Microbial Growth Pt.2 Flashcards
What is culture? What is pure culture? What are containments?
Culture – ability to grow microbes
Pure culture - contains only one type of microbe
Contaminants- unwanted organisms in a culture that can come from anything
Where does pure culture grow? Name some examples
Grows on solid media; examples include potato slices, agar, and gelatin
Describe the 3 types of plate isolations
Streak plate – streaking pattern on agar
Spread plate – drop of liquid on agar spread with a sterile glass rod
Pour plate - mix bacteria with melted agar that is cooled to 42oC
What is subculture? How does refrigeration and freezing play a role in it?
Subculture – place same bacteria on new media but there is a Risk of mutation. Refrigeration slows down growth of bacteria . Freezing in media containing glycerol or DMSO and Freeze drying stop bacterial growth
What is bacterial growth? How does it divide and what two types of growth does it have?
It deals with large numbers where Under ideal conditions microbes grow and divide constantly. It divide into 2 cells by binary fission. 2 types of growth either Increase in number or Increase in size
What’s doubling time? What is generation time?
Doubling time: amount of time required for population to double
Generation time: amount of time required for a complete division cycle
Describe Turbidity/turbidometry
A clear nutrient solution becomes turbid or cloudy as
microbes grow in it and the greater the turbidity, the larger the population size.
Describe a direct count- microscopic examination
Uses Petroff Hauser cell (microscope slide that has a checkerboard pattern ) and uses Hemocytometer
Problems: Tedious,:Not too sensitive ~106 bacteria/mL, and Living cells can not be distinguished from dead cells
Describe a direct, count Dash particle count 
Uses a Coulter counter that uses electricity to count cells but Can not distinguish live from dead cells
Describe a flow cytometer
Uses fluorescent dyes and lasers to count cells and Can distinguish live from dead cells
Describe a viable count
Uses a Spread plate or Pour plate that is Heat sensitive to where organisms can die
Limitations: Not all bacteria can grow on agar and # of colonies on a plate must be between 30 and 300
What is the most probable number method?
The Statistical method for measuring bacteria in liquid which is Used when bacteria can NOT grow on agar
What is batch culture? What are its phases?
a closed-system microbial culture of fixed volume in which the Typical growth curve for population of cells are grown
Lag phase: bacteria is getting use to new environment
Exponential phase: bacteria is experiencing rapid growth
Stationary phase: number of bacteria dividing = number of bacteria dying
Death phase: most bacteria are dying
What is the importance of the growth curve?
The tendency for populations to exhibit phases of rapid growth, slow growth, and death has implications in microbial control, food microbiology, and culture technology because bateris can be easier to kill in certain phases.
– Microbes in the exponential growth phase are more vulnerable to antimicrobial agents and heat.
– Actively growing cells are more vulnerable to conditions that disrupt cell metabolism and binary fission.
– A person actively shedding bacteria in the early and middle stages of infection is more likely to spread it than a person in later stages
What is continuous culture and examples of it? What is a Chemostat? What is dilution rate?
an open-system microbial culture of fixed volume - Examples include sewage, fermentation, pharmaceutical plants;
A Chemostat is the most common type of continuous culture device where Both growth rate and population density of culture can be controlled independently and simultaneously;
The Dilution rate is the rate at which fresh medium is pumped in and spent medium is pumped out for Concentration of a limiting nutrient
