Unit 1: Introduction and laboratory practice
General Microbiology notes · PTU syllabus (BMLS102-18)
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Unit summary
Medical microbiology studies the microbes that cause disease and how to identify them safely in the laboratory. This unit covers the definition and history of medical microbiology, the host–microbe relationship, laboratory safety, the care and handling of glassware, and the equipment of a clinical microbiology laboratory.
After this unit you can
- Trace the history of medical microbiology
- Explain the host–microbe relationship
- Apply biosafety measures in the laboratory
- Describe glassware care and laboratory equipment
PTU syllabus topics
- Definition and history of medical microbiology
- host-microbe relationship
- safety measures
- glassware care and handling
- equipment used in a clinical microbiology laboratory
Autoclave
Moist heat sterilisation
Hot air oven
Dry heat for glassware
Incubator
Grows cultures at 37 °C
Biosafety cabinet
Protects worker and sample
Microscope
Views microbes
Laminar air flow
Sterile work area
Topic 1
Definition and history of medical microbiology
- Medical microbiology: the study of microorganisms — bacteria, viruses, fungi and parasites — that cause human disease, their diagnosis, treatment and prevention.
- 1
Antonie van Leeuwenhoek (1676)
First saw "animalcules" with a simple microscope — father of microbiology
- 2
Edward Jenner (1796)
Smallpox vaccination using cowpox
- 3
Louis Pasteur (1860s)
Disproved spontaneous generation; pasteurisation; rabies and anthrax vaccines — father of modern microbiology
- 4
Joseph Lister (1867)
Antiseptic surgery with carbolic acid
- 5
Robert Koch (1876–1882)
Koch's postulates; isolated anthrax, tuberculosis and cholera bacilli
- 6
Alexander Fleming (1928)
Discovered penicillin
- 1
- The organism is found in every case of the disease
- 2
- It can be isolated and grown in pure culture
- 3
- The pure culture causes the disease in a susceptible animal
- 4
- The organism is re-isolated from the infected animal
Topic 2
Host–microbe relationship
Symbiosis (mutualism)
Both benefit
Gut bacteria making vitamin K
Commensalism
Microbe benefits; host unaffected
Staphylococcus epidermidis on skin
Parasitism
Microbe benefits at the host's expense
Mycobacterium tuberculosis
Opportunistic pathogen
Harmless normally; causes disease when immunity falls
Candida, Pseudomonas in hospital patients
- Normal flora protects by competing with pathogens. Pathogenicity is the ability to cause disease; virulence is its degree, determined by adhesion, invasion, toxins (exotoxins, endotoxins) and evasion of immunity.
Topic 3
Safety measures in the microbiology laboratory
- BSL-4
Life-threatening exotic agents — Ebola; full-body suits, isolated facility
- BSL-3
Serious airborne agents — M. tuberculosis; biosafety cabinet, negative pressure
- BSL-2
Moderate risk — Staphylococcus, hepatitis B; lab coats, gloves, biosafety cabinet for aerosols
- BSL-1
Minimal risk — non-pathogenic E. coli; standard practices
- Personal protective equipment
- Lab coat, gloves, mask, eye protection
- No mouth pipetting
- Use pipette aids
- Hand hygiene
- Wash before and after work
- Disinfect work surfaces
- Before and after use, and after spills
- Sharps
- Puncture-proof containers; never recap needles
- Spills
- Cover with disinfectant (1% hypochlorite) for 30 minutes before cleaning
- Vaccination
- Hepatitis B for laboratory staff
Topic 4
Care and handling of glassware
- 1
Decontaminate used glassware by autoclaving or soaking in disinfectant
- 2
Wash with detergent and brush
- 3
Soak stubborn deposits in chromic acid or mild acid
- 4
Rinse with tap water, then distilled water
- 5
Dry in an oven
- 6
Plug and sterilise before use
- Types: borosilicate (Pyrex, Borosil) resists heat and chemicals; soda-lime glass is cheaper but cracks with heat. Handle carefully; discard chipped glassware.
Topic 5
Equipment of a clinical microbiology laboratory
Autoclave
Sterilises media and discarded cultures
121 °C, 15 lb/in², 15–20 minutes
Hot air oven
Sterilises glassware
160 °C for 2 hours
Incubator
Grows cultures
Usually 37 °C
Biosafety cabinet
Protects worker and sample from aerosols
Class II most common
Laminar air flow
Sterile work area for media pouring
Protects the product only
Microscope
Examines stained smears
Oil immersion 100×
Refrigerator and deep freezer
Store media, reagents, sera, isolates
2–8 °C; −20 °C to −80 °C
Centrifuge
Separates sediments
Balance tubes
Water bath
Keeps fluids at set temperature
Melting agar, serology
Automated systems
Blood culture, identification and sensitivity
BACTEC, VITEK, MALDI-TOF
Key terms
- Koch's postulates
- Criteria linking a microbe to a disease
- Commensal
- Microbe living on a host without harm
- Virulence
- Degree of pathogenicity
- Biosafety cabinet
- Enclosed workspace filtering aerosols with HEPA filters
- Borosilicate glass
- Heat-resistant laboratory glass
Quick revision
- Leeuwenhoek, Jenner, Pasteur, Lister, Koch, Fleming.
- Koch's postulates.
- Mutualism, commensalism, parasitism; normal flora; virulence factors.
- BSL-1 to 4; PPE; spills; sharps.
- Glassware cleaning; autoclave, oven, incubator, BSC, microscope and other equipment.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.Who is called the father of microbiology?
- Q2.State Koch's postulates.
- Q3.Distinguish commensalism and parasitism.
- Q4.What is an opportunistic pathogen?
- Q5.What is the difference between a biosafety cabinet and laminar air flow?
- Q6.Give the standard autoclave conditions.
Long-answer questions
- Q1.Describe the history of medical microbiology.
- Q2.Explain the host–microbe relationship.
- Q3.Describe safety measures in a microbiology laboratory.
- Q4.Describe the equipment used in a clinical microbiology laboratory.
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