Bacterial growth

1. Dr. Jyotsna Agarwal
Professor, Dept. of Microbiology,
King George’s Medical University
Bacterial Taxonomy

2. • Classification: Orderly arrangement and
placement of bacteria based on certain characters
ie. Address
• Nomenclature: giving Names
What is taxonomy

3. • Families - related bacteria eg. Enterobacteriaceae
• Within a family - numerous genus eg. Escherichia,
Klebsiella, Salmonella
• A genus contains many species eg. E. coli, E. tarda

4. Species
• Taxonomical unit
• Based on morpholopgy, biochemical properties &
antigenic characters
• Nucleotide base ratio constant for a given species
(AT : GC)
• Genetic homology demonstrated by DNA
hybridization > 98%

5. Interspecies Classification
They are identical, may show some differences
due to mutation
• Biotype - based on biochemical reactions
• Serotype - based on antigens on bacteria
• Phage type - susceptibility to particular phage
• Colicin type - substance secreted by some bacteria
• Molecular typing: Plasmid profile, DNA sequence

6. • A bacterial population derived from a single
bacteria by binary fission is called CLONE
• A bacterial population obtained from a particular
source is called STRAIN

7. Nomenclature
• Casual name / Scientific name:
eg. Gonococcus / Neisseriae gonorrhoeae
Pneumococcus / Streptococcus pneumoniae
• Name could be a character: Staphylococcus aureus
• Place of discovery: Salmonella london
• Scientist: Clostridium welchii
• Disease: Clostridium tetani

8. Bacterial Growth
& Metabolism

9. Prokaryotes
• Asexual reproduction - binary fission
• Generation time or doubling time
• Clinical implication?

10. Bacterial Growth Curve
4 phases

11. What is a Bacterial colony?
• Colony - visible growth on a
culture plate.
• Colony Forming Unit- CFU ?

12. Bacterial Nutrition
• Autotrophs - photo /chemo
• Heterotrophs
– Need preformed organic compounds
– Includes most pathogenic bacteria
• Fastidious heterotrophs

13. Bacterial Metabolism
• Help us in identifying bacteria by their end
products
• Help us in knowing how to inhibit bacteria

14. Energy Generating Process
• Sugars formed or obtained - broken down to
release energy
– Aerobic respiration
– Anaerobic respiration
– Fermentation
• Microbes that use aerobic respiration, detoxify
generated waste:
Catalase: H2O2 ------- H20 and 02
Superoxide dismutase : oxygen radical ----- H20 and O2

15. Energy Generating Process
• Aerobic respiration:
– COMPLETE breakdown of glucose to CO2 & H2O
– Final electron receptor O2
– Yield = 38 ATP
• Fermentation:
– Yield = 2 ATP
– Endproducts: Lactic acid/Alcohol
– Final electron receptor is organic molecule
• Anaerobic respiration:
– Yield >2 <38 ATP
– Absence of oxygen

16. Factors affecting bacterial
growth
• Oxygen : Obligate /facultative; aerobes /
anaerobes; microaerophilics
• Temperature
• Ph
• Osmotic pressure
• CO2

17. Summary
• Bacterial Taxonomy
• Bacterial growth curve
• Fastidious /non fastidious bacteria
• Obligate/facultative anaerobe
• Obligate aerobes