Microorganisms

Question 1

Define the terms: Colonisation, commensalism and symbiosis

Answer 1

• Colonisation: acquisition of a micro-organism by the host
• Commensalism: a state of infection that results in no damage to the host
* Symbiosis/Mutualism: a state of infection where both the host and microbe benefit from the interaction

Question 2

Why are commensal microorganisms beneficial for us?

Answer 2

• Comprise the normal microflora of the skin, oral, respiratory and gastrointestinal tracts
• Provides important stimuli for the development of immunity and gut development
• Can protect the host by physically and metabolically preventing colonisation by other more pathogenic organisms
• Can synthesize metabolites that are essential nutrients for the host and aid breakdown of non-digestible food components (symbiosis)

Question 3

What are the processes involved in gram staining?

Answer 3

1. Fixation: The clinical materials are “fixed” or glued/stuck onto the surface of a microscopic slide either by heating or using methanol
2. Crystal violet: this stains all cells bluish purple
3. Iodine treatment: Is added to form a crystal violet iodine complex
4. Decolorization: AN organic solvent like acetone or ethanol extracts the blue dye complex from the thin walled gram negative bacteria than the thick walled gram positive bacteria. The -ev bacteria will become colorless while the +ev will be blue
5. Safranin: The red dye safranin stains the decolorized -ev cells red/pink.

Question 4

What are examples of non-specific immunity in the oral cavity? (5)

Answer 4

• In the oral cavity, saliva washes the mucosal surfaces
• Epithelial cells release anti-microbial peptides
• Local blood vessels respond to alarm signals by releasing migrating phagocytic white blood cells
• There are various junctions between epithelial cells. They help prevent the entry of bacteria
* Toll like receptors detect microorganisms connected to the inflammatory response

Question 5

What are the terms to describe shapes and arrangements of bacteria?

Answer 5

Predominant shapes are:
• Cocci (coccus, s.): round or spherical
• Bacilli (bacillus, s.): rod-shaped
• Spirochaetes (Spirilla): spiral-shaped
• Other shapes: filamentous, curved, square, pleomorphic

Can be arranged as: 
Staphylo: clumps 
Strepto: chains 
Diplo: in twos 
Tetrads: in fours  
Cubic: in eights