Microbiology

Fungi

• Fungi are eukaryotic organisms.
• Candida is an important fungal species relevant to dentistry.
• Fungi exist in two structural forms: yeasts and molds.
• Some fungi are dimorphic, meaning they can exist in both forms.

Yeast

• Yeasts grow as large single cells.
• Yeasts are unicellular.
• Yeasts are very common, found on fruit, in the stomach of mammals, the oral cavity, and vaginal areas.
• Yeasts appear white and thready and are usually oval.
• Yeasts do not have true hyphae, but they form multicellular structures called pseudohyphae.
• Yeasts are not sporing fungi.
• Yeast color is less vibrant compared to molds (they are usually colorless), but collectively seem yellow-creamy.
• Yeasts can grow in both aerobic and anaerobic conditions.
• Yeasts can cause infections for individuals with compromised immune systems.
• Yeasts often feature lateral projections of daughter cells, which split from the mother cell in a process called budding.
• Some yeasts reproduce through binary fission.
• Yeasts produce pseudohyphae, chains of elongated budding cells.
• Candida forms pseudohyphae in the oral cavity.

Moulds

• Moulds grow as a series of tubular branches.
• Moulds are multicellular.
• Moulds are typically found in damp, dark, or humid areas.
• Moulds have a fuzzy appearance and come in various shapes.
• Moulds have microscopic filaments called hyphae.
• Moulds are sporing fungi.
• Moulds are very colorful and can be orange, green, black, brown, pink, or purple.
• Moulds only grow in aerobic conditions.
• Moulds usually cause allergic reactions and respiratory problems.

Bacteria

• Small, single-celled microorganisms
• Ancient life forms
• Lack chlorophyll
• Lack membrane-bound organelles
• Usually have a single circular DNA chromosome found within cytoplasm
• Same basic functions as other living cells

Features of Bacteria

• Size: Varies by species (micrometers)
• Shape:
  • Coccus: Round, spherical
  • Bacillus: Rod-shaped
  • Spirillum: Spiral shaped
• Arrangement:
  • Diplo: Pairs
  • Staphylo: Clusters
  • Strepto: Chains

Structure of Bacteria

• Flagellum: Tail-like structure for movement
• Ribosomes: Sites of protein synthesis
• Cytoplasm: Gel like substance that fills the cell
• Nucleoid: Region containing the bacterial DNA (chromosome)
• Plasma membrane: Encloses the cell and regulates what enters and exits
• Cell wall: Rigid outer layer that provides shape and protection
• Capsule: Outer layer that can help the bacteria evade the host's immune system
• Pilus: Hair-like structure for attachment to surfaces

Gram Staining

• A technique used to distinguish and classify bacterial species into two groups:
  • Gram-positive bacteria: Thick cell wall with peptidoglycan
  • Gram-negative bacteria: Thin cell wall with peptidoglycan but a thick lipopolysaccharide outer layer

Environmental Requirements

• Moisture: Most require water for survival
• Oxygen:
  • Aerobic: Require Oxygen
  • Anaerobic: Do not require oxygen, some may be killed by it
  • Facultative anaerobic: Can survive with or without oxygen
• Carbon dioxide: Necessary for building cell components
• Temperature: Varies by species (thermophiles thrive in high temperatures, psychrophiles in low temperatures)
• pH: Impacts bacterial growth and survival
• Light: Some photosynthetic bacteria require light
• Osmotic effects: Bacterial growth and survival is affected by the concentration of solutes in their environment (hypertonic, hypotonic)
• Mechanical stress: Can affect bacteria growth and reproduction

Naming Bacteria

• Taxonomy: The system of classification of organisms into ordered groups
• Genus: A group of similar species
• Species: A distinct type of organism within a genus
• Name:
  • Combination of the genus and species
  • Written in italics
  • Genus name is capitalized, species name is lowercase (e.g. Streptococcus salivarius)
  • Genus names can be abbreviated (e.g. S. salivarius)

Classification of Bacteria

• Kingdom: Procaryote
• Division: Firmicutes
• Subdivision: Low DNA content
• Family: Streptococcaceae
• Genus: Streptococcus
• Species: Streptococcus salivarius

Bacteria Growth

• Several environmental factors affect bacterial growth: temperature, pH, water availability, light exposure, nutrient availability, and respiratory conditions.

Bacterial Features

• Bacteria are microscopic, single-celled organisms.
• They are among the oldest forms of life on Earth.
• Bacteria share basic functions with other living cells.
• They lack chlorophyll, meaning they cannot photosynthesize for energy.
• Most bacteria have a single, circular DNA chromosome located in the cytoplasm.
• They lack membrane-bound organelles.

Bacterial Shapes

• Bacteria come in diverse shapes:
  • Coccus: Spherical or round
  • Coccobacillus: Short, rod-shaped with rounded ends
  • Vibrio: Comma-shaped
  • Bacillus: Rod-shaped
  • Spirillium: Spiral or helical shaped
  • Spirochete: Long, flexible, spiral-shaped

Gram Staining

• Gram staining differentiates bacteria into two main groups:
  • Gram-positive bacteria: Retain the crystal violet stain due to a thicker peptidoglycan layer in their cell walls.
  • Gram-negative bacteria: Do not retain the crystal violet stain, instead appearing red after counterstaining with safranin.
• When writing about bacteria, their names must be in italics.

Bacteria and Dentistry

• Specific bacteria are associated with dental health problems:
  • Carious process: Tooth decay caused by bacteria
  • Acute necrotising ulcerative gingivitis: Inflammatory disease of the gums caused by bacteria
  • Infective endocarditis: Inflammation of the inner lining of the heart chambers caused by bacteria
  • Legionella: A genus of bacteria that can cause lung infections
  • MRSA: Methicillin-resistant Staphylococcus aureus, a drug-resistant bacterium that can cause skin infections
  • MMSA: Methicillin-susceptible Staphylococcus aureus, a susceptible bacterium to methicillin antibiotic, often causing skin infections

Fungi & Mould Features

• Fungi are eukaryotic organisms with a nucleus in their cells.
• There are two main structural types of fungi:
  • Yeast: Single-celled fungi
  • Mould: Multicellular fungi
• Fungi cell walls contain chitin, a hard substance found in exoskeletons of insects or crustaceans.
• Most fungi reproduce through both sexual and asexual methods.
  • Asexual reproduction: Occurs through the release of spores or mycelial fragmentation.
  • Mycelial fragmentation: The mycelium (body of the fungus) separates into multiple pieces that grow independently.
• Yeast: Can reproduce through binary fission, where the organism copies its DNA and splits into two identical parts.
• Mould: Is exclusively a multicellular organism.
• Yeast: Can be both unicellular and multicellular.

Oral Cavity Fungi

• The oral cavity harbors a commensal fungal flora, a group of fungi that coexist with the host without causing disease.

Transmission of Disease

• Kissing, sexual contact, touching, and the use of vehicles or vectors are all ways for disease to be transmitted.
• Vehicles are inanimate objects or substances that transmit disease, including air, water, food, and fomites.
• Vectors are living organisms that transmit disease, including insects such as mosquitoes, ticks, and fleas.

Indirect Transmission

• Indirect transmission happens when an infected host transmits disease to a healthy host through an object or vector.
• Airborne transmission occurs when droplets or dust particles containing microbes remain suspended in the air for long periods.
• Waterborne transmission happens when water is contaminated by the excreta of animals or humans.
• Soil transmission occurs when contact with soil contaminated with spores or parasites.
• Food transmission happens when food becomes contaminated by bacteria, viruses, or parasites.
• Fomites are inanimate objects that can harbor and transmit pathogens.
• Blood and body fluids can transmit infections when they come into contact with mucous membranes or the bloodstream of an uninfected person.

Koch's Postulates

• To understand how diseases spread, there are postulates.
• Koch's postulates are a set of criteria designed to establish a causal relationship between a microbe and a disease.

Transmission Chain

• To spread, infection must be able to move through a chain of events.
• The parts of the transmission chain are:
  • Agent: The pathogen that causes the infection.
  • Reservoir: The place where the pathogen lives and multiplies.
  • Exit: The way the pathogen leaves the reservoir.
  • Mode of transmission: The mechanism by which the pathogen is transmitted from the reservoir to a susceptible host.
  • Portal of entry: The way the pathogen enters the susceptible host.
  • Susceptible host: An individual who is at risk of getting infected.

Classifying Transmission of Disease

• Transmission of infectious disease can be classified as follows:
  • Horizontal transmission: The transmission of disease from one person to another.
  • Vertical transmission: The transmission of disease from a parent to their offspring.
  • Direct contact transmission: Occurs when there is physical contact between an infected person and a susceptible person.
  • Indirect transmission: Occurs when a pathogen is transmitted through an intermediate object or vector.

Modes of Transmission

• Direct transmission includes modes of transmission like kissing and sexual contact.
• Indirect transmission includes modes of transmission like airborne transmission, waterborne transmission, food transmission, and fomites.
• Vector transmission occurs when an insect, such as a mosquito, bites a person and transmits a pathogen.
• Soil transmission occurs when a person comes into contact with soil contaminated with spores or parasites.

Preventing the Ingress of Disease

• The body has many different ways to prevent infections from entering.
• Ways the body prevents the ingress of disease include:
  • Skin: The outer layer of the skin acts as a barrier to infection.
  • Mucous membranes: Mucous membranes line the respiratory, digestive, and urinary tracts.
  • Cilia: Cilia are tiny hair-like structures that line the respiratory tract and help to trap and remove pathogens.
  • Stomach acid: The stomach contains acid that can kill many pathogens.
  • The lymphatic system.

Managing the Ingress of Disease

• Once a pathogen enters the body, the immune system goes to work.
• The immune system has many mechanisms to fight infection and diseases.
• Some of these mechanisms include:
  • Phagocytosis: The process by which immune cells engulf and destroy pathogens.
  • Inflammation: A localized response to infection.
  • Antibody production: The production of antibodies, which are proteins that bind to and neutralize pathogens.

Introducing Microbiology

• Microbiology is the study of organisms too small to be seen with the naked eye.
• These organisms are known as microorganisms or microbes.

Types of Microorganisms

• Bacteria
• Viruses
• Fungi
• Algae
• Protozoa

Microorganisms in Health

• Microorganisms are essential for human health and play a vital role in digestion, immune system development, and overall well-being.
• The human gut is a diverse ecosystem teeming with trillions of microorganisms known as the microbiome.
• The composition of the microbiome is influenced by several factors:
  • Mode of delivery
  • Diet
  • Age
  • Environment

The Importance of Microbiology

• Microorganisms play a critical role in:
  • Health
  • Disease
  • Prevention
  • Manipulation of the host
  • Infection
  • Clinical manifestations
  • Host response
  • Infection control
  • Treatment and management options
  • Antibiotic resistance
  • Local and global health impacts

Eukaryotes and Prokaryotes

• Eukaryotes:
  • Large and complex cells
  • Have a clearly defined nucleus
  • Possess membrane-bound organelles
  • Can be single-celled or multicellular organisms
• Prokaryotes:
  • Small and simple cells
  • Have a nucleoid (a region containing DNA) without a membrane
  • Lack internal membrane structures
  • Uni-cellular (single-celled)

How Microorganisms Cause Disease

• The disease-causing potential of microorganisms is related to their:
  • Products:
    • Toxins (endotoxins and exotoxins)
    • Metabolites
    • Enzymes
  • Antigenic nature: Ability to trigger an immune response.
  • Defences: Mechanisms that enable them to evade the host's immune system.
  • The host: The individual's susceptibility and health status.

Endotoxins

• Part of the bacterial cell wall, mainly in Gram-negative bacteria.
• Released upon bacterial death.
• Can cause fever, inflammation, and shock
• Examples: Lipopolysaccharide (LPS)

Exotoxins

• Secreted by living bacterial cells.
• Highly toxic and can cause specific symptoms.
• Examples: Botulinum toxin, tetanus toxin, diphtheria toxin.

Metabolites

• Waste products generated by microorganisms during their metabolism
• Can be harmful to the host.
• Examples: Organic acids produced by Streptococcus mutans which initiate tooth decay.

Enzymes

• Biological catalysts produced by microorganisms.
• Help them break down or synthesize substances.
• Enzymes contribute to invasiveness, allowing microorganisms to:
  • Spread easily
  • Obtain nutrients
  • Evade host defences

Microbial Growth Conditions

• Temperature
• pH
• Water
• Light
• Nutrition
• Respiration

Temperature

• Different microorganisms have optimal temperature ranges for growth.
• Temperature extremes can inhibit or kill microbes.

pH

• Optimal pH range varies for different microorganisms.
• pH extremes can inhibit or kill microbes.

Water

• Microorganisms require water for growth and survival.
• Drying can be tolerated to different degrees by various species.

Light

• Most parasitic microorganisms prefer darkness.
• Ultraviolet (UV) light can be lethal and is used to sterilize surfaces.
• X-rays can damage microbial DNA and are used to sterilize medical supplies.

Nutrition

• Microorganisms have similar basic nutrient requirements to higher life forms, needing energy, nitrogen, carbon, water, and sulfur.
• They possess specific enzyme systems to break down nutrients.
• Their growth can be enhanced by enriching the growth medium with essential nutrients or retarded by adding growth inhibitors.

Viral Replication

• Viral replication involves a series of steps:
  • Attachment
  • Penetration
  • Uncoating
  • Replication
  • Assembly
  • Release

Viral Proteins

• Viral proteins are essential for various functions and are categorized into two groups:
  • Structural proteins
  • Non-structural proteins, which include enzymes

Viral Assembly

• Viral assembly involves encapsulating the viral nucleic acid within capsomeres.
• This assembly process can occur in various cellular locations.

Viral Release

• Two main release mechanisms are:
  • Lytic replication, where the host cell dies.
  • Lysogenic replication, where the host cell survives.

Viral Persistence

• Viral persistence refers to infections where the virus remains in the host cell for long periods.
• Persistent infections can alternate between silent and productive stages.

Viral Latency

• Viral latency is a type of persistent infection where the virus remains dormant within a cell.
• Latent viral infection differentiates from a chronic viral infection.

Viral Tropism

• Viral tropism is the ability of a virus to infect specific cells, tissues, or host species.

Viral Replication and Dissemination

• The time between infection and the production of new virions (eclipse period) can vary.

Adsorption

• Adsorption involves the attachment of the virus particle to specific receptors on the host cell's plasma membrane.

Penetration

• Penetration refers to the entry of the virus or its genome into the host cell.
• Penetration can occur through different mechanisms:
  • Endocytosis
  • Fusion
  • Translocation

Uncoating

• Uncoating refers to the removal of the lipid membrane and protein capsid surrounding the viral nucleic acid.

Transcription

• Transcription involves the synthesis of viral mRNA, which codes for the synthesis of enzymes essential for viral replication.
• Viruses utilize existing cellular structures for replication.

Environmental Factors for Bacterial Growth

• Bacteria need specific conditions to thrive.
• Temperature: Bacteria have optimal temperatures for growth. Some bacteria can survive harsh temperature extremes.
• pH: Bacteria grow best at specific pH levels. Some bacteria thrive in acidic or alkaline conditions.
• Water: Bacteria need water for survival.
• Light: Some bacteria require light for energy, but most are not photosynthetic.
• Nutrition: Bacteria need nutrients for growth. They can obtain these nutrients from various sources like organic matter or organic compounds.
• Respiration: Bacteria require oxygen or other molecules for respiration.

Key Features of Bacteria

• Tiny single-celled organisms: Bacteria are microscopic and can only be seen with a microscope.
• Ancient life form: Bacteria were among the first life forms to evolve.
• Basic cellular functions: Bacteria have the same basic functions as other living cells.
• Lack Chlorophyll: They cannot produce their energy from sunlight.
• DNA: Bacteria have a single circular DNA chromosome in the cytoplasm.
• No membrane-bound organelles: Their internal structure is simple.

Bacteria Shapes

• Coccus: Round or spherical.
• Coccobacillus: Short, oval, and rod-shaped.
• Vibrio: Curved or comma-shaped.
• Bacillus: Rod-shaped.
• Spirillum: Spiral-shaped.
• Spirochete: Thin and flexible, spiral-shaped.

Gram Staining

• Distinguishes bacteria based on differences in cell wall structure.
• Gram-positive bacteria: Thick cell wall with a high amount of peptidoglycan, staining purple.
• Gram-negative bacteria: Thinner cell wall with a lower amount of peptidoglycan, staining pink.

Bacteria and Dentistry

• Carious process: Bacteria play a key role in tooth decay, converting sugars into acids.
• Acute necrotizing ulcerative gingivitis: A severe gum infection caused by bacteria.
• Infective endocarditis: A serious heart condition caused by bacteria from the mouth entering the bloodstream.
• Legionella: Bacteria associated with Legionnaires' disease, a type of pneumonia.
• MRSA: Methicillin-resistant Staphylococcus aureus, a potentially harmful bacterium.
• MMSA: Methicillin-sensitive Staphylococcus aureus, a less resistant form of Staphylococcus aureus.

Fungi & Mould

• Eukaryotic: Have a nucleus unlike bacteria.
• Two structural types:
  • Yeast: Unicellular, rounded fungi. Some can form chains or clusters.
  • Mould: Multicellular fungi with filamentous growth.
• Cell wall: Contains chitin, a hard substance, similar to the exoskeleton of insects or crustaceans.
• Reproduction: Both sexual and asexual.
  • Asexual: Spore release, mycelial fragmentation (mycelium breaks into pieces that develop into new fungi).
  • Yeast can reproduce asexually by binary fission.

Oral Cavity and Fungi

• Fungi are present in the oral cavity as part of the commensal flora.
• Commensal organisms live in harmony with the host.

Viral Genome

• Contains either DNA or RNA, never both.
• Can be linear or circular.
• Can be single-stranded or double-stranded.

Capsid

• Protective outer layer of a virus.
• Surrounds the nucleic acid core.
• Composed of numerous morphological subunits called capsomeres.
• Capsomeres are made of protomers.
• Provides symmetry to the virus.

Envelope

• Outer layer surrounding the nucleocapsid in some viruses.
• Composed of a bilayer of lipoprotein and glycoproteins.
• Viruses lacking an envelope are called "naked viruses."

Enzymes

• Essential for the viral infection process.
• Some viruses contain their own nucleic acid polymerases, which transcribe the viral genome into mRNA during replication.

Obligate Intracellular Parasites

• Viruses can only multiply within a living host cell.

Icosahedral Capsid

• Polygonal shape with:
  • 12 corners
  • 20 facets (equilateral triangles)
  • 30 edges
• Most stable capsid shape.
• Found in human pathogenic viruses like herpes.
• Composed of hexagons and pentagons.

Filamentous Capsid

• Linear, thin, thread-like or rod-shaped.

Head-Tail Capsid

• Combination of icosahedral head and filamentous body.

Viral Tropism

• Refers to the specific cells, tissues, or hosts that a virus can infect.
• Influenced by:
  • Presence of cellular receptors for viral entry.
  • Availability of transcription factors for viral replication.
  • Cellular receptors for proteins on the cell or viral surface.

Varicella-Zoster (Human Herpes Virus 3)

• Causes chickenpox in children and shingles in adults.

Chickenpox Management

• Hydration.
• Good diet.
• Non-steroidal anti-inflammatory drugs (NSAIDs) like paracetamol and ibuprofen to relieve fever.

Shingles

• Reactivation of the varicella-zoster virus.
• Virus resides in the dorsal root ganglia.
• Reactivation triggered by trauma, immunosuppressant drugs, and other factors.
• Reactivated virus travels through nerve fibers to the skin, presenting unilaterally.

Shingles Management

• Not typically managed by dentists.
• Can lead to Ramsay Hunt syndrome (shingles of the facial nerve), characterized by:
  • Unilateral facial palsy.
  • Tinnitus.
  • Altered or loss of taste.
  • Dry mouth.
  • May manifest in the mouth, causing toothache-like symptoms due to hyposensitivity.

Herpangina

• Viral infection affecting the soft palate.
• Most common in children aged 3-10 years.
• Lasts up to 10 days.
• Contagious for 3-8 weeks after infection.
• Can cause difficulty swallowing.

Epstein-Barr Virus (Human Herpes Virus 4)

• Associated with:
  • Burkitt's lymphoma, a malignant tumor common in developing countries.
  • Nasopharyngeal carcinoma, prevalent in South China and linked to dietary factors.

Oral Hairy Leukoplakia

• White, hairy lesions on the tongue.
• Most common in people with HIV/AIDS.

Paramyxoviridae Viruses

• Family of viruses including:
  • Mumps

Mumps

• Characterized by painful swelling of the parotid gland (side of the face).
• Spread through coughs and sneezes.
• Most contagious 2-3 days before symptoms appear.
• Lasts 1-2 weeks.
• Requires a soft diet for management.
• Can have long-term consequences.

Measles (Measles Morbillivirus)

• Oral lesions may appear on:
  • Buccal mucosa.
  • Hard and soft palate.

Herpes Simplex Virus 1 and 2

• Causes primary gingivostomatitis, characterized by:
  • Malaise.
  • Swollen lymph nodes.
  • Eruptive sores around the face and inside the oral cavity.
  • Lasts 5-10 days.
  • No scarring.

Genital Herpes

• Contracted during intercourse or sexual practices.

Herpetic Whitlow

• Recurrent herpes simplex infection affecting the fingers, often seen in dental professionals.

Encephalitis

• Swelling of the brain.
• Can be fatal.

Secondary Infections

• Herpes Labialis (cold sores)
  • Virus resides in the trigeminal ganglion and reactivates under certain conditions:
    • Stress.
    • Trauma (lip biting).
    • Sunlight (UV rays).
    • Menstruation.
    • Immunosuppression.
    • Fatigue.