L13 - Normal microbiota Flashcards
What does symbiosis mean?
Two or more organisms co-exist in close physical association
What are the 4 types of symbiosis?
- mutualism
- neutralism
- commensalism
- parasitism
Mutualism is a type of symbiosis. What does it mean?
Both organism benefit from symbiosis (benefit from co-existing in close physical association)
Neutralism is a type of symbiosis. What does it mean?
Neither organism derives benefit nor harm
Commensalism is a type of symbiosis. What does it mean?
One organism benefits, the other derives neither benefit nor harm
Parasitism is a type of symbiosis. What does it mean?
One organism (parasite) benefits at the expense of the other (host)
In parasitic symbiosis, does the host organism benefit or derive harm?
The host derives harm
It is the parasite that benefits at the expense of the host
In sterile sites of the body, sterility is maintained by 3 mechanisms. What are these?
- by surface cleaning
- by barriers
- by physical separation
Give an example of a sterile site in the body where sterility is maintained by surface cleaning
Lower respiratory tract (cilia in lungs etc)
Give examples of sterile sites in the body where sterility is maintained by barriers that allow unidirectional flow
- upper genital tract (cervix)
- urinary tract (urethra)
- middle ear (eustachian tube)
Give examples of sterile sites in the body where sterility is maintained by physical separation from non-sterile sites?
- pleural cavity
- peritoneal cavity
- spinal cord and meninges
What is tissue tropism?
Propensity for a particular organism to grow in a particular habitat
Which bacteria live on the skin? (skin flora)
- coagulase-negative staphylococci (staphylococcus epidermis)
- staphylococcus aureus (esp. in nasal carriers)
- propionibacterium species (propionibacterium acnes)
Which bacteria live in the mouth? (mouth flora)
- viridans/oral streptococci
- anaerobes
- many others
Which bacteria live in the nostrils?
- skin flora
- staph. aureus (20% - nose is main carrier site)
Which bacteria live in the pharynx?
Respiratory and other pathogens
- strep. pyogenes (group A)
- haemophilus influenzae
- strep. pneumoniae
- neisseria meningitidis
- staph. aureus
Which bacteria live in the vagina pre-puberty?
- skin flora
- lower GI flora (mainly E. coli)
What causes the change in vagina flora post-puberty?
Glycogen produced due to circulating oestrogens
- Lactobacillus acidophilus
ferments glycogen resulting in very acidic pH killing normal flora
Which bacteria live in the vagina post-puberty?
- lactobacillus spp. Lactobacillus acidophilus
- skin flora
- a few C. albicans
In the vagina post-puberty, there is lactobacillus acidophilus. What does this do?
Ferments glycogen
Maintains pH at 3, preventing overgrowth of other species
There is an association between H. pylori and which conditions?
duodenal and gastric ulceration
What inhibits bacterial growth in the stomach?
Low gastric pH due to hydrochloric acid
The flora of the stomach and small intestine is predominantly aerobic or anaerobic bacteria?
AEROBIC
few or no anaerobes
Which bacteria live in the stomach and small intestine?
- acid-tolerant lactobacilli
- helicobacter pylori
The flora of the large intestine is predominantly aerobic or anaerobic?
95-99% ANaerobic
Which anaerobic (95-99%) bacteria live in the large intestine?
- Bacteriodes spp. Clostridium spp. Bifidobacteria spp
Which aerobic bacteria live in the large intestine?
Enteric gram-negative bacilli
- escherichia coli
- klebsiella spp. enterobacter spp. proteus spp. citrobacter spp.
How many microorganisms are in the large intestine?
10 to power 9 - 10 to power 11 organisms/gram
at least 400 species identified
What are the benefits of having normal flora?
- metabolism
- colonisation resistance
- induction of cross-reactive antibodies (may have a protective effect)
Synthesis and excretion of vitamins is a benefit of having normal flora. Give examples
- vitamins K and B12 are secreted by enteric bacteria
Colonisation resistance is a benefit of having normal flora. Give examples
- environmental manipulation eg. lowering pH
- antibacterial agents eg .colicins, bacteriocins, fatty acids, metabolic waste products
What is the main risk factor for clostridium difficile infection?
Antibiotic treatment
What are the symptoms of Clostridium difficile infection?
- diarrhoea
- pseudomembranous colitis
What treatment has recently made a comeback to treat recurrent C. diff infection?
Faecal transplants
What other diseases is it suggested that faecal transplants may be a possible treatment for?
- multiple sclerosis
- chronic fatigue syndrome (ME)
- idiopathic thrombotic purpura
- ulcerative colitis
- irritabel bowel syndrome
- diabetes mellitus
When does normal flora become problematic?
- overgrowth
- translocation
- cross-infection
Translocation is a possible pathology of normal flora. What does this mean?
Presence at the wrong site
- spread from one surface to another
- inoculation into a normally sterile site
Give an example of a condition that can be caused by overgrowth of normal flora?
Vaginal thrush
eg.
- treatment with broad spectrum antibiotics for sinusitis causing inhibition of colonisation resistance
- vaginal itch with creamy vaginal discharge
Give an example of a condition that can be caused by translocation (from one surface to another) of normal flora
Conjunctivitis
eg.
- red eyes and purulent conjunctival discharge following URTI with cough and runny nose
- haemophilus influenzae grown from eye swabs
Give an example of a condition that can be caused by translocation (inoculation into a normally sterile site) of normal flora
Intravascular catheter infection
eg.
- post bowel resection due to Chrohn’s
- spiking fevers
- associated with intravenous drug use
- blood culture grew coagulase-negative staphylococci
- problem resolved immediately after central line removed
Give an example of a condition that can be caused by cross-infection of normal flora
MRSA
eg.
- severe pancreatitis
- develops pneumonia
- MRSA grown from respiratory secretions
- died despite appropriate antibiotics
- MRSA isolated in nose swabs from 4 other patients
Give a list of conditions caused by normal flora
- dental caries, periodontal disease, pharyngitis
- abscesses
- endocarditis
- pneumonia
- gastroenteritis, peritonitis
- urogenital infections
what is the most common aerobic bacteria in the large intestine?
Escherichia coli
do healthier people have a less or more diverse range of flora?
more diverse
