Bacterial physiology and its growth factors

Bacterial physiology and its growth factors

1. Bacterial physiology and growth factors Santosh Yadav M.Sc. Clinical Microbiology Dept. of Microbiology Institute of Medicine Tribhuvan Univarsity Teaching Hospital, Nepal 1

2. Nutrition requirements Bacteria has same general chemical pattern as the cells of other organism. Principal constituent of the bacterial cell is water, proteins , polysaccharides , lipids, nucleic acids, mucopeptides and other low molecular weigth compounds. For growth and muliplication of bacteria,the minimum requirements are Water, Source of carbon and energy, Source of nitrogen,and Some inorganic salts. 2

3. Macronutrients Microorganisms require some elements in large quantities, because they are used to construct carbohydrates, lipids, proteins, and nucleic acids. 95% or more of cell dry weight is made up of a few major elements: C ,O , H, N , S and P. Required in large amount. 3

4. Trace Elements Microbes require very small amounts of other mineral elements, such as Fe , Cu, Mo , Zn, etc . Most are essential for activity of certain enzymes, usually as cofactors. Eg - Mg² ⁺ for Hexokinase , Ni ⁴⁺ for urease , Fe² ⁺ for cytochrome oxidase , etc… 4

5. 5 Ref:-Microbiology by Anderson and Neseter .

6. Growth Factors Organic compounds required in minute quantities and are not synthesized by bacteria, also called bacterial vitamins. Such as amino acids, vitamins, purines , and pyrimidines Eg … Neisseria spp require at least 40 additional ingredients, including 7 vitamins and all of the 20 amino acids. 6

7. Energy source Organism derive energy either from sunlight or from oxidation of chemical compounds. Phototrophs , and Chemotrophs . Carbon source Autotroph :- can synthesize all their organic compounds. Heterotroph :- can not synthesize and depends on preformed organic compounds. 7

8. Bactrial Growth It is an increase in number of population rather than in size. Bacteria divide by binary fission. 8

9. Binary fission 9 Ref:-Microbiology, Nester

10. Generation time Time required for a bacterium to give rise to 2 daughter cells under optimum conditions .Also called population doubling time. Escherichia coli – 20 mins . Mycobacterium tuberculosis – 20 hrs. M.leprae – 20 days . 10

11. Growth curve 11 Ref:-Microbiology, Nester

12. Lag phase Phase of adaptation in new medium . Necessary enzymes and metabolites are built up. Bacterial cell attain maximum size and is critical stage for multiplication. Length depends on generation time of bacteria, size of inoculum , quantity of culture medium, environmental factors, etc… Average time:- 2-6 hours. 12

13. Log or exponential phase Cell division occurs at maximum rate and number increases exponentially with time. Becomes smaller in size. Bacteria are most sensitive to antimicrobial substances. 13

14. Stationary phase Growth ceases due to exhaustion of nutrients, accumulation of of toxic metabolites and lowering of pH. Produce secondary metabolites. Frequently gram variable and stain irregularly. Sporulation occurs. 14

15. Death or decline phase Cells begin to die due to cessation of growth, accmulation of toxic products, autolytic and heterolytic enzymes. Rapid fall in viable count. Some cells remain survive at the expense of nutrients released from cell death. 15

16. Factors affecting bacterial growth 16

17. Water About 80% of bacterial cell is water hence it is essential requirement. Vehicle for entry of nutrients and elimination of waste products. Participate in metabolic reactions 17

18. Temperature Major environmental factor controlling growth. Minimum:- below which growth ceases. Optimum:- at which maximum growth occur. Maximum:- above which growth ceases. 18

19. Classification by tempr . requirement Psychrophiles :- best grow at low temprature (-5 -15⁰C) Produce enzymes that functions optimally in cold. eg . Yersinia enterocolitica , Listeria monocytogens , Pseudomonas fluorescens . 19

20. Mesophiles Temprature range for growth 25-45⁰C. Optimum growth temp 37⁰C. Are mostly pathogenic bacteria. Eg .. Escherichia coli , staphylococcus aureus , etc. 20

21. Thermophiles Range 45-70⁰C Contain heat stable enzymes and proteins. . Eg .. Bacillus sterothermophilus . Hyoerthermophiles - grow at temp above 70⁰C. Eg … Thermotoga , Methanopyrus . 21

22. Oxygen Different bacteria have different oxygen requirement. 22

23. Classification based on O 2 requirement Obligate aerobes:- Grow only in presence of oxygen. Eg .. Pseudomonas , Brucella , Mycobacteria , Nocardia spp etc. Facultative anerobes :- prefer aerobic condition but can grow without oxygen. Eg … Staphylococcus spp , Corynebacterium sps , Salmonella spp , Shigella spp , Escherichia coli, etc Microaerophiles :- Are aerobes but require little of oxygen for growth. Eg … Campylobacter jejuni , etc. 23

24. Obligate anaerobes:- Grow only in absence of oxygen and oxygen is lethal for them. Eg …Clostridium sps , Bacteroides sps , etc... Aerotolerent anaerobes:- Do not utilize oxygen , but can tolerate low amount of oxygen Eg ..Lactobacilli , anaerobic streptococci , etc 24

25. Carbondioxide ( CO 2 ) Small amount of CO2 is required by all bacteria. Some organisms grow best at higher CO2 tension and are called capnophillic . Eg .. Brucella sps , gonococcus, meningococcus . 25

26. Hydrogen ion concentration(pH) Most bacteria grow at neutral or slightly alkaline pH. 26

27. Classification Acidophiles :- grow at acidic pH. pH range ( < 5.0). Eg .. Lactobacillus sps Neutrophiles :- pH range ( > 5.0 and <8 ). Many pathogenic bacteria are neutrophiles . Alkalophiles :- pH range ( > 8 ). Eg .. Vibrio cholera , 27

28. Osmotic pressure Bacteria can withstand wide range of external osmotic pressure because of protective cellwall . 0.5% of NaCl is added in most culture medium to maintain suitable environment. 28

29. contd … Some bacteria grow at high pressure , i.e. 400-500 atm (mostly in deep sea) and are called barophiles . Eg .. Photobacterium shewanella 29

30. Symbiosis and antagonism When growth of one organism fascilitates another (symbiosis). E.g. Staphylococcus aureus helping the growth of Hemophilus influenza . When growth of one organism hampering another ( antagonism). Eg .. Pseudomonas aeruginosa hampering the growth of gonococcus and anthrax bacilli. 30