1. 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

2. Bacteria divide by binary fission

3. Biofilms are communities of bacteria

4. Generation times vary for each organism E. coli Staphylococcus aureus Mycobacterium tuberculosis

5. Why is generation time important? Food? Infections

6. Bacterial growth curve

7. Primary and Secondary metabolites

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

9. Optimum Growth Temperatures Psychrophiles- –optimum -5 to 15 o C Psychrotrophs- –range from 20-30 o C Mesophiles- –range from 25-45 o C Thermophiles- –range from 45-70 o C

10. pH influences the growth Bacteria-prefer a pH range of 6.5-7.5 Molds prefer a pH range of 5.0-6.0

11. Osmotic environment influences growth Salt concentrations are important for the class of bacteria termed Halophiles.

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

13. Why can some organisms grow in the presence of oxygen?

14. Toxic forms of oxygen need to be neutralized by enzymes –Superoxide dismutase –Catalase –Peroxidase

15. Oxygen Preferences of Bacteria

16. Candle jars increase CO 2 levels for growing capnophiles

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

18. Chemical requirements: Carbon What are possible sources of carbon? Bacteria are classified based on the source of carbon as either heterotrophs or autotrophs

19. Classification based on Energy and Carbon sources

20. Chemical Requirements: Nitrogen Why do bacteria need nitrogen?

21. Chemical requirements: Sulfur and Phosphorous Why do bacteria need sulfur? Why do bacteria need phosphorous?

22. Chemical requirements: trace elements Small amounts of minerals Usually function as cofactors

23. Culture Media Chemically defined –GSA

24. Chemically defined media

25. Culture Media Complex –Nutrient Agar –TSA –BHI

26. Culture Media Selective Differential –Blood Selective and Differential –EMB

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

28. Direct Counts

29. Plate counts require dilutions

30. Two techniques for plate counts

31. Turbidity gives a rough estimate