Normal Microbiota Flashcards
Which areas of the body tend to have a higher organism density?
moist or protected areas, such as the armpits or groin area dry, exposed areas of skin harbour fewer organisms
Where in the body has the highest organism density?
the oral cavities and colon
What is meant by normal flora/microbiota?
organisms found in a given location in a state of health
What is meant by colonisation?
the establishment of microorganisms at a site in the body
What is meant by microbiota?
all the organisms within a given community
What is meant by the microbiome?
all the genes present within the microbiota
What is meant by symbiosis?
when two or more organisms co-exist in close physical association
What is meant by mutualism in symbiosis?
When both organisms involved benefit from symbiosis
What is meant by neutralism in symbiosis?
When neither of the organisms involved derive benefit or harm from symbiosis
What is meant by commensalism in symbiosis?
When one organism benefits and the other derives neither benefit nor harm
What is meant by parasitism in symbiosis?
When one organism (parasite) benefits at the expense of the other (host)
What is the difference between sterile and non-sterile sites in the body?
non-sterile sites have normal flora sterile sites have no normal flora
What is significant about non-sterile sites?
They are exposed to the environment, either directly or indirectly There is no mechanism in place to maintain sterility
What are the 5 main non-sterile sites?
- conjunctiva 2. nasopharynx 3. GI tract 4. vagina 5. skin
When does the acquisition of normal flora begin?
at birth until birth, sterility is maintained throughout
How can blood cultures/CSF/ pleural fluid samples be contaminated?
they are obtained by passing a needle through the skin to the relevant sterile site there is potential for contamination with skin organisms
How are sputum samples obtained? What is the problem with sterility?
obtained by expectoration of lower airways secretions (sterile site) through the upper airways (non-sterile site) there is a risk of contamination
How are urine samples obtained? What is the problem with sterility?
obtained by passing urine from the bladder/upper urinary tract (sterile site) via the terminal urethra (non-sterile site) Risk of contamination
How is the risk of contamination minimised when collecting a urine sample?
by collecting an MSU sample (mid-stream urine)
What are the 3 ways in which sterility is maintained at sterile sites?
- sterility maintained by surface cleaning 2. sterility maintained by barriers that allow unidirectional flow 3. sterility maintained by physical separation from non-sterile sites
What are examples of areas where sterility is maintained by surface cleaning?
areas that are open to the environment such as the lower respiratory tract
What are examples of areas where sterility is maintained by barriers?
areas that are adjacent to non-sterile sites e.g. the urinary tract is protected by the urethra
What are examples of areas where sterility is maintained by physical separation?
any closed cavities e.g. spinal cord and meninges, pleural cavity
What is meant by tissue tropism?
the propensity for a particular organism to grow in a particular habitat
What are the 5 main physical variables that influence which organisms colonise which areas?
- moisture 2. temperature 3. pH 4. O2 availability 5. nature of the surface
Where are most bacteria found on the skin?
within the sweat glands
What is the temperature, O2 levels, nutrient levels and characteristics of the skin?
- variable temperature 2. dry and subject to abrasion 3. aerobic environment 4. nutrient-poor
What is the temperature, O2 levels, nutrient levels and characteristics of the gingival crevice?
- constant temperature 2. moist with few physical challenges 3. anaerobic environment 4. nutrient-rich
What are the 3 most common skin flora?
- coagulase-negative staphylococci 2. staphylococcus aureus 3. propionibacterium species
What is the problem when analysing bacteria on the skin?
the bacteria on the skin near any body orifice may be similar to those within the orifice
What are the typical flora found within the mouth?
viridans/oral streptococci anaerobes
What are the typical flora found within the nostrils?
- any of the skin flora 2. staphylococcus aureus - the nose is the main carrier site
What is the problem if the respiratory tract epithelium becomes damaged?
any of the microorganisms present in the pharynx can cause infection in the lower respiratory tract
What are examples of flora that are present within the pharynx?
- streptococcus pyogenes 2. haemophilus influenzae 3. streptococcus pneumoniae 4. s. aureus 5. neisseria meningitidis
What is the normal flora in the vagina pre-puberty?
- any of the skin flora 2. lower GI flora - mainly E. coli
What is the normal flora in the vagina post-puberty? Why does this change?
Glycogen is produced due to circulating oestrogens 1. lactobacillus acidophilus ferment glycogen 2. skin flora 3. a few C. albicans
What is significant about lactobacillus acidophilus fermenting glycogen?
they maintain the pH of the vagina at 3 This prevents the overgrowth of other species An overgrowth of C. albicans causes thrush
What are the typical flora found within the stomach and small intestine?
predominantly aerobic bacteria: 1. acid-tolerant lactobacilli 2. helicobacter pylori the low gastric pH inhibits bacterial growth
How can H. pylori survive in the stomach despite the acidic pH?
it produces urease that converts urea into ammonia and carbon dioxide
What are the normal flora found within the large intestine?
99% anaerobes such as: 1. bacteroides 2. clostridium 3. bifidobacteria The aerobic bacteria are enteric Gram-negative bacilli
What mechanism prevents the overgrowth of pathogens within the large intestine?
colonisation resistance by the normal gut microflora
How can the normal flora provide a health benefit through metabolism?
- vitamins K and B12 are secreted by enteric bacteria 2. unused energy substrates are fermented to produce short-chain fatty acids
What is the benefit of vitamin K production?
E. coli in the colon produce vitamin K It is essential for blood clotting and bone metabolism
What are the benefits of butyrate (SCFA)?
it helps to prevent bowel cancer and modulates immune responses
What are the benefits of propionate (SCFA)?
it promotes saiety it prevents lipid lipidogenesis it lowers cholesterol it provides anti-carcinogenic activities
How can normal flora provide colonisation resistance?
Through environmental manipulation e.g. lowering the pH Through production of antibacterial agents e.g. bacteriocins
In what other way can normal flora provide health benefits?
through induction of cross-reactive antibodies
In general, in what 4 ways can SCFAs provide health benefits to the body?
- help to inhibit enteropathogens 2. provide energy to epithelial cells/colonocytes 3. promote mucin production 4. affects gut hormone production and modulates appetite
How can antibiotics negatively impact normal flora?
antibiotics kill off pathogenic organisms and normal flora this reduces the diversity which is key to the health benefits of the normal flora
What is the main risk factor for clostridium difficile infection?
antibiotic treatment
What is the background behind C. difficile infection?
perturbation of normal colonic microflora allows C. difficile overgrowth this leads to toxin production
In what 3 ways may there be a pathology of the normal flora?
- overgrowth 2. translocation 3. cross-infection
What is meant by overgrowth of normal flora?
excessive growth at the normal site
What is meant by translocation of normal flora?
presence of the normal flora at the wrong site this may be as they have been spread from one site to another
What is an example of a condition caused by overgrowth of normal flora? What may have caused this?
thrush treatment with a broad spectrum antibiotic can lead to inhibition of colonisation resistance
What is an example of a condition caused by translocation where normal flora have been moved from one surface to another?
conjunctivitis red eyes with purulent conjuctivital discharge following URTI with cough and runny nose
What are typical clinical conditions caused by normal flora?
Why is it often difficult to determine the clinical significance of the presence of normal flora in a sample?
The opportunity for sample contamination is high
Organisms are often present in a sample benignly and are not the cause of symptoms
