Medical Bacteriology L1

the skin
1. first line of defense
  1. mechanisms to minimise microbial growth
    1. secretes lysozymes
      1. attacks and weakens bacterial cell walls
    2. produces sebum (fatty acid)
      1. Propionibacteria metabolizes to produce fatty acids (antimicrobial)ff
    3. lower pH than most microbes can survive
    4. resident microbiota
2. head, armpits, groin, hands and feet are most heavily colonized
  1. microbes + skin secretions = BO
    1. antimicrobial deoderant
      1. selective against gram positive bacteria
        reduces volatile aromatic products
        can promote the colonization by gram negatve bact
3. commensal microbiota
  1. coagulase‐negative staphylococci
    1. Staphylococcus aureus
      1. 40% of healthy adults
      2. 90% of hospital staff
      3. surgical wound infection
  2. micrococci
    1. Micrococcus sedentarius
      1. pitting of toughened foot skin
      2. produces methanethiol
  3. corynebacteria
  4. propionibacteria
  5. lactobacilli
  6. yeasts
    1. genus candida
      1. candida albicans, though, does not normally colonize the skin
  7. also host fungi and mites
    1. fungi
      1. Malassezia furfur
    2. mites
      1. Demodex folliculorum and Demodex brevis
        eat dead epithelium supplemented by sebum
  8. brevibacteria
    1. cheesy feet; degree doesn't correlate though
4. eyes have specialized skin
  1. bathed in tears
  2. resident microbiota
    1. Corynebacterium xerosis
the alimentary tract
1. oral cavity
  1. saliva
    1. washing
      1. swallow 30x/hour
    2. digestive enzymes & antimicrobials
      1. immunoglobin A (IgA)
      2. lysozyme
      3. lactoferrin
    3. α‐haemolytic streptococci
      1. Streptococcus salivarius
  2. eprithelial surfaces
    1. Streptococcus salivarius
  3. teeth
    1. Streptococcus mutans
    2. Streptococcus sanguis
  4. gingival crevices
    1. Bacteroides, Fusobacterium species and spirochaetes, forming intricate parasitic interactions
2. stomach
  1. low, acidic pH
  2. a few acid‐tolerant lactobacilli
    1. Helicobacter pylori
      1. ulcers
      2. highly active urease
    2. mycobacteria
      1. waxy cell wall
3. small intestine
  1. upper: duodenum, jejunum, upper ileum
    1. NO resident microbiota
      1. digestive secretions, bile acids, intestinal mucus and secretory antitbodies
      2. peristalsis
        if peristalsis is prevented, bacterial overgrowth (intestinal blind loop) occurs
  2. lower ileum
    1. microbiota like that of the mouth
  3. large intestine
    1. faecal microbiota
      1. anaerobes dominate
        bacteriodes
      2. less facultative microbes
        Escherichia coli
4. effects of microbiota
  1. microbiota's metabolism
    1. may produce carcinogens
    2. people w/o lactase
    3. digests oligosacccharides from beans
      1. creates flatulence
  2. controls flatulence
    1. utilize volatile products
    2. reduce our gas from 24 liters to 1 liter
the upper respiratory tract
1. microbiota of nostrils resembles skin
  1. staphylococci
  2. micrococci
  3. corynebacteria
2. microbes inhaled
  1. entrapped in the hairs
  2. entrapped in mucus membranes of the turbinate baffles
3. warm, moist upper resp. tract
  1. gram negative bacteria
    1. Moraxella
    2. Neisseria
    3. Haemophilus
  2. gram positive bacteria
    1. streptococcus
      1. Streptococcus pyogenes
        tonsilitis
        found in commmensal microbiota of healthy carriers
4. not normally colonised
  1. paranasal sinuses
  2. larynx
  3. lower respiratory tract
  4. lungs
    1. mucociliary escalator
      1. mucus traps microbes
      2. cilia drive mucus from the alveoli, up thru trachea
the genital tract
1. generally not v colonized
  1. regular flushing
  2. secretory antibodies
  3. in males: prostate secretions
2. on distal portion
  1. staphylococci
  2. gram-negative cocci
  3. corynebacteria
  4. mycoplasma
3. external genitalia
  1. Mycobacterium smegmatis
    1. may contaminate urine samples and confuse the laboratory diagnosis of renal tuberculosis
  2. pre‐pubescent and post‐ menopausal women
    1. enterococci, coagulase‐negative staphylococci, coliform bacilli and corynebacteria
  3. reproductive years
    1. lactobacilli,(Döderlein bacilli), in a mixed microbiota also containing yeasts, corynebacteria and mycoplasmas
microbiota
1. resident microbiota
  1. Adhere @ suitable niche on/in our body
    1. multiply
  2. form long‐term, stable, interdependent relationships with their neighbours and with the human that harbours them
2. transient microbiota
  1. 1)not find us a hospitable environment
  2. 2) are outcompeted by resident microbiota
  3. 3) are susceptable to host defenses
role of the commensal microbiota
1. coexist with host
2. Staphylococcus saprophyticus is commensal on skin
factors that affect the human comensal microbiota
pathogens
1. Staphylococcus saprophyticus causes harm and is pathogenic in the urinary tract
  1. in the gemale genital tract, it does not have competing microbiota
Microbial access to deep tissues is transient; in healthy individuals any organisms that do enter such sites are rapidly removed by the various host defence mechanisms
1. cerebrospinal fluid = sterile
2. muscle
3. joints
4. bones
5. connective tissue
6. kidneys
7. liver
8. urinary tract
9. spleen

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Medical Bacteriology L1

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	Created by Magdelyn Mueller about 8 years ago