normal microbiota

symbiosis

two or more organisms co-exist in close physical association

mutualism

both organisms benefit from symbiosis

neutralism

neither organism derives benefit or harm

commensalism

• one organism benefits

• other derives neither benefit nor harm

parasitism

one organism benefits at the expense of the other

dysbiosis

• shift in microbiota

• representative of a disease state

• pathobiont→ cause harm under certain circumstances

non-sterile sites

• exposed to environment→ directly or indirectly

• no mechanism to maintain sterility

• e.g.

  • skin

  • conjunctiva

  • nasopharynx

  • GI tract

  • vagina

sterile sites

• sterility maintained by surface cleaning

  • open to environment

• sterility maintained by barriers→ allow uni-directional flow

  • adjacent to non-sterile sites

• sterility maintained by physical separation from non-sterile sites

  • closed cavities

environment of skin

• variable temp

• dry

• subject to abrasion

• aerobic environment

• nutrient poor

• skin surface components

examples of organisms growing on skin

• coagulase-negative staphylococci

• staphylococcus aureus

• cutibacterium acnes

bacteria on skin near any body orifice may be similar to those in the orifice

environment of oral cavity

• constant temp

• moist

• few physical challenges

• anaerobic environment

• bathed in nutrients

• mucosal surface components

what grows in the oral cavity

• viridans/oral streptococci

• anaerobes

• red complex bacteria

what grows in the nasopharynx

• nostrils

  • skin flora

  • S. aureus

• pharynx

  • streptococcus pyogens

  • haemophilus influenzae

  • streptococcus pneumoniae

  • neisseria mingitidis

  • staph. aureus

what grows in the vagina

• pre-puberty

  • skin flora

  • lower GI flora→ E. Coli

• post puberty

  • lactobacillus acidophilus

  • skin flora

  • C. albicans

what grows in the GIT

• acid-tolerant lactobacilli

• helicobacter pylori

what grows in the large intestine

• at least 400 specied identified

• mostly anaerobes→ bacteroides, clostridium, bifidobacteria

• aerobic bacteria→ enteric gram-negative bacteria

benefits of normal flora

• metabolism→ synthesis secondary metabolites/vitamins

  • e.g. vit. K and B₁₂ secreted by enteric bacteria

• colonisation resistance

• immune regulation/education

role of acetate/butyrate/ propionate

• helps inhibit enteropathogens

• provides energy to epithelial cells/ colonocytes

• promotes mucin production

• affects gut hormone production

types of dysbiosis

• overgrowth→ excessive growth at normal site

• translocation→ presence at wrong site

• cross-infection

example of overgrowth

vaginal thrush

example of translocation

• conjunctivitis

• intravascular catheter infection

cross infection example

methicillin resistant S. aureus (MRSA)

clinical conditions caused by normal flora

• dental caries, peridontal disease, pharyngitis

• endocarditis

• urogenital infection

• gastroenteritis, peritonitis

• pneumonia

• abscesses