Unit 10

Applied Biology

Chapter 10.2

Microbial Diseases and Application of Microbiology

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Introduction

Definition Microbiology is the study of microorganisms such as bacteria, viruses, fungi, protozoa and microscopic algae. Microorganisms may cause disease, but many are also useful in food production, industry, agriculture, environmental management and biotechnology.

This Grade 12 chapter covers risk and hazard groups of microorganisms; selected microbial diseases; basic immunology and vaccines; applications in dairy and beverage industries; microbial contamination of water; sewage and drinking-water treatment; biocontrol agents; and biofertilizers.

1. Risk and Hazard Groups of Microorganisms

Microorganisms can be classified into risk groups according to their potential to cause disease, their ability to spread, and the availability of effective prevention or treatment.

Risk Group	General Meaning	Typical Concern
Risk Group 1	Unlikely to cause disease in healthy humans or animals.	Low individual and community risk.
Risk Group 2	Can cause disease but usually presents moderate individual risk and limited community risk.	Preventive or therapeutic measures are often available.
Risk Group 3	Can cause serious disease and presents high individual risk.	Community spread may occur; prevention or treatment may be available.
Risk Group 4	Can cause severe disease and may spread readily.	High individual and community risk; effective countermeasures may be limited.

Fig. 1 – Concept of Microbial Risk Groups

Laboratory SafetyRisk-group classification is a biosafety concept. Handling pathogenic microorganisms requires trained personnel, approved facilities and appropriate containment procedures.

2. Selected Human Microbial Diseases

The syllabus requires the introduction, causative agent, symptoms, prevention and control measures of selected diseases.

2.1 Typhoid

Causative agent	Salmonella Typhi bacterium.
Transmission	Mainly through food or water contaminated by fecal material from an infected person or carrier.
Common features	Prolonged fever, weakness, headache, abdominal discomfort and digestive symptoms may occur.
Prevention	Safe drinking water, sanitation, hand hygiene, safe food handling and vaccination where recommended.

Fig. 2 – Fecal-Oral Transmission Cycle

2.2 Tuberculosis (TB)

Causative agent	Mycobacterium tuberculosis.
Transmission	Primarily through airborne particles released by a person with infectious pulmonary TB.
Common features	Persistent cough, fever, night sweats, weight loss and fatigue can occur.
Prevention and control	Early diagnosis, complete prescribed treatment, respiratory hygiene, public-health follow-up and vaccination policies where applicable.

Fig. 3 – Airborne Spread of Respiratory Infection

2.3 HIV Infection

Causative agent	Human immunodeficiency virus (HIV).
Main effect	Targets immune cells, especially CD4 T lymphocytes, and can progressively weaken immune function if untreated.
Transmission	Through certain body fluids, including sexual transmission, contaminated blood exposure, shared injecting equipment and mother-to-child transmission.
Prevention and control	Safer sex, screened blood, sterile injecting equipment, testing, prevention of mother-to-child transmission and effective antiretroviral treatment.

Fig. 4 – HIV and CD4 T Cell Concept

2.4 Cholera

Causative agent	Vibrio cholerae.
Transmission	Usually fecal-oral through contaminated water or food.
Common features	Profuse watery diarrhea can cause rapid dehydration.
Prevention and control	Safe water, sanitation, hygiene, food safety and vaccination in appropriate settings.

2.5 Influenza

Causative agent	Influenza viruses.
Transmission	Primarily through respiratory particles and close contact.
Common features	Fever, cough, sore throat, body aches, headache and fatigue may occur.
Prevention and control	Vaccination, respiratory hygiene, hand hygiene and staying away from others when acutely ill.

2.6 Hepatitis

Hepatitis means inflammation of the liver. Several viruses can cause viral hepatitis, and their routes of transmission differ.

Type	Common Transmission Pattern	General Prevention
Hepatitis A	Fecal-oral, commonly contaminated food or water.	Sanitation, hygiene, safe water and vaccination where recommended.
Hepatitis B	Blood and certain body fluids; sexual and perinatal transmission.	Vaccination, safe injections, screened blood and safer sex.
Hepatitis C	Mainly blood exposure.	Safe injection practices, screened blood and avoidance of contaminated equipment.

2.7 Candidiasis

Causative agent	Usually Candida species, especially Candida albicans.
Nature	Opportunistic fungal infection that can affect skin, mouth, genital tract or, in vulnerable patients, deeper tissues.
Risk factors	Altered normal flora, immune suppression, certain medicines and moist environments may increase risk depending on the form of disease.
Control	Appropriate hygiene and medically guided antifungal treatment when needed.

Fig. 5 – Disease Summary by Microbial Type

Health NoteSymptoms listed here are study summaries and are not sufficient for self-diagnosis. Suspected infectious disease should be assessed by qualified healthcare professionals.

3. Basic Immunology and Vaccines

Definition Immunity is the ability of the body to recognize and defend against harmful biological agents or foreign substances.

Innate Immunity

Immediate, non-specific defence including barriers, phagocytic cells and inflammatory responses.

Adaptive Immunity

Specific immune responses involving lymphocytes and immunological memory.

Antigen

A molecule or structure that can be recognized by the immune system and may trigger an immune response.

Antibody

A specific immunoglobulin produced by B-cell-derived plasma cells that binds to an antigen.

Vaccination

A vaccine exposes the immune system to a safe representation of an antigen or genetic instructions for an antigen, allowing development of immune memory without requiring the disease itself.

Fig. 6 – Basic Principle of Vaccination

4. Application of Microorganisms in Dairy and Beverage Industries

Useful microorganisms carry out fermentation and other biochemical processes that help produce foods and beverages.

Application	Microbial Role	Product / Effect
Yogurt / curd	Lactic acid bacteria ferment lactose to lactic acid.	Acidification, texture and characteristic flavour.
Cheese	Starter bacteria and, in some cheeses, selected fungi contribute to acidification and ripening.	Texture, preservation and flavour development.
Alcoholic fermentation	Yeasts convert fermentable sugars mainly into ethanol and carbon dioxide under suitable conditions.	Beer, wine and other fermented beverages.
Vinegar production	Acetic-acid bacteria oxidize ethanol to acetic acid.	Vinegar.

Fig. 7 – Microbial Fermentation in Food Industry

5. Microbial Contamination of Water

Definition Microbial contamination of water is the presence of potentially harmful microorganisms in water, often associated with fecal pollution, sewage leakage or unsafe handling.

Sources

Untreated sewage entering rivers, ponds or groundwater.
Open defecation and poor sanitation.
Animal waste and agricultural runoff.
Leaking septic systems or sewer lines.
Unsafe storage and handling of drinking water.

Fig. 8 – Pathways of Water Contamination

6. Sewage and Drinking-Water Treatment

6.1 Sewage Treatment – Basic Concept

Sewage treatment removes solids, organic matter and harmful microorganisms before water is discharged or reused.

Fig. 9 – Simplified Sewage-Treatment Flow

6.2 Drinking-Water Treatment – Basic Concept

Drinking-water treatment typically combines physical clarification with filtration and disinfection to reduce turbidity and pathogenic microorganisms.

Fig. 10 – Simplified Drinking-Water Treatment

7. Microorganisms as Biocontrol Agents

Definition Biological control uses living organisms or their products to suppress pests or disease-causing organisms.

Microbial biocontrol can reduce reliance on broad-spectrum chemical pesticides in suitable agricultural systems.

Bacterial Agents

Some bacteria or their products are used against specific insect pests.

Fungal Agents

Certain fungi can infect or suppress agricultural pests and plant pathogens.

Antagonistic Microbes

Beneficial microorganisms may compete with or inhibit plant-pathogenic organisms.

Advantages

Potentially more target-specific and environmentally compatible when used correctly.

Fig. 11 – Concept of Microbial Biocontrol

8. Biofertilizers

Definition Biofertilizers are preparations containing beneficial microorganisms that improve nutrient availability or plant nutrition through biological activity.

Important Examples

Microorganism / Group	Role
Rhizobium	Forms symbiotic root nodules in legumes and fixes atmospheric nitrogen.
Free-living nitrogen fixers	Convert atmospheric nitrogen into biologically useful forms in soil.
Cyanobacteria	Some species contribute biological nitrogen fixation, especially in wet agricultural systems.
Mycorrhizal fungi	Form associations with plant roots and can improve uptake of phosphorus and other nutrients.

Fig. 12 – Rhizobium Root-Nodule Symbiosis

Benefits

Can reduce dependence on some synthetic fertilizers.
Support nutrient cycling and soil biological activity.
May improve nutrient-use efficiency in appropriate crops and soils.
Can contribute to more sustainable agricultural systems.

9. Quick Revision & Exam Points

Important Questions

Define microbiology and explain microbial risk groups.
Write the causative agent, symptoms, prevention and control of typhoid.
Write the causative agent, symptoms, prevention and control of tuberculosis.
Explain HIV infection and its major transmission routes.
Write the causative agent and prevention of cholera.
Write a short note on influenza.
What is hepatitis? Mention important viral types and transmission patterns.
What is candidiasis?
Differentiate innate and adaptive immunity.
Explain the basic principle of vaccination.
Write applications of microorganisms in dairy and beverage industries.
How does microbial contamination of drinking water occur?
Explain the basic steps of sewage treatment.
Explain the basic steps of drinking-water treatment.
Define biocontrol and biofertilizer.
Explain the role of Rhizobium and mycorrhizae in agriculture.

One-Minute Revision

Risk groups classify microorganisms by hazard.
Typhoid → Salmonella Typhi.
TB → Mycobacterium tuberculosis.
HIV attacks immune function.
Cholera → Vibrio cholerae.
Influenza is viral.
Hepatitis affects the liver.
Candidiasis is fungal.
Vaccines create immune memory.
Lactic acid bacteria are important in dairy fermentation.
Yeast is important in alcoholic fermentation.
Sewage treatment uses physical and biological processes.
Biocontrol uses living organisms against pests/pathogens.
Biofertilizers improve nutrient availability biologically.
Rhizobium fixes nitrogen in legume root nodules.

Diagram Practice Practice risk-group classification, fecal-oral transmission, airborne transmission, HIV and CD4-cell concept, disease classification, vaccination, fermentation, water contamination, sewage treatment, drinking-water treatment, biocontrol and biofertilizer diagrams.

Source note: Nepal eNotes identifies this page as Unit 10, Applied Biology, Chapter 10.2, Microbial Diseases and Application of Microbiology. Its visible page displays “PDF Link: View,” but the underlying Drive target is not exposed in the readable page data, so no Google Drive ID has been invented. The chapter headings and required disease list follow the verified Grade 12 Biology syllabus. Detailed explanations are educational expansions of those syllabus headings and are not claimed as verbatim transcription of the hidden PDF.