Lecture 3 Flashcards
2 levels of bacterial growth are
Cellular growth
Increasing mass at the cellular level - usually in preparation to divide
A single cell makes new cell components (proteins, cytoplasm, cell wall, DNA
Replication
Increasing mass at the population level
The number of cells increases exponentially due to binary fission
Binary fission is and the stages are
How bacteria replicate:
One bacterium divides into 2 identical daughter cells
2 stage process:
Replication of the bacterial chromosome, plasmids and other cell components
Separation into two equal and identical halves by forming a septum in the middle of the cell
Generation time
Time required for one round of binary fission
Or, the amount of time to double the time of bacteria
AKA doubling time
Different for all species
Depends on the environment - growth factors, temperature, oxygen, nutrients
Exponential growth
KNOW THE FORMULA ON POWERPOINT
The number of bacteria or population size doubles every generation
The bacterial growth curve and the stages are called
Observed when microorganisms are grown in culture in a closed system
Limited space and nutrients
Has four distinct phases:
Lag phase
Exponential
Stationary phase
Senescence and death phase
Lag phase
Period of adjustment after cells are inoculated into fresh media
Characterized by very slow growth
During the lag phase:
Cells adapt to the new conditions
Cells adapt, replenish spent materials
Increase in size due to synthesis of DNA, proteins
Minimal cell division
Varies in length - can be very short or absent
Exponential phase
AKA logarithmic phase, log phase
Bacteria have acclimatized and conditions are now optimal for growth
Excess nutrients, space
Lack of toxins
Rapid growth
Number of bacteria consistently consistently with every generation time
Why is log phase significant
Population is most uniform in terms of chemical and physical properties during this phase
Best time to conduct tests to identify the bacteria
Bacteria in the log phase of growth are most susceptible to antibiotics.
Because antibiotics tend to target a stage in binary fission
Stationary phase
Rate of replicating cells= rate of cell death
Overall number of bacteria stays constant
Occurs when growing condition are no longer ideal
Nutrients become depleted (starvation)
Overcrowding
Oxygen depletion
Accumulation of metabolic waste
Less susceptible to antibiotics
Senescence and death phase
Rate of cell death exceeds the rate of growth
Rapid decline in the number of viable bacteria
Majority of cells die by a process called autolysis
Autolysis= expression of specific self-digestion genes
Metabolically Inactive Bacteria
Dormancy is a response to potential or actual environmental change
Unfavorable environmental conditions include:
Lack of nutrients, lack of space, increased metabolic wastes, change in oxygen, change in temp
Presence of antibiotics
Examples of dormant states
Persister cells
Endospores
Persister cells
Most bacterial populations
Small number of cells that are slow or nongrowing
When environmental conditions improve, they reestablish population
Clinical significance of persister cells:
More difficult to kill with antibiotics
Endospores
Are a few medically significant bacteria that produce endospores
Bacillus,Clostridium
Form as a result of starvation
Endospores resistant to dry conditions, heat
Difficult to eliminate from contaminated medical equipment or food
When environment favorable, begin to grow
Why is it important to know which phase of growth bacteria are in
Bacteria are most correctly identified while in the log phase since many tests are based on metabolic processes and uptake of stain
Log phase bacteria are most vulnerable to heat, disinfectants and antibiotics
Cells in the stationary phase are more difficult to treat and to identify
Stages of growth often correspond to stages of infection
Factors that affect growth
Temp
O2 level
pH
Moisture
Osmotic pressure
Space
Temperature and bacteria
Temperature influences rate and amount of growth
Microbes cannot regulate their internal temperature
Each species has an optimal growth temperatureMost clinically relevant species are mesophiles with an optimal temperature of 30 to 40oC
Fever is a mechanism that the body uses to decrease microbial growth during an infection
The ability to withstand low and high temperatures would be considered a pathogenic factor
Optimal temp
Growth is maximal; enzymes have optimal function at certain temperatures
Incubator temperature for culturing
Maximum temp
Highest temperature at which growth will occur
If exceeded, proteins (enzymes) and nucleic acids denature; cell will die
Oxygen requirement
Levels of oxygen (O2) and carbon dioxide (CO2) influence growth
Bacteria require certain amounts of oxygen depending on the type of metabolic enzymes they express
Bacteria that produce energy (ATP) via oxidative phosphorylation and the electron transport chain require oxygen
Bacteria that produce ATP via fermentation do NOT require oxygen
Aerobe
Grown in the presence of 21% oxygen (atmospheric oxygen)
Obligate aerobe
Can’t grown without oxygen
Facultative anerobe
Grow best under aerobic conditions but can grow in the absence of oxygen
Obligate anaerobe
Cannot grow if exposed to oxygen
Very difficult to handle/isolate
