Staph Vaccine May Be on the Horizon

Researchers at Brigham and Women's Hospital and Harvard Medical School (Boston) have developed a vaccine that protects mice against multiple strains of Staphylococcus aureus (S. aureus), an increasingly stubborn microbe and the most common cause of hospital-acquired infections. The new vaccine is the first to be made from a bacterial molecule produced primarily during infection, rather than in laboratory culture. A report of the study, supported by the National Institute of Allergy and Infectious Diseases (Niaid), appears in the May 28, 1999, issue of Science.

"This is an intriguing finding and a hopeful step against a very worrisome pathogen," says Niaid Director Anthony S. Fauci. "Within the last two years, S. aureus has become increasingly resistant to antibiotics. Most troubling is the emergence of strains that are partially resistant to vancomycin, our last line of defense against S. aureus. New treatments and, ideally, an effective vaccine, are urgently needed."

Each year an estimated 500,000 patients in American hospitals contract staph infections. S. aureus, the chief culprit, also is a common source of community acquired infections, and causes illnesses that range from minor skin infections and abscesses to life-threatening diseases such as pneumonia, meningitis, bone and joint infections, and infections of the heart and bloodstream.

The research team identified a large sugar molecule that sits on the membrane of the microbe during infection known as PNSG (poly-N-succinyl Beta-1-6 glucosamine). This molecule was not found in laboratory grown cultures, leading the team to surmise that it might play an important role in the process of infection.

The scientists injected purified PNSG into rabbits, which produced large numbers of antibodies. These PNSG antibodies were then injected into mice, which were exposed to eight different strains of S. aureus, including strains resistant to the antibiotic methicillin and partially resistant to vancomycin.

None of the lab mice developed an infection.

"Presumably, these products are critical for infection and disease progression, and would therefore be logical targets for new therapeutics or vaccines," explains Gerald B. Pier, who led the research team that developed the new S. aureus vaccine.

"Our findings suggest that this vaccine has the potential to provide immunity to the multi-drug resistant S. aureus 'superbug' that we have heard alarming reports of in the last year or so," says Pier.

Pier and his colleagues note that in addition to S. aureus, other bacterial species classified as coagulase-negative staphylococci, or CoNS, also produce PNSG.

"Together, S. aureus and CoNS account for 40% to 60% of bacterial blood isolates from hospitalized patients," says Pier. "Therefore, an additional potential advantage of a PNSG vaccine might be protection against the spectrum of clinically important CoNS."

Pier adds that he and his colleagues hope to move the PNSG vaccine into human trials soon, but predicts that such trials are one to two years away. They currently are negotiating licensing rights for the vaccine.

For more information: Gerald B. Pier, Channing Laboratory, Harvard Medical School, 180 Longwood Ave., Boston, MA 02115. Tel: 617-432-2269. Fax: 617-731-1541. Email: gpier@warren.med.harvard.edu.