KINGDOM MONERA: THE BACTERIA

Prokaryotic cells:

Bacteria (bacterium, singular) are microorganisms that lack a nucleus, do not have membrane-bounded organelles except for ribosomes, and have a cell wall composed of peptidoglycan, a protein-sugar molecule.

A cell covering of this type is never found in eukaryotic (e.g. human) cells which makes it possible to attack pathogens without unduly damaging human cells.

What would happen if a medication prevented formation of new cell wall?

Bacteria are the most common organisms on earth and are intimately connected to the lives of all organisms.

Size:

Most bacteria are less than 1 micron (0.001 mm) in length. Remember a mm is the thickness of a dime.

Hundreds of thousands of bacteria can fit into a space the size of the period at the end of a sentence.

However, colonies of bacteria, such as those found on a laboratory culture plate can be viewed easily without a microscope.

Classification �

Bacteria are often classified on the basis of their physical shapes of which there are 3 main:

Bacteria can be spherical (cocci), and then classified as diplococci, streptococci, or staphylococci.

Some are rod-shaped (bacilli)

Others are corkscrew-shaped (spirochetes).

Another classification system divides bacteria into gram-negative or gram-positive according to the composition of their cell walls, a distinction identified by a staining technique called the Gram stain.

Scientists also classify bacteria according to whether or not they require oxygen to survive.

Bacteria that require oxygen are called aerobic bacteria, or aerobes.

Bacteria that live without oxygen are called anaerobic bacteria, or anaerobes. Some anaerobes cannot reproduce if there is even a trace of oxygen.

Botulism from improperly canned foods can be fatal.

Tetanus from puncture wounds can also be fatal.

Bacteria are also classified by their methods of obtaining carbon and energy. Carbon is the element needed to build the complex molecules required for life, and energy is required to carry out all life activities.

Some bacteria are autotrophs, organisms that obtain carbon from carbon dioxide. Autotrophs derive energy from different sources.

Photoautotrophs, represented by the cyanobacteria (formerly known as the blue-green algae), derive their energy from light and use it to carry out photosynthesis, the process in which light energy is converted to the chemical energy of glucose.

Chemoautotrophs, derive their energy from inorganic compounds such as hydrogen sulfide and use the energy to power the cell's activities. Found deep in the ocean where there is no light (a surprise to science when found some years ago).

The vast majority of bacteria are heterotrophs, organisms that obtain carbon by ingesting organic molecules released from decaying organisms or by being parasites in animals, including humans, although they may cause no disease and may even be helpful in some cases.

Structure �

Like all cells, bacteria contain genetic material known as deoxyribonucleic acid (DNA).

However, the DNA of bacteria is arranged in a single circular chromosome, unlike the DNA of eukaryote cells, which is arranged in several to many rod-shaped chromosomes. (Draw on board).

Bacteria also often have additional DNA in the form of smaller rings called plasmids.

Many bacteria feature small protrusions from their outside cell surface known as pili (singular, pilus).

These hairlike outgrowths assist the bacteria in attaching to teeth, intestines, rocks, and other surfaces. Sex pili are involved in reproduction.

Other hairlike extensions called flagella (singular, flagellum) are much longer than pili and can be found at either or both ends of a bacterium or all over its surface. Flagella beat in a propeller-like motion to help the bacterium move toward nutrients, away from toxic chemicals, or, in the case of the photosynthetic cyanobacteria, toward the light.

Some bacteria form thick-walled structures known as endospores in response to lack of nutrients or water. These thick-walled bodies are extremely resistant to environmental stresses and enable bacteria to survive harsh conditions for decades or even centuries.

Break from spores when favorable conditions occur.

Capsules: a slimy layer outside the cell walls of some which makes the bacteria resistant to phagocytosis. (Draw on board).

Reproduction �A bacterium reproduces by means of a process called binary fission.

In binary fission, the single chromosome is replicated, the bacteria divides into two cells, and each cell receives one chromosome.

The two cells are thus genetically identical.

Most bacteria reproduce quickly, some every 20 minutes. (Could produce more than a billion in 10 hours if had enough food and wastes removed.)

Bacterial growth curve is bell-shaped in keeping with events (draw on board).

Binary fission does not provide bacteria with a way to acquire genetic diversity. Such diversity is necessary to enable a species to withstand changing environments. Many higher organisms gain genetic diversity through the union of reproductive cells from two parents. Lacking this capability, bacteria shuffle DNA between cells by several processes, including transformation, conjugation, and transduction.

In transformation, bacteria take up fragments of DNA released into the soil or water as dead bacteria are decomposed. These fragments then taken up & incorporated into DNA by other bacteria.

In conjugation, a donor bacterium attaches itself to a recipient bacterium, generates a tube called a pilus, and transfers fragments of plasmid DNA to the recipient. Does this amount to sex?

Transduction involves the transfer of DNA fragments between bacteria cells by a bacteriophage, a virus that infects bacteria. Potential use in correcting gene defects-discuss.

Through mixing genetic material, bacteria share new traits, including the ability to withstand changes in acidity and temperature, and resistance to antibiotics. Discuss development of drug resistance.

Disease �

Of the thousands of bacterial species on the earth, only a small fraction cause disease.

Nevertheless, the history of human cultures around the world has been greatly shaped by bacterial infections.

Outbreaks of plague, the deadly disease caused by the bacterium Yersinia pestis, have killed hundreds of millions of people throughout recorded history.

Why study the Black Death? Quite simply, because it was a pivotal episode in human history.

No single event in all of medieval Europe was as horrifying or as devastating.

Every individual was touched by it in some frightful manner; those who did not suffer from the disease themselves fled from it in terror as their loved ones died.

The Black Death, which was at first called the Great Mortality or simply the Pestilence, originated in Asia in the early 1340s.

It probably began in China, and from there it spread to India, Egypt, and all of Asia Minor.

By 1346 word reached Europe of a horrible plague, with deaths estimated to be over 23 million.

Adding to the misery was an unsettling mystery: the people of the middle ages had no way of knowing what caused the disease.

They only knew it killed horribly, that it spread with frightening speed, and that no one, neither royalty nor peasant, rich merchant nor lowly servant, was immune.

Death by Numbers due to Plague

It is exceedingly difficult to arrive at a definitive conclusion concerning the number of people who died of the plague.

Contemporary chronicles tended to exaggerate, and while the survivors saw dead bodies overflowing the cemeteries and cluttering the streets, it's not hard to understand why.

The most conservative modern estimate is 20% throughout Europe, with some places losing as much as 40% of the population.

Writers of the time claimed a third of the continent, an estimated 20 million souls, died in a mere handful of years.

In Chapter 5 of A Distant Mirror, Barbara Tuchman provides the following statistics:

� While the plague raged, Pisa and Vienna lost 500 people a day.

� Florence, Venice, Hamburg and Bremen lost a minimum of 60% of their populations.

� At the peak of the epidemic, Paris lost 800 people a day, and by the end of its long run with the disease (which lasted there until 1349), half its population of 100,000 people had died.

As centers of trade, cities were hard hit, but once a small village encountered the plague the results were just as devastating.

Losses of 40% were common, and there were cases where the death toll was so high that the pitiful number of survivors were forced to abandon the village altogether.

In enclosed communities like monasteries and convents, when one individual contracted the plague it wasn't long before everyone did. And in almost every case, none survived.

What was it like for a victim of the plague?

It started with a headache.

Then chills and fever, which left him exhausted and prostrate.

Maybe he experienced nausea, vomiting, back pain, soreness in his arms and legs.

Perhaps bright light was too bright to stand.

Within a day or two, the swellings appeared.

They were hard, painful, burning lumps on his neck, under his arms, on his inner thighs.

Soon they turned black, split open, and began to ooze pus and blood.

They may have grown to the size of an orange.

Maybe he recovered. It was possible to recover. But more than likely, death would come quickly.

Yet... perhaps not quickly enough. Because after the lumps appeared he would start to bleed internally. There would be blood in his urine, blood in his stool, and blood puddling under his skin, resulting in black boils and spots all over his body.

Everything that came out of his body smelled utterly revolting. He would suffer great pain before he breathed his last.

And he would die barely a week after he first contracted the disease.

Causes of the black death:

Plague is carried by rodents like rats and squirrels, but it is transmitted to humans by the fleas who live on them.

A flea, having ingested plague-infected blood from its host, can live for as much as a month away from that host before he needs to find another warm body to live on.

When a blood-engorged flea attempts to draw blood from another victim, it invariably injects into that victim some of the blood already within it.

If the injected blood contains the bacterium yersinia pestis, the result is Bubonic Plague.

Fleas were, alas, such a part of everyday life that no one noticed them much. In this invisible manner the plague spread from rat to human and to cat and dog, as well.

Pneumonic plague is airborne. It is contracted by breathing the infected water droplets breathed (or coughed) out by a victim of the disease.

The pneumonic form was much more virulent and spread much more quickly and just as invisibly.

People died so swiftly and in such high numbers that burial pits were dug, filled to overflowing and abandoned; bodies (sometimes still living) were shut up in houses which were then burned to the ground; and corpses were left where they died in the streets.

Cholera is caused by Vibrio cholerae, a bacterium found in drinking water that has been contaminated with human feces that harbor the bacteria.

Cholera epidemics erupted repeatedly in the 1800s in Europe and Asia, claiming thousands of lives.

The epidemic in South America in the early 1990s caused over 6000 deaths.

The bacterium Mycobacterium tuberculosis has caused tuberculosis in millions of people throughout human history.

Although the incidence of tuberculosis greatly declined during the mid-20th century, the disease has recently become a major worldwide problem again mainly due to AIDS.

One of the primary drugs originally used to cure it, streptomycin, is ineffective today because the overuse of antibiotics has enabled resistant strains of bacteria to evolve.

Other bacterial diseases such as certain forms of pneumonia and strep throat are also proving resistant to antibiotics, a cause of grave concern among physicians and other health care professionals.

Anthrax is a current issue of concern due to terrorism.

What is anthrax?

Anthrax is an acute infectious disease caused by the spore-forming bacterium Bacillus anthracis.

Anthrax most commonly occurs in wild and domestic lower vertebrates (cattle, sheep, goats, camels, antelopes, and other herbivores), but it can also occur in humans when they are exposed to infected animals or tissue from infected animals.

How common is anthrax and who can get it?

Anthrax is most common in agricultural regions where it occurs in animals.

These include South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East.

When anthrax affects humans, it is usually due to an occupational exposure to infected animals or their products.

Workers who are exposed to dead animals and animal products from other countries where anthrax is more common may become infected with B. anthracis (industrial anthrax).

Anthrax in wild livestock has occurred in the United States.

How is anthrax transmitted?

Anthrax infection can occur in three forms: cutaneous (skin), inhalation, and gastrointestinal.

B. anthracis spores can live in the soil for many years, and humans can become infected with anthrax by handling products from infected animals or by inhaling anthrax spores from contaminated animal products.

Anthrax can also be spread by eating undercooked meat from infected animals.

It is rare to find infected animals in the United States.

What are the symptoms of anthrax?

Symptoms of disease vary depending on how the disease was contracted, but symptoms usually occur within 7 days.

Cutaneous: Most (about 95%) anthrax infections occur when the bacterium enters a cut or abrasion on the skin, such as when handling contaminated wool, hides, leather or hair products (especially goat hair) of infected animals.

Skin infection begins as a raised itchy bump that resembles an insect bite but within 1-2 days develops into a vesicle and then a painless ulcer, usually 1-3 cm in diameter, with a characteristic black necrotic (dying) area in the center.

Lymph glands in the adjacent area may swell.

About 20% of untreated cases of cutaneous anthrax will result in death. Deaths are rare with appropriate antimicrobial therapy.

Inhalation: Initial symptoms may resemble a common cold.

After several days, the symptoms may progress to severe breathing problems and shock.

Inhalation anthrax is usually fatal.

Intestinal: The intestinal disease form of anthrax may follow the consumption of contaminated meat and is characterized by an acute inflammation of the intestinal tract.

Initial signs of nausea, loss of appetite, vomiting, fever are followed by abdominal pain, vomiting of blood, and severe diarrhea.

Intestinal anthrax results in death in 25% to 60% of cases.

Where is anthrax usually found?

Anthrax can be found globally.

It is more common in developing countries or countries without veterinary public health programs.

Certain regions of the world (South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East) report more anthrax in animals than others.

Can anthrax be spread from person-to-person?

Direct person-to-person spread of anthrax is extremely unlikely to occur.

Communicability is not a concern in managing or visiting with patients with inhalation anthrax.

Is there a way to prevent infection?

In countries where anthrax is common and vaccination levels of animal herds are low, humans should avoid contact with livestock and animal products and avoid eating meat that has not been properly slaughtered and cooked.

Also, an anthrax vaccine has been licensed for use in humans. The vaccine is reported to be 93% effective in protecting against anthrax.

What is the anthrax vaccine?

The anthrax vaccine is manufactured and distributed by BioPort, Corporation, Lansing, Michigan.

The vaccine is a cell-free filtrate vaccine, which means it contains no dead or live bacteria in the preparation.

Anthrax vaccines intended for animals should not be used in humans.

Who should get vaccinated against anthrax?

The Advisory Committee on Immunization Practices has recommend anthrax vaccination for the following groups:

� Persons who work directly with the organism in the laboratory

� Persons who work with imported animal hides or furs in areas where standards are insufficient to prevent exposure to anthrax spores.

� Persons who handle potentially infected animal products in high-incidence areas. (Incidence is low in the United States, but veterinarians who travel to work in other countries where incidence is higher should consider being vaccinated.)

� Military personnel deployed to areas with high risk for exposure to the organism (as when it is used as a biological warfare weapon).

Pregnant women should be vaccinated only if absolutely necessary.

What is the protocol for anthrax vaccination?

The immunization consists of three subcutaneous injections given 2 weeks apart followed by three additional subcutaneous injections given at 6, 12, and 18 months.

Annual booster injections of the vaccine are recommended thereafter.

Are there adverse reactions to the anthrax vaccine?

Mild local reactions occur in 30% of recipients and consist of slight tenderness and redness at the injection site.

Severe local reactions are infrequent and consist of extensive swelling of the forearm in addition to the local reaction.

Systemic reactions occur in fewer than 0.2% of recipients.

How is anthrax diagnosed?

Anthrax is diagnosed by isolating B. anthracis from the blood, skin lesions, or respiratory secretions or by measuring specific antibodies in the blood of persons with suspected cases.

Is there a treatment for anthrax?

Doctors can prescribe effective antibiotics. To be effective, treatment should be initiated early. If left untreated, the disease can be fatal.

Bacterial toxins (poisons) are of two main types:

Exotoxins are secreted by living bacteria (e.g. diphtheria, scarlet fever, and tetanus).

Endotoxins are released only after death and lysis of the bacteria (e.g. botulism).

Opportunistic infections - part of the transient flora of the body which become a problem when the immune system is suppressed (AIDS or organ transplant anti-rejection medications).

History �In the late 17th century, the Dutch microscope maker Anton van Leeuwenhoek became the first person to systematically study bacteria.

Leeuwenhoek spent hundreds of hours to make the finest ground glass for his simple microscopes.

Considered the founder of microbiology, he was the first to discover and describe a variety of very minute organisms, many of which we now know were bacteria.

Leeuwenhoek's work set the stage for later researchers such as French biologist Louis Pasteur, who showed that microbes do not arise from nonliving matter, as scientists of his day believed, and German scientist Robert Koch, who showed that bacteria could cause disease.

Bacteria in Our Daily Lives �

Locations: Bacteria are like living paint, covering nearly every surface imaginable and living within a variety of living and nonliving things.

Symbiosis: Many exist in a symbiotic condition in which they function as partners with other organisms. This symbiosis has profound consequences on people's lives.

For example, the agricultural industry depends on the symbiosis between the roots of certain plants and nitrogen fixing bacteria, which transform the nitrogen gas from the atmosphere into ammonia in the soil that plants can use.

Cyanobacteria play an extremely important role in aquatic ecosystems.

They are a significant component of the phytoplankton, floating microscopic organisms that carry out photosynthesis.

In the process of photosynthesis, cyanobacteria produce the sugar glucose, which is sometimes stored as starch in their cells.

Cyanobacteria therefore are a rich food source for zooplankton, floating animal-like microorganisms, which in turn are food for larger aquatic organisms.

During photosynthesis, cyanobacteria also release oxygen, which dissolves in the water. A great variety of aquatic organisms rely entirely on this oxygen for their survival.

Many scientists are concerned that breakdown of the ozone layer may damage cyanobacteria and other phytoplankton, threatening the survival of the organisms that depend on them for food and oxygen.

Bacteria are also important recyclers.

Like fungi, many bacteria feed on dead and dying organisms, breaking down their tissues and cells into nutrient-rich molecules, some of which remain in the soil or water.

This process, known as decomposition, is as significant as photosynthesis, for it provides germinating seeds, algae, and other aquatic life forms with the nutrients needed for growth.

Further, without decomposition, fallen trees, leaves, and other refuse would simply pile up.

Bacteria also strongly influence the movement of key elements, such as sulfur, iron, phosphorus, and carbon, around the globe.

The weathering of rocks, which releases elements into the soil and atmosphere, is substantially enhanced by the metabolic activities of certain bacteria.

There are bacterial species involved with the production of many important products & services.

Foods such as cheese and yogurt are developed through the metabolic processes of bacteria.

Vinegar, which is used as both a flavor enhancer and an important food preservative, results from the conversion of ethyl alcohol to acetic acid by acetic-acid bacteria.

Specific enzymes extracted from bacteria are used in spot removers, meat tenderizers, laundry starches, and household detergents.

Bacteria that can digest petroleum are even used in oil-spill cleanups.

Bacteria have gained enormous importance throughout the biotechnology industry, where they are used in genetic engineering to develop new medications.

Bacteria in the human intestine (and other animals) help in digestion, help form feces, and compete for food & space with possible pathogens.

Some intestinal bacteria make vitamins, particularly Vitamin K.

Normal skin flora are important to compete with possible pathogens. Discuss inadvisability of regular use of antibacterial soaps. Discuss importance of hand-washing to prevent disease.