Culturing Microbes - MICR20010 Lecture 2

Lecture 2: Culturing Microbes

• Lecture title: Culturing Microbes
• Lecturer: Dr. Jennifer Mitchell
• Department: Microbiology, School of Biomolecular and Biomedical Science
• Module Code: MICR20010
• Contact: Tadhg O Croinin ([email protected])

Lecture 1: Introduction to Microbiology

• Topics covered for lecture 1 include:
  • Definition of Microbiology
  • Different types of microbes
  • Role and application of microbes
  • Importance of microbiology in:
    • Agriculture
    • Food Industry
    • Animal and plant health
  • Role of Microbiologists
  • History of Microbiology

Learning Outcomes

• How to culture microbes
• Difficulties working with microbes
• Sterile growth media
• Handling microorganisms (Inoculation, Incubation, Isolation, Inspection, Identification)
• Disposal of cultures
• Disinfectants and Antiseptics

How to Culture Microbes?

• In the 1880s, scientists realized the need to visualize and handle microorganisms for study.
• Preparation of sterile growth media is necessary
• Microbes need to be separated from each other
• Microbes are grown under controlled conditions
• Specimens are prepared for microscopic examination

Difficulties Working with Microbes

• Most microbes exist in complex communities (e.g., soil or human mouth).
• Individual bacterial species need to be isolated before they can be studied.
• Microbes need to be grown under artificial conditions.
• Microbes are invisible to the human eye, leading to contamination concerns.
• Aseptic technique prevents contamination.

Sterile Growth Media

• Sterile growth media is required before handling and growing microbes.
• Bacteria are grown in a medium containing nutrients.
• Media can be liquid (water-based broth), or solid (agar Petri plates).
• Common methods for sterilizing media include boiling, autoclaving (121°C for 30 minutes), and dry heat (150°C for 120 mins).

Handling Microorganisms: The Five I's

• Inoculation
• Incubation
• Isolation
• Inspection
• Identification

Inoculation or Producing a Culture

• A tiny sample (inoculum) is introduced into a nutrient medium.
• The nutrient medium provides an environment for microbial multiplication.
• Growth in nutrient broth is observed as a cloudy suspension, termed a culture.
• Nutrient agar provides a surface for colonies to develop.
• Inoculum can be clinical samples (blood), soil, water, sewage, or food samples.

Agar

• Agar melts at 100°C and solidifies at 40°C.
• Sterilized by autoclaving
• Bacteria grow as colonies.
• Single colony purification is a technique to isolate a single bacterial cell.

Single Colony Purification

• Each bacterial colony originates from a single cell.
• Single colony purification is used to obtain pure bacterial cultures.

Obtaining Pure Cultures from an Isolation Plate

• Used to obtain pure cultures from an isolation plate.

Growth of bacteria in Liquid Nutrient Medium

• Growth is observed as a cloudy suspension in liquid nutrient medium.

Incubation

• Microorganisms are grown in an incubator, which provides optimal temperature and gas content.
• An incubator speeds up the process of microbial multiplication.

Isolation

• Concept of separating cells from other cells and providing adequate nutrients and space for growth.
• Essential for studying microbial biology.
• Nutritional requirements of each microorganism vary.

Inspection

• Examination of colonies to determine if the culture is pure.
• Each colony forms from a single cell, representing an isolated bacterial species.
• Colony appearance aids in bacterial species identification.
• Different colony types indicate mixed or impure cultures.

Identification

• The identification of an organism involves various methods:
  • Macroscopic/colony morphology
  • Microscopic morphology
  • Biochemical characteristics
  • Genetic characteristics

Disposal of Cultures

• Sterilization removes or destroys all microbes from an object.
• Physical Methods: Heat (Moist/Dry Heat, autoclaving, incineration), Radiation
• Disinfectants / Antiseptics: Reducing bioburden on an object; often easier to apply but can not destroy all microbes.

Disinfectants and Antiseptics

• Disinfectants kill microbes but are not safe for use on living tissues
• Antiseptics kill microbes, but are harmless enough to apply to living tissues (skin/mucosal membrane)

Pasteurisation

• Use of heat to kill pathogens and reduce spoilage organisms in food (milk, fruit juice, wine, beer)

Further Reading

• Microbiology: An Introduction by Tortora, Funke, and Case (12th Ed.)
  • Chapter 6: Microbial Growth
  • Chapter 7: The control of Microbial Growth

This quiz covers important concepts from Lecture 2 on culturing microbes, focusing on techniques, challenges, and proper handling of microbial cultures. Students will learn about sterile growth media, inoculation, incubation, isolation, inspection, identification, and disposal protocols. Understanding these practices is vital for effective microbiological studies.