LQB362_Lecture_Week_1_25_se1

Course Information

• Course Name: LQB362 Fundamentals of Microbiology

• Instructor: Dr. Eva Hatje

• Contact: e.hatje@qut.edu.au

• Affiliation: Queensland University of Technology (QUT)

Acknowledgement of Traditional Owners

• QUT acknowledges the Turrbal and Yugara peoples as the First Nations owners of the land.

• Respect is paid to their Elders, customs, and traditions.

Textbooks

• Tortora, G. J., Funke, B. R., & Case, C. L. (2021). Microbiology: an introduction (13th ed.). Pearson Education.

• Madigan, M. T., et al. (2022). Brock biology of microorganisms (16th ed.). Pearson Education.

Learning Outcomes

1. Define normal and transient microbiota; identify factors affecting microbial populations and host risk factors for infection.

2. Define and compare host-microbe interactions: commensalism, mutualism, parasitism.

3. Recall normal microbial populations in various body regions (skin, respiratory, gastrointestinal, genitourinary).

4. Explain bacterial reproduction (binary fission) and growth phases, including generation times.

5. Describe methods for measuring bacterial growth.

Host-Microbe Interactions

• Types of Interactions:

  • Commensalism: One benefits, other is unaffected.

  • Mutualism: Both benefit.

  • Parasitism: One benefits at the expense of the other.

Microbial Populations

• Normal Microbiota:

  • Resident vs Transient microbes.

  • Dynamic nature; composition varies by body site.

Factors Influencing Microbial Populations

• pH, moisture, nutrient availability, temperature, host defenses.

Non-Sterile Body Sites

• Common sites of microbial presence:

  • Skin, conjunctiva, respiratory tract, gastrointestinal tract, genitourinary tract.

Sterile Body Sites

• Typically free of microbes:

  • Blood, brain, cerebrospinal fluid, internal organs.

Risk Factors for Infection

• Age, nutritional status, antibiotic use, health status, occupation, environmental considerations.

Protective Role of Normal Microbiota

• Prevent pathogen binding through competition, nutrient use, pH alteration, and secretion of inhibitory substances.

Specific Microbiota by Body Site

• Skin: Diverse, includes Corynebacterium, Staphylococcus, Cutibacterium, Malassezia (yeast).

• Eyes: Protective lysozyme in tears, common microbes include Staphylococcus spp.

• Respiratory Tract: Mucous membranes trap microbes; Staphylococcus spp., Streptococcus spp. common in upper respiratory.

• Gastrointestinal Tract: Heavily populated with diverse bacteria; unique conditions in stomach, small and large intestines.

• Genitourinary Tract: Vagina has acidic environment, dynamic microbial composition; bladder may host E. coli.

Bacterial Growth and Reproduction

• Bacterial Growth: Increase in bacteria number, not size.

• Reproduction: Primarily binary fission, asexual division.

• Bacterial Cell Division: Mediated by a multi-protein complex called the divisome, involving Z-ring and FtsZ protein.

• Generation Time: Time for one cell division; varies by species (e.g., E. coli ~20 mins).

Measuring Bacterial Growth

• Direct Methods: Cell counts, CFUs, Petroff-Hausser counter.

• Indirect Methods: Measuring turbidity with a spectrophotometer.

• Mathematical Calculations: CFU/mL = (colonies x dilution factor) / volume plated.

Bacterial Enumeration Techniques

• Spread Plate Method: Distributes diluted sample evenly on agar.

• Drop Plate Method: Drops a small diluted sample onto agar.

• Filtration Method: Used for liquid samples like wastewater.

• McFarland Standard: Visual standard for turbidity comparison in estimating bacterial density.