9. Normal Microbiota Flashcards
which areas of skin harbour more organisms?
moist, protected areas of skin, eg. armpits, groin or between the toes
in which parts of the body is organism density the greatest?
oral cavities and colon
what are normal flora?
organisms found in a given location in a state of health
what is colonisation?
establishment at a site in the body
what is symbiosis?
2 or more organisms co-exist in close physical association
what is mutualism?
both organisms benefit from the symbiosis
what is neutralism?
neither organism derives benefit or harm from the symbiosis
what is commensalism?
one organism benefits, the other one neither benefits nor is harmed
what is parasitism?
one organism (parasite) benefits at the expense of the other (host)
what are non sterile sites?
sites with normal flora, are exposed to the environment either directly or indirectly, and have no mechanism in place to maintain sterility
what are sterile sites?
those with no normal flora
when do humans acquire flora?
at birth
what are the 3 types of sterile sites?
- sterility maintained by surface cleaning
- sterility maintained by barriers that allow unidirectional flow
- sterility maintained by physical separation from non sterile sites
where is sterility maintained by surface cleaning?
those places that are open to the environment
efficient cleaning by ciliated epithelium, removal of bacteria by coughing, sneezing or swallowing
where is sterility maintained by barriers that allow unidirectional flow?
adjacent to non sterile sites eg. cervix and upper genital tract, urethra before urinary tract
where is sterility maintained by physical separation from non sterile sites?
close cavities eg. plural and peritoneal cavities, meninges
what factors influence what organisms colonise in which areas?
moisture temperature pH oxygen availability nature of surface
skin flora
coagulase -ve staph. eg. staph epidermis
staph aureus
propionibacterium acnes
the bacterium on the skin near any body orifice may be similar to those in the orifice
mouth flora
viridian’s/oral streptococci
anaerobes
what is the benefit of colonising in the mouth?
gain of nutrients, also provide the host with essential vitamins, synthesises by bacterial species
established normal flora can prevent colonisation of pathogenic flora
nasopharyngeal flora - nostrils
skin flora
Staph aureus
nasopharyngeal flora - pharynx
step. pyogenes haemophilus influenzae step. pneumoniae Neisseria meningitidis S. aureus
vaginal flora - pre-puberty
skin flora
lowe GI flora, mainly E. coli
vaginal flora, prost puberty
lactobacillus acidophilus
skin flora
C. albicans
why is there a difference in flora in the vagina pre and post puberty?
circulating oestrogen at puberty stimulates production of glycogen in the vagina. lactobacillus acidophilus ferment the glycogen and maintain a oH of 3, preventing overgrowth of other species
GI tract - stomach and small intestine flora
acid tolerant lactobacilli, H. pylori
due to inhibition of bacterial growth by low pH. predominantly aerobic becteria
Gi tract flora - large intestine
95-99% anaerobes
bacteroides, clostridium, bifidobacteria
aerobic bacteria
gram -ve bacilli
E. coli, Klebsiella, enterobacter, proteus, citrobacter
what are the benefits of normal flora?
- synthesis and excretion of vitamins, eg. via K and B12 secreted by enteric bacteria
- colonisation resistance by environmental manipulation and production of antibacterial agents
- induction of cross-reactive antibodies may have a protective effect
how can normal flora become pathogenic?
- overgrowth, e.g vaginal thrush
- translocation - presence on the wrong site - eg. through spread or inoculation
- cross-infection eg. MRSA
