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Medical Microbiology Unit 4

Medical Microbiology Unit 4. Structure/Behavior of Bacteria Conditions Needed for Bacterial Growth Tools of the Laboratory. Bacterial Structure. Prokaryotic Cell External Appendages Flagella Pili Fimbriae Glycocalyx Capsule, slime layer Cell Envelope Cell wall Cell membrane

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Medical Microbiology Unit 4

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  1. Medical Microbiology Unit 4 Structure/Behavior of Bacteria Conditions Needed for Bacterial Growth Tools of the Laboratory

  2. Bacterial Structure • Prokaryotic Cell • External • Appendages • Flagella • Pili • Fimbriae • Glycocalyx • Capsule, slime layer • Cell Envelope • Cell wall • Cell membrane • Internal • Cytoplasmic matrix • Ribosomes • Inclusions • Nucleoid/chromosome • Actin cytoskeleton • Endospore

  3. External Appendages • Flagella • Motility (chemotaxis) • 3 parts: filament, hook (sheath), basal body

  4. Pili – found in gram-negative bacteria for sexual reproduction (conjugation) • Fimbriae – small, bristlelike fibers emerging from the surface of many bacterial cells. Stick to each other

  5. Glycocalyx • External layer to protect from environmental changes and help adhere • Slime layer • Ex: layer on teeth • Capsules • “block” phagocytosis

  6. Cell Envelope • Cell Wall • Peptidoglycan • Gram Positive • Gram Negative • Cell Membrane

  7. Internal Structures • Chromosome • Plasmid • Ribosomes • Inclusions • Glycogen, poly β-hydroxybutyrate (PHB), gas vesicles, granules

  8. Endospores • Dormant bodies produced by bacteria Bacillus, Clostridium, and Sporosarcina • 2 phase life cycle between vegetative cell and endospore • Decrease in nutrients like amino acids begin sporulation • Bacillus anthracis, C. tetani, C. botulinum

  9. Bacterial Shapes

  10. Unique prokaryotes • Most Bacteria are free-living or parasites that can reproduce on their own. • Two groups of bacteria- rickettsia and chlamydia- have adapted to life inside a host cell

  11. Rickettsia • Rickettsias are very tiny, gram-negative bacteria • They alternate between mammalian hosts and blood-sucking arthropods such as fleas, lice, and ticks. • Rickettsia can not carry out metabolism completely on their own. • Cause the diseases Rocky Mountain spotted fever and endemic typhoid fever

  12. Chlamydia • Also tiny and parasitic but not related to rickettsia • Do not require transmission by arthropods • Chlamydia trachomatis can cause blindness and is a common STD that gives off a milk white discharge

  13. Conditions Needed for bacterial growth • Conditions Required: • Food • Moisture • Warmth • Proper gases • pH • Salt concentration • Spore formation • Pressure

  14. Food • Autotrophs • Photoautotrophs • Chemoautotrophs • Heterotrophs • Carnivore • Herbivore • Omnivore • Saprobe (decomposer) • Parasite

  15. Warmth • Psychrophiles – 00-200 C (320 -680F) • Thermophiles – 400-700C (1040-1580F) • Hyperthermophiles – 800C and up (above 1760F) • Mesophiles – 100-450C (500-1130F) • Bacteria in body at optimal temperature – 370C (98.60F)

  16. Proper gases • Aerobic • Anaerobic • Facultative anaerobes (staph, E. coli) • Obligate anaerobes (tetanus, botulism) • Obligate aerobes (anthrax, TB) • Microaerophilic (syphilis, Lyme disease)

  17. Growth and Reproduction • Reproduction • Transverse or binary fission • Rate (one cell every half hour) • Generation time (time between cell division) • Growth • Give off poisonous wastes and enzymes (toxins) • Four phases of growth • Lag phase • Log phase (disease symptoms appear) • Stationary phase • Death phase

  18. Phases of growth

  19. Tools of the laboratory • Methods of Culturing Microorganisms • Inoculation (producing a culture) • Introduction of microbe into nutrient medium • Growth of microbe called culture • Sterile environment • Isolation (separating microbes from one another) • Requirements: medium, Petri dish/test tube, inoculating tools • Small # of bacteria separated • Placed on nutrient surface • Grow into colony • Methods (streak plate, loop dilution/pour plate, spread plate)

  20. Isolation methods • Streak plate • Loop dilution/pour plate • Spread plate

  21. Media • Types of media • Chemical content of media • Chemically defined compositions (exact proportions of all ingredients) • Nonsynthetic or complex medium (not chemically defined) • Function of media

  22. Types of Media • Liquid media • Broths, infusions, milks • Semisolid media • Used for motility; inoculating needle used • Solid media • Agar

  23. Functions of media • General purpose • Media with specific purpose • Enriched medium (complex nutrients – blood, serum; special growth factors – vitamins and amino acids) • Fastidious medium – complex and nutrients and growth factors included • Selective media – permit growth of desired microbes only • Differential media – bring out visible variations in growth • Reducing medium – reduces oxygen • Assay – test effectiveness of antimicrobial agents • Enumeration – count # of organisms in milk, water, food • Transport – preservation of specimens held for period of time • Live media

  24. Incubation and inspection • Culture placed in incubator at specific temperature • Subculture – to get pure culture • Mixed culture • Contaminated culture • Inspection • Examined/evaluated macroscopically or microscopically

  25. Identification and proper disposal • Identification • Macroscopic appearance – morphology • Microscopic appearance – morphology • Biochemical reactions • Genetic characteristics (DNA profile) • Proper Disposal • Steam sterilizing (autoclave) • Incineration (burning)

  26. Preparing specimens for optical microscopes • Living slides (wet mount) • Fixed slides • Smear technique (spread thin film on slide, air dry) • Fixation (heat, chemicals) • Stain • Negative vs positive staining

  27. Negative vs positive staining • Basic (not acidic) dyes with positive charges • Surface of microbe negatively charged, dye is attracted. Called positive staining (ex: crystal violet, methylene blue, safranin, malachite green) • Acidic dyes with negative charges • Surface of microbe negatively charged, dye is repelled and stains background. Called negative staining (ex: nigrosin, India ink)

  28. Types of positive staining • Simple • Use one single dye • Differential • Use 2 different dyes to distinguish between cell parts or types • Primary stain and counterstain • Types: gram staining (positive = purple, negative = red), acid-fast stain (acid-fast = pink, non-acid-fast = blue), spore stain (cell stains different from spore) • Structural • Emphasizes cell parts

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