human microbiota

what is microbiota

• they are groups of micro-organisms living in a specific environment

• they are not usually harmful and are actually vital to our health

• individuals microbiota is unique to their age, diet lifestyle and the time of year

• they can be describes as indigenous human commensals as they benefit from being on the human and the human also benefits from them being there as they protect against pathogens

• but they can be opportunistic pathogens as they can cause harm if normal conditions change like during burns, injury weakened immunity and they can cause disease.

what is the function of the gut microbiome

• it is essential for the breakdown of our food

• synthesis of vitamins B12 and vitamin K

• potentially involved in obesity, allergies, immune disorders too

describe the microbiota on the skin

• its divided into 3 microenvironments

dry skin ( arms and legs ), moist skin areas ( armpits ), areas rich with sebaceous glands ( oily skin )

• typically contains gram positive bacteria ( they contain a thick cell wall resistant to drying )

e.g streptococcus and staphylococcus

• they dont usually cause disease but skin wound can lead to infection

e.g staphylococcus aureus

describe the microbiota on the upper respiratory tract ( nose and throat )

• extensive bacterial flora

• typically consists of streptococcus and staphylococcus

• bacteria like , Neisseria meningitidis and haemophilus influenzae can cause bacterial meningitis

describe the microbiota in the lower respiratory tracts ( trachea, lungs )

• it is usually sterile

• but its a common site of infection typically chest infections and pneumonia and tuberculosis

describe the microbiota in the digestive system- mouth

• its a very complex microbial ecosystem

• the mouth is split into different micro-environments: tongue, cheeks gum, teeth

• cheeks and gums- facultative aerobes (e.g. streptococcus)

• tooth enamel- facultative aerobes ( e.g. streptococcus )

• where the teeth meets the gum- anaerobes

• e.g. Bacteroides, actinomyces= they can cause gum disease and

describe the microbiota in the main digestive system ( the stomach, small intestines and large intestines)

• stomach

acidic environment with less than 10CFU/ml ( colony forming units )

Heliobacter pylori which may cause stomach ulcers are present

• small intestines

the duodenum has around 10³ -10⁴ CFU/ml

the ileum has more due to being even less acidic around 10⁵ - 10⁷ CFU/ml

• large intestines

contains the must microbiomes

big mix of gram positive and gram negative bacteria unique to the person

they contain anaerobes and facultative anaerobes. the most common is Bacteroides fragilis and Escherichia coli ( e.coli)

when acidity decreases what happens to the bacterial growth

bacterial growth increases

e.g. the small intestines compared to the stomach

describe the microbiota in the urinary tract

• kidneys, ureters and bladder

usually sterile as otherwise can cause kidney infection

• urethra

it has a flushing effect which removes most bacteria but ones like e.coli contain small like hair

lightly colonised. typically staphylococcus epidermis

its a frequent site of infection ( UTI) due to e.coli

describe the microbiota in the female genitalia tract

it contains a very complex microbiota, which depends of age, childbirth, menstrual cycle and menopause

the vagina is an acidic environment

it contains candida albicans ( a yeast ) that can cause a thrush infection infection

since we are already covered in bacteria why don’t we get more infections ?

as we have various barriers to infection,

what are the barriers against infection

• the natural microflora must compete with the pathogens for adhesion to sites and food

• the skin which acts as a physical barrier

• there are also mucosal defences

• non-specific defences: blood and tissues

explain how the skin is able to act as a physical barrier against pathogens

epidermis ( thin outer layer )

• physical barrier

• dry, acidic

• shedding cells

• indigenous bacteria decrease colonisation

sweat glands

• they produce lysozyme which break down peptidoglycan so the gram positive bacteria are more prone to the break

sebaceous glands ( associated with hair follicles )

• lysosomes

• oily sebum which is acidic

• these both inhibit bacterial growth

lymphoid tissue

• induces local inflammatory response

what are the barriers/defences of the mucosal surfaces

mucus

• it traps bacteria

• has lysozyme that kills gram positive bacteria

• lactoferrin that binds iron

• lactoperoxidase which kills bacteria

epithelium

• acts as a physical barrier

• shedding cells

• cilia

• indigenous bacteria which decrease colonisation

lymphoid tissues

• induces local inflammatory response

what are the barriers to infection in the blood and tissue

• there are a variety of cells that go and mop up pathogens

• this is done by the granulocytes- basophils, neutrophils and eosinophil they are activated when there’s inflammation

• also monocytes which can go onto produce macrophages and they can kill bacteria by phagocytosis

• there are also other defences such as the: complement system, transferrin and mannose-binding lectin