Archive for December 13th, 2009

Immunity to Bacteria

Another article is up on www.jameswatts.co.uk, this one is about how the immune system deals with bacteria – Below is only the introduction, if you would like to read more then remember to check out the above ^^^

Introduction

Bacteria exist naturally on many biological surfaces, for example the skin or the lining of the intestines. Bacteria like these make up the body’s natural flora and have a range of symbiotic relationships; a good example would be the flora of the rumen in cattle which degrade food materials, providing energy for both the cattle and the bacteria. The three main types of symbiotic relationship are:

•Mutualism – Both members of the symbiotic relationship benefit

•Commensalism – No apparent harm/benefit occurs to either member of the relationship

•Parasitism – One member of the relationship is living at the expense of the other resulting in disease

The pathogenicity of a certain bacteria depends on its survival inside the host – how well is it able to resist or evade host defence mechanisms and immune response. The resulting disease/damage caused to tissue is due to either the pathogenicity of the bacteria or the immune response of the host itself.

Bacterium Structure

Prokaryotes vs. Eukaryotes

Bacteria are prokaryotes, they differ from eukaryotic cells (such as those in humans) because the structures within prokaryotic cells are typically not compartmentalised. Prokaryotes also lack nuclear membranes, mitochondria, endoplasmic reticulum, a Golgi body, phagosomes and lysosomes (unlike eukaryotes). Also, prokaryotes only have a single, circular chromosome – unlike the nucleus of a eukaryotic cell.

Gram Staining

Bacteria can be very broadly categorised into two groups, gram negative and gram positive. This describes whether or not the bacterial will stain when using a gram stain. Gram-negative bacteria do not take up the gram stain; this is due to an extra outer membrane. Gram-positive bacteria do not have this extra outer membrane and so will take up the gram stain.

Bacterial Structures

•Plasmids – This is an extra-chromosomal strand of circular DNA, it is able to replicate independently from the main chromosome in the bacteria and the genes which the plasmid codes for aren’t typically essential for survival. The plasmid may be shared between bacteria which may be of concern as the plasmid often codes for pathogenesis and anti-bacterial resistance.

•Cell Envelope – This is the extra outer membrane seen in gram-negative bacteria

•Flagella – A protein organelle (consisting of flagellin) which is used for locomotion

•Pili (Fimbriae) – This is the organelle which allows adhesion to the epithelium of host cells.

•Capsules and ‘slime’ layers – These are layers outside of the cell envelope in some specialised bacteria. This extra layer allows the inhibition of ingestion by phagocytes as they are unable to detect the bacterium. A well-defined layer is known as a capsule, a lesser defined layer is known as a slime layer.

•Endospores – This is a term given to dormant forms of bacteria which are able to survive harsh conditions

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Bacterial Immunity

This article can be found in full length at www.jameswatts.co.uk – Only the introduction is shown here

Introduction

Bacteria exist naturally on many biological surfaces, for example the skin or the lining of the intestines. Bacteria like these make up the body’s natural flora and have a range of symbiotic relationships; a good example would be the flora of the rumen in cattle which degrade food materials, providing energy for both the cattle and the bacteria. The three main types of symbiotic relationship are:

  • Mutualism – Both members of the symbiotic relationship benefit
  • Commensalism – No apparent harm/benefit occurs to either member of the relationship
  • Parasitism – One member of the relationship is living at the expense of the other resulting in disease

The pathogenicity of a certain bacteria depends on its survival inside the host – how well is it able to resist or evade host defence mechanisms and immune response. The resulting disease/damage caused to tissue is due to either the pathogenicity of the bacteria or the immune response of the host itself.

Developing Immunity in New-Borns

The start if the article about new-born immunity is below, if you would like to see this in full then please remember to visit www.jameswatts.co.uk where you can also find a multitude of other articles and stories as well!

Introduction

Any new-born animal is born from a sterile environment (e.g. a mother’s womb) into an environment which is filled with microbes and pathogens. Therefore it is important that the newly born animal is able to protect itself in its new, harsh environment. In most species (especially those with longer gestation periods) at birth, the immune system is well on its way to being fully developed but is not yet complete, taking some time (up to several weeks) to become fully functional.

For the immune system to develop, antigenic stimulation must occur, along with the development of antigen sensitive cells. This means that for the first few weeks of a new-borns life they are vulnerable to infection as their immune system is not yet complete. To overcome this, a temporary support system is provided by the mother. The mother is able to pass to her offspring antibodies and T-cells. These are able to temporarily support the animal whilst it builds up its own immune system. This is known as passive immunity.

The Developing Immune System

The development of the immune system in mammals as a foetus follows a consistent pattern. The initial lymphoid organ which develops is the thymus which is then followed by the secondary lymphoid organs (e.g. tonsils, Peyer’s patches, spleen, adenoids, skin etc.). The ability of the foetus to initiate a cell-mediated immune response develops around the same time as antibody production begins.

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