Microbial Growth and Cultivation (Bacterial and Fungal)

Question 1

Bacterial growth

Answer 1

• continuous macromolecular synthesis
• asexual process - “binary fission”
• geometrical division: with each division, the population doubles

Question 2

Growth rate

Answer 2

time for the cell to reproduce

Question 3

Generation time

Answer 3

• time for a complete fission cycle (1 parent cell -> 2 new daughter cells)
• formation of each new bacterial cell, its growth, and eventual division into 2 cells

Question 4

Fungal growth

Answer 4

• hyphae -> mycelium

- apical growth - extension at tip, continuous protoplasm movement into tip, provides PENETRATING POWER

Question 5

Catalase

Answer 5

H2O2 —–> H2O + O2

Question 6

Superoxide Dismutase

Answer 6

2(O2-) + 2 H+ —–> H2O2 + O2

Question 7

All-purpose medium

Answer 7

• supports growth of most microorganisms

- i.e. nutrient agar and broth, trypticase soy broth

Question 8

Enriched media

Answer 8

• basal growth support media with nutritive supplements added
• i.e. blood agar

Question 9

Reduced medium

Answer 9

• addition of a reducing agent to the medium (i.e. thioglycolate, cystine, ascorbate)
• reducing agent removes oxygen (so anaerobes can grow)

Question 10

Transport medium

Answer 10

• preserve microorganisms in transit following isolation from a patient until cultivated

Question 11

Selective medium

Answer 11

• allows just one species to grow while suppressing the growth of others
• do this by specifying carbon or energy source, adjusting pH, increasing osmotic pressure or adjusting oxygen tension

i.e. Salmonella-Shigella agar, mannitol salt agar

Question 12

Differential

Answer 12

• more than one type of organism can grow but separation is based upon genera and species

i.e. MacConkey agar - Enterobacteriaceae
Eosin-methylene blue (EMB) - E.coli and Enterobacter
aerogenes

Question 13

Sabouraud’s Agar

Answer 13

• primary: selective isolation
• peptone (protein hydrolysate)
• pH 5.6 (inhibits fast-growing bacteria)
• antibiotics: penicillin, streptomycin, tetracycline (inhibit bacteria)
• cultivates fungi (i.e. dermatophytes) and filamentous bacteria (i.e. Nocardia)

Question 14

Corn Meal Agar

Answer 14

• secdonary: culture and species identification
• incubated at 25 degrees celsius for several days
• characteristic sexual structures develop
• ID based on morphology (microscopy)