Lec 17 Flashcards
Three ways microbes and a human host can interact
- Commensal = unaffected
- Mutualistic = benefit for both
- Pathogenic = benefit microbe harm human
1,2 = normal flora
Normal Flora
Total microbial pop. associated with healthy human (mainly bacteria)
one human = 10^13human cells + 10^14 bacteria cells
Found all external body sites (internal site exposed to external = inner lumen of intestinal tract)
Highly variable and changeable
Where do you not find normal flora
Internal tissues/organs and the fluids within those organs
Conization
infection
Disease
Colonization = Microbe grows on external body surface
Infection = Multiplies within body tissue triggers immune response
Disease= infection causes dmg to body
NF = 1,
Types of Normal flora (defined by length of time they are associated with host)
2
- Transient Normal Flora
- short term (hours to days)
- Highly variable in types and numbers of species present
- influenced by external factors (hygiene) - Resident Normal Flora
- Long term association with host (months to life)
- more stable in types and numbers
- less influenced by external factors
Origin of Normal flora in Humans
Fetus in uterus is sterile
At birth exposed to microbes (vaginal tract, medical personnel, environment) most are transient flora
- oral, nasopharyngeal, skin flora established within hours of birth
- gastrointestinal tract flora established within 1-2 days
stable pop. take weeks
What factors determine composition (types of species) of a persons normal flora
Varies
Site to site differences:
- Types and amounts of nutrients, pH, oxygen concentration
- Presence/absence of anti-microbial substances (lysozyme in tears)
Person to person differences:
-Age, sex, diet, hygiene, living conditions
Normal flora of different body sites
Skin
- Less species diversity (mostly species that survive dry salty condition eg Staphylococcus)
- Transient pop. on exposed surfaces; Resident pop. in protected areas (pores)
- Mostly commensal interactions (some mutualism)
e. g. Metabolize lipids for nutrition - acidic waste that lower ph and prevent pathogen growth
-cause disease if introduced to underlying tissue
The “skin flora” problem in diagnostic microbiology
Blood culture” = patient’s blood inoculated into broth media to test for the presence of bacterial pathogens (“bacteremia”)
Normal flora contaminate blood culture
Collect 2 or 3 blood samples from different sites
Normal flora of different body sites
Respiratory Tract
Mouth, tongue, teeth, saliva
- often present as biofilm communities (plaque on teeth)
- free bacteria in saliva
Nasal Area/ Upper respiratory tract
- similar flora to skin & mouth
- staph. aureus part of normal flora in 10-15% (Food borne diseases)
Lower Respiratory Tract (eg. Trachea into lungs)
-No normal flora (occasional transient microbes)
Normal flora of different body sites
Genito-urinary
- Urine in bladder is sterile in healthy video (no normal flora)
- First 1 cm of urethra transiently colonized (flushing action)
Normal flora of different body sites
Intestinal Tract (stomach, small intestine, colon)
Stomach = too acidic for most bacteria, only acid tolerant survive
Small intestine = Fewer bacteria at Ant. end vs Post. end
Colon = 25% of fecal mass is normal flora
99% anaerobes or facultative anaerobes
Coliforms (E.coli and co)
Intestinal tract: Greatest total number flora/ greatest diversity of species
Composition of gut flora influenced by diet:
Site of Mutualistic microbe host interactions (Gut E. coli)
Intestinal Tract
Lactose-intolerance related to intestinal flora
Lactose (lactase) = Glucose + galactose
-reduced lactase production, lactose not broken down and passes un-digested into large bowel - lactose used as nutrient by lactic acid bacteria - release gas and acidic waste
Important contributor to human nutrition
- Intestinal bacteria add metabolic abilities that humans don’t have:
- synthesize essential vitamins (B and K)
- Salvage nutrient that would escape digestions (carbs into short chain fatty acids)
But some metabolic activities of intestinal flora may be harmful
(over abundance of bacteria causes excess release of acid, gas metabolic wastes as they grow)
Maintaining proper balance of intestinal flora important
A defense against infection by pathogens
Priming (or training) of immune system
-early age exposure of IS required
(germ free has poor immune systems)
Exclusion of pathogens from body sites
- pathogens compete with normal flora
- pathogens inhibited by chemical produced by normal flora
