Microbe Interactions Flashcards
what do microbes play a pivotal role in
both health and disease of their hosts
what is a dynamic ecosystem
where both partners contribute to the outcome of the relationship
what are the number of different outcomes for a Host-Microbe symbiosis
Parasitic
Mutualistic
Commensal
what is parasitic
-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
what is Mutualistic
-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 ??
what is Commensal
-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.
how many cells are in humans
-40 x 1012 cells
40 trillion!
how is the human body shared with microbes
1,000, x 1012 microbes
1000 trillion!
Skin
Respiratory tract
Gut
how much bodyweight is microbial
1-2kg
where are microbes resident on
-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.
what organisms encounter host surfaces on a daily basis (what are they not adapted to ?)
-a huge number of transient organisms
-normally not adapted to remain in this environment and are rapidly lost
what is normal microbiota
-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
what is the microbiota also called
microflora
what are some examples of opportunistic pathogens
Neisseria meningitidis= common in respiratory tract, can cause meningitis
Staphyloccocus aureus= common on skin, can cause wound infections
what is the microbiome (what has to be considered)
-Habitat focused
-Organisms, associated genes and environmental factors all to be considered
what does the microbiota form part of
-a microbiome
-microbiota refers to microorganims present
where are the site of microbial residence on the human body
-Skin
-Respiratory tract
-Genitourinary tract
-Conjunctiva ??
-Gastrointestinal tract
why is the skin a hostile environment for most microbes
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)
look at diagrams in booklet
what organisms are normally resistant to drying
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%
How do we study skin microbiota- original methodology
-Sample skin with sterile swab
-Transfer to selective growth media
-Different media support different organisms
-No one medium that will support every organism
How to study skin microbiota- current methodology
-Sample skin with sterile swab
-Extract DNA from sample
-Amplify universal target gene
-16S rRNA
-Sequence all 16s RNA genes
-Compare with database
what are the current findings on human microbiota
-51 students
-4,742 “species”
~150 species/person
-Females have greater diversity than males
-Differences between right and left hands
what are the microbes in the upper respiratory tract
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.
what are many of the specieis in the upper respiratory tract (anaerobes)
Many species inhabiting this region are anaerobes (both facultative and obligate).
what are the microbes like in the lower respiratory system (transients but no permanent population)
Transient microbes may be detected but there is no permanent, resident population.
Bronchi
Alveoli
how is the lower respiratory tract sterile (non specific defence mechanism)
This region is “sterile” due to the efficiency of the non-specific defence mechanisms.
Alveolar macrophages
Mucocilliary escalator
where are the microbes in the oral cavity
teeth, saliva and buccal epithelium
what does the salvia contain
The saliva contains nutrients yet also contains inhibitory substances which regulate the population=
lysozyme and lactoperoxidase
how is the Upper genitourinary tract normally sterile
due to regular flushing with urine= bladder, kidney, ureter
what microbes are in the lower genitourinary tract
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
what are the microbes in the vagina like
Vagina has a resident microbiota
mucosal surface
hormone regulated
what happens to Lactobacillus spp after puberty
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.
what surface has a large daily inoculum of microbes (types of environment)
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
How to study GI microbiota- original methodology
-Collect faecal sample
-Transfer to selective growth media
-Different media support different organisms
-No one medium that will support every organism
How to study GI microbiota-current methodology
-Collect faecal sample
-Extract DNA from sample
-Amplify universal target gene= 16S rRNA
-Sequence all 16s RNA genes
-Compare with database
-Metagenomics
what is metagenomics
-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
Are we all the same with respect to gut microbiota?
No - Three ENTEROTYPES identified
what are the new gut bacteria
Identified in last ~5 years following metagenomic investigation of gut microbiome
-Faecalibacterium prausnitzii
-Prevotella copri
-Akkermansia muciniphila
what are Faecalibacterium prausnitzii
-Gram-positive, rod, anaerobe
-Most abundant bacterium
-Low levels linked to digestive problems, obesity, asthma and depression
what are Prevotella copri
-Gram-negative, rod, anaerobe
-High levels linked to developing Rheumatoid arthritis??
what are Akkermansia muciniphila
-Gram-negative, oval, anaerobe
-Low levels linked to digestive problems, obesity and IBD
Gnotobiotic V Normal Microbiota
similar gross morphology, but Major biochemical/metabolic/immunologic differences
what is Gnotobiotic
-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
how can gut microbiota regulate obesity
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
