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Bacterial Growth Curve Cheatsheet Cheat Sheet by

Bacterial Growth Curve Cheatsheet


The bacterial growth curve represents the growth pattern of a population of bacteria over time.

Applic­ations of Bacterial Growth Curve:

Microb­iol­ogical research: Unders­tanding microbial physiology and behavior.
Biotec­hno­logy: Optimi­zation of microbial fermen­tation processes.
Food science: Assessing food spoilage and preser­vation methods.
Medicine: Studying bacterial infections and antibiotic efficacy.
Industrial applic­ations: Monitoring and contro­lling microbial growth in various processes.

Measur­ement of Bacterial Growth

1. Direct Cell Count (This method involves directly counting the number of bacterial cells in a liquid culture. A Petrof­f-H­ausser chamber or a specia­lized counting chamber, such as a hemocy­tom­eter, is used for micros­copic observ­ation and cell counting. This method provides an accurate cell count but can be time-c­ons­uming and labor-­int­ens­ive.)
2. Plate Count (The plate count method is based on the ability of viable bacteria to form colonies on nutrient agar plates. The culture is serially diluted to obtain a countable range of colonies, which are then counted after incubation under suitable condit­ions. The results are expressed as colony­-fo­rming units (CFUs) per milliliter of the original culture. This method provides inform­ation about viable, culturable cells and is commonly used for estimating the total number of viable cells in a sample.)
3. Most Probable Number (MPN) (The MPN method is a statis­tical procedure used to estimate the number of bacterial cells in a sample, partic­ularly when they cannot be detected using the plate count method. It involves inocul­ating multiple tubes or wells with different dilutions of the sample and observing growth or lack of growth after incuba­tion. By referring to MPN tables or using software, the most probable number of cells can be determined based on the pattern of positive and negative growth.)
4. Indirect Cell Count (This method measures the cell density of a culture indirectly by assessing the turbidity or optical density of a liquid suspen­sion. A spectr­oph­oto­meter is commonly used to measure the absorbance of light passing through the sample. The more turbid or opaque the culture, the higher the absorbance or optical density, which correlates with a higher cell density. This method provides a quick and easy estimation of bacterial growth but does not distin­guish between viable and non-viable cells.)

Phases of the Bacterial Growth Curve

a. Lag Phase:
Period of adjustment where bacteria adapt to the enviro­nment. Little to no increase in cell count occurs. Cells prepare for active growth.
b. Expone­ntial (Log) Phase:
Rapid growth phase. Cells divide at their maximum rate. Population size increases expone­nti­ally. Ideal phase for harvesting cells or studying active metabo­lism.
c. Stationary Phase:
Growth rate stabil­izes. Number of dividing cells equals the number of dying cells. Nutrient depletion and waste product accumu­lation limit further growth. Cells enter a quiescent state.
d. Death Phase:
Decline in population size. Number of dying cells exceeds the number of dividing cells. Conditions become unfavo­rable for growth. Can be influenced by nutrient depletion, build-up of toxic byprod­ucts, or other stressors.

Bacterial Growth Curve


Factors Influe­ncing Bacterial Growth Curve

Nutrient availa­bility: Presence of essential nutrients required for growth.
Temper­ature: Optimal temper­ature range for growth varies among bacterial species.
pH: Bacteria have specific pH requir­ements for growth.
Oxygen levels: Aerobic, anaerobic, or facult­ative growth condit­ions.
Enviro­nmental condit­ions: Light, pressure, salinity, etc.
Bacterial species: Each species has specific growth charac­ter­istics.

Experi­mental Techniques

Serial dilution: Diluting bacterial samples to obtain viable counts.
Plating techni­ques: Pour plate, spread plate, or streak plate methods for colony counting.
Optical density measur­ement: Using a spectr­oph­oto­meter to measure cell density based on turbidity.
Molecular techni­ques: Quanti­tative PCR (qPCR) or real-time monitoring of specific genes or markers.

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