Microbes and humans Flashcards
- Microflora/microbiota
2. Microbiome
- everyday microbes of a person
- collective genomes of all microorganisms that live on a person
(used interchangeably)
Microbes colonize human surfaces
3 points
- in contact with the ‘outside world’ (respiratory tract, nose, mouth, gut, skin, gut lumen)
- In healthy people microbes don’t enter internal tissues. Inside of bodies relativley sterile
- If microbes enter beyond surface = possible disease
Microbes at birth
4 points
- Babies born relatively sterile (some bacteria may be passed from placenta)
- Hours after birth gut colonised by microbes from mothers, nurses, bedding etc. [some picked up from birthing canal]
- Microbial community established by 3 yrs old (adult like) [diversity is increasing from birth to 3 yrs]
- Established gut microbiota contributes to overall health, gut physiology and immune system
The skin microbiota
2 points
- Average human skin 2m2
2. Many of 1012 bacteria on skin are commensals or transient [not long lasting, get washed off] microbes
Skin is unsuitable for many microbes
5 points
- pH slightly acidic
- High concentration of sodium chloride
- Often very dry
- Contains antimicrobial properties
- Variable temperatures
Mouth Microbiota
2 points
1. Good environment Lots of water Lots of nutrients Neutral pH Stable optimal temperature
- However
Bacteria must adhere/attach strongly to gums and teeth or they will be washed away
Tolerate antimicrobial properties of saliva e.g. lysozyme
Microbiota
4 points
- linked with various disesases, diabetes, IBD, obesity
- Involved in development of immune system. Dysbiosis [microbiota isnt healthy] is linked to allergies
- 2 main phyla - firmicutes & bacteroidetes [which break down indigestible polysaccharides]
- Gut microbiome has large capacity for degrading complex carbohydrates
Human Pathogens and disease
4 points
- Human associated microorganisms mostly commensals benefit but don’t affect or mutualists both benefit
- Some may cause harm - disease
- Microbes (bacteria fungi, viruses) that cause disease called pathogens (pathos =greek for suffering) larger organism is host
- Opportunistic pathogens - microbes that become pathogens in compromised host (e.g. open wound, trauma, cancer, impaired immune system, antibiotics)
Disease
An injury to a host organism, caused by a pathogen or other factor, that affects host function
Pathogenicity
The ability to cause disease
Virulence
The severity/extent of disease
Infection
Refers to the multiplication of a pathogen in a host
Vector
Another organism that transfers the pathogen to the host (eg. ticks, mosquitoes)
Endemic
A disease that is common to a particular area
eg. Malaria in endemic in some parts of Africa
Epidemic
when the disease occurs higher than expected in a localised area over a short period of time (eg. Seasonal Flu in Western world, Ebola in Africa 2014)
Epidemic –Pandemic
a epidemic that has spread over a very large area over a longer period of time (small pox, tuberculosis, black death, AIDS is currently pandemic)
Human pathogen 3 examples
- Fungal - skin disease - dermatophyte
- Bacterial - food poisoning - Ecoli 0157
- Virus - haemorrhagic fever - ebola
Fungal dermatophytes
4 points
- Common fungal pathogens
- Grow dead skin cells and nails
- Conditions such as ring worm, athletes foot
- Several species of dermatophytes cause similar symptoms
Fungal dermatophytes - ring worm
5 points
- Feed on outer non living layer of epidermis [skin]
- Like other fungi they are saprotrophs feeds on/derives nourishment from decaying organic matter
- Secrete proteases onto skin to digest keratin (keritinase)
- Metabolic by-products cause irritation and inflammation = red, itchy areas
- Grow from point of inoculation active hyphae form growing ring
bacterial pathogens
E.Coli 0157
8 points
- Some strains aquired virulence factors that make them pathogenic [aquired from other sources]
- E.coli food posioning usually due to strain E. coli 0157 (outbreaks in resteraunts, kids nurseries etc.)
- E.coli (EHEC) can colonise cattle without causing infection (asymptomatic no symptoms). Cattle is likely reservoir
- Cattle manure on salads [not washed appropriately] undercooked beef common sources
- EHEC attaches strongly to epithelial cells of gut [has to get through other microbes and mucus layer that sits on top of epithelial cells]
- Stays on outside of epithelial gut & injects its own receprot through type 3 secretion
- Other injected proteins (effector proteins) disrupt gut physiology =diarrhoea & vomiting
- Secrete Shiga toxins inhibit protein synthesis and target kidney and blood vessels [serious infection]
Ebola Virus
3 points
- Cause by Ebola filovirus
- Endemic in african countries
- Recent epidemic in africa due to highly virulent strain = 1000s deaths
Ebola Virus - signs and symptoms
- Patients may suffer from ‘post-Ebola syndrome’ can last for yrs as virus can hide in body [can reoccur]
Ebola Virus Genome codes for 7 proteins
- Polymerase L plus VP35 - replicates viral RNA in cytoplasm
- Nucleoprotein - encapsulates RNA
- VP30 - transcription factor
- Glycoprotein (GP) - thought to be responsible for attachment to host cells
- Viral proteins VP24, Matric VP40 and GP associate with cell membrane
After RNA coated by nucleoprotein buds out through cell membrane gaining outer lipoprotein coat from cell [hides from immune system
How ebola causes disease
4 points
- Enters body through mucosal surfaces (eye, mouth, gut etc.) [human, animal contact]
- Targets most tissues including immune cells - inhibits immune system
- Quickly travels through body - replicates quickly \
- Destroys tissues by interfering with cell-cell adhesion of endothelial cells liing blood vessels > massive internal bleeding (Haemorrhagic fever [fever & lots of bleeding]
Ebola a Zoonotic disease
5 points
- Ebola is a zoonotic disease can be transmitted from animals to man [key]
- Reservoir host unlikely to be monkey/ape as often die
- Bats appear to be natural resevoir as can be carriers without disease (asymptomatic)
- Transmission between human to human - fluid secretions
