Anti-Adhesion Methods (World of Microbiology and Immunology)
The adhesion of bacteria and other microorganisms to nonliving and living surfaces is a crucial part of the contamination and infection processes. In fact, the growth of microorganisms on surfaces is the preferred mode of existence. The ability to block adhesion would prevent surface growth.
There are numerous examples of surface growth of microorganisms. Adherence and growth of bacteria such as Escherichia coli on urinary catheters (synthetic tubes that are inserted into the bladder to assist hospitalized patients in removing urine from the body) is a large problem in hospitals. The chance of a urinary tract infection increases by up to10% for each day of catheterization. Neiserria meningitidis, the agent that causes meningitis, relies upon adhesion with host cells. The adhesion of this and many other bacteria, including disease causing Escherichia coli, is mediated by a surface tube-like protein appendage called a pilus.
Other bacterial proteins are involved in adhesion, typically by recognizing and biding to another protein on the surface of the host cell. Microorganism proteins that function in adhesion are generically known as adhesins.
Some strains of E. coli that infect intestinal cells do so by manufacturing and then releasing an adhesin, which is incorporated into the membrane of the host cell. Thus, the bacteria install their own receptor in the host tissue.
Adhesion need not rely on the presence of adhesins. The chemistry of the surface can also drive adhesion. For example, the surface of the spores of bacillus and the capsule surrounding Pasteurella multocida are described as being hydrophobic; that is, they tend not to associate with water. This hydrophobicity will drive the spore or bacterium to associate with a surface of similar chemistry.
In order to block adhesion that is the result of the above mechanisms, the molecular details of these mechanisms must be unraveled. This is an on-going process, but advances are being made through research.
Adhesion of Escherichia coli can depend on the presence of an adhesin called FimH. Antibodies to FimH can block adhesion, presumable by binding to the FimH protein, preventing that protein from binding to the receptor on the surface of the host cell. Furthermore, the three-dimensional structure of this adhesion is similar to that of adhesins from other bacteria. A vaccine devised against FimH might then have some protective effect against the adhesion of other bacteria.
In the case of the capsule-mediated adhesion, such as the example above, capsular antibodies may also thwart adhesion. The drawback with this approach is that capsular material is not a potent stimulator of the immune system.
For microorganisms that secrete their own receptor, such as Escherichia coli, or which have receptor molecules protruding from their own surface (an example is the hemagglutinin protein on the surface of Bordetella pertussis), adhesion could be eliminated by blocking the manufacture or the release of the receptor molecule.
In Canada, field trials began in the summer of 2001 on a vaccine to the adhesin target of Escherichia coli O157:H7. This pathogen, which can be permanently debilitating and even lethal to humans who ingest contaminated food or water, often lives in the intestinal tracts of cattle. By eliminating the adhesion of the bacteria, they could be "flushed" out of the cattle. Thus, a vital reservoir of infection would have been overcome. The vaccine could be ready for the market by as early as 2003.
Another anti-adhesion strategy is to out-compete the target bacteria for the available spots on the surface. This approach has been successful in preventing bacterial vaginal infections. Suppositories loaded with bacteria called Lactobacillus are administered. Colonization of the vaginal wall by the Lactobacillus can retard or even prevent the subsequent colonization of the wall by a harmful type of bacteria. The same bacteria are present in yogurt. Indeed, consumption of yogurt may help prevent intestinal upset due to colonization of the gut by harmful organisms.
Non-living surfaces, such as catheters and other implanted material, are colonized by, in particular, bacteria. In seeking to prevent adhesion, scientists have been experimenting with different implant materials, with the incorporation of antimicrobial compounds into the implant material, and with the "pre-coating" of the material. In the case of antimicrobial compounds, promising results have been obtained in laboratory studies using material that can slowly release antibiotics. The disadvantage of this approach is that the presence of residual antibiotic could encourage the formation of resistance. Pre-coating implant material with an antimicrobial compound that is permanently bonded has also been promising in lab studies.
See also Biofilm formation and dynamic behavior; Infection and resistance; Probiotics