L31 - human microbiota & barrier to defence Flashcards
outcomes
- describe microbiota on body surfaces
- describe non-specific barriers to infection
what are microbiota?
- microorganisms on our body surfaces
- groups of micro-organisms living in a specific environment
- e.g group of bacteria living in your stomach or mouth
facts about microbiota
- not usually harmful
- often vital to health
how is an individuals microbiota usually unique?
- microbiota develops from birth
- age, diet, lifestyle, time of year
what are indigenous human commensals?
- commensal bacteria that colonise our body surfaces: indigenous human commensals
- beneficial for bacteria + host
- protects us against pathogens
how do indigenous human commensals protect us against pathogens?
- pathogens need to adhere to a surface and gain nutrients from the host
- this is harder to do if commensal bacteria are already established
- have to compete
what do commesal bacteria do?
- colonise our bodies
- community develops + establishes over first 3 years of life into diverse ecosystem
- continues to develop
- affected by whole range of factors
- only know as indigenous if colonise body SURFACE
what is the gut microbiome essential for?
- breakdown of our food
- synthesis of essential vitamins B12 + vitamin K
why do we assume humans are getting essential vitamins from gut bacteria?
- plants and animals are unable to synthesise vitamin B12 and K
- so we assume they’re from our gut bacteria
examples of things gut bacteria can influence
- obesity
- malnutrition
- allergies
- mental health immune disorders
what can indigenous human commensals also be?
- opportunistic pathogens which CAN cause harm
- when status quo is perturbed
- most of time do not cause infection but will if have chance
what is pseudomonas?
- example of opportunistic pathogen
- common soil + water bacteria
- found in a burns patient, cystic fibrosis or weakened immune system
what is E.coli?
- opportunistic pathogen
- naturally inhabits gut
- causes UTI if get into wrong place
- colonic bacteria
skin flora
- caused by opportunistic pathogen staphylococcus sp.
- bacteria cause infection on wound or if you have surgery
oral flora
- caused by opportunity streptococcus sp.
- tooth decay if it become imbalanced
normal human microbiota
- skin
- upper respiratory tract: nose + throat
- lower respiratory tract
- digestive system
- urinary tract
- adult female genital tract
all are mucosal.
diff environments have diff colonisers/ microbiota
what is the skin human microbiota divided into?
- 3 microenvironments
1. dry skin (arms + legs)
2. moist skin areas (armpits)
3. areas rich in sebaceous glands
why is moist skin most susceptible to colonisation?
- have water
- which bacteria need to grow
what are most natural colonisers of the skin?
- gram positive bacteria = less susceptible to drying due to thick cell wall
- staphylococcus, streptococcus
- corynebacterium, propionibacterium
- don’t usually cause disease
- but skin wound can lead to infection
what does MRSA stand for?
Methicillin-resistant Staphylococcus aureus
normal microbiome in upper respiratory tract (nose and throat)
- lots of bacteria flora
- streptococcus, staphylococcus
- neisseria, Haemophilus
what can cause bacterial meningitis?
3 species of bacteria (streptococcus,
neisseria, Haemophilus)
normal microbiota of lower respiratory tract
- usually sterile
- common site of infetion
- chest infections/ pneumonia = haemophilus, streptococcus
- tuberculosis: mycobacterium tuberculosis
- trachea, bronchi, lungs
normal microbiota of digestive system: mouth (oral cavity)
- over 600 species
- gingival groove: anaerobes: cause gum disease
- tooth enamel: facultative aerobes: some cause plaque + tooth decay
- cheeks + gums: facultative aerobe: some colonise saliva
normal microbiota of digestive system: stomach
- stomach has less bacteria than mouth: least colonised part of digestive system
- strong acidic conditions
- highly mobile
- helicobacter pylori can airs in stomach
- they decrease acid secretion, cause neutralisation of acid, increase bacteria growth
- cause gastric ulcers
- linked to cancer
normal human microbiota of digestive system: small intestine
- duodenum is very acidic
- lots of digestive enzymes
- highly mobile
- low amount of bacteria
- the ileum is less acidic, less enzymes, less motile, numbers of bacteria increase
the normal microbiota of the digestive system: large intestine
- most heavily colonised part of system
- little oxygen so all bacteria are anaerobes or facultative anaerobes
- most common bacteria is bacteroides fragilis: usual cause of appendicitis
- enterococcus faecalis can cause problems if it moves from intestine (infections in heart, biofilms endocarditis)
- e.col (not a problem, unless it ends up in urthera)
