Defense and immunity

Disease prevention can focus on the prevention of transmission, inoculation against
the disease or treatment of the infection.

LAB Investigation:

The term bacterial growth generally refers to the growth of a group of bacteria rather than a single cell. Single cells generally do not get larger in size, so the term growth refers to the reproduction of cells and can be seen as a colony or a continuous growth, depending on the type of inoculation. The type of count and, therefore, plate inoculation should be clear before beginning an investigation.
Bacteria most commonly reproduce by fission, the process by which a single cell divides to produce two new cells. The process of fission may take anywhere from 15 minutes to 16 hours, depending on the type of bacterium.
A number of factors influence the rate at which bacterial growth occurs, the most important of which are moisture, temperature, and pH. These factors should be kept constant.

READ some recent articles on bacterial infections. From an area that interests you, choose an area to investigate bacteria growth in order to practise healthier hygiene, food preparation, food storage or food choices etc

After deciding on a general aim, write a focused research question (RQ) that includes your variables.

List your variables

Write a short theory that discusses the background information concerning your aim and say why you have chosen to focus your research on this particular RQ. You should have at least one source cited.
List the materials

Describe the method including safety and sterile techniques, as well as innoculating technique and how you will measure/read your plates (data)
Explain how you will keep the variables controlled, constant

Some ways that bacterial growth can be measured:

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Example set up - Petri dish labeled for experiment (bottom of plate labeled).

for growth and relevant data:
Sterile work area, sterile inoculating loop (if used), sterile Petri dish and media, quick replacement of Petri dish lid following inoculation, upside down Petri dish during incubation (moisture control), temperature controlled at 37 oC and pH controlled by supplied nutrient media..

Antibiotic Control of Microbes

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Plate first painted with a liquid culture of Staphylococcus epidermidis. Antibiotic disks of penicillin, sulfadiazine and ciprofloxacin (clockwise, starting from top) were placed on inoculated medium and the plate was then incubated. Zones of inhibition are the areas surrounding the antibiotic disks where no bacterial growth is found. Data shows that the Penicillin was most effective in preventing bacterial growth, followed by Cipro then the sulfa drug.

Escherichia Bacteria growth after streak innoculation

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Plates of Echerichia coli streak plated and grown on TSY media.

Bacterium Cell

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Sources (citation and reference needed) for basic bacteria inoculation techniques : GCSE Biology macKean p 290; Biology roberts p. 25. proper innoculation technoques should be included in your specific investigation.


Title: Antimicrobial Resistance in Agriculture

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Antimicrobial drugs ( include antibiotics) have played a vital role in health management of both humans and animals for more than 50 years. In agriculture, antimicrobials are used to treat, control or prevent disease caused by micro-organisms, and to improve production or growth.
The use of antimicrobials in animals that are ready for market has always been closely monitored. Until recently, the focus has been on antimicrobial residues in food intended for human consumption. Some residues can lead to allergic reactions in a small percentage of the population. Other antimicrobial residues may increase the risk of other adverse health outcomes, such as cancer, and are banned by Health Canada for use in food-producing animals. There is increasing concern that the use of antimicrobials in agricultural production systems may contribute to antimicrobial resistance, primarily in zoonotic bacteria. Zoonotic bacteria can cause disease in both animals and humans, and are usually transferred from animals to humans by direct contact or through food.
The other areas of concern are transference of resistance, and multi-drug resistance. Resistance genes can transfer from bacteria of agricultural origin to disease-causing bacteria of human origin. Disease caused by bacteria that are multi-drug resistant can result in compromised treatment options, prolonged recovery, or in the worst case, treatment failure.

**=== ===

**What is an antimicrobial?Antimicrobials are natural, semi-synthetic or synthetic substances, including antibiotics, which inhibit or kill micro-organisms (microscopic life forms such as bacteria).

What is an antibiotic?

Antibiotics are natural substances produced by micro-organisms that, at low concentrations, are able to inhibit or kill other micro-organisms. penicillin is produced by bread mold and prevents the growth of bacteria.

Some colony shapes
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Some different ways to graph your results

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Population "S" curve
The following can happen to the bacteria population if it is left too long - food and space run out!
The dotted line would happen if the space, resources and the population maintained a balance - called the carrying capacity.

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See Links above:
The following link shows phagocytic macrophage andT cell-B cell and antibody interactionshttp:
The following link describes the human lymphatic system

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The lymphatic system
has two main functions: To pick up, transport .and return extracellular (interstitial) fluids to the circulatory system and to fight infection (p488)
Lymph comes from the Latin word lympha, meaning "clear water." Slightly yellowish but clear, lymph is any tissue or interstitial fluid that enters the lymph vessels. It is similar to blood plasma, but contains more white blood cells. Lymph also carries other substances, depending on where it is in the body. In the limbs, lymph is rich in protein, especially albumin. In the bone marrow, spleen, and thymus, lymph contains higher concentrations of white blood cells and at the intestine, lymph contains fats absorbed during digestion. fats are

Lymph vessels, also called lymphatics, carry lymph in only one direction—to the heart. Throughout all the tissues of the body, lymph vessels form a complicated, spidery network of fine tubes. The smallest vessels, called lymph capillaries, have closed or dead ends (unlike vessels in the cardiovascular system, which form a closed circuit). The walls of these capillaries are composed of only a single layer of flattened cells. Material in the interstitial fluid passes easily through the gaps between these cells into the capillaries. Lymph capillaries in the villi (tiny fingerlike projections) of the small intestine are called lacteals. These specialized capillaries transport the fat products of digestion, such as fatty acids and vitamin A.
external image villus.gifThe green colored lacteal is a part of the lymphatic system.

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Lymph nodes are masses of lymphatic tissue that act as a filtering and cleansing system against disease-causing organisms. (Illustration by Electronic Illustrators Group.)
Lymph nodes are masses of lymphatic tissue that act as a filtering and cleansing system against disease-causing organisms. (Illustration by Electronic Illustrators Group.)


6.3.1 Pathogen (define)

  • A pathogen is an organism that can cause disease.
  • Pathogens include bacteria, viruses, protista, fungi and other parasitic multicellular organisms.

6.3.1 Antibiotic Action

Anitgens are particles, ususally containing, protein thaour body recognizes as foreign. Antigens can be any of a wide range of substances such as the cell wall of a pathogenic bacteria or fungi, or a protein coat of a pathogenic virus.

Antibodies are proteins produced by B cells and specific to an antigen that it will subsequently destroy.

Antibiotics block specific metabolic pathways found in pathogens such as bacteria. Metabolic pathways are synthetic pathway reactions which build molecules needed for structure and function or breakdown pathways needed for smaller molecules for certain body processes.

Viruses, however, reproduce using the host cell metabolic pathways, which are not affected by antibiotics.
  • Viruses do not have metabolic pathways like bacteria and therefore antibiotics do not work on viruses.
  • Viruses can only be treated by their specific anti-microbial agent and antibiotics should never be prescribed for viral infections (such as flu)
    Antibiotics are NOT effective against viruses because viruses use the metabolic pathways of their host cell and these pathways are not affected by antibiotics.
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Antibiotics block specific metabolic pathways found in bacteria, but not in eukaryotic cells.

These graphs show how the two kinds of drug (see below) affect bacterial growth curves.

How antibiotics work:

A number of common antibiotics target a unique component of the cell walls of bacteria. It is the reason those antibiotics kill bacteria and not you; you do not have cell walls. Although some eukaryotes such as plants have them, their cell walls do not have a large molecule called peptidoglycan, which is present in many bacteria. Because it is unique to bacteria, it makes an ideal drug target. The building blocks of peptidoglycan are sugars (which are also the building blocks of complex carbohydrates or polysaccharides) and amino acids (which are also the building blocks of proteins).

In the diagram below, the antibiotic is designed to enter the bacterial cell and interefere with the assembly of peptidoglycon, needed in a bacterial cell wlal. Without a cell wall the bacteria will not grow
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Here is a flat diagram of how the peptidoglycan structure that makes up the cell wall of bacteria is situated outside the lipid bilayer, the plasma (cell) membrane. Remember that these layers are actually covering the entire outside of three-dimensional bacteria cells. Notice the connections between the peptidoglycan molecules. Those are not formed in new cells when the bacteria are dosed with antibiotics.
The synthesis and assembly of peptidoglycan unites occurs inside the cell as seen in the diagram above, so the antibitoic must enter the bacteria cell. Because the antibiotic enters the cell itself, the bacteria can form a resistant plasmid gene against the antibiotic.

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Antibiotic Resistance

Anitbiotics have been helpful in preventing disease throughout the worl;d for example, strep throat can lead to heart disease if left untreated. Antibiotics have decreased incidences of strep-throat related heart disease. However, bacteria have developed a resistant gene to many antibiotics and it is becoming difficult to treat many bacterial infections by antibiotics; for example, staph infections in hospitals have become quite dangerous and antibiotic dose levels so high that they can make the patient ill.

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Natural pathway for fighting disease -

3.3 Barriers to infection

As a first line of defence the body has many mechanism to try to stop microbes entering the body, particularly the blood-stream. These are :

  • The skin is a tough, impenetrable barrier (which is why we use it to make leather shoes) that keeps most pathagens out. . The outer layer, the epidermis, is 20-30 cells thick (about as thick as a sheet of paper) and its cells are toughened by the protein keratin. The next layer, the dermis, is 20-40 times thicker and provides the main structure for the skin as well as all the receptor cells, blood vessels and hairs. Cells are constantly being lost from the surface of the skin (to form dust) and are replaced by new cells from further down.
  • The respiratory tract is another potential entry route, but it is protected by sticky mucus secreted by glands in the bronchi and bronchioles, which traps microbes and other particles in inhaled air before they can reach the delicate alveoli. Mucus contains lysozymes, and cilia constantly sweep the mucus upwards to the throat, where it is swallowed so that the microbes are killed by the stomach acid.

3. 4 Cellular defence

The second line of defence is the non-specific immune system, a host of quick, non-specific methods of killing microbes that have passed the first line of defence and entered the body and into the blood stream. . Phagocytic leucocytes are an example of this type of defence from infection. A particularly large phagocyte, called a macrophage, plays an important role in the destruction of pathogens when they enter the blood stream
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  • Phagocytes are large, irregularly-shaped leukocyte cells that remove bacteria, vi-ruses, cellular debris and dust particles.
  • The phagocytes are constantly changing shape, and they flow over microbes, surrounding and ingesting them through the process of phagocytosis to form a phagosome.
  • The phagosome then fuses with lysosomes - small vesicle containing lysozymes, which are released into the phagosome, killing and digesting the microbe.
  • Different phagocyte cells work in different locations: neutrophils circulate in the blood, while macrophages are found in lymph, tissue fluid, lungs and other spaces, where they kill microbes before they enter the blood.

6.3.5 Antigens and Antibodies

  • Third line of defense - the immune system: lymphocytes and antibody production
  • If the pathogen is not destroyed by the macrophage, protein particles of the pathogen (called antigens), which have been incorporated into the macrophage's plasma membrane, are read by the helper T - lymphocyte cells. This helper T-cell now stimulates the B-lymphocyte cells to begin antibody production. B cells are located in the lymph nodes. The antibodies coat the antigen, preventing it from entering the host cell; for example the tuberculosis bacterium in the lung cell.
  • Once the B cell has been exposed to an antigen and produced antibodies against it, the B cell remembers the antigen by incorporating the antibody into its plama membrane.
  • Many different kinds of lymphocytes exist, having been formed by an antigen they were previously exposed to. Each kind carries antigen-specific binding sites in its cell membrane. As soon as B lymphocyte recognizes an antigen it responds by dividing to form a clone cell. Many clones are produced thus many antibodies against the antigen. The response is faster when the B cell has memory antibodies in its plasma membrane. This is why vacines work well against pathogen caused diseases..

  • See cells alive link above showing antibody production

  • Antigens described
  • **An antigen is a large molecule (protein, glycoprotein, lipoprotein or polysaccharide) on the outer surface of a cell.
    • All living cells have these antigens as part of their cell membrane or cell wall.
    • The capsid proteins of viruses and even individual protein molecules can also be classed as antigens.
    • Their purpose is for cell communication, and cells from different individuals have different antigens, while all the cells of the same individual have the same antigens.
    • Antigens are genetically controlled, so close relative have more similar antigens than unrelated individuals.
    • Blood groups are an example of antigens on red blood cells, but all cells have them.
The link with infection is that when a pathogen or toxin enters the body it this that the immune system reacts against.
Antibodies are proteins secreted from lymphocytes that destroy pathogen and antigen infections
    • B-cells make antibodies.
    • An antibody (also called an immunoglobulin) is a protein molecule that can bind specifically to an antigen.
    • Antibodies all have a similar structure composed of 4 polypeptide chains (2 heavy chains and 2 light chains) joined together by strong disulphide bonds to form a Y-shaped structure.
    • The stem of the Y is called the constant region because in all immunoglobulin's it has the same amino acid sequence, and therefore same structure.
    • The ends of the arms of the Y are called the variable regions of the molecule because different immunoglobulin molecules have different amino acid structure and therefore different structures.
    • These variable regions are where the antigens bind to form a highly specific antigen-antibody complex, much like an enzyme-
    • substrate complex
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      • Each B-cell has around 10 5 membrane-bound antibody molecules on its surface and can also secrete soluble antibodies into its surroundings.
      • Every human has around 108 different types of B cell, each making antibodies with slightly different variable regions.
      • Between them, these antibodies can therefore bind specifically to 108 different antigens, so there will be an antibody to match almost every conceivable antigen that might enter the body

    • 6. 3.6 Antibody production

external image clone_selection.gif(a) There are many different lymphocytes.
(b) The antigen infects and is presented to the lymphocytes
(c) The lymphocyte with a surface epitope complementary to the antigen is selected.
(d) The Lymphocyte clones to produce many plasma cells. This occurs in the lymph nodes.
(e) The clone of plasma cells
(f) The gene for the antibody is expressed and secreted into the plasma and tissue fluid.
(g) The antibody circulated in body fluids destroying the infectious antigen

    • Once the pathogens has been isolated by the antibodies, the macrophages are back in business

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6.3.7 HIV and the immune system

external image HIV2.gifHIV is a virus that selectively infects Lymphocytes
(a) Different lymphocytes
(b) HIV virus
(c) Infection as the virus attaches then enters the host lymphocyte.
(d) The infected lymphocyte is 'disabled' by the virus
(e) When an antigen infection is presented the lymphocyte cannot produce antibodies.
(f) The antigen is not challenged by the immune system and is able to freely proliferate
The consequence is that the infected individual will have no immune and develop that disease.

Therefore an individual who is HIV +ve (infected ) will eventually develop a disease which will go unchecked. The consequence is that that disease will severely damage the infected person and will eventually bring about their death.

In the case of the pathogen, human immunodeficiency virus (HIV), the T-Cells are directly attacked and destroyed by the HIV virus. Now there are too few T-cells to trigger B-cells to produce antibodies againt the virus. The HIV can multiply, and the further lack of T-cells means that other types of pathogens getting by the macrophages, can also escape antibody attack. They multiply, causing disease, and the person infected is said to have AIDS. These are called opportunistic diseases.

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Also, See Campbell CD chpt on defense with HIV reproduction chapter.

The HIV virus injects its DNA into the host T - cell where in makes copies of its genetic code and uses the host cell to make its proteins. After several hundred copies of the virus has been made, they break the cell open, and escape to invade more T-cells. It has been shown that the T-cells have a receptor (CD4) that recognises the HIV virus. The virus "anchors" to the receptor where in then injects its DNA into the cell. A co receptor CCRR5 is necesary to co function this event.
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HIV viruses anchor to T-cell

6.3.8 Transmission and social implications of AIDS**
Source: Aids takes an economic and social toll by Belinda Beresford Africa Recovery June 2001
AIDS: Acquired Immuno deficiency syndrome.
  • Acquired relates the infectious nature of AIDS through the transmission of the HIV virus.
  • Immuno deficient relates to the way diseases cannot be resisted.
  • Syndrome relates to the variation in the way the disease manifest itself. People who develop AIDS can be a affected by quite different set of diseases.
Cause: is the HIV retro-virus that selectively infects cells of the immune system effectively disabling primary and secondary response to infection.
Transmission: Through contact with the body fluids of an infected person. In particular the fluids are blood and semen, vaginal mucus. There is a very low risk ( almost zero) associated with salivary mucus.

Cause and effect

autoimmune deficinency syndrome (AIDS) is caused by human immunodeficiency virus (HIV)
HIV is a retrovirus (RNA virus) with its own enzyme, reverse transcriptase, to copy its RNA into DNA after it enters the hostcell.
host cell for HIV is the T lymphocyte cell which triggers the B-cell response
thus, immune system is weakened
and greater opportunity for opportunistic diseses
Transmission through body fluids
  • Sexually transmitted
  • man to woman/man to man/woman to man
  • mother to fetus
  • breast milk/other body fluids
  • use of dirty needles
  • blood transfusions

Social Implications
  • many orphaned children
  • social discrimination
  • problems obtaining employment/life insurance
  • costs are high on health system
  • drug treatment expensive for individuals and health care system
  • encourages use of condoms/reduces promiscuity