Bacteria Chapter 3-4: Microbiota of Humans Flashcards
Where in the human body are there normally no bacteria (sterile)?
- blood
- brain
- muscle
How do bacteria benefit from the host?
- nutrient supply
- stable environment
- mode of transport
How do hosts benefit from bacteria?
- microbial antagonism
- nutritional synergisms (bacteria in GI tract)
- stimulation of immune system
What is microbial antagonism?
microbiota inhibits colonization by pathogens
- occupy adherence sites
- use nutrients
- produce inhibitory byproducts
- affect pH
- affect oxygen availability
What are bacteria in GI tract involved in?
- synthesis and excretion of excess vitamins, which can be absorbed as nutrients by host (vitamin K, vitamin B12)
- steroid metabolism, which is then reabsorbed by host
- organic acid production
- glycosidase reactions
What are natural antibodies?
antibodies produced against components of microbiota
How do bacteria stimulate host immune system?
- microbiota can induce antibody response in host
- low levels of natural antibodies can cross react with certain related pathogens, preventing infection or invasion
Bacteria of the microbiota resist innate immune defences and do not elicit strong adaptive immune responses that would lead to their elimination.
How can microbiota possible detoxify the microbiota’s LPS?
induction of phosphatase in intestinal epithelial cells by bacteria of the microbiota
could render them less sensitive to innate immune system
What are harmful/unwanted aspects of the host-microbiota relationship?
- microbiota could become pathogenic if introduced into other locations in the body
- production of intestinal gas in large intestine
When are humans free of microorganisms?
prior to birth (fetal)
How is microbiota obtained from the environment immediately after birth?
- passage through birth canal
- exposure to other humans (and pets)
- ingestion of food and fluids
- inhalation of air-borne microorganism
What happens to the composition of the microbiota once it is established?
remains relatively constant, but can change with changing circumstances (ie. diet)
What are factors that can affect composition of microbiota?
- diet
- infection
- oral antibiotic therapy
What are the 3 explanations for why bacteria of the microbiota are located at a particular anatomical site?
tissue preference for colonization
- host provides essential growth factor
- some sites are inhospitable for colonization
host receptors that interact with specific bacterial ligands at colonization sites are expressed in only certain areas of the host body
biofilm
- some members of microbiota can construct biofilms on tissue surface
- other members of microbiota establish themselves as part of biofilm built by another species
What are the locations of microbiota that live on and in the human body?
- upper respiratory system
- mouth
- skin
- small intestine
- colon
- appendix
- urethra
- vagina
Skin
What are most skin microorganisms associated (directly or indirectly) with? Why?
sweat glands – armpit, genitals, between toes
- warm
- high moisture
supports activity and growth of high density of bacteria
Skin
Why is the upper region of hair follicles (just below epidermis) good for microorganisms?
secretions of sebaceous gland of hair follicle contain microbial nutrients – urea, amino acids, salts, lactic acid and lipids
Skin
What prevents microorganisms from multiplying?
majority of skin microorganisms are transient (removed/transferred easily)
Skin
What does not support the growth of most microorganisms?
- low moisture
- low pH (acidic)
- competition with permanent residents of the microbiota
Skin
What are some bacteria that can be found as part of the microbiota of skin?
- Staphylococcus epidermidis (non-pathogenic, commensal)
- Micrococcus (non-pathogenic, commensal)
- Propionibacterium acnes (potentially pathogenic on hands and face/nostrils)
Oral Cavity
Does saliva support microorganism growth?
no
- few nutrients
- antibacterial substances (lysozyme, lactoperoxidase)
Oral Cavity
What does lysozyme do?
weakens bacterial cell walls by cleaving glycosidic linkages in peptidoglycan
Oral Cavity
What does lactoperoxidase do?
kills bacteria in a reaction that generates singlet oxygen
