B.Sc. 1st Year Microbiology Notes

History and Development of Microbiology

1.1 Introduction

Microbiology is the branch of biological science concerned with the study of microorganisms and their activities. It includes the study of bacteria, fungi, protozoa, microscopic algae and viruses.

The development of microbiology was closely associated with the invention of the microscope, development of culture techniques, understanding of infectious diseases and discovery of microbial processes.

1.2 Robert Hooke

Robert Hooke studied microscopic structures using an early compound microscope. In 1665, he published Micrographia.

While observing cork, he saw small compartments and called them cells.

1.3 Antonie van Leeuwenhoek

Antonie van Leeuwenhoek constructed simple microscopes with high magnification for his time. He observed microorganisms in pond water, dental plaque and other materials.

He called the microscopic organisms he observed animalcules. He is considered one of the pioneers of microbiology because he provided some of the earliest detailed observations of microorganisms.

1.4 Spontaneous Generation

Spontaneous generation was the historical belief that living organisms could arise directly from non-living matter.

For example, it was believed that maggots could arise from decaying meat and microorganisms could develop spontaneously in nutrient materials.

1.5 Francesco Redi

Francesco Redi demonstrated that maggots found on meat were associated with flies. His experiment challenged the idea that maggots developed spontaneously from meat.

1.6 Lazzaro Spallanzani

Spallanzani heated nutrient broth and sealed some containers. Properly heated and sealed broth remained free of visible microbial growth.

His work provided evidence that microorganisms came from pre-existing microorganisms rather than being spontaneously generated.

1.7 Louis Pasteur

Louis Pasteur made major contributions to fermentation, germ theory, pasteurization, vaccination and the rejection of spontaneous generation.

Swan-neck flask experiment

Pasteur boiled nutrient broth in flasks with long curved necks. Air could enter, but dust and microorganisms were trapped in the curved neck. The broth remained sterile as long as contamination was prevented.

When the broth was exposed to trapped environmental material, microbial growth occurred.

1.8 Germ Theory of Disease

The germ theory of disease states that particular microorganisms can cause particular infectious diseases.

The work of Pasteur and Robert Koch provided important experimental evidence supporting this concept.

1.9 Robert Koch

Robert Koch made major contributions to medical bacteriology. He demonstrated relationships between particular bacteria and particular diseases and developed methods for obtaining pure cultures.

Important organisms associated with his work include Bacillus anthracis, Mycobacterium tuberculosis and Vibrio cholerae.

1.10 Koch's Postulates

1. The suspected pathogen should be associated with diseased individuals.
2. The organism should be isolated and grown in pure culture.
3. The cultured organism should reproduce the disease in a susceptible host.
4. The same organism should be re-isolated from the experimentally infected host.

1.11 Edward Jenner

Edward Jenner demonstrated protection against smallpox using material from cowpox lesions. His work became a foundation for vaccination.

1.12 Joseph Lister

Joseph Lister applied the developing knowledge of microorganisms to surgery and introduced antiseptic practices to reduce microbial contamination.

1.13 Alexander Fleming

Alexander Fleming discovered penicillin in 1928 after observing that a mold inhibited the growth of staphylococci around it.

1.14 Important Scientists

Classification and Nomenclature of Microorganisms

2.1 Classification

Classification is the systematic arrangement of organisms into groups based on their similarities, differences and evolutionary relationships.

2.2 Taxonomy

Taxonomy is the science of classification, identification and nomenclature of organisms.

• Classification: arranging organisms into groups.
• Identification: determining the identity of an organism.
• Nomenclature: assigning scientific names.

2.3 Characteristics Used in Microbial Classification

• Morphological characteristics
• Staining characteristics
• Physiological characteristics
• Biochemical characteristics
• Serological characteristics
• Genetic characteristics
• Molecular characteristics
• Ecological characteristics

2.4 Prokaryotic and Eukaryotic Microorganisms

2.5 Three-Kingdom Concept

The three-kingdom classification divided organisms into Plantae, Animalia and Protista. Protista included many unicellular organisms that did not fit clearly into plants or animals.

2.6 Five-Kingdom Concept

Robert H. Whittaker proposed a five-kingdom system consisting of:

• Monera
• Protista
• Fungi
• Plantae
• Animalia

Monera included prokaryotic organisms, whereas the remaining kingdoms mainly contained eukaryotic organisms.

2.7 Modern Three-Domain Concept

The three-domain system recognizes:

• Bacteria
• Archaea
• Eukarya

This system is strongly influenced by molecular comparisons such as ribosomal RNA sequences.

2.8 Binomial Nomenclature

Scientific naming commonly follows binomial nomenclature, in which an organism receives a two-part name consisting of its genus and species.

Example: Escherichia coli

• Escherichia = genus
• coli = species epithet

2.9 Basic Rules of Scientific Naming

• Genus begins with a capital letter.
• Species epithet begins with a small letter.
• The scientific name is italicized when typed.
• When handwritten, genus and species are separately underlined.
• After first use, the genus may be abbreviated.

2.10 Bergey's Manual

Bergey's Manual of Systematic Bacteriology is an important reference for bacterial classification, identification and characterization.

Modern bacterial classification uses phenotypic, biochemical and molecular characteristics together with phylogenetic information.

Scope and Applications of Microbiology

3.1 Beneficial Microorganisms

• Food fermentation
• Antibiotic production
• Vitamin production
• Industrial enzyme production
• Waste treatment
• Bioremediation
• Biofertilizer production
• Biopesticide production
• Biotechnology and genetic engineering

3.2 Harmful Microorganisms

• Human diseases
• Animal diseases
• Plant diseases
• Food spoilage
• Water contamination
• Food poisoning
• Production of microbial toxins

3.3 Medical Microbiology

Deals with microorganisms responsible for human disease, mechanisms of pathogenesis, diagnosis, prevention and treatment.

3.4 Public Health Microbiology

Involves microbiological examination of drinking water, food, environmental samples and public-health-related specimens.

3.5 Agricultural Microbiology

Studies microorganisms associated with soil, plants, nutrient cycling, nitrogen fixation, plant disease and agricultural productivity.

3.6 Food Microbiology

Deals with microorganisms involved in food fermentation, spoilage, preservation and foodborne disease.

3.7 Industrial Microbiology

Uses microorganisms for commercial production of antibiotics, enzymes, organic acids, alcohols, vitamins, solvents and other useful products.

3.8 Pharmaceutical Microbiology

Deals with microorganisms related to pharmaceutical products, sterility testing, contamination control, antibiotics, vaccines and quality control.

3.9 Environmental Microbiology

Studies microorganisms in soil, water and air and their role in decomposition, nutrient cycling, pollution control and bioremediation.

3.10 Microbial Biotechnology

Uses microorganisms, microbial genes or microbial products to develop useful products and processes.

Morphology of Bacteria

4.1 General Characteristics

Bacteria are unicellular prokaryotic microorganisms. They generally lack a membrane-bound nucleus and membrane-bound organelles.

4.2 Bacterial Shapes

• Coccus: spherical
• Bacillus: rod-shaped
• Vibrio: comma-shaped
• Spirillum: rigid spiral
• Spirochete: flexible spiral
• Filamentous: thread-like

4.3 Bacterial Arrangements

• Diplococci
• Streptococci
• Staphylococci
• Tetrads
• Sarcinae
• Diplobacilli
• Streptobacilli

4.4 Bacterial Cell Structure

Capsule and slime layer

The glycocalyx is an external layer that may occur as a well-organized capsule or a less organized slime layer. It may contribute to adhesion, protection from environmental conditions and resistance to phagocytosis.

Cell wall

The bacterial cell wall provides shape and mechanical protection. Peptidoglycan is a major structural component of bacterial cell walls.

Plasma membrane

The plasma membrane controls movement of substances into and out of the cell and contains components involved in energy generation and transport.

Cytoplasm

The cytoplasm contains enzymes, metabolites, ribosomes and other cellular components.

Nucleoid

The nucleoid contains the major bacterial chromosome. It is not enclosed by a nuclear membrane.

Plasmid

Plasmids are usually small, circular extrachromosomal DNA molecules that can replicate independently. They may carry genes such as antibiotic resistance genes.

Ribosome

Bacterial ribosomes are 70S and are involved in protein synthesis.

Flagella

Flagella provide motility in many bacteria.

Fimbriae and pili

Fimbriae mainly help attachment to surfaces, while sex pili participate in bacterial conjugation.

Endospore

Some bacteria such as species of Bacillus and Clostridium form highly resistant endospores during unfavorable conditions.

4.5 Gram-Positive and Gram-Negative Bacteria

4.6 Bacterial Cell Appendages

Major appendages include flagella, fimbriae and pili. These structures contribute to motility, adhesion and genetic exchange.

Growth and Physiology of Bacteria

5.1 Bacterial Nutrition

Microorganisms require nutrients for energy generation, biosynthesis, growth and maintenance.

5.2 Nutritional Types

5.3 Macronutrients

Major elements include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Potassium, magnesium, calcium and iron are also required by many microorganisms.

5.4 Micronutrients

Trace elements such as manganese, zinc, cobalt, molybdenum, nickel and copper are required in very small amounts.

5.5 Entry of Nutrients into Bacterial Cells

Simple diffusion

Molecules move from higher concentration to lower concentration without energy expenditure.

Facilitated diffusion

Substances move through specific membrane proteins without direct energy input.

Active transport

Substances are transported against their concentration gradient using energy.

Group translocation

A transported substance is chemically modified during its entry into the cell. The phosphotransferase system is an important example.

5.6 Bacterial Growth

Bacterial growth refers mainly to an increase in cellular mass and eventually an increase in cell number through cell division.

5.7 Binary Fission

5.8 Bacterial Growth Curve

In a closed batch culture, bacterial growth generally follows four major phases.

• Lag phase: cells adapt to the new environment.
• Log phase: rapid exponential cell division occurs.
• Stationary phase: growth rate becomes approximately equal to death rate.
• Death phase: viable cell numbers decline.

5.9 Factors Affecting Growth

• Temperature
• pH
• Oxygen
• Water availability
• Osmotic pressure
• Nutrient availability
• Light
• Pressure

5.10 Temperature Groups

• Psychrophiles
• Psychrotrophs
• Mesophiles
• Thermophiles
• Hyperthermophiles

5.11 Oxygen Requirements

• Obligate aerobes
• Obligate anaerobes
• Facultative anaerobes
• Aerotolerant anaerobes
• Microaerophiles

5.12 pH Requirements

Most bacteria grow near neutral pH, although acidophilic and alkaliphilic organisms can grow under more extreme conditions.

Isolation, Enumeration and Culture of Bacteria

6.1 Culture Media

Culture media provide nutrients and suitable environmental conditions for microbial growth.

6.2 Types of Culture Media

• Simple or basal media
• Enriched media
• Enrichment media
• Selective media
• Differential media
• Transport media
• Reducing media
• Indicator media

6.3 Streak Plate Technique

A sterile loop is used to progressively dilute microorganisms across the surface of an agar plate. Individual colonies can develop from separated cells.

6.4 Spread Plate Technique

A measured sample is placed on the surface of solid agar and spread uniformly using a sterile spreader.

6.5 Pour Plate Technique

A measured sample is mixed with molten agar and allowed to solidify. Colonies develop both within and on the agar medium.

6.6 Membrane Filtration

A liquid sample is passed through a membrane filter that retains microorganisms. The membrane can then be placed on a suitable culture medium.

6.7 Most Probable Number Method

The MPN method is a statistical method used to estimate the number of viable microorganisms, particularly when direct colony counting is difficult.

6.8 Direct Microscopic Count

Cells are counted directly using a counting chamber or microscopic method. This method can count both living and dead cells unless a viability indicator is incorporated.

6.9 Biochemical Tests

Biochemical tests identify bacteria based on metabolic characteristics.

• Indole test
• Methyl red test
• Voges-Proskauer test
• Citrate utilization test
• Urease test
• Catalase test
• Oxidase test
• Carbohydrate fermentation tests
• Hydrogen sulfide production

6.10 Aerobic Culture

Aerobic organisms are cultivated in the presence of oxygen using suitable media and incubation conditions.

6.11 Anaerobic Culture

Anaerobic organisms require reduced oxygen conditions. Anaerobic jars, reducing media and anaerobic chambers may be used.

6.12 Culture Preservation

• Refrigeration
• Deep freezing
• Lyophilization
• Periodic subculturing

Microbial Metabolism

7.1 Definition

Microbial metabolism is the total collection of chemical reactions occurring within a microbial cell.

Metabolism consists mainly of:

• Catabolism: breakdown of molecules with energy release.
• Anabolism: synthesis of cellular molecules using energy.

7.2 ATP

ATP is the major immediate energy currency of the cell.

7.3 Glycolysis

Glycolysis is the pathway through which glucose is converted to pyruvate. It occurs in the cytoplasm and does not directly require oxygen.

7.4 Major Steps of Glycolysis

1. Glucose → Glucose-6-phosphate
2. Glucose-6-phosphate → Fructose-6-phosphate
3. Fructose-6-phosphate → Fructose-1,6-bisphosphate
4. Fructose-1,6-bisphosphate → Glyceraldehyde-3-phosphate + DHAP
5. Glyceraldehyde-3-phosphate → 1,3-Bisphosphoglycerate
6. 1,3-Bisphosphoglycerate → 3-Phosphoglycerate
7. 3-Phosphoglycerate → 2-Phosphoglycerate
8. 2-Phosphoglycerate → Phosphoenolpyruvate
9. Phosphoenolpyruvate → Pyruvate

7.5 Pyruvate Oxidation

7.6 TCA Cycle

The tricarboxylic acid cycle, also called the citric acid cycle or Krebs cycle, oxidizes acetyl-CoA and produces reduced electron carriers.

Important intermediates include citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate and oxaloacetate.

7.7 Electron Transport Chain

The electron transport chain transfers electrons through membrane complexes and generates a proton gradient used for ATP synthesis.

7.8 Oxidative Phosphorylation

ATP synthase uses the proton motive force to synthesize ATP from ADP and inorganic phosphate.

7.9 Fermentation

Fermentation is an anaerobic metabolic process in which an organic molecule acts as an electron acceptor.

7.10 Pentose Phosphate Pathway

The pentose phosphate pathway produces NADPH and pentose phosphates important for biosynthesis.

7.11 Entner-Doudoroff Pathway

The Entner-Doudoroff pathway is an alternative pathway for glucose catabolism found in several bacteria.

7.12 Glycogenesis and Glycogenolysis

Glycogenesis is the synthesis of glycogen, while glycogenolysis is its breakdown to provide glucose-derived intermediates.

7.13 Beta Oxidation

Beta oxidation breaks fatty acids into acetyl-CoA units while producing reduced electron carriers.

7.14 Amino Acid Metabolism

Amino acids can be used for protein synthesis or metabolized through reactions such as transamination and deamination.

Microbial Genetics

8.1 Genetic Material

Genetic information in bacteria is mainly stored in DNA. DNA contains genes that determine cellular characteristics and biological functions.

8.2 DNA Structure

DNA is composed of nucleotides containing a sugar, phosphate group and nitrogenous base. The bases are adenine, thymine, guanine and cytosine.

8.3 DNA Replication

DNA replication produces a new DNA molecule using the existing DNA strands as templates. It is described as semiconservative.

8.4 RNA

RNA is involved in gene expression. Important forms include:

• mRNA
• tRNA
• rRNA

8.5 Central Dogma

8.6 Genetic Code

The genetic code consists of nucleotide triplets called codons. Each codon specifies an amino acid or a termination signal.

8.7 Plasmids

Plasmids are extrachromosomal DNA molecules capable of independent replication. They may carry genes responsible for antibiotic resistance, virulence or specialized metabolic functions.

8.8 Mutation

A mutation is a heritable change in the genetic material.

Types of mutation

• Point mutation
• Substitution
• Insertion
• Deletion
• Frameshift mutation

8.9 Horizontal Gene Transfer

Horizontal gene transfer allows genetic material to move between organisms without reproduction.

8.10 Transformation

Transformation is the uptake of free DNA from the environment by a competent bacterial cell.

8.11 Conjugation

Conjugation is direct transfer of DNA between bacterial cells, commonly involving a conjugative plasmid and cell-to-cell contact.

8.12 Transduction

Transduction is the transfer of bacterial genetic material from one bacterium to another through bacteriophages.

8.13 Importance of Genetic Exchange

• Acquisition of antibiotic resistance
• Acquisition of virulence factors
• Adaptation to environmental changes
• Genetic diversity

Microscopy and Techniques for Handling Microorganisms

9.1 Microscopy

Microscopy is the use of microscopes to observe objects too small to be seen clearly by the unaided eye.

9.2 Bright-Field Microscope

The specimen appears darker against a bright background. It is widely used for stained bacterial preparations.

9.3 Dark-Field Microscope

The background appears dark while the specimen appears bright. It is useful for observing thin organisms such as spirochetes.

9.4 Phase-Contrast Microscope

Phase-contrast microscopy converts differences in light phase into differences in intensity, allowing observation of living unstained cells.

9.5 Fluorescence Microscope

Fluorescent dyes or fluorescently labeled antibodies are used to detect specific structures or microorganisms.

9.6 Electron Microscope

Electron microscopes use electron beams rather than visible light and provide much higher resolving power.

• Transmission electron microscope — internal ultrastructure.
• Scanning electron microscope — surface structure.

9.7 Simple Staining

A single basic dye is used to increase contrast and demonstrate cell shape, size and arrangement.

9.8 Differential Staining

Differential stains distinguish different groups of microorganisms. Important examples include Gram staining and acid-fast staining.

9.9 Gram Staining

1. Crystal violet
2. Iodine
3. Decolorizer
4. Counterstain

Gram-positive bacteria retain the crystal violet-iodine complex and appear purple, whereas Gram-negative bacteria become pink/red after counterstaining.

9.10 Acid-Fast Staining

Acid-fast staining is useful for organisms with waxy cell walls containing mycolic acids, particularly members of the genus Mycobacterium.

9.11 Aseptic Technique

Aseptic technique includes procedures used to prevent unwanted microbial contamination during handling, transfer and culture of microorganisms.

9.12 Basic Handling Principles

• Use sterile equipment.
• Minimize exposure of sterile materials.
• Disinfect working surfaces.
• Properly label cultures.
• Dispose of contaminated materials safely.
• Follow appropriate biosafety procedures.

Control of Microorganisms

10.1 Definition

Control of microorganisms refers to methods used to inhibit growth, destroy microorganisms or remove microorganisms from materials and environments.

10.2 Sterilization

Sterilization is the complete elimination of all forms of microbial life, including bacterial endospores, from an object or environment.

10.3 Disinfection

Disinfection reduces or eliminates many pathogenic microorganisms on inanimate objects but may not reliably destroy bacterial spores.

10.4 Antisepsis

Antisepsis refers to the use of antimicrobial substances on living tissues to reduce microorganisms.

10.5 Physical Methods

• Moist heat
• Dry heat
• Filtration
• Radiation
• Low temperature

10.6 Autoclaving

Autoclaving uses pressurized saturated steam for sterilization. It is effective because moist heat causes denaturation and coagulation of microbial proteins.

10.7 Dry Heat

Dry heat sterilization may be performed using a hot-air oven. It kills microorganisms mainly through oxidative damage and dehydration.

10.8 Filtration

Filtration physically removes microorganisms from liquids or gases. It is particularly useful for heat-sensitive solutions.

10.9 Radiation

Ultraviolet radiation can damage microbial DNA and is useful for surface and air disinfection. Ionizing radiation has greater penetration and can be used for sterilization of selected materials.

10.10 Chemical Agents

• Alcohols
• Halogens
• Phenolics
• Aldehydes
• Quaternary ammonium compounds
• Oxidizing agents

10.11 Factors Affecting Antimicrobial Action

• Microbial population size
• Type of microorganism
• Presence of organic matter
• Temperature
• pH
• Concentration of agent
• Exposure time

Host-Parasite Interaction

11.1 Host

A host is an organism that provides a suitable environment for another organism, particularly a pathogen or parasite.

11.2 Parasite

A parasite is an organism that obtains nutrients or other benefits from a host, generally causing some degree of harm.

11.3 Normal Microbiota

Normal microbiota are microorganisms normally present on or within the body without causing disease under ordinary conditions.

11.4 Symbiotic Relationships

• Mutualism: both organisms benefit.
• Commensalism: one benefits and the other is not significantly affected.
• Parasitism: one benefits while the host is harmed.

11.5 Pathogen

A pathogen is a microorganism capable of causing disease.

11.6 Opportunistic Pathogen

An opportunistic pathogen usually causes disease when host defenses are weakened or when it reaches an unusual body site.

11.7 Virulence

Virulence refers to the degree of pathogenicity of a microorganism.

11.8 Virulence Factors

• Capsules
• Adhesins
• Invasins
• Toxins
• Enzymes
• Biofilm formation
• Mechanisms of immune evasion

11.9 Portals of Entry

• Respiratory tract
• Gastrointestinal tract
• Genitourinary tract
• Skin and mucous membranes
• Parenteral route

11.10 Portals of Exit

• Respiratory secretions
• Feces
• Urine
• Blood
• Skin lesions
• Genital secretions

11.11 Stages of Infection

• Entry
• Adherence
• Colonization
• Invasion
• Multiplication
• Tissue damage
• Exit and transmission

11.12 Host Defense

The host protects itself through physical barriers, innate immunity and adaptive immunity.

• Skin
• Mucous membranes
• Phagocytosis
• Complement
• Antibodies
• T lymphocytes
• Inflammatory responses

Introduction to Virology

12.1 Definition of Virus

Viruses are acellular infectious agents that contain nucleic acid surrounded by a protein coat and depend on living host cells for replication.

12.2 General Properties of Viruses

• Acellular organization
• Contain DNA or RNA as genetic material
• Require living cells for replication
• Do not possess independent cellular metabolism
• Can be crystallized under suitable conditions

12.3 Structure of Virus

Genome

The viral genome may consist of DNA or RNA and may be single-stranded or double-stranded depending on the virus.

Capsid

The capsid is the protein coat surrounding the viral genome. It consists of protein subunits called capsomeres.

Envelope

Some viruses possess a lipid envelope derived largely from host-cell membranes and containing viral proteins or glycoproteins.

12.4 Viral Symmetry

• Helical
• Icosahedral
• Complex

12.5 Bacteriophages

Bacteriophages are viruses that infect bacteria.

12.6 Lytic Cycle

1. Attachment
2. Penetration
3. Synthesis
4. Assembly
5. Release

12.7 Lysogenic Cycle

In the lysogenic cycle, viral genetic material becomes associated with the host genome and may replicate with the host cell before entering a productive cycle.

12.8 Viral Replication

Viral replication generally involves attachment, entry, uncoating, synthesis of viral components, assembly and release.

12.9 Cultivation of Viruses

Viruses cannot generally be grown on ordinary cell-free bacteriological media. They require living cells.

Depending on the virus, cultivation may involve:

• Cell cultures
• Embryonated eggs
• Laboratory animals

12.10 Detection of Viruses

• Microscopy
• Antigen detection
• Antibody detection
• PCR and other nucleic-acid amplification methods
• Virus isolation

Introduction to Parasitology

13.1 Definition

Parasitology is the branch of biology concerned with parasites, their hosts and the interactions between them.

13.2 Parasites

Parasites obtain nutrients or other benefits from their hosts. Parasites of medical importance commonly include protozoa and helminths.

13.3 Protozoa

Protozoa are microscopic eukaryotic organisms. Many are unicellular and some species are medically important parasites.

13.4 Important Protozoan Groups

• Amoebae
• Flagellates
• Ciliates
• Apicomplexans

13.5 Helminths

Helminths are multicellular parasitic worms.

13.6 Major Helminth Groups

• Nematodes — roundworms
• Cestodes — tapeworms
• Trematodes — flukes

13.7 Host Types

• Definitive host: host in which the adult parasite or sexual stage occurs.
• Intermediate host: host in which larval or asexual development occurs.
• Reservoir host: host that maintains the parasite in nature.
• Vector: organism that transmits a pathogen or parasite between hosts.

13.8 Life Cycle

A parasite's life cycle describes the sequence of developmental stages through which it passes, including the hosts involved in transmission.

13.9 Direct and Indirect Life Cycle

A direct life cycle requires only one host for completion, whereas an indirect life cycle requires two or more hosts.

13.10 Transmission

• Fecal-oral route
• Food and water
• Vector transmission
• Skin penetration
• Consumption of undercooked meat

13.11 Diagnosis

Parasitic infections may be diagnosed by microscopic examination, antigen detection, molecular methods and other laboratory techniques.

Introduction to Mycology

14.1 Definition

Mycology is the branch of biology concerned with the study of fungi.

14.2 General Characteristics of Fungi

• Eukaryotic organisms
• Usually non-photosynthetic
• Obtain nutrients by absorption
• Possess cell walls mainly containing chitin
• May be unicellular or multicellular
• Reproduce by sexual or asexual methods

14.3 Yeasts

Yeasts are generally unicellular fungi. Many reproduce by budding. Saccharomyces is an important example.

14.4 Molds

Molds are multicellular filamentous fungi consisting of thread-like structures called hyphae.

14.5 Hyphae and Mycelium

A group of fungal hyphae forms a network called a mycelium.

14.6 Septate and Aseptate Hyphae

Septate hyphae contain cross-walls called septa, whereas aseptate or coenocytic hyphae generally lack regular cross-walls.

14.7 Fungal Spores

Fungi produce spores for reproduction, survival and dispersal.

14.8 Reproduction

Asexual reproduction

• Budding
• Fragmentation
• Conidia
• Sporangiospores

Sexual reproduction

Sexual reproduction involves compatible fungal cells or structures and may involve plasmogamy, karyogamy and meiosis.

14.9 Dimorphic Fungi

Some fungi can exist in two different morphological forms depending on environmental conditions, particularly temperature. Such fungi are called dimorphic fungi.

14.10 Culture of Fungi

Fungi can be cultivated on suitable fungal culture media under appropriate temperature, moisture and pH conditions.

14.11 Isolation of Fungi

Fungal isolation involves obtaining fungal growth from a specimen using appropriate collection, inoculation and incubation procedures.

14.12 Medical Importance

Some fungi are pathogenic and cause superficial, cutaneous, subcutaneous, systemic or opportunistic infections.

14.13 Economic Importance

• Bread production
• Alcoholic fermentation
• Antibiotic production
• Food production
• Enzyme production
• Decomposition

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