3.1. Microbial Growth

Question 1

How do prokaryotic cells divide

Answer 1

Via binary fission

- A cell prepares for division by enlarging its cell wall, plasma membrane and overall volume, DNA 	replication then starts
- The septum begins to grow inward as the chromosomes move toward the opposite ends of the cell. 	Other cytoplasmic components are distributed to the two developing cells
- The septum is synthesised completely through the cell centre creating two separate cell chambers.

Question 2

What are the different stages of microbial growth

Answer 2

• Lag phase: the initial period in the life of a bacterial population when cells are adjusting to a new environment
• Exponential growth phase: cells gradually increases, the cells grow at a constant, maximum rate.
• Stationary phase: Growth ceases but cells remain metabolically active, several physical and molecular changes take place

Death phase: cells in batch culture can’t grow continuously, viable cell numbers decline and a constant rate of death

Question 3

How can microbial growth be affected

Answer 3

• During exponential growth the population doubles

- Influenced by the environment: Solutes, pH, temperature, O2, Pressure and radiation

Question 4

How can microbial growth be treated?

Answer 4

• Physical methods: autoclaving, pasteurisation, heat
• Radiation - ionising radiation (most damaging)
• Chemical agents - phenols, halogens, alcohols
• Mechanical agents - filtration, scraping

Question 5

How is microbial growth calculated?

Answer 5

Through the expression of generation time and the doubling time of the bacteria population.
G=t/n

Plate method, incubate small amount of sample, dilute and count

Question 6

What are the different terms used to describe methods of microbial control

Answer 6

• Sterilisation: the complete removal or destruction of all viable microorganisms, used on inanimate objects
• Decontamination: the mechanical removal of most microbes
• Disinfection: the destruction or removal of vegetative pathogens but not bacterial endospores. Usually used only on inanimate objects.
• Antisepsis: chemicals applied to body surfaces to destroy or inhibit vegetative pathogens