Humans are not the only ones whose survival depends on keeping together
it is not only humans that have understood the importance of sticking together for success. For long we have known that animals also keep together for survival. But few expected that tiny microbes also adopt this strategy to ward off the efforts of drugs and doctors to finish them. Now scientists are increasingly recognising this new weaponry in the hands of the bugs. That the bacteria have learnt to counter the might of both the immune system and antibiotics thrown at them to combat infections by this new strategy has just been reported.
Such treatment has generally proved ineffective if bacteria cluster in colonies called biofilms. Biofilms are organised groups of bacteria that work together to defend against attack from antibiotics and the body's immune system. Biofilms can grow from a bacterium that attaches to a surface, such as a cell lining a blood vessel. The bacterium may then begin to multiply and spread across the surface. When the cells reach a certain density, they build a complex biofilm structure. The all pervasive nature of this slimy conglomerate can be understood by the fact that they cause problems in a host of varied infections and organs. Biofilms foul tubules and implants, such as heart valves and artificial hips and they attack body tissues like teeth and gums, the lungs, the ears, and the urogenital tract.
According to the best known disease sleuths at the Centres for Disease Prevention and Control, Atlanta, usa , an estimated 65 per cent of all human bacterial infections involve biofilms ( Science , Vol 283, No 5409). Bacteria sequestered in biofilms are shielded from attack by the hosts' immune system and are often much harder to kill with antibiotics than their free floating cousins, says William Coserton, director of the Centre for Biofilm Engineering at Montana State University in Bozeman. This is why it is hard to rid the body permanently of some infections, such as those of the ear or the urinary tract.
Take for example the largest kind of infection suffered by humans -- dental caries. The bacteria living in the mouth synthesise gummy adhesives that accumulate on the teeth, gums, and tongue. Researchers have discovered that the wily bacteria attach themselves to solid surfaces in areas such as the mouth where they might be otherwise washed away. The bacteria thus create dental plaque, tooth decay and gum disease.
It can be fatal in the lungs of patients with cystic fibrosis. Nels Holby of the University of Copenhagen in Denmark showed that biofilms containing Pseudomonas aerogenosa clog the lungs of 80 to 90 per cent of their patients. This eventually leads to death due to respiratory failure. Antibiotics do kill some germs but what saves the germs from the onslaught of the drugs is the biofilm. Similar viscous clumps have been discovered in the sputum of patients with tuberculosis. Researchers suspect that biofilms formed by Mycobacterium tuberculosis helps them successfully hide inside the lungs.
Besides affecting the urinary tract, there is evidence now to link such infection with prostatitis, a common inflammation of the prostrate gland that produces chronic pain and sexual dysfunction. It was perplexing, until recently, since no bacteria could be cultured from prostatic fluid.
Subsequent studies through electronic the micrograph showed that the inflammation was due to the biofilms of the bacterium. Now that researchers are beginning to understand biofilms, the fight to combat the new strategy by the germs has begun in right earnest. "It has become more and more clear that we need to begin to think of bacteria in groups working together," writes E. Peter Greenberg, professor of microbiology at the University of Iowa, Iowa City ( Science , Vol 284, No 5416). Microbiologists are beginning to document the changes that allow bacteria to form biofilms -- information that could help design new therapies. But as Dennis Mangan of the National Institute of Dental and Craniofacial Research, who is spearheading these efforts says: "We still do not know how to treat or prevent biofilms. That's a big reason for more research."
Among the strategies adapted is the identification of biochemical signals for the formation of biofilms by the bacteria. Any battle plan against biofilm infections will need to involve strategies for compromising the bacteria's sense of community, Greenberg said.
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