Lec 5 - Bacterial Growth

Bacterial growth

increase in number of cells not cell size

Bacterial growth

1 cell becomes a colony of million cells

Generation time

Time required for cell to divide for population to double

1-3 hours

Average generation time for bacteria

20 mins

Generation time for E. coli

Approx 20 generations and 7 hours

No. of generations & GT for 1 cell to become 1 million cells

Lag phase

making new enzymes in response to new medium

• Type of bacteria

• Better medium, shorter lag phase

• Phase of culture from which inoculum is taken

• Size or volume of inoculum

• Environmental factors like temperature

Length of lag phase depends on

Log phase

logarithmic or exponential phase: bacterial cells start dividing and their number increase by geometric progression with time

Metabolism

Bacteria have a high rate of _________

Antibiotics & radiation

Bacteria are more sensitive to ______

Stationary phase

nutrients becoming limited or waste products becoming toxic

Division rate

Death rate = ______

• Depletion of nutrients

• Accumulation of toxic products and sporulation

After sometime , rate of multiplication and death becomes almost equal which maybe due to

Death or decline phase

in this phase, death exceeds division thus population decreases due to death of cells

• Nutritional exhaustion

• Toxic accumulation

• Autolysis by enzymes

Death is due to ____

1. Dilution plating

2. Turbidity analysis – spectrophotometer

3. Direct count – hemocytometer

4. Optical detection – Coulter counter

Enumerate ways to measure bacterial growth

• Pour plate

• Spread plate

2 methods of Inoculate Petri plates from serial dilutions

Number of colonies on plate x reciprocal of dilution sample

Formula for serial dilution (no. of bacteria per mL)

Environmental factors

• pH - measure of H+

• temperature

• salt concentration

• moisture

• nutrition

• oxygen requirements

Acidophiles

optimum pH range 1-4

Alkaliphiles

optimum pH range 8.5-11

Lactic acid bacteria

optimum pH range 4-7

Thiobacillus thiooxidans

optimum pH range 2.2-2.8

Fungi

optimum pH range 4-6

buffers, ion pumps

Internal pH regulated by _____ and near neutral adjusted by _____

Human blood and tissues pH

pH 7.2+/- 0.2

Acidity or alkalinity

_____ or _______of environment can greatly affect microbial growth

pH 6 and 8

Most organisms grow best between ph ___ and __

neutral

Internal pH of cell must be relatively close to ____ even though external pH is highly acidic or basic

low pH

Acidophiles grow best at

Helicobacter pylori, Thiobacillus thiooxidans

2 examples of acidophiles

high pH

Alkaliphiles grow best at _____

Vibrio cholera

example of alkaliphiles

Minimum temperature

Temperature below which growth ceases or lowest temperature at which microbes will grow

Optimum temperature

Temperature at which growth rate is fastest; most favors development

45 to 80 ‘C

Optimum temperature is between

Maximum temperature

Temperature above which growth ceases or highest temperature at which microbes will grow

Psychrophiles (temp)

0 to 15’C

Mesophiles (temp)

midrange temperature

Psychrophiles

Most representatives inhabit permanently cold environment

Mesophiles

Found in warm-blooded animals in terrestrial and aquatic environments in temperate and tropical latitudes

18 to 25’C

Room temperature

37.5’C

Body temperature

Thermophiles (temp)

50 to 70’C

Hyperthermophiles (optimum temp)

greater than 80’C

Hyperthermophiles

Organisms inhabit hot environments like boiling hot springs, and undersea hydrothermal vents that can have temperatures greater than 100’C

Eurytherms

wide range of temperature

Stenotherms

narrow range of temperature

Halophiles

grow best at reduced water potential and some extreme halophiles require high levels of salt for growth

Halobacterium

example of halophiles

Halotolerant

can tolerate some reduction in water activity of their environment but generally grow best in the absence of added solute

Staphylococcus aureus

Sexample of halotolerant

Xerophiles

able to grow in very dry environment

moist medium

medium for streptococcus

dry medium

medium for tubercle bacilli

Streptococcus

long chains in fluid, short chains on agar

Staphylococcus

can survive in dry environment

Autotrophs

CO2 as sole source of carbon

Heterotrophs

organic source of carbon

Parasites

living host

Obligate parasites

viruses

Saprophytes

non-living matter

Pathogenic bacteria

cause disease; all heterotrophic

Aerobes

Require oxygen for metabolism; obligate

Microaerophiles

require oxygen in small amounts

Obligate anaerobes

grow without oxygen

Facultative anaerobe

grow with or without oxygen

2 cells

Number of cells in 1 generation

4 cells

Number of cells in 2 generation

8 cells

Number of cells in 3 generation

16 cells

Number of cells in 4 generation

32 cells

Number of cells in 5 generation