Lecture 5 microbial growth Flashcards Preview

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Flashcards in Lecture 5 microbial growth Deck (10)
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1
Q

Bacterial growth times

A
  • Asexual process known as binary fission; division is geometrical
  • Generation time (optimal conditions) ex.

B. stearothermophilus: 11 min.

E. coli: 20 min.

S. aureus: 28 min.

L. acidophilus: 60 to 80 min.

M. tuberculosis: 360 min

T. pallidum: 1980 min.

2
Q

Fungal growth

A
  • moulds hyphae -> mycelium
  • extension at tip (apical growth)
  • up to 40 microns/min.
  • provides penetrating power (fresh nutrients)
3
Q

Temp adaptations

A

Psychtrophile: no harm to humans

  • Opt. temp < 15 C (cannot grow > 20 C)
  • found in snow fields, polar ice, deep ocean

Facultative Psychtrophile: harmful to humans (contaminants in deli meats in fridge)

  • grow slowly in cold conditions
  • Optimal temp > 20 C
  • Ex. S. aureus, L. monocytogenes

Mesophile: very harmful

  • Opt. temp. @ 20 to 40 C (capable @ 10 to 50 C)
  • group containing human pathogens
  • Ex. E. coli

Thermophile

  • Opt. temp >45 C (capable 45 to 85 C)
  • incapable of growth at usual body temp
4
Q

Microbes divided into 4 groups based on oxygen requirements

A
  1. Obligate aerobes
  2. Microaerophiles: grow in presence of O2 but tolerate only 4% b/c lack catalase
  3. Obligate Anaerobes: brief exposure will kill; No SOD or catalase
  4. Facultative Anaerobes: can switch b/w 2 types of O2 metabolism (presence or absence); grow best under aerobic conditions, Ex.

Notes:

  • Bacteria: all 4 groups
  • Fungi/moulds: normally aerobic
  • Yeasts & Enterobacteriacea: facultative anaerobes
5
Q

Water activity microbial categories

A
  1. Xerotolerant: lower Aw
    - fungi & yeasts grow @ Aw=0.60
    - cold cuts, grated cheese
  2. Halophiles
    - high [solute], low Aw
6
Q

Chemical factor microbial categories (partial)

A

Hydrogen/electron

  • lithotrophs: reduced inorganic molec
  • organotrophs: organic molec

Note: most pathogens are chemorganotrophic heterotrophs

See Lecture 5 slide 34-35 for rest

7
Q

Reduced medium

A
  • addition of reducing agent Ex. thioglycolate, cystine or ascorbate
  • removes O2 so anaerobes can grow
8
Q

Differential media

A
  • more than 1 type of organism can grow but separation b/w genera & sp. (visible changes in media)

ex. MacConkey agar: selective medium designed to selectively grow Gram-negative bacteria and differentiate them for lactose fermentation
- lactose present as sole nutrient source
- so E. coli will use the lactose and produce acid to produce red
- S. Typhi does not use lactose
- P. aeruginosa produces grey/blue pigment on Mac cultures.

ex2. Eosin-methylene blue (EMB): E. coli & enterobacter aerogenes

Note: media can be selective & differential or enriched and differential at the same time

9
Q

Fungal cultivation

A
  1. Primary (isolation): Sabouraud’s Agar
    - peptone (protein hydrolysate)
    - pH 5.6 (inhibits faster growing bacteria)
    - antibiotics: penicillin, streptomycin, tetracycline (inhibit bacteria)
  2. Secondary (culture & species id): Corn meal agar
    - incubated @ 25C, several days
    - characteristic sex structures develop
    - ID based on morphology (microscopy)
10
Q

Enriched media & hemolysis

A
  • basal growth support media + nutritive supplements added Ex. Blood agar
  • Beta-hemolysis (clearing): complete hemolysis due to molecular mimicry; Ex. Strep. pyogenes
  • Alpha-hemolysis (greening): Ex. Strep. viridans, Strep. pneumoniae
  • Gamma-hemolysis (no change): Ex. Enterococcus faecalis