Normal Flora

Question 1

define - human microbiome

Answer 1

– a mixture of microorganisms that colonise different sites of the body
Humans are free from microbes until they are rapidly colonised.

Question 2

Four major sites of colonisation:

Answer 2

• Skin
• Oral cavity
• Respiratory tract
• Gastrointestinal tract
• Urogenital tract

Question 3

What can affect mammalian normal flora?

Answer 3

• Birth
• Weaning
• Diet (+/- meat)
• Geography
• Age (puberty)
• Chemotherapy (antibiotic use – can make you lose some normal flora)

Question 4

Skin

Answer 4

Generally unfavourable place for microbial growth
Mostly dry
Varies greatly in chemical composition
Diverse community - bacteria + fungi (yeasts)
Largest physical barrier - large SA
Complex - variety of microenvironment - dry & moist
Mix of aerobes and anaerobes
residents are joined by transient microorganisms (from touching surfaces etc)
- don’t last long - unsuitable conditions

Question 5

Microorganisms found on skin

Answer 5

Gram positive bacteria dominates skin flora
- thick cell wall

e.g, staphylococci

Question 6

Oral cavity

Answer 6

Made up of diverse habitats – soft (palate, cheeks + tongue) & hard tissue (teeth, bridges + dentures)
It contains a diverse flora
Areas can be aerobic/anaerobic
First ‘internal’ biofilm

Question 7

The bacterial flora of oral cavity include:

Answer 7

Streptococci – 22% of plaque and gingival crevice flora (association)

Question 8

Defence mechanisms of the mouth include:

Answer 8

Salvia, secreted antibodies (IGG) and enzymes (lysozymes and lactoperoxidase)
Brushing – can get rid of plaque

Question 9

Periodontal disease/gingivitis:

Answer 9

• Occurs in the gingival crevice leading to inflammation of gums, periodontal fibres
• Can cause halitosis, leading to loss of the tooth
• Additional health complications – associated with heart issues – mitral valves
• If streptococci associated with plaque enters the blood stream, they have a predominance to enter the mitral value and cause a secondary biofilm - endocarditis

Question 10

Respiratory tract

Answer 10

[divided into upper and lower respiratory tract]

Upper RT: nasopharynx, oral cavity and throat
Nasal passages heavily colonised by – staphylococcus and corynebacterium
Throat (phaynx)
- Streptococci spp.
- Gram-negative cocci
Generally bacteria is found in the URT
Moist, higher temperature (37), neutral pH and more nutrients
Delicate
URT – normal flora
Many infections are brought into the body in this way

Question 11

Infections in respiratory tract

Answer 11

Viruses e.g., influenza
Bacteria – whooping cough and diphtheria
Fungi – aspergillus spp.

URT can carry potential pathogenic bacteria:
- 30% of the population carry staphylococcus aureus in their nares

Lower RT (trachea, bronchi and lungs) is essentially free of microorganisms.
-	This can change in illness