Objectives



  1. Describe the body’s general defence mechanisms. (natural/innate/non-specific immunity).
  2. Describe the inflammatory response to bacterial infection.
  3. Describe the normal flora of the skin.
  4. Describe the structure of a bacterial cell, and state the major differences between these and eukaryotic (e.g. human) cells.
  5. Discuss possible local treatments for wound infections by bacteria and explain when they would be used, and how they work.
  6. Discuss the importance of infection control, both for medical personnel and for patients; and also how antiseptic agents may promote this.

Site: http://academic.pgcc.edu/~aimholtz/AandP/206_ONLINE/Immune/nonspecificimmune.html


+ T cells

CD4+ T cells bind an epitope consisting of an antigen fragment lying in the groove of a class II histocompatibility molecule. CD4+ T cells are essential for both the cell-mediated and antibody-mediated branches of the immune system:
  • cell-mediated immunity
These CD4+ cells bind to antigen presented by antigen-presenting cells (APCs) like phagocytic macrophages and dendritic cells. The T cells then release lymphokines that attract other cells to the area. The result is inflammation: the accumulation of cells and molecules that attempt to wall off and destroy the antigenic material (an abscess is one example, the rash following exposure to poison ivy is another).
Discussion of cell-mediated immunity.
  • antibody-mediated immunity
These CD4+ cells, called helper T cells, bind to antigen presented by B cells (as shown above). The result is the development of clones of plasma cells secreting antibodies against the antigenic material.

Bacterium
A bacterium is a group of microorganism all of which lack a distinctive nuclear membrane, these cells are more primitive than animal cells they have a unique cell composition and hence antibiotics is required to destroy the cell walls. Many bacteria are unicellular hence the cell can have different forms, they can be spherical (coccus), rod-shaped (bacillus), spiral (spirillum), comma-shaped (vibrio) or corkscrew (spirochaete). However their general size can vary between 0.5 to 5 μm. Motile species are able to move around with special organelles called flagella, however bacteria reproduce asexually and DNA is transmitted across bacteria through conjunction. There are two places where DNA is being held, the usual “chromosome” where DNA is packed tightly however there is no nuclear membrane surrounding the nucleus (prokaryote) and additionally the DNA can be extrachromosomal in the plasmid. The DNA in bacteria are lacking introns which means the whole DNA will be copied, wheras introns allow a specific part of the DNA to be copied.
The ribosomes in bacteria are the size of 70s and the size of ribosomes in eukaryotic cells are 80s (s is referring to a unit used when a particle is under heavy centrifugal force in ultracentrifuge). Gram stains are very important for classification and identification of the different types of bacteria if a bacteria is gram-negative peptidoglycan (consisting of sugar and amino acids) is thinner than a gram positive bacteria.
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Gram Positive
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Gram Negative
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1.A very thick cell wall (peptidoglycan)
2.If a flagellum is present, it contains two rings for support (an additional two rings are not necessary, unlike in Gram-negative bacteria, because the thick cell wall is supportive enough)
3.Teichoic acids are present, which serve to act as chelating agents, and also for certain types of adherence

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1. Cell walls only contain a few layers of peptidoglycan (which is present in much higher levels in Gram-positive bacteria)
2. Cells are surrounded by an outer membrane of lipopolysaccharide outside the peptidoglycan layer
3. Porins exist in the outer membrane, which act like pores for particular molecules
4. There is a space between the layers of peptidoglycan and the secondary cell membrane called the periplasmic space
5. The S-layer is directly attached to the outer membrane, rather than the peptidoglycan
6. If present, flagella have four supporting rings instead of two
7. No teichoic acids are present
8. Lipoproteins are attached to the polysaccharide backbone whereas in Gram-positive bacteria no lipoproteins are present.
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Fimbriae or pili are used for attachment or adhesion; sex fimbrae are associated with conjugation.
Capsules: This is the tissue which surrounds the bacteria it is polysaccharide in most of the cases however it can be protein in some others as well.

Bacteria receive energy through metabolising preformed organic molecules, however there are bacterias who can metabolise aerobically or anaerobically, depends on the environment of the bacteria. They can take the nutrients up through their walls.

Bacteria divide every 30-40 minutes depending on the quantity of the nutrition which is available, however some bacteria are not affected with that at all, they will grow at the same rate even in the best condition. If a bacteria are introduced into a new environment they will eventually have a sluggish phase, then increase exponentially, but then stay constant and eventually decline as nutrition has depleted and toxins have increased.





What is Innate/non-specific response Immune response?

Innate immunity is immunity present naturally inside the body and has no relation if there is a exposure to any pathogens, e.g. humans are naturally have immune against some diseases which other species aren’t. Innate immunity only breaks down in the case of HIV infection.
The immune system of mammals is composed of a complex constellation of cells, organs and tissues, arranged in an elaborate and dynamic communications network and equipped to optimize the response against invasion by pathogenic organisms. The immune system is, in its simplest form, a cascade of detection and adaptation, culminating in a system that is remarkably effective.
The immune system protects the body from infection by employing three basic strategies:
· Creating and maintaining a barrier that prevents bacteria and viruses from entering the body.
· If a pathogen breaches the barriers, and gets into the body, the innate immune system is equipped with specialized cells that detect, and often eliminate, the invader before it is able to reproduce and cause potentially serious injury to the host.
· If a pathogen is able to successfully evade the innate immune cells, the immune system activates a second, adaptive immune response against the pathogen. It is through the adaptive immune response that the immune system gains the ability to recognize a pathogen, and to mount an even stronger attack each time the pathogen is encountered.
When the immune system is deficient in one or more of these functional components, immune responses are usually compromised, resulting in a condition known as an immunodeficiency disorder. These disorders can be inherited or acquired (such as HIV), or can result from the use of immunosuppressive drugs.
Efficient host defense by the immune system depends on the recognition of “self” (the host) and the identification of “non-self” (the foreign invaders). Occasionally, the immune system mistakes the host for an invader, and launches an attack on the body’s own cells, leading to a condition known as autoimmunity. In other situations, the immune system may make an overabundant response to an invader or to an innocuous substance, resulting in a hypersensitivity response, or an allergy.
Advances in the field of immunology (the study of the immune system) have enabled humans to manipulate the immune system in many ways, such as; to inhibit overzealous responses, such as those seen in autoimmunity and allergy, or, to artificially stimulate protective responses against pathogens, in a process known as immunization.
Inflammation

This is a non-specific immune response to counter damaged tissue, there are many reasons why inflammation can occur the main reasons however are pathogens, abrasions, chemical irritation and disturbance of cells.
The main symptoms of Inflammation are as follows:
The Major three steps which occur during inflammation are as follows:
1. vasodilation & increases permeability of blood vessels
The increased Blood Flow even removes toxins and dead cells. The reasons why blood vessels dilate:
Histamine is ebing released by platelets and basophils and histamine. Neutrophils and macrophages are being attracted through these processes.
Antibodies and defensive mechanisms and clotting factors can enter the wound area much easier.
Kinins, polypeptides are formed in blood from inactive precursors called kininogens induce vasodilation and they increase vasodilation and act as chemotactic agents for pahgocytes.
Prostaglandins these lipids amplify the effects of histamine and kinins, they also stimulate the emigration of phagocytes through capillaries.
Leukotrienes they are produced by basophils and mast cells, they cause increased permeability and do the same as above.
Complement: they cause increased permeability and some of the components destroy bacteria,

· Redness (erythma) & Heat
Redness & heat is due to increased blood flow to the affected area as vasodilation increases permeability and hence nutrients which are usually kept in the blood can move into the tissue. As the blood increases metabolic processes can occur much better and in this creates additional heart.

· Pain
This happens as neurons are damaged due to toxins released by the microbes, however kinins affect the nerve endings as well conjoining inflammation with pain, the same occurs with prostaglandin, and the swelling can be a factor as well.
· Swelling (edema)
Occurs due to increased permability of blood vessels this allows more fluid to be moved trough the vessels into the affected area.

2. emigration of phagocytes from blood into the interstitial fluid
Within a hour the inflammatory process starts phagocytes appear and neutrophils stick on the endothelium of blood vessels, the neutrophils try to reach the affected area, this process is called emigration and depends on chemotaxis, neutrophils try to destroy the microbes by phagocytosis, and a steady stream of leukocytes is held by red bone marrow. The term for this is leukocytosis. Neutrophils are predominant in the initial steps, they die off fast, then monocytes follow neutrophils into the affected area and transform into macrophages, and they are much stronger than the neutrophils. They are large enough to engulf damaged tissue, worn out neutrophils and microbes. After couple of days a pocket of dead phagocytes and damaged tissue forms pus, which is a collection of dead tissue, pus is formed until and mostly even after the inflammation has ended, usually pus remains after the infection and is destroyed internally and absorbed or it drains into internal cavities.

3. tissue repair
The increased permeability allows the movement of clotting factors into the blood and hence the fibrinogen is changed into fibrin which blocks the spread of microbes.

Inflammation can lead to loss of functions like touch or sensitivity or overall movement is reduced.

Normal Skin flora

Skin is full of microorganisms including yeasts and bacteria, which can not be killed by any amount of washing or cleaning, in general these organism keep each other in check so no infection occurs, however if there is a imbalance due to not properly cleaning of the skin can lead to infections.

What is antiseptic, and what does it do?
These are chemicals which inhibit or destroy the growth of disease causing bacteria and microbes, however the antiseptic is and should be toxic for the microbes and bacteria only but not for the skin, they are applied to clean the mucous membranes and to prevent infections entering the wound.
Mainly antiseptics are used for either chemically or physically to kill off bacteria.

Discuss possible local treatments for wound infections by bacteria and explain when they would be used, and how they work.
The wound should be cleaned and a non fluffy pad and bandage should be put onto that, the support and injured part should be raised so the swelling will be reduced, depending on how far the infection went, a doctor should be called or the patient should be taken to the A&E.