Microbe Interactions

Question 1

what do microbes play a pivotal role in

Answer 1

both health and disease of their hosts

Question 2

what is a dynamic ecosystem

Answer 2

where both partners contribute to the outcome of the relationship

Question 3

what are the number of different outcomes for a Host-Microbe symbiosis

Answer 3

Parasitic
Mutualistic
Commensal

Question 4

what is parasitic

Answer 4

-Where one partner is harmed while the other may, or may not, derive benefit.
-Infectious disease.
-Host Harm – easy to detect
-Parasite benefit- difficult to prove
completing life cycle in host is an obvious benefit
-Sleeping sickness

Question 5

what is Mutualistic

Answer 5

-Both partners benefit from the interaction.
-This would be exemplified by organisms that are normally resident on the host.
-Bovine rumen.
Cellulose digestion – benefit to cow
Supply of cellulose – benefit to microbes ??
-Human GI tract
Nutrient absorption - benefit to human host
Immune stimulation - benefit to human host
Supply of nutrients - benefit to microbes ??

Question 6

what is Commensal

Answer 6

-There is no harm perpetrated but no demonstrated benefit either:

-This would be exemplified by organisms that are normally resident on the host
We probably do not understand these interactions well enough.
-Will PROBABLY be reclassified as we understand the systems better.

Question 7

how many cells are in humans

Answer 7

-40 x 1012 cells
40 trillion!

Question 8

how is the human body shared with microbes

Answer 8

1,000, x 1012 microbes
1000 trillion!
Skin
Respiratory tract
Gut

Question 9

how much bodyweight is microbial

Answer 9

1-2kg

Question 10

where are microbes resident on

Answer 10

-a host surface
-internal organs are normally sterile!
resident surface population relatively stable
-on occasion, the residents can invade their hosts and initiate disease i.e. behave in a parasitic manner.
-opportunistic pathogens.

Question 11

what organisms encounter host surfaces on a daily basis (what are they not adapted to ?)

Answer 11

-a huge number of transient organisms
-normally not adapted to remain in this environment and are rapidly lost

Question 12

what is normal microbiota

Answer 12

-Organism focused.
-Microbes that are normally resident on a healthy individual.
-Microbes participating in mutualistic and commensal interactions contribute to the normal microbiota of an animal, plant or human.
-Microbes that occasionally participate in parasitic interactions can also contribute to the normal microbiota.
Opportunistic pathogens

Question 13

what is the microbiota also called

Answer 13

microflora

Question 14

what are some examples of opportunistic pathogens

Answer 14

Neisseria meningitidis= common in respiratory tract, can cause meningitis
Staphyloccocus aureus= common on skin, can cause wound infections

Question 15

what is the microbiome (what has to be considered)

Answer 15

-Habitat focused
-Organisms, associated genes and environmental factors all to be considered

Question 16

what does the microbiota form part of

Answer 16

-a microbiome
-microbiota refers to microorganims present

Question 17

where are the site of microbial residence on the human body

Answer 17

-Skin
-Respiratory tract
-Genitourinary tract
-Conjunctiva ??
-Gastrointestinal tract

Question 18

why is the skin a hostile environment for most microbes

Answer 18

due to….
-thick, keratinised surface layer
-low pH
-low H2O availability
-antimicrobial secretions from glands= Apocrine, Eccrine and Sebaceous

Distribution of glands is not uniform therefore resident microbiota not uniform (microenvironments)

Question 19

look at diagrams in booklet

Question 20

what organisms are normally resistant to drying

Answer 20

gram postive and yeasts
e.g candida albicans are gram rods and have an avergae frequency of isolation is less than 10%
e.g enteric bacteria are gram rods and have an average frequency of isolation of 60%

Question 21

How do we study skin microbiota- original methodology

Answer 21

-Sample skin with sterile swab
-Transfer to selective growth media
-Different media support different organisms
-No one medium that will support every organism

Question 22

How to study skin microbiota- current methodology

Answer 22

-Sample skin with sterile swab
-Extract DNA from sample
-Amplify universal target gene
-16S rRNA
-Sequence all 16s RNA genes
-Compare with database

Question 23

what are the current findings on human microbiota

Answer 23

-51 students
-4,742 “species”
~150 species/person
-Females have greater diversity than males
-Differences between right and left hands

Question 24

what are the microbes in the upper respiratory tract

Answer 24

Microbes move from the skin to populate this region by colonising mucosal surfaces.
Nose
Nasopharynx
Oropharynx
Resident bacterial populations are established by organisms capable of attaching to mucosal epithelial cells.

Question 25

what are many of the specieis in the upper respiratory tract (anaerobes)

Answer 25

Many species inhabiting this region are anaerobes (both facultative and obligate).

Question 26

what are the microbes like in the lower respiratory system (transients but no permanent population)

Answer 26

Transient microbes may be detected but there is no permanent, resident population.
Bronchi
Alveoli

Question 27

how is the lower respiratory tract sterile (non specific defence mechanism)

Answer 27

This region is “sterile” due to the efficiency of the non-specific defence mechanisms.
Alveolar macrophages
Mucocilliary escalator

Question 28

where are the microbes in the oral cavity

Answer 28

teeth, saliva and buccal epithelium

Question 29

what does the salvia contain

Answer 29

The saliva contains nutrients yet also contains inhibitory substances which regulate the population=
lysozyme and lactoperoxidase

Question 30

how is the Upper genitourinary tract normally sterile

Answer 30

due to regular flushing with urine= bladder, kidney, ureter

Question 31

what microbes are in the lower genitourinary tract

Answer 31

has a normally transient population that originates from the intestinal tract or from the skin surface e.g
Staphylococcus epidermidis
Enterococcus faecalis
Corynebacterium spp.
Neisseria spp.
Enterobacteriaceae

Question 32

what are the microbes in the vagina like

Answer 32

Vagina has a resident microbiota
mucosal surface
hormone regulated

Question 33

what happens to Lactobacillus spp after puberty

Answer 33

they become the dominant population metabolising glycogen and releasing organic acids as a metabolic by-product
Low pH makes the environment inhibitory to most other bacteria.

Question 34

what surface has a large daily inoculum of microbes (types of environment)

Answer 34

mucosal
-Different environments= Stomach, small intestine and large intestine
-Hostile environments (highly adapted)=
pH extremes, temperature changes, bile salts, digestive enzymes, Peristalsis
and large commensal population

Question 35

How to study GI microbiota- original methodology

Answer 35

-Collect faecal sample
-Transfer to selective growth media
-Different media support different organisms
-No one medium that will support every organism

Question 36

How to study GI microbiota-current methodology

Answer 36

-Collect faecal sample
-Extract DNA from sample
-Amplify universal target gene= 16S rRNA
-Sequence all 16s RNA genes
-Compare with database
-Metagenomics

Question 37

what is metagenomics

Answer 37

-the study of the structure and function of entire nucleotide sequences isolated and analyzed from all the organisms (typically microbes) in a bulk sample
-Gut samples from 39 individuals
-Total DNA extraction
-Amplification of 16s rRNA sequences
-Matching sequences to databases to identify organisms in each individual

Question 38

Are we all the same with respect to gut microbiota?

Answer 38

No - Three ENTEROTYPES identified

Question 39

what are the new gut bacteria

Answer 39

Identified in last ~5 years following metagenomic investigation of gut microbiome
-Faecalibacterium prausnitzii
-Prevotella copri
-Akkermansia muciniphila

Question 40

what are Faecalibacterium prausnitzii

Answer 40

-Gram-positive, rod, anaerobe
-Most abundant bacterium
-Low levels linked to digestive problems, obesity, asthma and depression

Question 41

what are Prevotella copri

Answer 41

-Gram-negative, rod, anaerobe
-High levels linked to developing Rheumatoid arthritis??

Question 42

what are Akkermansia muciniphila

Answer 42

-Gram-negative, oval, anaerobe
-Low levels linked to digestive problems, obesity and IBD

Question 43

Gnotobiotic V Normal Microbiota

Answer 43

similar gross morphology, but Major biochemical/metabolic/immunologic differences

Question 44

what is Gnotobiotic

Answer 44

-thin intestinal epithelium
-enlarged caecum
-vitamin requirements
-lower cardiac output
-lower metabolic rate
-poor development of:
lymphatic system
B cells
reticuloendothelial cells
-susceptible to infection= low infective doses
-susceptible to infection= infection by opportunistic pathogens

Question 45

how can gut microbiota regulate obesity

Answer 45

4 human female twin pairs discordant for obesity
One fat (ob) and one thin (ln)

transferred the intestinal microbiota in fecal samples from each of them into the intestines of germ-free mice.

Animals receiving a transplant from the obese (Ob) twin donors developed increased adiposity compared to those receiving transplants from lean (Ln) twin donors.

Diet and gut microbiota were both responsible for obesity