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L10 Normal Microbiota


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density
organism _______ is greatest in oral cavities and the colon
normal flora
organisms found in a given location in a state of health
colonisation
establishment by a certain organism at a site in the body
microbiota
all the organisms in a given community
microbiome
all the genes present within the microbiota
symbiosis
two or more organisms co-existing in close physical association
mutualism
symbiosis: both organisms benefit
neutralism
symbiosis: neither organism derives benefit or harm
commensalism
symbiosis: one organism benefits, the other derives neither benefit or harm
parasitism
symbiosis: one organism benefits at the expense of the other host
non-sterile
___-_______ sites have normal flora
sterile
______ sites have no normal flora
environment
non-sterile sites are (directly or indirectly) exposed to the _______
surface cleaning
1) sterility maintained by .... (open to environment; e.g lower respiratory tract)
barriers
2) sterility maintained by .... (adjacent to non-sterile sites; allow unidirectional flow; e.g. upper genital tract protected by cervix / urinary tract protected by urethra)
physical separation
3) sterility maintained by... (from non-sterile sites; closed cavities; e.g. pleural cavity, peritoneal cavity, spinal cord and meninges)
tissue tropism
propensity for a particular organism to grow in a particular habitat
skin
variable temperature, dry, subject to abrasion, aerobic environment, nutrient poor, ___ surface components
gingival crevice
constant temperature, moist, few physical challenges (toothbrush!), anaerobic environment, bathed in nutrients, mucosal surface components
skin flora
Examples: Coagulase-negative staphylococci (Staph. epidermis), Staph. aureus (esp. in nasal carriers), Propionibacterium species (P. acnes)
mouth flora
Examples: Viridans/oral streptococci, anaerobes & many others
nasopharyngeal flora
Examples: (upper) Stathylococcus aureus (20%); (lower) Streptococcus pyogenes (group A), Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, S. aureus
vaginal flora
Examples; lactobacillus spp. (L. acidophilus), skin flora, and some C. albicans
3
Lactobacillus species in the vagina ferment glycogen and prevent overgrowth of other species by maintaining a pH at __
glycogen
post-puberty, _______ is produced in the vagina due to circulating oestrogens
puberty
vaginal flora consists primarily of skin flora and lower GI flora (E.coli) before...
stomach & small intestine
low pH inhibits bacterial growth, predominantly aerobic bacteria (acid tolerant Lactobacilli & H.Pylori); counts decrease distally, few or non anaerobes
large intestine
most extensively studied area; at least 400 species; 95-99% Anaerobes (Bacteroides spp, Clostridium spp, Bifidobacteria spp; Aerobic bacteria: enteric Gram- bacilli (e.g. E.Coli)
metabolism
benefit of normal flora: synthesising secondary metabolites/vitamins (e.g. Vit K & B12 secreted by enteric bacteria; fermenting unused energy substrates (SCFA))
colonisation resistance
benefit of normal flora: by environmental manipulation (e.g. reduced pH) or production of antibacterial agents (eg colicins, bacteriocins, fatty acids, metabolic rate products)
induction of cross-reactive antibodies
benefit of normal flora: may have protective effect by 'priming' immune system
nitric oxide
benefit of normal flora: study of oral microbiota; production of _____ ____; 25% of ingested nitrate returned to mouth; oral bacteria reduce nitrate to nitrile; absorbed and converted to __ __; essential for vascular health and low BP; chlorhexadine mouthwash use for 7 days increases BP significantly
short chain fatty acids
help to inhibit enteropathogens; provide energy to epithelial cells / colonocytes; promotes mucin production; affects gut hormone production - modulates appetite; e.g. acetate, butyrate, propionate
alpha diversity
diversity within a microbiome
beta diversity
comparison of diversity in different microbiomes
antibiotic treatment
main risk factor for Clostridium difficile infection due to perturbation of normal colonic microbiota
pseudomembranous colitis
diarrhoea resulting from toxin production in C.diff infection
faecal transplant
use of bowel-derived matter for disease treatment hoes back 2500 years! First reported us in humans in 1958. Recently been making a comback to treat recurrent C.diff infection
overgrowth
pathology of normal flora: excessive growth at normal site; e.g. thrush
translocation
pathology of normal flora: presence at the wrong site (spread from one surface to another - e.g. conjunctivitis following URTI - or inoculation into a normally sterile site - e.g. IV catheter infection)
cross-infection
pathology of normal flora: normal flora on one individual transferred to immunocompromised individual; e.g. MRSA on ITU