Microorganisms: Bacteria, Viruses, Fungi & Protozoa

Microorganisms are a high-frequency topic in Kerala PSC science sections. Questions cover classification, disease-causing organisms, useful microorganisms, and their applications. The tables below organize all frequently tested facts.

1. Classification of Microorganisms

Type	Cell Type	Examples
Bacteria	Prokaryotic (no true nucleus)	E. coli, Mycobacterium, Lactobacillus
Viruses	Acellular (neither prokaryotic nor eukaryotic)	HIV, Influenza, COVID-19 (SARS-CoV-2)
Fungi	Eukaryotic	Yeast, Penicillium, Aspergillus, Mushrooms
Protozoa	Eukaryotic (unicellular)	Amoeba, Plasmodium, Paramecium
Algae	Eukaryotic (mostly)	Spirogyra, Chlamydomonas, Spirulina

2. Bacteria — Key Facts

Feature	Detail
Cell type	Prokaryotic
Cell wall	Present (made of peptidoglycan)
Shapes	Coccus (sphere), Bacillus (rod), Spirillum (spiral), Vibrio (comma)
Reproduction	Binary fission (asexual)
Discovered by	Antonie van Leeuwenhoek (1676)
Father of Bacteriology	Robert Koch
Gram staining	Gram-positive (violet) and Gram-negative (pink) — developed by Hans Christian Gram

Bacterial Shapes

Shape	Name	Example
Spherical	Coccus	Staphylococcus, Streptococcus
Rod	Bacillus	E. coli, Bacillus anthracis
Spiral	Spirillum	Treponema pallidum (syphilis)
Comma	Vibrio	Vibrio cholerae (cholera)

3. Diseases Caused by Bacteria

Disease	Bacterium	Transmission	Affected Organ/System
Tuberculosis (TB)	Mycobacterium tuberculosis	Air (droplets)	Lungs
Cholera	Vibrio cholerae	Contaminated water	Intestines
Typhoid	Salmonella typhi	Contaminated food/water	Intestines
Plague	Yersinia pestis	Rat flea bite	Lymph nodes, lungs
Leprosy (Hansen’s disease)	Mycobacterium leprae	Prolonged contact	Skin, nerves
Tetanus	Clostridium tetani	Wound infection	Nervous system
Diphtheria	Corynebacterium diphtheriae	Air (droplets)	Throat
Pneumonia	Streptococcus pneumoniae	Air (droplets)	Lungs
Gonorrhoea	Neisseria gonorrhoeae	Sexual contact	Reproductive system
Syphilis	Treponema pallidum	Sexual contact	Multiple organs

4. Viruses — Key Facts

Feature	Detail
Cell type	Acellular (not living outside host)
Structure	Protein coat (capsid) + nucleic acid (DNA or RNA)
Reproduction	Only inside living host cells
Discovered by	Dmitri Ivanovsky (1892) — Tobacco Mosaic Virus
Term “virus” coined by	Martinus Beijerinck (1898)
Smallest known virus	Parvovirus
Largest known virus	Mimivirus
Bacteriophage	Virus that infects bacteria

5. Diseases Caused by Viruses

Disease	Virus	Transmission	Vaccine/Treatment
COVID-19	SARS-CoV-2	Air (droplets/aerosol)	Covishield, Covaxin, etc.
AIDS	HIV (Human Immunodeficiency Virus)	Blood, sexual contact	No vaccine; antiretroviral therapy (ART)
Rabies	Rabies virus	Animal bite (dog, bat)	Post-exposure prophylaxis (PEP)
Dengue	Dengue virus (Flavivirus)	Aedes aegypti mosquito	Supportive treatment
Polio	Poliovirus	Contaminated water	OPV (oral), IPV (injectable)
Measles	Measles virus (Paramyxovirus)	Air (highly contagious)	MMR vaccine
Hepatitis B	HBV	Blood, body fluids	Hepatitis B vaccine
Influenza	Influenza virus	Air (droplets)	Annual flu vaccine
Chickenpox	Varicella-zoster virus	Air, contact	Varicella vaccine
Ebola	Ebola virus	Body fluids	rVSV-ZEBOV vaccine

6. Fungi — Key Facts

Feature	Detail
Cell type	Eukaryotic
Cell wall	Made of chitin
Nutrition	Saprophytic (dead organic matter) or parasitic
Reproduction	Spores (sexual and asexual)
Father of Mycology	Pier Antonio Micheli
Study of fungi	Mycology

Diseases Caused by Fungi

Disease	Fungus	Affected Area
Ringworm	Trichophyton, Microsporum	Skin
Athlete’s foot	Trichophyton	Feet
Candidiasis (Thrush)	Candida albicans	Mouth, skin
Aspergillosis	Aspergillus	Lungs

7. Protozoa — Key Facts

Feature	Detail
Cell type	Eukaryotic, unicellular
Movement	Pseudopodia (Amoeba), Cilia (Paramecium), Flagella (Trypanosoma)
Nutrition	Holozoic or parasitic

Diseases Caused by Protozoa

Disease	Protozoan	Vector/Transmission
Malaria	Plasmodium (vivax, falciparum)	Female Anopheles mosquito
Amoebic dysentery	Entamoeba histolytica	Contaminated water/food
Sleeping sickness	Trypanosoma brucei	Tsetse fly
Kala-azar (Leishmaniasis)	Leishmania donovani	Sandfly
Giardiasis	Giardia lamblia	Contaminated water

8. Useful Microorganisms

Microorganism	Use
Lactobacillus	Curd/yogurt making
Saccharomyces cerevisiae (Yeast)	Bread making, alcohol fermentation
Penicillium notatum	Penicillin antibiotic (discovered by Alexander Fleming, 1928)
Rhizobium	Nitrogen fixation in legume root nodules
Streptomyces	Source of streptomycin antibiotic
Azotobacter	Free-living nitrogen fixer in soil
Acetobacter	Vinegar production
Aspergillus niger	Citric acid production
Clostridium butylicum	Biogas production
Blue-green algae (Cyanobacteria)	Nitrogen fixation; biofertiliser

9. Antibiotics — Key Facts

Antibiotic	Source	Discovered By	Year
Penicillin	Penicillium notatum	Alexander Fleming	1928
Streptomycin	Streptomyces griseus	Selman Waksman	1943
Chloromycetin	Streptomyces venezuelae	—	1947
Tetracycline	Streptomyces aureofaciens	—	1948

10. Vaccines — Important for Exams

Vaccine	Disease	Type
BCG	Tuberculosis	Live attenuated
OPV	Polio	Live attenuated (oral)
IPV	Polio	Inactivated (injectable)
MMR	Measles, Mumps, Rubella	Live attenuated
DPT	Diphtheria, Pertussis, Tetanus	Toxoid + killed
Hepatitis B	Hepatitis B	Recombinant
Covaxin	COVID-19	Inactivated whole virus
Covishield	COVID-19	Viral vector (Oxford-AstraZeneca)

11. Previous Year Question Patterns

• “Penicillin was discovered by?” — Alexander Fleming (1928)
• “Malaria is caused by?” — Plasmodium (transmitted by female Anopheles mosquito)
• “Bacteria that fixes nitrogen?” — Rhizobium
• “AIDS is caused by?” — HIV
• “Yeast is used in?” — Bread making and alcohol fermentation
• “Cholera is caused by?” — Vibrio cholerae
• “Bacteriophage infects?” — Bacteria
• “Father of Bacteriology?” — Robert Koch
• “BCG vaccine is for?” — Tuberculosis