Microb Growth

Question 0

Binary Fission

Answer 0

Asexual reproductive process of bacteria. Results in two daughter cells.

Question 1

Fungal Growth

Answer 1

Moulds:

• Hyphae to Mycelium
• Apical growth - protoplasm movement into tip.
• Spores (sexual or Asexual)

Yeast:
-Budding (asexual process)

Question 2

Physical factors affecting microbial growth

Answer 2

• Temperature: Minimun, Maximum, optimum
• Gas Requirements: Electron receptor - Catalase/Superoxide dismutase
• Water Activity(Aw): most grow at 1.0Aw, Bacteria unable to grow below 0.9Aw
• Effects of pH

Question 3

Psycrophile

Answer 3

Microbe that growth under cold conditions:
Opt temp below 15C
Capable of growth at 0C
Cannot grow above 20C

Question 4

Psychrotroph

Answer 4

Facultative Psycrophile
Grow slowly in cold conditions BUT have opt temp above 20C
CONCERN: Contaminants of food/dairy products

Question 5

Mesophile

Answer 5

Opt temp 20-40oC
Capable of growth 10-50C (minor fact)
Group containing HUMAN PATHOGENS (30-37C)!!!!

Question 6

Thermophile

Answer 6

Opt temp >45oC
Capable of growth 45-85oC
Incapable of growth at usual body temp
(NOT INVOLVED in HUMAN INFECTIONS)

Question 7

Fungi and Temperature

Answer 7

FREE-LIVING STATE
– Mycelial or hyphal form (mold)
– At sub-physiological temperature (25C)

PARASITIC STATE
– Yeast form
– Due mainly to physiologic temperature (37C)

Question 8

Obligate Aerobes

Answer 8

• Uses O2 dependent system for ATP.
• Have catalase and superoxide dismutase to remove H2O2 and free radicals
• Can tolerate high [O2]

Question 9

Microaerophiles

Answer 9

Grow in presence of O2 BUT tolerate only 4%

Possess superoxide dismutase only, BUT if toxic products incrase, enzyme systems overload INHIBITING GROWTH

Question 10

Facultative Anaerobes

Answer 10

Grow in presence or absence of O2 
 Presence: Aerobic respiration  
 Absence:  Fermentation for energy prodn 
 Grow best under AEROBIC CONDITIONS 
**ALL YEASTS

Question 11

Obligate anaerobes

Answer 11

Grow ONLY in ABSENCE of O2
Effect of presence: LETHAL
LETHAL - org’s lack enzymes to remove toxic products
Brief exposure will KILL

Question 12

Xerotolerant

Answer 12

Ability of microbes to grow with reduced water requirements.
Fungi able to grow Aw 0.60
Yeasts (conc sugar soln’s Aw = 0.60)

Question 13

Halophile

Answer 13

Salt-tolerant bacteria (high [solute], low water activity)

Question 14

Chemical Factor Affecting Microbial Growth

Answer 14

Nutrient Concentration: CHNOPS, Minterals (Ca++, etc.), trace elements (Zn, Cu, etc.)

  - Autotroph - CO2 primary source of C
  - Heterotroph - organic materials source of C

Question 15

Sabouraud’s Agar

Answer 15

Fungal Cultivation for primary: selective isolation
-Peptone (protein hydrolysate)
-pH 5.6 (inhibits faster growing bacteria)
-Antibiotics: Penicillin, Streptomycin, Tetracycline (inhibitbacteria)
Cultivated at 25C and 37C for molds and Yeast

Question 16

Corn Meal Agar

Answer 16

Fungal Cultivation for Secondary: species identification
– Incubated at 25C, several days
– Characteristic sexual structures develop– ID based on morphology (microscopy)