Some bacteria are capable of forming a surrounding capsule that serves as a protective shield around a bacterium and help the cell to evade immune response. The formation of a granuloma is also a protective mechanism for bacterium. A granuloma is a lesion formed in response to infection by some intracellular pathogens. Viable bacteria are walled off in the granuloma and thus prevented from further colonization. In antigenic mimicry, a bacterial cell may be able to trick the immune system by presenting antigens (molecules recognized by antibodies) that are similar to host antigens. Immunological cells therefore have difficulty distinguishing between the bacterium and a host cell.
PUBLIC HEALTH AND ANTIBIOTIC RESISTANCE
When penicillin became widely available during the Second World War, it was a medical miracle. Discovered initially by a French medical student, Ernest Duchesne, in 1896, and then rediscovered by Scottish physician Alexander Fleming in 1928, the product of the soil mold Penicillium halted the progression of many types of disease-causing bacteria. But just four years after drug companies began mass-producing penicillin in 1943, microbes began appearing that could resist it (4). The first bug to battle penicillin was Staphylococcus aureus. This bacterium is often a harmless passenger in the human body, but it can cause illness, such as pneumonia or toxic shock syndrome, when it overgrows or produces a toxin.
In 1967, another type of penicillin-resistant pneumonia caused by Streptococcus pneumoniae and called pneumococcus, surfaced in a remote village in Papua New Guinea. At about the same time, American military personnel in Southeast Asia were acquiring penicillin-resistant gonorrhea from prostitutes. In 1983, a hospital-acquired intestinal infection caused by the bacterium Enterococcus faecium joined the list of bacterium that was resistant to penicillin.
Antibiotic resistance spreads fast. Between 1979 and 1987, for example, only 0.02% of pneumococcus strains infecting a large number of patients surveyed by the national Centers for Disease Control and Prevention were penicillin-resistant (3). Today, 6.6% of pneumococcus strains are resistant, according to a report in the June 15, 1994, Journal of the American Medical Association by Robert F. Breiman, M.D., and colleagues at CDC (2). The agency also reports that in 1992, 13,300 hospital patients died of bacterial infections that were resistant to antibiotic treatment.
New forms of bacteria have mutated into resistant strains that can counteract modern antibiotic drugs. The Centers for Disease Control in Atlanta, GA reports that organisms now exist that are resistant to every known antibiotic drug (3). The emergence of bacterial strains that are resistant to treatment by current antibiotics is an important public-health concern. Antibiotics are chemical substances produced by microorganisms that inhibit bacterial growth or kill bacterial cells. It is apparent that bacteria are mutating to become resistant to once effective antibiotics. Since antibiotics first became widely used in the World War II era, countless lives have been saved, and serious complications of many diseases and infections have been attenuated. However, after more than 50 years of widespread use, many antibiotics are exhibiting a diminished effect. Some bacteria have developed ways to resist the effects of antibiotics. Widespread use of antibiotics is thought to have spurred evolutionary changes in bacteria. Diseases such as tuberculosis, gonorrhea, malaria, and childhood ear infections are more difficult to treat today than they were decades ago. Drug resistance is an especially difficult problem for hospitals because they harbor critically ill patients who are more vulnerable to infections than the general population and therefore require more antibiotics. Heavy use of antibiotics in these patients increases bacterial mutations that bring about drug resistance (4).
Nearly two million patients in the United States get an infection in the hospital each year. Of those patients, about 90,000 die each year as a result of their infection-up from 13,300 patient deaths in 1992 (3). More than 70% of the bacteria that cause hospital-acquired infections are resistant to at least one of the drugs most commonly used to treat them.
Infectious bacteria adapt quickly to new environmental conditions. Bacteria have small numbers of genes, and a single random gene mutation can greatly affect their ability to cause disease. Most microbes reproduce by dividing every few hours, which results in rapid bacterial evolution. A mutation that helps a microbe survive exposure to an antibiotic drug quickly becomes dominant throughout the microbial population.
Bacteria are capable of controlling the ecosystem, and are often responsible for the creation of viruses that wipe out dangerous organisms. Life would not be possible without bacteria. If every bacterium in the human body was eliminated, life could not be sustained. In addition, a balance of bacteria is essential for sustaining life. Essentially, bacteria would survive without human hosts, but humans could bot survive without bacteria.
In addition to other ecological roles, procaryotes, especially bacteria, are used industrially in the manufacture of foods, drugs, vaccines, insecticides, enzymes, hormones and other useful biological products. The genetic systems of bacteria are the foundation of the biotechnology industry. In the foods industry, lactic acid bacteria such as Lactobacillus and Streptococcus are used the manufacture of dairy products such as yogurt, cheese, buttermilk, sour cream, and butter. Lactic acid fermentations are also used in pickling process. Bacterial fermentations can be used to produce lactic acid, acetic acid, ethanol or acetone. In many parts of the world, various human cultures ferment indigenous plant material using Zymomonas bacteria to produce the regional alcoholic beverage. For example, in Mexico, a Maguey cactus (Agave) is fermented to "cactus beer" or pulque. Pulque can be ingested as is, or distilled into tequila. In the pharmaceutical industry, bacteria are used to produce antibiotics, vaccines, and medically useful enzymes.
Bacterial products are used in the manufacture of vaccines for immunization against infectious disease. Vaccines against diphtheria, whooping cough, tetanus, typhoid fever and cholera are made from components of the bacteria that cause the respective diseases. It is significant to note here that the use of antibiotics against infectious disease and the widespread practice of vaccination (immunization) against infectious disease are two twentieth-century developments that have drastically increased the quality of life and the average life expectancy of individuals in developed countries.
The biotechnology industry uses bacterial cells for the production of human hormones such as insulin and human growth factor (protropin), and human proteins such as interferon, interleukin-2, and tumor necrosis factor. These products are used for the treatment of a variety of diseases ranging from diabetes to tuberculosis and AIDS.
Bacteria are often the cause of human and animal disease, yet probiotic bacteria far outnumber the pathogenic variety in the body. Probiotic bacteria maintain a system of checks and balances and can inhibit the growth of harmful, disease-causing bacteria. Probiotic bacteria are especially prevalent in the gastrointestinal or GI tract and may assist in the digestion of food and the absorption of essential vitamins. In addition, probiotic bacteria modulates the immune system in helping to fight infection. Research suggests a positive correlation between health maintenance and an increase of friendly bacteria in the body.
1. Bergey's Manual of Systematic Bacteriology (2nd Edition). 1989. Williams, S.T., Sharpe, M.E., Holt J.G. Lippincott Williams & Wilkins
2. Breiman RF, Butler JC, Tenover FC, Elliott JA, Facklam RR. (1994). Emergence of drug-resistant pneumococcal infections in the United States. JAMA. 1994 Jun 15;271(23):1831-5.
3. Center for Disease Control and Prevention. Antibiotic/Antimicrobial resistance. http://www.cdc.gov/drugresistance/actionplan/html/
4. Jones RN, Pfaller MA (1998). Bacterial resistance:…