Virus Is Front-Line Fighter in Bacteria War
Scientists use bug to fight bug
FRIDAY, Dec. 7, 2001 (HealthDayNews) -- An enzyme produced by a virus literally chews up the cell walls of the Streptococcus pneumoniae bacteria and kills it, say scientists at Rockefeller University in New York City.
However, you won't be able to say goodbye to ear infections, meningitis and other ills any time soon, the researchers add. That's because the tests were done on mice, and even if a human application were available, it probably wouldn't be for general use.
Every year in the United States, S. pneumoniae causes about 7 million cases of otitis media, an ear infection that usually occurs in small children, and 60,000 cases of pneumonia, meningitis and other invasive diseases, 10 percent of which are fatal.
Up to 50 percent of children and 30 percent of adults harbor reservoirs of the bacteria in their nose and throat passages at any one time. When the bacteria reach a critical mass, they can trigger illness. Even if a person isn't sick, he can easily spread the bacteria to others, especially in such crowded places as daycare centers and old-age homes.
Pneumococcal vaccines exist but are mostly given to those over 65 and other high-risk people -- and the shots don't get at the root of the problem.
"We were looking for something new that would help us to treat or to kill Streptococcus pneumoniae," says Dr. Jutta Loeffler, lead author of the study and a post-doctoral associate in the Laboratory of Bacterial Pathogenesis at Rockefeller University. "We thought if we could eliminate the reservoir of bacteria, we would probably be able to reduce the incidence of disease significantly."
The scientists have found an apparent solution in the form of an enzyme purified from a bacteriophage, a virus that attacks and kills bacteria.
Although researchers have been using bacteriophages in research for decades, this is one of the first times the viruses have been investigated as a possible treatment.
"The concept of these viruses attacking bacteria is certainly not new, but potentially using a bacteriophage to treat infection or colonization is a novel idea," says Dr. Dennis L. Stevens, chief of infectious diseases at the Veterans Affairs Medical Center in Boise, Idaho. "It's not affected by resistance to antibiotics, so it provides a new avenue."
"Bacteriophages have been struggling with bacteria for eons, and they have developed over time an almost perfect way to kill them," says Loeffler. "We are basically using what the bacteriophage has learned over a very long time for our own fight against bacteria."
The researchers' findings appear in the Dec. 7 issue of Science.
In their study, the scientists at Rockefeller University were particularly interested in the enzyme Pal. Using test tubes, the team let the Pal enzyme loose on 15 different strains of S. pneumoniae, including three that are highly resistant to penicillin. The results were, literally, explosive.
Bacteria are wrapped in a fragile membrane that, in turn, is encased in a stiff cell wall structure. The enzyme made holes in the stiff outer wall, and the inner membranes leaked through and exploded. Most of the bacteria were killed within 30 to 40 seconds of contact.
The researchers then tried the enzyme on one type of the bacteria in lab rodents.
"I treated the mice, then flushed the nose to see how many bacteria were left, and in all the mice treated, there were no bacteria left," says Loeffler. Furthermore, a single dose of the enzyme prevented pneumococci from recolonizing the nose and throat area in the mice.
The technique is not fit for human consumption just yet, but Loeffler and her colleagues are hopeful.
"It's completely nondangerous for humans," she says, referring partly to the fact that the enzyme is highly specific and does not kill off any of the "good" flora in our bodies.
"There's a tremendous number of bacteria that reside in the throat that probably prevent infections. So you wouldn't want to get rid of them, or the area would get colonized with worse bugs, like staph," says Stevens. "This material is fairly specific, so that's good."
Even if the enzyme passes rigorous human testing, it probably won't be used as a panacea for the general population.
"I don't think you would want to put the enzyme in drinking water just to eradicate pneumococcus from everyone's throat," says Stevens. "You'd have to think of situations where it would be clinically useful."
Such sites could include daycare centers, nursing homes or even prisons. Several years ago, victims of an outbreak of pneumococcal meningitis at a jail in Houston might have benefited from just such a therapy. Certain people -- those with damaged immune systems, for instance -- might also benefit.
What To Do
Visit this site for more information on the work being done by Rockefeller University's Laboratory of Bacterial Pathogenesis and to see a video of Pal killing pneumococci in a test tube.