Growth of bacteria

Definition of bacterial growth
Modes of multiplication in bacteria
List the salient features of bacterial growth curve.
Concepts of generation time and growth curve
Calculations of generation time
 

1. Growth of bacteria Mrs. V. A. Warad Assistant Professor Pharmaceutical Microbiology PES, Modern College of Pharmacy, (for Ladies), Moshi, Pune Microbiology/Bacterial growth/VAW 1

2. Objectives Definition of bacterial growth Modes of multiplication in bacteria List the salient features of bacterial growth curve. Concepts of generation time and growth curve Calculations of generation time   Microbiology/Bacterial growth/VAW 2

3. Definition of growth in bacteria Bacterial size – v ery small Growth can not be defined or observed as increase in size or mass Hence growth in bacteria is defined as increase in number of bacterial cells. Microbiology/Bacterial growth/VAW 3

4. Modes of reproduction in bacteria Bacteria reproduce mainly by asexual methods . Binary fission – Major mode of reproduction in bacteria One bacterial cell divides into two equal cells Ex. - B. subtilis, S. aureus Other modes are less common, observed in few bacteria Budding – Rhodopseudomonas acidophila Fragmentation – Nocardia Spore formation – Streptomycetes Microbiology/Bacterial growth/VAW 4

5. Sexual methods of reproduction in bacteria Rarely bacteria reproduced by sexual methods. Sexual methods are: Transformation Transduction Conjugation Microbiology/Bacterial growth/VAW 5

6. Generation time It is time required for bacterial cell to divide. It depends on bacterial species, nutrients and incubation conditions . Bacterium Generation time (min) E. coli in broth 17 E. coli in milk 12 S. aureus 27-30 Mycobacterium tuberculosis 792-932 Microbiology/Bacterial growth/VAW 6

7. Calculations of generation time Bacteria multiply by binary fission and bacterial population increases exponentially 1 → 2→ 2 2 → 2 3 → 2 4 →→→ 2 n N = 1 x 2 n Where n = No. of generation N= Final population N₀= initial population N = N₀ x 2 n Microbiology/Bacterial growth/VAW 7

8. Calculations of generation of time Log N = log N₀ + n log 2 n = log N – log N₀ / log 2 n = log N – log N₀ / 0.3010 n = 3.3(log N – log N₀) g = t /n g = t / 3.3 (log N – log N₀) Growth rate: No. of generations of bacteria per hour Growth rate = 1/g = 3.3(log N – log N₀) /t Microbiology/Bacterial growth/VAW 8

9. Puzzle E. coli cells take 2 hrs. produce 1024 cells. How much time they will take to produce 2048 cells? ( Generation time of E.coli is 20 min ) Microbiology/Bacterial growth/VAW 9

10. Puzzle Generation time of Pseudomonas aeruginosa is 30 min. calculate its growth rate? Microbiology/Bacterial growth/VAW 10

11. Growth curve of bacteria Microbiology/Bacterial growth/VAW 11 Bacterial inoculum is added to nutrient medium and incubated. Samples from medium are removed immediately and every hour for 48hrs. Number of viable cells are counted every hour and growth curve is plotted. Definition : It is a graph of log of number of viable bacterial cells verses time in hours

12. Growth curve of bacteria Microbiology/Bacterial growth/VAW 12

13. Different phases of growth curve Lag phase Logarithmic / Exponential growth phase Stationary growth phase Logarithmic / Exponential death phase Microbiology/Bacterial growth/VAW 13

14. 1. Lag phase There is no increase in number of cells. It is time taken by cells to adjust with new environment. Synthesis of proteins, enzymes, coenzymes occurs. Cells enlarge in size. Cells start dividing at the end of lag period. All cells do not divide at same time. Microbiology/Bacterial growth/VAW 14

15. There is gradual increase in number. And there is gradual increase in growth rate Duration of lag phase depends on state of organisms used for inoculation. Lag phase is long when inoculum is obtained from old culture. Lag phase is short if inoculum is obtained from young culture / from log phase. Microbiology/Bacterial growth/VAW 15

16. 2) Logarithmic growth phase Cell population increases exponentially. Generation time is constant and shortest. Growth rate is constant and highest. Cell population is uniform with respect to chemical composition, metabolic activities, relative concentrations of metabolites. Cell population is metabolically very active. Cells size is small. Cells are sensitive to physical and chemical agents. It lasts for few hours. Microbiology/Bacterial growth/VAW 16

17. 3 ) Maximum stationary phase There is further decrease in nutrient level and accumulation of metabolic waste There is no net increase in number of bacteria. Growth Rate and death rate are equal.(no. of cells newly formed = no. of cells dying) Cells are resistant to physical and chemical agents. Microbiology/Bacterial growth/VAW 17

18. Exponential death phase Death rate is more than growth rate . Bacteria die faster than new cells are produced. Number of viable cells decrease exponentially. Cell population becomes half in same time interval. Microbiology/Bacterial growth/VAW 18

19. At the end of exponential death phase very few viable cell remain in culture and survive for few days. For most of the bacteria this phase lasts for 3-4 days. In case of endospore producing bacteria it may last for few months. Microbiology/Bacterial growth/VAW 19

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