1. Microbial Growth
Chapter 4

2. Objectives What are the factors that influence bacteria growth?
Oxygen requirements
Nutrient requirements
Carbon, Nitrogen, Sulfur, Phosphorous
Counting microogranisms

3. Microbial Growth
Growth= an increase in the number of cells, not an increase in size
Generation=growth by binary fission
Generation time=time it takes for a cell to divide and the population to double

4. Bacteria divide by binary fission

5. Biofilms are communities of bacteria

6. Examples of Biofilms

7. Generation times vary for each organism
E. coli
20 minutes (optimal conditions)
Mycobacterium tuberculosis
24 hours
6 week incubation for clinical diagnosis

8. Bacterial growth curve
Questions:
Antibiotics would have the greatest impact on which phase?
Why do microbes enter the stationary phase?
At which phase(s) would spores be formed?

9. Primary and Secondary metabolites
Metabolites are required for growth
Metabolites are required for survival

10. Requirements for bacterial growth
Environmental factors that influence
Temperature, pH, osmotic pressure, oxygen
Nutritional factors
Carbon, nitrogen, sulfur, and phosphorous
Trace elements

11. Optimum Growth Temperatures
Psychrophiles-
optimum -5 to 15oC
Psychrotrophs-
range from 20-30oC
Mesophiles-
range from 25-45oC
Thermophiles-
range from 45-70oC

12. pH influences the growth
Bacteria-prefer a pH range of
Molds prefer a pH range of

13. Osmotic environment influences growth

14. Oxygen preferences of organisms
Obligate aerobes
Facultative anaerobes
Obligate anaerobes

15. Why can some organisms grow in the presence of oxygen?
Reactive Oxygen Species are byproducts of Aerobic Respiration
They are extremely toxic to both Prokaryotic and Eukaryotic cells
DNA Damage Oxidize Amino Acids Inactivate Enzymes Disrupt Membranes Activate Immune System

16. Why can some organisms grow in the presence of oxygen?
Toxic forms of oxygen need to be neutralized by enzymes
Superoxide dismutase
Accepts electrons to make H2O2
Catalase
Converts to 4H2O2 to 2H2O + 2O2
Peroxidase

17. Oxygen Preferences of Bacteria

18. Candle jars increase CO2 levels for growing capnophiles

19. Anaerobic jars eliminate the oxygen for anaerobes to grow.

20. Chemical requirements: Carbon
What are possible sources of carbon?
Bacteria are classified based on the source of carbon as either heterotrophs or autotrophs
Heterotrophs take carbon from the environment (consumes), Autotrophs use carbon from carbon dioxide

21. Classification based on Energy and Carbon sources

22. Chemical Requirements: Nitrogen
Why do bacteria need nitrogen?
Component of Amino Acids and Nucleic Acids

23. Chemical requirements: Sulfur and Phosphorous
Why do bacteria need sulfur?
Why do bacteria need phosphorous?
Sulfur is a component of some Amino Acids, Phosphorous is a component of ATP, nucleic acids, membrane lipids.

24. Chemical requirements: trace elements
Small amounts of minerals
Cobalt, zinc, copper, manganese, etc.
Usually function as cofactors

25. Culture Media
Chemically defined
GSA
GSA – Glucose Salt Agar

26. Chemically defined media

27. Culture Media Complex Nutrient Agar TSA BHI
TSA – Trypticase Soy Agar, BHI – Brain/Heart Infusion Media

28. Culture Media Selective Differential Selective and Differential Blood
EMB
EMB – Eosin Methyl Blue, Chocolate – lysed blood media

29. Ways to measure bacterial growth
Direct Count
Plate Count/Viable Cell Count
Measure Turbidity

30. Direct Counts

31. Plate counts require dilutions

32. Two techniques for plate counts

33. Turbidity gives a rough estimate

34. Standard Curves
You may determine the precise concentration of suspension by running knowns amounts and extrapolating data
Normalized absorbance
Concentration, mg