How Do Bacteria Make People Sick?: Bacterial Pathnogenicity, Virulence Factors and Infectious Disease

In order to cause disease, potentially harmful bacteria must first enter the body, usually through breaks in the skin, penetrating the mucous membrane or colonizing the gastrointestinal (GI) tract. This is considered infection, when bacteria breech the first line defenses of the body.

Bacterial disease starts with infection, but infection does not always result in disease. Many bacteria are beneficial. And even when pathogens infect the body, the immune system may be able to eliminate the infection before symptoms of disease occur.

Bacterial Pathogenicity and Virulence

To cause disease, bacteria must be present in sufficient numbers. But what is it about bacteria that make an infected person ill? Disease is not merely caused by the presence of microbes.

Pathogenicity (path-o-jen-ISS-ity) refers to a microbe’s ability to cause disease, and some microbes are more pathogenic—better able to cause disease—than others. The degree of a microbe’s pathogenicity is considered its “virulence.” For example, highly virulent bacteria frequently cause disease, whereas less virulent bacteria may only cause disease when present in large numbers or within hosts that have weakened immune systems.

Many pathogenic, or disease-causing bacteria have special weaponry, traits that enable them to infect and damage host tissue. These disease-causing traits are called “virulence factors”. The following sections describe different types of virulence factors.

Adhesion Factors, Glycocalyces and Biofilms

Once bacteria get into the body, they must be able to stick to the host’s cells in order to increase in number. Bacteria that are able to stick to host cells have special structures or chemicals, collectively called adhesion factors. These adhesins are found on bacterial cell extensions, such as fimbriae and flagella, and also on glycocalyces, a sticky layer surrounding some bacterial cells that enable bacteria to stick to surfaces and to each other in biofilms. For example, the inside of the mouth and teeth are covered with a sticky bacterial biofilm, particularly in the morning, before brushing, because bacteria have been multiplying in the mouth throughout the night.

Bacterial Extracellular Enzymes

Some pathogenic bacteria are able to produce and secrete enzymes that compromise cell structure of the host and enable the bacteria to work their way further into the body.

Bacterial Toxins

Bacteria may also produce toxins that cause damage to host cells either directly, by destroying tissue, or indirectly, by triggering an intense or prolonged host immune response. Bacterial toxins fall into two general categories based on their position relative to the cell that produces them; exotoxins, which are secreted by bacteria, and endotoxins, such as lipid-A, which are part of the Gram-negative bacterial cell.

Evading Host Immune System

The human immune system has special white blood cells called phagocytes, which search out, engulf and digest invading pathogens. The sooner a pathogen can be eliminated from the body, the less damage it will have the opportunity to cause. However, bacteria have developed means of evading phagocytes.

The bacterial capsule, a type of glycocalyx, can help a bacterium hide from the immune system. This coating is often made of chemicals that are found in the human body, and that don’t trigger an immune response.

Other bacteria produce chemicals that prevent them from being digested once engulfed by a phagocytic white blood cell, allowing the bacteria to live and reproduce inside the host cells designed to eliminate them. Other antiphagocytic chemicals can prevent bacteria from being engulfed by white blood cell, or can even destroy white blood cells.

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How We Hear – Travel Along a Sound Wave from Ear to Brain

Hearing happens in an instant – quick transformations to energy until the movement of molecules is meaningful to a listener. It’s not magic, but the small size and complexity of shapes, movements and structures involved in energy transformation makes the process seem magical. To be able to hear beautiful music or birdsong in spring or mother’s voice is an awesome act of nature.

To put it very simply, sound is a type of energy and to get it from outside the head to the place in the brain where it can be “heard,” sound energy has to be sent from the microphone to the amplifier, along wiring, and on to the translating device.

Outer Ear

The ear that seen on the side of the head acts like a satellite dish that catches waves of sound. This outer ear is shaped to funnel and swirl the sound of energy made when molecules move as they are displaced by air, water or solid objects. The displacement forms waves that flow into the ear hole. In the tunnel that leads to the ear’s complex structures, the molecules move closer together and become louder.

On to the Middle and Inner Ear

Just about an inch past the ear that is seen outside the body and inside the ear hole, sound energy beats on the ear drum. The rhythm is taken up and passed along by three very tiny bones. In the middle ear compartment, the mechanical action of the bones amplify the air waves.

Now in the form of mechanical energy, the wave moves on to another tiny membrane that leads to the shell-shaped and fluid-filled inner ear. In the shell, called the cochlea, sound energy swims through the fluid and strums across teeny, tiny hairs that bend and snap.

On to the Brain

Energy fires neurons bundled into the nerve of hearing, the auditory nerve. The nerve’s long wires or axons zings energy forward to lower brain structures until the energy in analyzed in the cortex of the brain.

Now, if anything is really magical, it’s this part of hearing. How does that electrical energy get processed into meaningful words and sentences? Researchers are just beginning to understanding how the brain works and new discoveries are revealing more and more amazing information every day.

Sound Traveled, Energy Converted, Hearing Accomplished

Hear that? Fast, wasn’t it?

To summarize, the sound energy from the air is captured by the ear, knocks on the ear drum, is amplified by the bones of the middle ear, swims into the waters of the inner ear where waves wash over tiny hairs, which snap an electrical message along nerve wiring to the brain. The energy zaps to the cortex where analysis takes place and a response unfolds next.

Although it happens in an instant, it’s not magic. But hearing is still rather miraculous … or magical … don’t you agree?

Long Point Waterfowl A Leading Researcher: Ontario Organization Studies Waterfowl Issues

Based in Long Point, Ontario, Long Point Waterfowl is a non-profit, non-government organization dedicated to waterfowl and wetland-related research, conservation and training. Long Point Waterfowl also promotes Canada’s outdoor heritage.

Long Point Waterfowl was originally formed as Long Point Waterfowl and Wetlands Research Fund in the 1980s. Conservation-minded hunters at Bluff’s Club, a private hunting club on Long Point, were behind the efforts. Funding is still mainly from the Bluff’s Club members, but is also supported by Ducks Unlimited Canada, Waterfowl Research Foundation, Syndenham Conservation Foundation and the Ontario Federation of Anglers and Hunters.

The headquarters for Long Point Waterfowl is at Bird Studies Canada in Long Point, which is also the administrator.

The primary purpose of Long Point Waterfowl is to study the staging ecology and requirements of waterfowl on the lower Great Lakes. Long Point Waterfowl scientists also monitor trends in the distribution and abundance of waterfowl, research waterfowl habitat and provide information regarding waterfowl management.

Research results are published in scientific journals and presented at leading symposiums.

Long Point Waterfowl Research Centre

A former Ontario Youth Ranger Camp, Long Point Waterfowl leased this facility near Turkey Point as a place to host students and hold youth programs.

Youth Involvement In Conservation

One of the more unique events at Long Point Waterfowl is its young biologists workshop. This annual summer event is aimed at teenagers who are thinking of a future career as a biologist, conservation officers, wildlife technician or other related fields.

Participants learn about banding ducks, habitat, wildlife ecology, the role of hunting in conservation and a wide variety of other topics. The multi-day event includes meals and a stay at the Long Point Waterfowl Research Centre. Participants also learn about the educational requirements of future careers and hear from professionals in those fields.

Long Point Waterfowl also hosts a multi-day event where teenagers can stay at the centre and take all the training for their hunting certification.

Fund executive director Scott Petrie is also a teacher at the University of Western Ontario and sees that the students coming in don’t have the same background in the outdoors.

“Within our profession, people aren’t getting the training,” he said. “When I get a 22-year-old, they’re behind the eight-ball because they don’t have the passion.”

Research Projects at Long Point

Tundra swans are regular visitors to Long Point on their migration route from wintering grounds on the Atlantic seaboard to the high Arctic breeding grounds. Since little was known about these long-distant migrants, one of the first projects Petrie undertook was a satellite tracking study to learn more about tundra swan migration routes.

This was groundbreaking research, as such a study had never been undertaken with tundra swans in North America.

Resulting research has shown much about the swans, how much time they spent on migration, feeding habits along the way, when they arrive in the Arctic and much more. A map of the migration is available on Long Point Waterfowl’s web site

When a problem began to appear that numbers of lesser and greater scaup were declining relative to the health of other waterfowl species, Long Point Waterfowl again turned to satellite transmitters to learn more about the birds. This effort is still ongoing and is part of a cooperative venture between several research organizations investigating the problem.

Another major research initiative looked at the historical abundance and distribution of phragmites at Long Point. This tall grass with feather-like tops, an invasive species, was rapidly expanding at Long Point and displacing native vegetation. Research showed it is less preferable as waterfowl habitat than native vegetation. Other researchers have since identified it is a problem at other locations in Southwestern Ontario.

A current study is looking at the expanding population of Greater Sandhill Cranes in Ontario and the impact on agriculture.

Louis Pasteur – A Pioneer: Contributions of Pasteur to the Development of Microbiology

Louis Pasteur, one of the greatest scientists the world has seen, was born on December 27, 1822, in Dole, France. His father was a poor tanner but he wanted Louis to get a good education. Pasteur attended school in a nearby town called Arbois. His headmaster saw potential in him and encouraged him to go to Paris to further his education.

Early Life of Louis Pasteur

Pasteur’s first sojourn to Paris did not go too well. He got homesick and came back to study in a town called Besancon, where he received degrees in Letters and Mathematical Sciences. He got admitted to an elite college in Paris called Ecole Normale Superieure. He obtained his doctorate degree in 1847 and a year later he became professor of Chemistry at the University of Strasbourg. He courted and married Marie Laurent, the daughter of the University Hostel’s Rector, in 1849.

Birth of Stereochemistry

Pasteur’s first landmark contribution was to the field of chemistry where he showed the presence of chiral molecules of sodium ammonium tartarate. Chiral compounds have the same molecular formula but they are mirror images of each other. This discovery triggered the search for chiral molecules of many other compounds giving rise to a new branch of chemistry called Stereochemistry. In 1856, he was made the administrator and director of scientific studies at Ecole. By 1857, Pasteur had become a world famous scientist.

Pasteurization

During his time at the University of Lille, Pasteur was approached by the wine manufacturers of the region. They were concerned about many recent batches of their wine turning sour and this problem was seriously affecting the reputation (and profits) of the famous French Wine Industry. Careful analysis by Pasteur showed that a bacterium had “contaminated” the wine fermentation batches and was producing an acid which was resulting in souring of the wine.

He found out that gentle heating of the wine to around sixty degrees centigrade for about thirty minutes was enough to destroy the bacterium and prevent souring. This came as a great relief for the French Wine Industry and also helped Pasteur’s reputation go far and wide. This technique of Pasteur’s was applied to other beverages as well and particularly to milk where it came to be known as pasteurization.

Discovery of Germ-Disease Relationship

Pasteur also rescued the French Silk Industry which was plagued by a disease called pebrine which affected the caterpillars which died before making their cocoons. Pasteur found out that the disease was caused by a bacterium. He thus found out the connection between bacteria and diseases. He worked with the silk industry to devise methods to keep their hatcheries bacteria-free and thus, disease-free.

Discovery of Attenuation

One of the most important discoveries of Pasteur is, without doubt, attenuation. He was working on a disease which plagued chickens and was affecting the poultry farmers of France. This disease called “chicken cholera” was caused by a bacterium. Pasteur isolated the bacteria from diseased chickens, cultured them outside and when he inoculated this fresh culture into healthy chickens, they developed the disease and died. Legend has it that he left a bottle of culture in his laboratory and went for a couple of weeks’ vacation. When he returned, he inoculated the “old” culture into healthy chickens. The chickens became sick but recovered, much to the chagrin of Pasteur who had expected them to die.

Pasteur then inoculated fresh “virulent” bacterial culture into the same chicken, which surprisingly, failed to die. Pasteur deduced that the bacterial culture had lost its “virulence” or disease-causing ability and had been “attenuated.” This forms the basis of vaccination. Pasteur applied this technique to help protect sheep from anthrax, another fatal bacterial disease. But Pasteur is best remembered for his work on the rabies vaccine, the first human vaccine.

The Rabies Vaccine

Pasteur inoculated the fluid taken from a rabid dog that had just died, into a rabbit. The rabbit developed rabies and died. Pasteur removed the spinal cord of the rabbit, dried it and powdered it. He injected this into a healthy rabbit, which was later inoculated with the virulent inoculums. The rabbit failed to develop rabies. The first person on whom the rabies vaccine was tested was a young boy named Joseph Meister. The boy repaid the benevolence of Pasteur by returning to Paris and working for him. When Meister was key keeper of the Pasteur Institute in Paris, the Nazis raided it and forced Meister to hand over the keys of Pasteur’s crypt. Instead of handing over the keys and betraying his benefactor, Meister shot himself.

Pasteur dedicated his entire life to the goodwill of humankind. He faced personal tragedies during his life with three of his five children dying at a young age. It is a general belief that had the Nobel Prize been instituted earlier, Pasteur would have won it a number of times for his various important contributions. Pasteur died on September 18, 1895 from complications arising from a stroke he had suffered a few years previously.

Bruce Lipton’s The Biology of Belief: A Look at Unleashing the Power of Consciousness, Positive Thought

In the Biology of Belief, Bruce Lipton lays a scientific foundation that positive thoughts are a biological mandate for a happy, healthy life.

Bruce Lipton, Ph.D., is a cell biologist and his book The Biology of Belief: Unleashing the Power of Consciousness, Matter & Miracles is about how his work with cells led him to believe that genes and DNA do not control a person’s biology.

Rather, Lipton claims that signals from outside the cell, including the energy from positive and negative thoughts, control biology.

Lipton’s Theory on Cell Receptors

All cells have receptors that respond to their environment. For example, receptors detect estrogen, insulin, histamines, etc., which is how these substances affect the body’s cells. But not only do a cell’s receptors respond to physical substances, they also respond to vibrational energy fields such as light, sound, and radio frequencies.

Lipton’s research with cells led him to the conclusion that it is not the DNA in the cell’s nucleus that “programs” the cell, as traditionally believed, but the signals that come in through the cell’s receptors. That is, the physical and energetic environment controls the life of a cell.

Biology and Quantum Physics

According to quantum physics, physical atoms are made up of spinning, vibrating vortices of energy. Each atom has its own specific energy signature, and collections of atoms (molecules) have their own identifying energy patterns. All physical matter is made up of molecules, including human beings, and each piece of matter (or person) radiates its own unique energy signature.

Lipton points out that because Western biologists have ignored the energy component while focusing on the physical things that affect cells. Lipton claims that they have arrogantly dismissed 3,000 years of effective Eastern medicine as unscientific, even though it’s actually based on a deeper understanding of the universe. Lipton goes on to say that, “vibrational frequencies can alter the physical and chemical properties of an atom as surely as physical signals like histamine and estrogen.”

Thoughts and Perceptions

Lipton claims that cells respond to vibrational frequencies. Thoughts and perceptions are vibrational frequencies; therefore, cells respond to thoughts and perceptions. The problem is that not all a person’s thoughts and learned perceptions are accurate.

Biologically speaking, human brains have the ability to rapidly download “an unimaginable number of beliefs and behaviors into our memory.” The subconscious minds of young children become programmed with the fundamental behaviors, beliefs, and attitudes that are observed in their parents. These programs control a person’s biology for the rest of their lives, unless they consciously figure out a way to reprogram the mind.

A stimulus automatically engages the behavioral response that was learned when the signal was first experienced. Although the conscious mind can observe what is happening and step in and change the behavior, a person must be fully conscious. This can be difficult, which is why willpower so often fails.

Methods for Changing Perceptions

Although the Biology of Belief explains the science of why thoughts and perceptions are important, and even notes that a person can choose what to see, and choosing to look at negative rather than the positive aspects of life makes a person susceptible to disease,

Lipton doesn’t actually get into how to change thoughts and perceptions. However, many methods are available today to change beliefs, including Emotional Freedom Techniques (EFT), the Sedona Method or Abundance Course (also known as Lester Levenson’s Release Technique), Ho’oponopono, the Work of Byron Katie, and PSYCH-K.

Lipton concludes that because controlling perceptions equal beliefs, beliefs control biology. And that leads to the conclusions that learning to harness you mind to promote growth is the secret of life, and positive thoughts are a biological mandate for a happy, healthy life.

The Science of Autumn or Fall Leaves: Why Do Leaves Change Colour and Fall From the Trees?

Autumn’s beauty is clear for all to see, the myriad shades of red, yellow and brown lifting the heart on a cold but bright October morning. But the curious mind wonders “Why?” Why do the trees go through this process every year, only to grow fresh leaves every spring? And why such a variety of colours and shades – of which any artist would be proud?

Using Chlorophyll

The green leaves of summer contain chlorophyll, which drives photosynthesis – the molecular factory transforming carbon dioxide and light into glucose – which gives energy to the plant and cellulose for growth. When summer ends and autumn arrives, it is the short days which trigger the changes in deciduous trees. The chlorophyll is taken back from the leaves to be recycled, but the leaves become not just superfluous, but a liability.

Abscission Zones

In order to exert a force of suction, to draw water from the ground during the summer, leaves sweat through their high surface area. In winter these same leaves could cause the trees to dry out and die, so they must be removed. The scientific process of leaf-removal is known as abscission. When the shorter days of Autumn arrive, a number of chemical changes occur and the abscission zone at the base of the year begins to swell, cutting off the flow of nutrients from the tree to the leaf and vice-versa. The zone then begins to tear, the leaf falls off or is blown away, and a protective layer seals the wound, preventing water evaporation and entry of bugs.

Anthocyanins and Aphids

But why do the leaves go so many different colours? The removal of the chlorophyll reveals other colours in the leaf – yellow, orange and brown – but some leaves turn red or purple for another important reason. The shorter days which trigger the process of abscission, also initiate another process in the leaves of certain trees to produce a group of chemicals called anthocyanins, which are deep red or purple in colour. This is not, however, just vanity on behalf of the tree.

In fact, the red colours are used to conceal the shades of yellow which attract aphids. So, trees which are more susceptible to aphids, or are native to areas where aphids are more of a problem, are able to confuse their enemies and survive to grace another spring.

The Structure and Growth of Flowering Plants: A Comparison Between Monocots and Dicots

An overview of the structure and function of an angiosperms’ root system, stem and leaves, and flowering plant’s adaptations to their environment.

Angiosperms are the most diverse and widespread group of plants. There are over 280,000 known species of flowering plants.

Plant Adaptations to the Environment

Like other organisms, plants have evolved over time, often reflecting the environment in which they live. For example, the cactus that has reduced its leaf size and uses its stem for photosynthesis as a way of reducing water loss. Or plants that live in water that have adapted feathery leaves to increase surface area for photosynthesis.

For most plants however, conditions are not that extreme, and could vary on a daily, weekly or seasonal basis. Because of this, plants have developed physiological adaptations.

Plants produce a hormone that closes stomata when there is not much rainfall or water in soil. Stomata are pores in the plant leaves through which water is lost, or released. In wetter conditions, plants will open their stomata to excrete extra water.

The Difference Between Monocots and Dicots

Monocots:

  • One cotyledon (embryo)
  • Veins in leaves usually parallel
  • Stems have vascular bundles, complexly arranged
  • Fibrous root system
  • Floral parts usually in multiples of threes

Examples of monocots include grasses (wheat, rice, corn), cattails, lilies, palms trees, orchids, bamboos and yuccas.

Dicots:

  • Two cotyledons
  • Leaf veins are usually netlike
  • Stems have vascular bundles arranged in a ring
  • Taproot usually present
  • Floral parts usually in multiples of four or five

Examples of dicots include many trees, and most ornamental and crop plants such as roses, sunflowers or beans.

Plant Structure

The three basic organs of a plant are:

  • Roots
  • Stems
  • Leaves

Plants are multi-cellular organisms. They have organs composed of different tissues, and tissues composed of different cells.

Plant Roots

A plant’s roots are what anchors it to the soil and how the plant takes up nutrients. Monocots have fibrous root systems that expand a mat of thin roots below the surface of the soil to increase the plants exposure to water and minerals.

Dicots have a taproot, which is one large root, which produces smaller lateral roots. These taproots often store food for the plant to consume during flowering and fruit production.

One both monocot and dicot root systems are tiny root hairs, which reside near the root tip. The purpose of these root hairs is to increase the surface area of the root for optimal absorption of water and minerals.

Plant Stems

Plant stems are a system of nodes, internodes, axillary buds and terminal buds.

  • Nodes: the point where leaves attach to stem
  • Internodes: stem segments between nodes
  • Axillary buds: structures that can form vegetative branches, but are usually dormant
  • Terminal buds: where growth of young shoots occurs. Terminal buds have developing leaves and a complete series of nodes and internodes. Terminal buds suppress the growth of axillary buds. This is referred to as apical dominance.

Apical dominance is an evolutionary adaptation that makes the plant grow taller and this exposes the plant to more sunlight. In cases where the top of the plant is damaged (ie: eaten by an animal), or light intensity is strongest at the sides of the plant then the top, axillary buds break dormancy and start to grow, complete with their own terminal buds, axillary buds and leaves.

Plant Leaves

Most photosynthesis occurs in the leaves although green stems can also perform photosynthesis. Leaves generally consist of:

  • A flattened blade
  • A stalk
  • The petiole: which joins the leaf to the node of the stem

Leaves can vary in structure, however. Grasses for example (and many other monocots) lack petioles. Instead the leaf base forms a sheath around the stem. Plant taxonomists use plant leaves to determine plant identity and classification.

Differences in plant leaves aside from shape, spatial arrangement and vein pattern, are:

  • Simple leaf: leaf that has a single, undivided blade
  • Compound leaf: which are divided into several leaflets
  • Double compound leaf: leaf that is further divided into several leaflets

Most large leaves are compound leaves or doubly compound, which allows for strength against strong wind (less tearing) and protection against pathogen spread (ie: able to confine some pathogens to a single leaf rather then whole leaf).

How Did Recombinant DNA Start? Cutting and Pasting of DNA Molecules in the Laboratory

A series of critical scientific discoveries were required before the manipulation and propagation of engineered DNA molecules could be undertaken.

The DNA molecule was discovered in the mid-1800s. It was not proven to be critical to the mechanisms of inheritance until the 1940s. Since the 1950s, and the seminal work of Watson and Crick to characterize the chemical structure of DNA and how it could be copied, the understanding of the biochemistry of DNA and the ability to manipulate it in the laboratory has grown exponentially. Breakthroughs studying DNA now come fast and furious, but several key discoveries are largely responsible for the development of modern recombinant DNA technology.

The Genetic Code

Knowing that DNA is the molecule of heredity is one thing. Knowing how it maintains and transmits crucial genetic information is something else entirely. In the early 1960s, Marshall Nirenberg and colleagues working at the US National Institutes of Health cracked the genetic code. Using synthetic RNA molecules and radioactively labeled amino acids they proved that DNA used a three letter code (three nucleotide bases made a “codon”) to specify individual amino acids, the codons in RNA molecules were contiguous, they did not overlap, and there were punctuation marks, places specifying “start” and “stop”.

Episomes and Plasmid DNA

In the 1950s and 1960s, numerous scientists were studying how DNA was handled in bacteria, viruses and yeast. From their combined work came the knowledge that bacteria could carry small, circular molecules of DNA that were not integrated as part of their chromosomal DNA. Most important of all, these “plasmids” or “episomes” could be isolated and more importantly they could be transferred back into other bacteria.

Restriction Endonucleases

One of the key factors in recombinant DNA technology is the ability to “cut” DNA molecules and to be able to “paste” pieces together, often in a new order. Werner Arber, a Swiss microbiologist, was the first to recognize that there were enzymes that would cut DNA molecules in specific ways. Shortly after this work was published studying the bacterium E. coli, Hamilton Smith and colleagues identified a “restriction endonuclease” from another bacterium, Haemophilusinfluenza, and then showed that it cut at a very specific sequence of DNA bases. Today there are hundreds of restriction enzymes known to cut DNA at specific occurrences of base sequences.

Recombinant DNA Molecules

In 1972, scientists Herbert Boyer and Stanley Cohen were in Hawaii attending a scientific meeting about plasmids when they met to discuss the work that they were each pursuing. What ultimately came from this meeting was the birth of recombinant DNA cloning, the start of the biotechnology industry and a new era in molecular biology. Collaborating on the use of newly identified restriction enzymes and DNA manipulation techniques, they published seminal papers showing that DNA from one source could be cut with restriction enzymes and then placed into the midst of cut DNA from another source, and these could be placed into bacteria and grow stably with the “recombined” DNA maintained in the newly arranged form.

Herbert Boyer went on to found the biotech company Genentech and the research world has never been the same. Recombinant DNA methods are now used to make things from insulin for diabetics to proteins that can make individual cells, or even whole organisms, glow green, blue or red under just the right light. Remarkable.

To read more about the cracking of the genetic code by Nirenberg and colleagues visit the history page at the US National Institutes of Health.

Antibiotic Susceptibility Tests – Types and Ways: Antibiotic Evaluation, Antimicrobial Effectiveness In Vitro In Vivo

Proper antibiotic susceptibility testing of microbial pathogens isolated from patients is critical. The use of an ineffective antibiotic could lead to a patient’s death

Today, if someone gets a bacterial infectious disease the first thought is “what antibiotic will help or work?” The doctor and the patient both desire the best and most effective antibiotic. This is what makes testing and analysis of antibiotics very interesting.

In the 1950’s and 60’s there were sufficient antibiotics on the medical scene to require a closer look at standardized testing of antibiotics. A better way was sought to accurately and precisely forecast which antibiotic would work and which would not.

Drs. Kirby, Bauer, and Sherris established a defined scientific approach to antibiotic testing (KBS technique) . This greatly improved the accuracy and results of testing. There are several important ways to determine antibiotic susceptibility.

Solid, Liquid and Animal Tests of Antibiotics

  • When chemicals and antibiotics were first tested they were added to nutrient agar petri dishes (circular glass, or plastic, with larger top glass cover overlapping a bottom reservoir) with bacteria streaked over the surface. The next day a zone of inhibition was looked for as shown in figures below (click to enlarge these figures).
  • Bacteria can also be tested in test tubes with nutrient broth. Sequential dilutions of the chemical or antibiotic are done first, followed by addition of a measured bacterial inoculum to each tube. After overnight incubation the tubes are analyzed: clear tubes indicate inhibition and cloudy tubes indicate bacteria not inhibited by that concentration or titer of antibiotic. In this way scientists can correlate later how much antibiotic yields what zone size on agar.
  • The zone sizes produced on plates by dropped antibiotic disks are plotted versus the amount in the disk. Simply, this is a regression analysis graph. It is possible to establish MIC (minimum inhibitory concentration) values in broth, blood or serum in this way. Typically, the more resistant a microbe is the smaller the zone. The more susceptible, the bigger the zone.
  • Finally, if an antibiotic looks promising, it can be tested in mice or rabbits for toxicity (harmful) and effectiveness.

Measurement of the amount of antibiotic injected, or ingested, is the dose. The antibiotic titer is the MIC = minimum inhibitory concentration ( an actual value attainable in blood or serum). MIC is measured in micrograms or units. MIC can be evaluated in blood and tissue fluids . The higher the MIC the more resistant the bacterium is to that antibiotic.

Standardized Antibiotic Testing

Antibiotic testing should always be done with a pure culture of the organism.

The KBS technique eliminates the variables that affect the zone size and could cause false positives or false negatives.

The agar used is Mueller-Hinton. The depth and pH of the agar,inoculum size and incubation temperature are standardized. The click-on photos below show several things:

  • different antibiotics have characteristic zone sizes for MIC
  • the same antibiotic at different concentrations will give different zone diameters
  • resistant bacteria cause zone size decreases. No zone = complete resistance
  • regression analyses enable microbiologists to determine MIC vs disk zones
  • populations of the same species vary from susceptible (S) to intermediate (I) to resistant R)

Recently, the valuable E-test (see photo) allows determination of MIC of a microbe with one disk that forms an antibiotic gradient. This permits rapid, clear medical evaluations of antibiotic effectiveness.

Review of the Primer of Conservation Biology: A Teaching Tool on the Topic of Conservation Biology

Learning about conservation biology is the first step to making a difference, and through the text by Richard B. Primack that becomes possible.

Conservation biology is the field that seeks to study and protect the living world and its biological diversity. So says Richard B. Primack at in the prefix of his book called A Primer of Conservation Biology. His intent with that statement is to provide a specific definition of what conservation biology is, and to lay the beginning framework of what the rest of his book is about.

What is Conservation Biology?

Conservation Biology is still a relatively new field, because there hasn’t always been a movement to save the Earth. Resources are burnt thorough quite quickly, and in doing so the environment is hurt in more ways than one. No matter what side of the “environmental argument” someone’s on, there is debate that the planet is being harmed more every day. What Primack hopes to do with this book, is to show what is happening, and what people interested in the field can do about it.

Thoughts on Conservation Biology

The first part of the book describes conservation, and why it is needed. Resource management is a huge step in the right direction and the methods to do it are explained with depth. This is a great section about exactly what is being done wrong, and where the mistakes can be fixed if subtle changes are made in the way that people do things. The text relates about extinctions that are taking place all the time, and the rates at which those extinctions are occurring.

From there he goes into discussions about the threats to biological diversity that are beginning to happen as more and more species are threatened. Those aren’t just limited to the larger animals that are in the news, but plants, bugs, and even microscopic creatures that depend on other species to keep living. He also gives examples of why these extinctions are happening.

Putting Conservation Biology into Practice

Conservation at the population and species level, and conserving biological communities are what Primack dives into as the book progresses. He shows how designing networks of protected areas, and managing them, along with ecological restoration of those areas that some of these problems can be slowed down. Conservation isn’t something that can be implemented right away, and it’s key to take the steps and put the procedures in place so that it can become something that everyone focuses on more.

Through the roles of agencies (both public and private) and through Government programs conservation is becoming something more center-stage to the public. The key here is to learn as much as possible about the field to get involved in helping conservation, and Primack’s book is a good stepping off point.

Primack explains the terms well, and the theories and facts of everything he talks about are phrased so even the most novice reader can understand. The entire book does a great job of telling the reader the basics of conservation, what has been implemented so far, and what still needs to be done for it to all work out. Conservation Biology is an important field that is slowly becoming more popular as people realize just how badly the environment is being treated.

Final Recommendation on the Primer of Conservation Biology

For those interested in anything to do with conservation, this is a great tool to provide knowledge that would be necessary to be active. The book comes in at 320 pages, is paper back, and can be found online or in most bookstores. It is highly recommend it to anyone wanting to read more about conservation biology.