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Module: BIOM - 1009

Lecturer: Dr Ioannou

Date: 04/10/16

Gram Positive Bacteria
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Important structural features in Gram positive bacteria include:
 Capsule formation, e
...
Streptococcus pneumoniae
 Spore formation, e
...
Bacillus spp

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A capsule is a layer of material often seen on the surface of cells when using Gram staining
 It is a well organised, dense structure, usually
consisting of polysaccharides
 It helps bacterium evade the immune system by
acting as a protectant against phagocytosis
 It may also defend the bacteria from
desiccation
 It unusually doesn’t show up on a Gram stain and is
instead a clear film around the bacteria
 The image on the right is Klebsiella pneumoniae, a
bacterium under a Gram stain
...
One side then engulfs the other thus having 2 layers
 These spores are highly resistant to heat, UV radiation, chemical disinfectants and
desiccation
 Some bacteria with this can survive in boiling water for an hour
 Spores are impermeable to most stains and so go colourless in a Gram stain
 The position of the spore during staining is used to identify the species of bacteria
 Bacillus cereus is an example of a spore former, as seen below during a spore stain:

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Below is a table showing some Gram positive bacteria and their associated diseases:

Microbe

Disease

Staphylococcus aureus

MRSA & MSSA

Streptococcus pyogenes

Sore Throat & Scarlet Fever

Streptococcus pneumoniae

Pneumonia

Bacillus cereus

Food Poisoning

Clostridium botulinum

Severe Food Poisoning



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