PMB: External microbial Flora

Question 1

NOTE

Answer 1

Internal organs are generally free of microorganisms

In this context digestive / urinary etc. tracts counts as outside the body

Surface tissue has lots of microorganisms

Question 2

What is a microbiome?

Answer 2

Collectively the microbial community associated with an organism is called its microbiome

Question 3

What is the main type of microbe in the human microbiomes?

Describe the population changes

Answer 3

Bacteria

Colonise from birth onwars and population changes over time

Question 4

What are earlier colonisers referred to as?

What do they do?

Answer 4

• Early colonisers are commensal bacteria
• Normally mutualistic / symbiotic relationship with the host
  
  • Access to nutrients
  • Defence
  • Multiple factors influence early colonisers

Question 5

NOTE

Answer 5

However, occasionally there can be infections

Opportunistic organism which can cause problems for the host

Some examples may be long-term incubators

Question 6

What acts as a barrier to bacteria attacks?

What happens instead?

Answer 6

• Healthy (intact) skin acts as a reliable barrier to most bacterial attacks
• However many microbes will adhere to the surface of the skin
• Some bacteria are able to attach to surfaces and grow (biofilms)
• Often involves attachment of bacterial adhesins to the glycoproteins of the skin surface

Question 7

Describe the distribution of microbes on skin and the factors which affect distribution

Answer 7

• However although bacteria can colonise much of the skin, the distribution is not even. Certain areas have more microbes than others.
• Also different species in different places
• Factors influencing distribution:
  
  • Nutrients
  • Moisture
  • Temperature
  • pH
  • Skin shedding
  • Fluid osmolarity
  • Potential inhibitors

Question 8

Where are most bacteria typically found

Answer 8

Regions with most apocrine sweat glands

Question 9

Where is the most hair distributed

Answer 9

• Other than the head most confined to:
• Axillary regions (armpits)
• Genital regions

Question 10

Why do microbes grow in places with hair?

What do these microbes produce?

Answer 10

• As hair follices secrete sebaecous fluid which acts as a nutrient
• The microbes then generate by-products which have odours
• Examples include volatile fatty acids (VFAs) e.g. propionic acid

Question 11

What are the 2 types of skin microbes?

Answer 11

• Resident
• Transient

Question 12

Describe transient microbes

Answer 12

• Transient microbes tend to come in contact with the skin and may attach
• However conditions are often not favourable for them and they cannot replicate and multiply, so die off

Question 13

Describe resident microbes

Answer 13

• Note that the resident population tend to have evolved to preserve their access to nutrients in this niche.
• They often produce bacteriocins which can kill the transient species, or help the resident species to outcompete transients

Question 14

Where are large numbers of transients typically found?

What is this influnced by

Answer 14

• Influenced by environmental, domestic and occupational factors
• Exposed areas of the body have higher numbers of transients
• Typically face, neck, hands, etc.
• High temp and humidity = more
• Cold climate = less
• Good personal hygeine and clean living spcae = less
• Young children = more and greater diveristy. More potenitally pathogenic Game -ve species

Question 15

1. What are the 3 regions of skin to consider
2. What is the main class of bacteria. Why?

Answer 15

1. exposed, oily, moist
2. Mainly gram positve.

Much of the skin is relatively dry

This means that some bacteria are prone to desiccation

Therefore less Gram negative bacteria – Acinetobacter being an exception

Question 16

What type of bacteria are mainly present based on pH?

Answer 16

pH of secretions 4-6 therefore most acidophilrd. Neutrophiles tend not to survive

Question 18

How are enteric species spread

Answer 18

Many enteric species can be spread by faecal contamination

Also contact with non-biological material which has become infected

Question 19

What are examples of bacteria which can be spread?

Answer 19

Example species which can be spread:

• Staphylococcus epidermis
• Staphylococcus hominis
• Micrococcus luteus
• Corynebacterium spp.

Question 20

What are ways to reduce spread?

Answer 20

There may be methods we can put in place to reduce the spread of microbes

• Push pads instead of door handles
• Fist bumps instead of hand shakes

Question 21

Discuss scalp and eye infectios

Answer 21

• This can include both bacteria and fungi on the scalp
• The eye also harbours a number of bacterial species
• Note that this will normally be more moist than the skin
• Some potential problems – e.g. conjunctivitis (pink eye) – both viral and bacterial forms exist