🦠 Concepts & Terminology and Principles of Microbiology

Detailed Notes for 1st Year B.Sc Nursing (INC Syllabus)

PART 1 — CONCEPTS AND TERMINOLOGY IN MICROBIOLOGY

Understanding terminology is essential because nurses must correctly interpret lab reports, infection control guidelines, and treatment protocols.

1. Microorganisms (Microbes)

Definition

Microorganisms are microscopic living organisms that cannot be seen with naked eye.

Types of Microorganisms

Type	Description	Example	Disease
Bacteria	Single-celled prokaryotic organism	E.coli	UTI
Virus	Non-cellular particle requiring host cell	HIV	AIDS
Fungi	Multicellular or unicellular	Candida	Candidiasis
Protozoa	Single-celled eukaryotes	Plasmodium	Malaria
Algae	Photosynthetic organism	Chlamydomonas	Rare infection

Characteristics of Microorganisms

• Very small in size

• Multiply rapidly

• Found everywhere (air, water, soil, body)

• Some are beneficial

• Some cause disease

Normal Flora (Normal Microbiota)

Microorganisms normally present in body without causing disease.

Examples:

• Skin bacteria

• Intestinal bacteria

Functions of normal flora

• Prevent harmful microbes growth

• Help digestion

• Produce vitamins (Vitamin K, B)

Pathogen

Microorganism capable of causing disease.

Examples:

• Streptococcus → throat infection

• Mycobacterium tuberculosis → TB

Opportunistic Pathogen

Normally harmless microbes that cause disease when immunity decreases.

Example:

Candida infection in diabetic patient

🧠 Mnemonic – Types of Microorganisms

"BVFPA"

B – Bacteria

V – Virus

F – Fungi

P – Protozoa

A – Algae

2. Infection

Definition

Entry, multiplication and growth of microorganisms in body tissues causing damage.

Types of Infection

Type	Meaning
Local infection	Limited to one area
Systemic infection	Spreads throughout body
Acute infection	Sudden onset
Chronic infection	Long duration
Nosocomial infection	Hospital acquired infection
Opportunistic infection	Occurs when immunity decreases

Source of Infection

• Patient

• Environment

• Contaminated equipment

• Healthcare workers

3. Contamination

Presence of microorganisms on non-living object or body surface.

Example: Contaminated dressing tray

4. Colonization

Presence of microbes without causing disease.

Example: Staphylococcus on skin

5. Host

Organism that harbors microorganism.

Types:

• Human

• Animal

6. Immunity

Body's ability to resist infection.

Types of Immunity

Type	Explanation
Innate immunity	Present from birth
Acquired immunity	Develops after infection
Active immunity	Body produces antibodies
Passive immunity	Antibodies transferred

Example: Mother to baby via breast milk

7. Antigen

Substance that stimulates immune response.

Example: Bacteria toxin

8. Antibody

Protein produced by immune system to fight antigen.

9. Sterilization

Complete destruction of all microorganisms including spores.

Methods:

• Autoclave

• Dry heat

• Radiation

10. Disinfection

Destruction of harmful microorganisms (not spores).

Example:

• Phenol

• Alcohol

• Chlorine

11. Antiseptic

Chemical used on living tissues to destroy microbes.

Examples:

• Dettol

• Savlon

• Betadine

12. Asepsis

Practice of preventing infection.

Types:

Medical asepsis

Clean technique

Example:

Hand washing

Surgical asepsis

Sterile technique

Example:

Operation theatre

🧠 Mnemonic – Infection related terms

"PICASO HAS"

P – Pathogen

I – Infection

C – Colonization

A – Antigen

S – Sterilization

O – Opportunistic infection

H – Host

A – Antibody

S – Sepsis

PART 2 — PRINCIPLES OF MICROBIOLOGY

Principles explain how microorganisms live, grow, reproduce and cause disease.

1. Germ Theory of Disease

States that specific microorganisms cause specific diseases.

Developed by Louis Pasteur and Robert Koch.

Examples:

Microorganism	Disease
Mycobacterium	Tuberculosis
Vibrio cholera	Cholera
Salmonella	Typhoid

2. Koch’s Postulates

Guidelines to identify disease causing organism.

Criteria:

1. Organism present in diseased person

2. Organism isolated and cultured

3. Cultured organism causes disease in healthy person

4. Same organism recovered again

3. Chain of Infection

Explains how infection spreads.

Six components:

Step	Description
Infectious agent	Pathogen
Reservoir	Place where microbes live
Portal of exit	Path leaves body
Mode of transmission	Spread method
Portal of entry	Entry into body
Susceptible host	Person at risk

Example of Chain of infection

TB infection:

Agent → Mycobacterium tuberculosis

Reservoir → infected person

Exit → cough droplets

Transmission → air

Entry → lungs

Host → low immunity person

4. Microbial Growth Principles

Microorganisms grow rapidly under suitable conditions.

Factors affecting growth:

Factor	Effect
Temperature	Optimum growth
Moisture	Required for survival
Oxygen	Aerobic or anaerobic growth
Nutrients	Provide energy
pH	Suitable acidity level

Growth phases of bacteria

1. Lag phase

2. Log phase

3. Stationary phase

4. Death phase

🧠 Mnemonic – Growth phases

"LLSD"

L – LagL – LogS – StationaryD – Death

5. Principles of Sterilization and Disinfection

Used to control infection.

Sterilization methods:

Physical methods:

• Heat

• Radiation

Chemical methods:

• Ethylene oxide

• Formaldehyde

Disinfection levels:

Level	Activity
High level	kills most microbes
Intermediate	kills bacteria
Low level	kills some microbes

6. Host-parasite relationship

Relationship between microorganism and host.

Types:

Type	Meaning
Symbiosis	both benefit
Commensalism	one benefits
Parasitism	host harmed

Example:

Parasite: Tapeworm

Host: Human intestine

7. Infection control principles

Breaking chain of infection prevents disease.

Methods:

• Hand hygiene

• PPE use

• Sterilization

• Isolation

Clinical Importance for Nurses

Nurses must:

• Follow aseptic technique

• Prevent cross infection

• Educate patients

• Maintain hygiene

• Handle specimens properly

Summary Table

Topic	Key Idea
Microorganisms	tiny living organisms
Pathogen	disease causing microbes
Infection	invasion of microbes
Immunity	body defense
Germ theory	microbes cause disease
Chain of infection	infection spread
Sterilization	destroys all microbes