10 - Normal Microbiota Flashcards
Mutualism definition
Both organisms benefit from symbiosis
Neutralism definition
Neither organism derives benefit or harm
Commensalism definition
One organism benefits, the other derives neither benefit nor harm
Parasitism definition
One organism benefits at the expense of the other
Do sterile sites have normal flora?
No
Mechanisms of formation of sterile sites
Surface cleaning - lungs
Barriers with uni-directional flow - urinary tract
Sterility maintained by physical separation - spinal cord
Tissue tropism definition
Propensity for a particular to grow in a particular habitat
Physical variables affecting bacterial growth
Moisture Temperature pH O2 availability Nature of surface
Bacteria on skin
Staph. epidermis
Staph. aureus (mainly nasal)
Propionibacterium acnes
Note: bacteria near orifice similar to bacteria in orifice
Nasopharyngeal flora
Staph. aureus Haemophilus influenzae Strep. pneumoniae Neisseria meningitidis Staph. pyogenes
Vaginal flora
prepubescent - skin flora, low GI flora, mainly E.Coli
post-puberty - glycogen produced due to circulating oestrogens. E.g. lactobacillus acidophilis, ferment glycogen. Skin flora. A few C.albicans
GI tract - stomach + small intestine - bacteria present
Acid-tolerant lactobacilli
Helicobacter pylori
GI tract - large intestine
95-99% anaerobes
Aerobic bacteria - enteric gram–ve bacilli
e.g. E.Coli
Benefits of normal flora
Synthesis and excretion of vitamins - K&B12
Colonisation resistance - environment manipulation e.g. pH; antibacterial agents
Induction of cross-reactive antibodies
C.diff infections
Hospital acquired infection usually >60 years
Main risk factor being antibiotic treatment
Destroys layers of bacteria allows C.diff invasion
