BACTERIAL GROWTH. Refers to an increase in bacterial cell number (multiplication). Results from bacterial reproduction (binary fission)

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2 BACTERIAL GROWTH Refers to an increase in bacterial cell number (multiplication). Results from bacterial reproduction (binary fission) parameter called generation time (the average time required for cell numbers to double). drjamil taher 2

Bacterial Reproduction Bacteria reproduce a sexually by

3) The two sister chromosomes attach to the mesosome.

3 Bacterial Reproduction Bacteria reproduce a sexually by simple binary fission. 1) Elongation of the bacterial cell. 2) Duplication of the chromosome. 3) The two sister chromosomes attach to the mesosome. 4) Cell membrane and cell wall will form a transverse septum that divides the mother cell into 2 equal daughter cells. drjamil taher 3

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5 Bacterial Reproduction o The number of bacteria (n) increases logarithmically etc = 2 n The doubling (generation) time: The time required by the bacteria to double its number, varies from one species to another. The generation time varies from one species to another e.g. 1-V. cholera has a generation time 17 minutes. 2-Escherichia coli has a generation time 20 minutes. By contrast, 3-Mycobacterium tuberculosis has a generation time of 24 drjamil taher 5

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7 Growth bacteria Most bacteria will grow on artificial culture media prepared from extract from animal or plant tissues, which supply pre-formed nutrients and vitamins Some bacteria, cannot grown in vitro; e.g. 1- Mycobacterium leprae (leprosy) 2-Treponema pallidum (syphilis),. Other bacteria, only replicate intracellular within host cells and are therefore grown in tissue culture. e.g. 1-Chlamydia spp. 2-Rickettsia spp.,

8 Growth Requirements o In order to grow bacteria have certain requirements: Nutrients Growth factors Suitable temperature Suitable ph Oxygen Carbon dioxide Moisture. drjamil taher 8

9 Nutrients o Nutritional requirement for growth include: 1- Macromolecules: needed in larger amounts. Examples: - CHNOPS - Mineral salts: Ca, Fe, Mg, k,.. 2- Micromolecules: required in trace amounts. - Mn, Zn, Co, Ni drjamil taher 9

10 Nutritional requirements Bacteria are classified into: 1- Autotrophic bacteria: (auto= self/ troph= feeding) Autotroph= use carbon dioxide as a source of carbon and ammonium salts as a source of nitrogen, from which they synthesize organic substances, e.g protein, CHO, drjamil taher 10

11 Nutritional requirements 2- Heterotrophic bacteria: (hetro= other) Use preformed organic compounds (made by others) they derive their energy by oxidation or fermentation of organic compounds (glucose). drjamil taher 11

12 Most bacteria of medical importance are heterotrophic bacteria drjamil taher 12

13 Growth factors omany pathogenic species of bacteria require for growth essential substances, which they can not synthesize, like vitamins, amino acids, Fastidious bacteria: are those which require unusually complex nutrients. drjamil taher 13

14 Temperature Different microbial species vary widely in their optimal temperature ranges for growth: Psychrophilic: grow best at low temp (15-20 C) Mesophilic: grow best at C. Thermophilic forms: grow best at C drjamil taher 14

15 Temperature drjamil taher 15

16 Hydrogen ion concentration (ph) Most bacteria of medical importance can grow at a ph of 6-8 (neutralophiles). Some forms (acidophiles) have optima as low as ph 3.0,e.g lactobacilli. Others (alkaliphiles) have optima as high as ph 10.5, e.g. Vibrio cholerae. drjamil taher 16

17 ph Acidophiles Neutralophiles (most bacteria) Alkalophiles drjamil taher 17

18 Oxygen Class Obligate (strict) aerobe Obligate (strict) anaerobe Facultative anaerobe Microaerophilic bacteria Definition Grow only in the presence of O2 Can not grow in the presence of O2 Can grow in the presence or absence of O2 Require low O2 tension Examples Mycobacterium tuberculosis Clostridium tetanus Most pathogenic bacteria of medical Campylobacter

19 CO2 Most bacteria require CO2 in low concentration. Certain bacterial species (Carboxyphilic) require higher concentrations of CO2, e.g.: - Neisseria species require 5-10%. - Brucella abortus require 20% CO2. drjamil taher 19

20 Moisture Four-fifth of bacteria cell weight consists of water, and moist is necessary for growth. drjamil taher 20

21 Bacterial Growth Curve If a small number of bacteria are inoculated into a liquid nutrient medium and the bacteria are counted at frequent intervals and the results plotted, a characteristic growth curve with 4 phases is obtained: drjamil taher 21

22 Bacterial Growth Curve drjamil taher 22

Bacterial Growth Curve 1- Lag phase: -Metabolite-depleted cells adapt to new environment. -No cell division (constant number). - The bacteria form the enzymes and molecules needed for replication.

23 Bacterial Growth Curve 1- Lag phase: -Metabolite-depleted cells adapt to new environment. -No cell division (constant number). - The bacteria form the enzymes and molecules needed for replication. 2- Logarithmic (exponential) phase: - Rapid cell division occurs. - The number of living bacteria increases by time. - Clinical significance: this phase = symptoms and signs of the disease. drjamil taher 23

24 Bacterial Growth Curve 3- Stationary phase: - Nutrients are exhausted. - Waste products are accumulated (toxic products). - The number of dying cells = number of new cells - (The number of living bacteria remains constant). drjamil taher 24

25 Bacterial Growth Curve 4- Decline phase: - Nutrients are more exhausted. - Waste products are more accumulated. - The number of dying cells > number of new cells. The number of living bacteria decreases by time. o Clinical significance: this phase = recovery and convalescence. drjamil taher 25

26 Bacterial Metabolism Many bacteria secretes enzymes(lipases, nucleases, proteinases,..) that break down the nutritive material in to simpler molecules. Theses molecules are then oxidized by bacteria to yield energy, and the degradation products are used to build up structural components and essential molecules for cell metabolism. drjamil taher 26

27 Bacterial Metabolism Depending on the biochemical mechanisms used, bacterial metabolism can be categorized in to : OXIDATION - Aerobic respiration. - An aerobic respiration. Fermentation. drjamil taher 27

28 Bacterial Metabolism Oxidation: Removal of electrons and hydrogen ions. The substrate to which hydrogen ions are released is called H acceptor. In aerobic respiration the hydrogen acceptor is oxygen. This results in the production of toxic substances e.g hydrogen peroxide (H2O2) and (superoxide). Aerobes and facultative anaerobes; contain certain enzymes, e.g. catalase and superoxide dismutase which degrade these toxic compounds and protect bacteria from their effect. drjamil taher 28

29 Bacterial Metabolism In the anaerobic respiration the ultimate hydrogen acceptor is an inorganic compounds (not hydrogen), because these bacteria does not contain protective enzymes. drjamil taher 29

30 Bacterial Metabolism Fermentation: - Refers to the break down of sugar to pyruvic acid and then usually to lactic acid. - Fermentation is also called glycoltic cycle, and this is the process by which facultative bacteria generate ATP in absence of oxygen. - If oxygen present, the pyruvate produced by fermentation enters the Krebs cycle bacteria and generates CO2 and water. drjamil taher 30

31 Bacterial Metabolism The fermentation of certain sugars is the basis of the laboratory identification of some pathogens. The acids produced lower the ph, and this can be detected by the change in color of indicator dyes. drjamil taher 31

BACTERIAL GROWTH. FYBSc.

BACTERIAL GROWTH. FYBSc. BACTERIAL GROWTH FYBSc. Bacterial growth Binary fission Generation time Phases of growth 4-2 Binary fission 1. Prokaryote cells grow by increasing in cell number (as opposed to increasing in size). 2.