Clues To New Anti-Microbial Treatments

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Dartmouth Research Offers Clues To New Anti-Microbial Treatments

HANOVER, NH -- The race to stay ahead of bacteria that develop resistance to

frequently used antibiotics may be paying off. Dartmouth Medical School (DMS)

researchers have discovered how to block a pathway many bacteria use to infect

organisms.

Dr. , professor of microbiology, and Christian LaPointe, a graduate

student, report a way to inhibit the enzyme that many types of bacteria need to

infect and damage a variety of hosts, from plants to humans. Their work,

reported in the January 14 issue of the Journal of Biological Chemistry, could

provide a foundation for developing new agents to combat bacterial infections.

" In this age of antibiotics, people have come to expect a ready cure for the

majority of common ailments caused by infectious microbes, from acne to ear

aches. However, the microbes have been fighting back, and increasing numbers are

becoming resistant to all available antibiotics at an alarming rate, " says

.

" These recent findings may advance screening for additional compounds that can

be developed into novel therapeutic or prophylactic antimicrobial agents, at a

time when many of the mainstay antibiotics are no longer useful due to the

development of resistant bacteria. "

's laboratory has delineated mechanisms for a common bacterial enzyme or

protease that bacteria need to secrete their toxins or other virulent factors

that cause damage. Treating bacteria with compounds to prevent protease function

could augment therapies against a number of infectious diseases. For example

protease inhibitors have been used with success to inhibit replication of the

Human Immunodeficiency Virus (HIV-1) in AIDS.

Their work, says , might be a useful adjunct for cystic fibrosis treatment

by inhibiting the growth of Pseudomonas that colonizes patients' lungs and is

notable for resistance to antibiotics. It might lead to particularly useful

approaches against infections such as meningitis by providing a way to clear

bacteria without the potential complication of toxic shock that is associated

with conventional treatments.

The researchers have identified the active site and biochemical pathway for type

four prepilin peptidase (TFPP), a protease that cleaves the precursor form of

pilin and related proteins prior to their secretion by bacteria. Pilins are

protein building block subunits of hair-like fibers called pili that protrude

from the bacterial surface and allow pathogenic bacteria to colonize on or in

their hosts. Related proteins, termed pilin-like proteins, form channels across

the bacterial membrane to facilitate the movement of toxins or other virulent

factors the bacteria produce. If the TFPP function is absent, neither the pili

nor the secretion apparatus can form and the pathogenic bacteria cannot spread

or cause disease.

The Dartmouth researchers developed an assay to monitor TFPP activity in the

laboratory and used the assay to identify a compound that inhibited the TFPP

activity. They found that the compound worked the way their genetic analysis had

predicted and demonstrated that the TFPPs represent a novel family, unlike other

proteases.

and his colleagues tested the activity of the TFPP in the Vibrio cholerae

bacterium, which the laboratory studies. The organism causes cholera, a severe

life-threatening diarrheal disease spread by ingestion of contaminated water or

food. Cholera is not common in the United States due to efficient sewage

treatment, but it is a large problem in many areas of the world. The recent

findings could also lead to therapies for use in conjunction with the primary

form of cholera treatment that relies heavily on rehydrating the patient.

V. cholerae bacteria secrete two major virulent factors that are both needed to

cause disease. One is cholera toxin (CT), which enters intestinal cells of an

infected individual, causing them to lose copious amounts of fluid and

electrolytes that leads to rapid dehydration serious enough to be fatal. The

second factor is the toxin coregulated pilus (TCP) that allows the bacterium to

colonize the human intestine. Without colonization, toxin production and

delivery to the host cannot occur.

Each factor utilizes a different member of the TFPPs during transport outside

the bacterium and both of these corresponding TFPPs, termed VcpD for toxin

secretion and TcpJ for pilin secretion, were first discovered in the

laboratory. These two TFPPs were the model molecules used to work out the

mechanisms of action and inhibition for the TFPPs that have been identified in

at least 50 bacterial species.

The research was funded by grants from the National Institutes of Health.

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Note: This story has been adapted from a news release issued by Dartmouth

Medical School for journalists and other members of the public. If you wish to

quote from any part of this story, please credit Dartmouth Medical School as the

original source. You may also wish to include the following link in any

citation:

http://www.sciencedaily.com/releases/2000/01/000113233426.htm