LQB362 Lecture Week 1_25_se1 (1)

Page 1: Introduction to Microbiology

• Course Information: LQB362 - Week 1 Lecture on Host-microbe interactions and bacterial reproduction

• Instructor: Dr. Eva Hatje (Email: e.hatje@qut.edu.au)

• Affiliation: School of Biomedical Sciences, Faculty of Health

• Provider ID: TEQSA Provider ID PRV12079

• CRICOS No: 00213J

Page 2: Acknowledgment of Traditional Owners

• First Nations Acknowledgment: Recognizing the Turrbal and Yugara as traditional owners of the land.

• Respect for Elders: Acknowledging the elders, laws, customs, and spirits of creation.

• Significance of Land: Recognition of these lands as places of teaching and learning.

Page 3: Textbook References

• Primary Textbooks:

  • Tortora, G. J., Funke, B. R., & Case, C. L. (2021). Microbiology: An Introduction (13th Edition). Pearson Education Limited, Chapters 6 & 14.

  • Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2022). Brock Biology of Microorganisms (16th Edition). Pearson Education Limited, Chapter 24.

Page 4: Learning Outcomes

1. Microbiota Definitions:

   • Define normal and transient microbiota.

   • Identify factors affecting microbial populations and host risk factors for infection.

2. Host-Microbe Interactions:

   • Define and compare commensalism, mutualism, and parasitism.

3. Normal Populations:

   • Recall microbial populations in skin, respiratory, gastrointestinal, and genitourinary tracts.

4. Bacterial Reproduction:

   • Describe binary fission and explain growth phases and generation times.

5. Measuring Bacterial Growth:

   • Describe methods to measure bacterial growth.

Page 5: Human Microbiome

• Microbial Cell Count: Equivalent number of microbial cells to human cells in the body.

• Human Microbiome: Sum of microorganisms that reside in the human body, predominantly bacteria.

• Dynamic Nature: The microbiota composition varies across different body sites.

Page 6: Types of Microbiota

• Normal Microbiota: Resident microbes that usually inhabit the body.

• Transient Microbiota: Non-permanent microbes that can be present temporarily.

• Contamination: Introduction of non-native microbes to the environment.

• Outdated Term: 'Flora' is an old term that has been largely replaced by 'microbiota'.

Page 7: Factors Affecting Microbial Populations

• Influencing Factors:

  • pH

  • Moisture

  • Nutrients

  • Temperature

  • Host Defenses

• Regional Colonization: Different bacteria colonize different anatomical sites.

Page 8: Microbial Sites in the Body

• Non-Sterile Sites: Normal locations for microbes include:

  • Skin

  • Eyes (conjunctiva)

  • Nose and throat

  • Mouth

  • Gastrointestinal tract

  • Genitourinary tract

• Sterile Sites: Should be devoid of microorganisms (blood, brain, CSF, internal organs).

Page 9: Factors Influencing Microbial Populations

• Changing Factors:

  • Age

  • Nutritional status

  • Antibiotic use

  • Health and occupation

  • Environmental factors

Page 10: Host Risk Factors

• Increased Infection Risk:

  • Age

  • Stress

  • Diet

  • Compromised immune system

Page 11: Reiteration of Learning Outcomes

• (Reiterates content from Page 4 regarding microbiota and interactions)

Page 12: Host-Microbe Interactions

• Types of Interactions:

  • Symbiosis: Interaction where both hosts are affected; includes commensalism, mutualism, and parasitism.

Page 13: Protection Against Pathogens

• Role of Normal Microbiota:

  • Competitive exclusion against pathogens.

  • Mechanisms:

    • Prevent binding of pathogens.

    • Compete for nutrients.

    • Alter local pH.

    • Secrete bacteriocins (substances inhibiting growth of other bacteria).

Page 14: Review of Learning Outcomes

• (Again reinforces objectives outlined in Page 4)

Page 15: Normal Microbiota in Body Sites

• Microbial Populations:

  • Skin

  • Respiratory system

  • Gastrointestinal system

  • Genitourinary system

Page 16: Skin as an Organ

• Characteristics: Largest organ, low pH, presence of lysozyme and salt.

• Microenvironments:

  • Moist: e.g., armpits, nostrils

  • Dry: e.g., forearms

  • Sebaceous: Oily regions like the forehead.

Page 17: Skin Microbiota Variations

• Bacterial Species:

  • Increased presence in moist areas vs dry.

  • Common species: Corynebacterium spp., Staphylococcus spp., Cutibacterium spp., Propionibacterium spp., and Malassezia (fungus).

Page 18: Influences on Skin Microbiota

• Influencing factors include:

  • Weather (temperature, humidity)

  • Age

  • Hygiene practices (poor hygiene leads to higher microbial load).

Page 19: Eyelid and Conjunctiva Microbiota

• Anatomical Features:

  • Cornea, conjunctiva, eyelids protected by tears containing lysozyme.

  • Flushing action of tears removes bacteria.

• Common bacteria: Gram-positive cocci such as Staphylococcus spp.

Page 20: Respiratory Tract Microbiota

• Upper Respiratory Tract: Portal of entry protected by mucous membranes and nasal hairs.

• Lower Respiratory Tract: Typically lacks resident microbiota; in CF patients, colonized by Pseudomonas spp.

Page 21: Upper Respiratory Tract Bacteria

• Common bacteria present:

  • Staphylococcus spp.

  • Streptococcus spp.

  • Aerobic diphtheroids

  • Haemophilus spp.

Page 22: Gastrointestinal Tract Microbiota

• Mucous Membrane Characteristics:

  • Nutrient-rich, heavily populated.

  • Common bacteria include Streptococcus spp. and others.

Page 23: Stomach and Small Intestine Environment

• Stomach: Low pH (~2), mechanical movement present; pathogens like Helicobacter pylori may exist.

• Small Intestine: Starts at low pH (~4-5), bacterial counts increase due to peristalsis.

Page 24: Large Intestine Microbiota

• Characteristics of the Large Intestine:

  • Longer transit time, higher bacterial numbers, pH neutral.

  • Anaerobic fermentation with prevalent species including E. coli, Bacteroides, and more.

Page 25: Functions of Large Intestinal Microbiota

• Physiological Roles:

  • Synthesis of vitamins like B12 and K.

  • Gas and odor production.

  • Metabolism of steroids and complex carbohydrates.

Page 26: Genitourinary Microbial Populations

• Upper Urinary Tract: Typically sterile.

• Lower Urinary Tract: Urine flushing action; common bacteria include E. coli, Proteus, and Lactobacillus.

Page 27: Reproductive Tract Microbiota

• Female Vagina: Slightly acidic due to glycogen fermentation; hosts Lactobacillus, E. coli, and Candida.

• Male Reproductive Tract: Shares urethra, with prostate secretions providing antimicrobial effects.

Page 28: Reiteration of Learning Outcomes

• (Reiterates primary goals from Page 4)

Page 29: Bacterial Growth Overview

• Key Concept: Bacterial growth refers to an increase in cell numbers rather than cell size.

• Division Method: Commonly through binary fission (asexual reproduction).

Page 30: Process of Binary Fission

• Steps:

  1. Bacterial cell elongates and replicates circular chromosomes.

  2. Cell wall and plasma membrane constrict.

  3. Cross-wall forms, separating DNA copies.

  4. Cells separate into two.

Page 31: Bacterial Divisome Functionality

• Divisome Complex: A multi-protein complex mediating cell division.

• Cytoskeletal Element: Z-ring composed of FtsZ, a tubulin homologue.

Page 32: Generation Time Information

• Definition: The time required for one cell to divide.

• Examples:

  • E. coli: ~20 mins

  • Pseudomonas aeruginosa: ~2-4 hours.

Page 33: Visualizing Bacterial Growth

• Visualization: Representations often use logarithmic scales.

Page 34: Bacterial Growth Curve

• Plotting: Involves sampling bacteria at regular intervals to create a growth curve.

Page 35: Reiteration of Learning Outcomes

• (Reiteration of main objectives from Page 4)

Page 36: Measuring Bacterial Growth

• Estimation Methods: Calculating bacterial number in a sample by volume (e.g., /ml or /g).

• Measurement Techniques:

  • Direct Methods: Cell counts via counting chambers or CFU counts.

  • Indirect Methods: Turbidity measurements against standards.

Page 37: Direct Counting Method

• Direct Counting Techniques: Utilize light microscopy (like the Petroff-Hausser cell counter).

• Considerations: Must account for motility and live vs. dead cells.

Page 38: Serial Dilution in CFU Counting

• CFU Counting: Required serial dilution to count viable cells.

• Viable Colony Count: Typically aiming for 30-300 colonies.

Page 39: CFU Calculation Formula

• Formula:CFU/mL = (Number of colonies x reciprocal of dilution factor) / Volume inoculated (mL)

Page 40: Spread Plate Method

• Technique: Known volume of diluted sample is spread across agar surface.

• Considerations: Time for incubation and potential need for multiple plates.

Page 41: Drop Plate Method

• Technique: Small volume of diluted sample dropped onto agar surface.

• Considerations: Less media required than spread plate; time for incubation needed.

Page 42: Filtration Method

• Use Case: Utilized for CFU counts from liquid samples, e.g., wastewater tests.

Page 43: Indirect Measurement of Turbidity

• Correlation: Turbidity correlates with bacterial growth; higher turbidity indicates more cells.

• Measurement Tool: Optical density measured using a spectrophotometer.

Page 44: McFarland Standards

• Standard Solutions: Barium chloride and sulfuric acid create specific turbidity for comparison.

• Approximate Cell Density Standards:

  • 0.5 MFU = 1.5 x 10^8 cells/mL

  • 1.0 MFU = 3.0 x 10^8 cells/mL

  • 2.0 MFU = 6.0 x 10^8 cells/mL

  • 3.0 MFU = 9.0 x 10^8 cells/mL

  • 4.0 MFU = 12 x 10^8 cells/mL