Unit 4. Bacteria

Soap and water and common sense are the best disinfectants.

Sir William Osler, Canadian physician and Oxford professor of medicine

Exercise 1. What do you know about bacteria?

1. What is a bacterium? Why are bacteria classified into a separate Kingdom?

2. What is the difference between eubacteria and archaebacteria?

3. How are archaebacteria adapted to survive in the extreme conditions of their habitat?

4. What processes and mechanisms do bacteria use to obtain energy and nutrients?

5. What is the purpose of Gram staining?

6. How do bacteria reproduce? What is the difference between binary fission and conjugation?

7. What are the functions of bacteria in the environment?

8. What is their significance for humans?

9. In what ways do disease-causing bacteria damage human organism?

Exercise 2. Explain the following terms in English:

prokaryote strain colony pathogen endospore

antibiotics resistance (to antibiotics) nitrogen fixation obligate aerobes obligate anaerobes

coccus bacillus spirillum Staphylococcus bacteria Streptococcus bacteria

Exercise 3. Read and translate the following text.

Antibacterial Products May Do More Harm Than Good

Antibacterial soaps and other cleaners may actually be aiding in the development of superbacteria.

By Coco Ballantyne

Tuberculosis, food poisoning, cholera, pneumonia, strep throat and meningitis: these are just a few of the unsavory diseases caused by bacteria. Hygiene—keeping both home and body clean—is one of the best ways to curb the spread of bacterial infections, but lately consumers are getting the message that washing with regular soap is insufficient. Antibacterial products have never been so popular. Body soaps, household cleaners, sponges, even mattresses and lip glosses are now packing bacteria-killing ingredients, and scientists question what place, if any, these chemicals have in the daily routines of healthy people.

Traditionally, people washed bacteria from their bodies and homes using soap and hot water, alcohol, chlorine bleach or hydrogen peroxide. These substances act nonspecifically, meaning they wipe out almost every type of microbe in sight—fungi, bacteria and some viruses—rather than singling out a particular variety. Soap works by loosening and lifting dirt, oil and microbes from surfaces so they can be easily rinsed away with water, whereas general cleaners such as alcohol inflict sweeping damage to cells by demolishing key structures, then evaporate. "They do their job and are quickly dissipated into the environment," explains microbiologist Stuart Levy of Tufts University School of Medicine.

Unlike these traditional cleaners, antibacterial products leave surface residues, creating conditions that may foster the development of resistant bacteria, Levy notes. For example, after spraying and wiping an antibacterial cleaner over a kitchen counter, active chemicals linger behind and continue to kill bacteria, but not necessarily all of them. When a bacterial population is placed under a stressor—such as an antibacterial chemical—a small subpopulation armed with special defense mechanisms can develop. These lineages survive and reproduce as their weaker relatives perish. "What doesn't kill you makes you stronger" is the governing maxim here, as antibacterial chemicals select for bacteria that endure their presence.

As bacteria develop a tolerance for these compounds there is potential for also developing a tolerance for certain antibiotics. This phenomenon, called cross-resistance, has already been demonstrated in several laboratory studies using triclosan, one of the most common chemicals found in antibacterial hand cleaners, dishwashing liquids and other wash products. "Triclosan has a specific inhibitory target in bacteria similar to some antibiotics," says epidemiologist Allison Aiello at the University of Michigan School of Public Health.

When bacteria are exposed to triclosan for long periods of time, genetic mutations can arise. Some of these mutations endow the bacteria with resistance to isoniazid, an antibiotic used for treating tuberculosis, whereas other microbes can supercharge their efflux pumps—protein machines in the cell membrane that can spit out several types of antibiotics, Aiello explains. These effects have been demonstrated only in the laboratory, not in households and other real world environments, but Aiello believes that the few household studies may not have been long enough. "It's very possible that the emergence of resistant species takes quite some time to occur…; the potential is there," she says.

Apart from the potential emergence of drug-resistant bacteria in communities, scientists have other concerns about antibacterial compounds. Both triclosan and its close chemical relative triclocarban (also widely used as an antibacterial), are present in 60 percent of America's streams and rivers, says environmental scientist Rolf Halden, co-founder of the Center for Water and Health at Johns Hopkins Bloomberg School of Public Health. Both chemicals are efficiently removed from wastewater in treatment plants but end up getting sequestered in the municipal sludge, which is used as fertilizer for crops, thereby opening a potential pathway for contamination of the food we eat, Halden explains. "We have to realize that the concentrations in agricultural soil are very high," and this, "along with the presence of pathogens from sewage, could be a recipe for breeding antimicrobial resistance" in the environment, he says.

Triclosan has also been found in human breast milk, although not in concentrations considered dangerous to babies, as well as in human blood plasma. There is no evidence showing that current concentrations of triclosan in the human body are harmful, but recent studies suggest that it acts as an endocrine disrupter in bullfrogs and rats.

Further, an expert panel convened by the Food and Drug Administration determined that there is insufficient evidence for a benefit from consumer products containing antibacterial additives over similar ones not containing them. "What is this stuff doing in households when we have soaps?" asks molecular biologist John Gustafson of New Mexico State University in Las Cruces. These substances really belong in hospitals and clinics, not in the homes of healthy people, Gustafson says.

Of course, antibacterial products do have their place. Millions of Americans suffer from weakened immune systems, including pregnant women and people with immunodeficiency diseases, points out Eugene Cole, an infectious disease specialist at Brigham Young University. For these people, targeted use of antibacterial products, such as triclosan, may be appropriate in the home, he says. In general, however, good, long-term hygiene means using regular soaps rather than new, antibacterial ones, experts say. "The main way to keep from getting sick," Gustafson says, "is to wash your hands three times a day and don't touch mucous membranes." (From Scientific American Online, June 07, 2007)

Exercise 4. Using the information from the text and other facts you know prove that:

1. Hygiene is one of the most important medical achievements of human civilization.

2. Pharmaceutical companies and the media are heavily promoting antibacterial products.

3. There are a lot of traditional substances effective to maintain hygiene.

4. Antibacterial components of modern cleaners stimulate the development of resistant bacteria.

5. Bacteria can develop resistance even to those antibiotics they have never come in contact with.

6. More research is needed to demonstrate the negative effects of antibacterial products in the household.

7. Antibacterial products can contaminate both households and the environment.

8. They can also present potential danger for human health.

9. There are some categories of people who really require additional antibacterial protection.

Exercise 5. Make 15 two-word expressions connected with medical treatment by combining words from the two lists: A and B. Then match each expression with the appropriate phrase below. The first one has been done for you as an example.

A allergic balanced bedside biological bone brain clinical digestive general general heart malignant plastic primary surgical

B anaesthetic attack clock death diet intervention manner marrow practitioner reaction surgery system tooth trial tumour

1. A condition in which the heart has a reduced blood supply because one of the arteries becomes blocked by a blood clot, causing myocardial ischaemia and myocardial infarction (heart attack)

2. A substance given to make someone lose consciousness so that a major surgical operation can be carried out

3. Soft tissue in cancellous bone.

4. The treatment of disease or other condition by surgery.

5. Any one of the first twenty teeth which develop in children between about six months and two-and-a-half years of age, and are replaced by the permanent teeth at around the age of six.

6. Surgery to repair damaged or malformed parts of the body.

7. A condition in which the nerves in the brain stem have died, and the person can be certified as dead, although the heart may not have stopped beating.

8. The way in which a doctor behaves towards a patient, especially a patient who is in bed.

9. An effect produced by a substance to which a person has an allergy, such as sneezing or a skin rash.

10. A trial carried out in a medical laboratory on a person or on tissue from a person.

11. A tumour which is cancerous and can grow again or spread into other parts of the body, even if removed surgically.

12. A doctor who provides first-line medical care for all types of illness to people who live locally, refers them to hospital if necessary and encourages health promotion.

13. The rhythm of daily activities and bodily processes such as eating, defecating or sleeping, frequently controlled by hormones, which repeats every twenty-four hours.

14. The set of organs such as the stomach, liver and pancreas which are associated with the digestion of food.

15. A diet that provides all the nutrients needed in the correct proportions.

Exercise 6. Fighting Bacteria.

Divide into two groups. Each group should read either Text A or Text B about two unusual methods of fighting bacteria. Then in pairs discuss your text with the partner. Try not to miss any details.

Text A. Tea Aids Oral Health

By Sarah Graham

A spot of tea may offer more than just a pleasant way to pass the afternoon. Research findings presented this week at the 103rd General Meeting of the American Society for Microbiology in Washington, D.C. suggests that it can help fight bad breath and may boost the powers of toothpaste.

Christine Wu and Min Zhu of the University of Illinois at Chicago College of Dentistry isolated chemical components of tea leaves known as polyphenols and tested them against three species of bacteria known to cause bad breath. The researchers found that the compounds, specifically catechins and theaflavins, inhibited growth of the oral bacteria over a 48-hour incubation period. What is more, lower concentrations of the chemicals interfered with the enzyme that catalyzes the production of hydrogen sulfide, which has the notorious smell of rotten eggs, and reduced its production by 30 percent. The compounds studied by the scientists are present in both green tea and black tea, although they are more abundant in the latter.

In a second study, researchers reported that green tea may provide additional benefits. Milton Schiffenbauer of Pace University and his colleagues tested tea's ability to fight bacteria that cause infections such as strep throat and dental caries. They found that green tea extracts and polyphenols--particularly those from caffeinated beverages--inhibited bacterial growth. Adding these agents to toothpaste and mouthwash, he notes, may make them more effective at combating microbial agents. (From Scientific American Online, May 21, 2003)

Text B. Scientists Explain Why Vegetable Recipes Skimp on Spices

By Kate Wong     

Several years ago, a team of researchers from Cornell University proposed that the spices used in traditional meat-based cuisines originally served not as flavor, but to stave off bacteria and fungi. Now new research is providing further food for thought: findings reported in the June issue of Evolution and Human Behavior explain why vegetable-based dishes tend to lack such spiciness.

Plants, it turns out, don't require so much protection against microorganisms as meats because they have their own natural chemical and physical defenses, which continue to function after cooking. Cornell neurobiologist Paul W. Sherman and undergraduate Geoffrey Hash thus predicted that if spices first served as antimicrobials, especially in warmer climates, vegetable recipes in the same countries surveyed for the meat research should feature fewer spices. Subsequent investigation bore this out. Analyzing 2,129 traditional vegetable recipes from 36 different countries, the team found that spice usage was far lower than that found in meat-based dishes from the same cultures. Indeed, of the 41 spices considered, 38 appear more frequently in meat recipes; the three that don't fit this pattern - sesame, caraway and sweet pepper - offer little protection anyway.

"Humans have always been in a co-evolutionary race with parasites and pathogens in foods, and our cookbooks are the written record of that race," Sherman asserts. "We haven't had to 'run' as hard when we ate vegetables. We haven't had to use extra pharmaceuticals to make vegetables safe for consumption." (From Scientific American Online, July 11, 2001)

Exercise 7. Speak about bacteria and their role on our planet. Summarize all facts which have been discussed in this unit.