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Bacterial growth . Bacteria don\'t grow in dimensions. Each bacterial cell saves the same size during its lifeBacterial growth means usually growth of bacterial population depending on bacterial multiplication. Mechanisms of bacterial multiplication. 1. MULTIPLICATION BY DIVISIONOne cell is divided - PowerPoint PPT Presentation

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2. Bacterial growth Bacteria don’t grow in dimensions. Each bacterial cell saves the same size during its life Bacterial growth means usually growth of bacterial population depending on bacterial multiplication

3. Mechanisms of bacterial multiplication 1. MULTIPLICATION BY DIVISION One cell is divided intwo other identical “daughter cells” which are identical to parental cells. The division of the chromosome is realised by the division of the double helical structure of DNA. A complex mechanism involving DNA polymer is the division of the double-helix structure of the chromosome in two identical strands A complementary strand is synthesized by new nucleotides arranged by the information encoded in each parental strand. The re-association of the old and the new strands are enzymatically controlled and directed to new double helicoidally DNA molecule – the chromosome of the future “cell daughter”

4. Mechanisms of bacterial multiplication (2) The division of the cytoplasm is performed by two possible mechanisms: Division by strangulation Cytoplasm membrane starts to invaginate in the middle of the cell At the same time the cell wall thickens in the adjacent area and advances circularly towards the middle of the cell Later a septal wall divides the bacteria, each half containing chromosomal body, cytoplasm with plasmids and storage materials and the cytoplasmic membrane the new born bacteria can separate or remain attached, constituting chains of different size: streptococci, streptobacilli Division by transversal septum After a first septal division follows another transversal resulting 4 identical bacterial cells. Arranged / tetrades or heaps, for ex. Staphylococci.

5. Mechanisms of bacterial multiplication (3) 2. Multiplication by budding Happens to: Yeasts Fungi - Candida

6. Generation time Variable: 9 minutes – B. megaterium 20 minutes – Escherichia 1080 minutes – Mycobacterium 1980 minutes - Treponema

7. Sporulation Resistant form of bacteria in hostile living conditions of: Nutrients environment Spore germination – new generation – vegetative forms - multiplication

8. Bacterial multiplication in liquid media 1. Methods of evaluation Physical methods: determine total bacteria (alive and dead) Wet weight Spectrophotometry – ? 490-550 nm Light scattering Coulter counter Bacteriological methods: determine live microorganisms only (CFU) Surface agar counting – for arobic bacteria Deep agar counting – for total bacteria number

9. Bacterial multiplication in liquid media 2. Growth fases – growth curves The lag phase: No detectable growth Bacteria adjust to new growth condition Has a variable duration depending on: Bacteria species Growing factors Temperature of incubation The exponential (logarithmic) growth phase: The maximum growth of the culture Multiplication is not synchronised Limiting nutrient factors or some accumulated toxic products can reduce the log phase

10. Bacterial multiplication in liquid media 2.Growth phases – growth curves (cont.) The stationary phase Growth ceases: the viable cells remain constant (equal with dying) The death phase – the number of viable cells decreases Explanation Exhausting nutrient sources of the media Reducing O2 – drop of energetic systems Increasing of toxic catabolites – lyses Nutrient reserves of the cell exhausted – degradation of ?RNA (may become source of energy) – death of the cells. By interrupting protein synthesis

12. Bacterial growth curve

13. Continuous culture of bacterial cells the chemostat Container – thermostat, aeration Continuous systems of Supplying with sterile media Harvesting developed culture Purposes – obtaining large amounts of bacterial masses

14. Bacterial growth on solid media Is possible I aerobic conditions only Solidifying agents Koch – potato, gelatin Frau Hess - agar Destination Isolation in pure culture Determining of: Nutrient activity Antibacterial activity CFU in: liquid media, on surfaces

15. Bacterial multiplication on solid media Colony forming One colony: result of active multiplication in a limited space – visible growth Morphology: S type colonies Round Smooth surface Regular Continuous edge M mucoid type colonies Sticky colonies Smooth surface Round shape R type colonies Rough surface (ombilicated) Flat Irregular edges

16. Types of media used in medical microbiology Nutrient media

17. Types of media used in medical microbiology Enrichment media: Always liquid Promote the growth of some bacterial groups inhibiting commensal organisms Selective media Inhibit undesirable microorganisms Bacteria – groups, species fungi Contain Nutrient complex Inhibitory system Indicatory system minerals

18. Types of media used in medical microbiology Selective media: For Gram-positive Cocci bacilli For Gram-negative Enterobacteriaceae Vibrio Campylobacter For anaerobes For fungi

19. Types of media used in medical microbiology Test media For metabolic investigation Contain: Nutrient complex (not always) Substrate Indicator system Substrates: Proteins/ derivatives Hydrocarbonates Sugars Organic acids lipids Indicator of catabolic activity: pH indicator

20. Blood agar

21. TSI = triple sugar iron

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