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. Binary Fission Here is a video of bacterial fission of Streptococcus bacteriavideo

3. Bacteria divide by binary fission

4. Biofilms are communities of bacteria

5. Generation times vary for each organism E. coli Mycobacterium tuberculosis

6. Why is generation time important? E. coli scenario…… Salmonella

7. Bacterial growth curve

8. Primary and Secondary metabolites

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

10. 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

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

12. Osmotic environment influences growth

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

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

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

16. Oxygen Preferences of Bacteria

17. Candle jars increase CO 2 levels for growing capnophiles

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

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

20. Classification based on Energy and Carbon sources

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

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

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

24. Culture Media Chemically defined –GSA

25. Chemically defined media

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

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

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

29. Direct Counts

30. Plate counts require dilutions

31. Two techniques for plate counts

32. Turbidity gives a rough estimate