulent C. difficile are different from those earlier shown to increase risk for infection with normal strains. “With the older strains of C. difficile, clindamycin and beta-lactam antibiotics such as penicillin and the cephalosporins were the ones associated with C. difficile infection,” Guglielmo says. A different class of antibiotics called fluoroquinolones, the best known of which is ciprofloxacin, appears to foster infection with the hypervirulent strain of C. difficile. “While it’s not proven yet, there is a concern that the broad use of fluoroquinolones in the community is a risk factor for this hypervirulent form,” Guglielmo says.
Related Links:Antibiotic-Resistant Staph Bacterium Reveals its Deadly Secrets
Science Café, April 22, 2010