Microbiology

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Questions and Answers

What is a distinguishing feature of yeasts that sets them apart from moulds?

They are always colorful.

They can only grow in anaerobic conditions.

They grow as large single cells. (correct)

They form microscopic filaments called hyphae.

In what type of environments are moulds typically found?

In dry and well-ventilated areas.

In non-aerobic conditions exclusively.

In damp, dark, or humid areas. (correct)

On fruits and in the oral cavity.

Which statement accurately describes the reproduction of yeasts?

They can only reproduce in aerobic conditions.

They reproduce by budding from the mother cell. (correct)

They reproduce primarily through binary fission.

They only reproduce by sporing.

What is the primary health risk associated with yeasts?

Infections in individuals with compromised immune systems. Signup and view all the answers

Which characteristic is true of moulds?

They have a fuzzy appearance and are multicellular. Signup and view all the answers

What structural form do yeasts use that is not considered true hyphae?

Pseudohyphae. Signup and view all the answers

Which of the following is a feature of moulds regarding oxygen requirements?

They only grow in aerobic conditions. Signup and view all the answers

What color appearance is typically associated with yeasts compared to moulds?

Colorless or less colorful. Signup and view all the answers

What distinguishes Gram-positive bacteria from Gram-negative bacteria?

Gram-positive bacteria have a thick peptidoglycan layer. Signup and view all the answers

Which structure is not found in bacterial cells?

Golgi apparatus Signup and view all the answers

What is the function of the flagellum in bacteria?

To aid in movement. Signup and view all the answers

Which of the following is the correct order of taxonomic classification from broadest to most specific?

Kingdom, Division, Family, Species Signup and view all the answers

Which environmental requirement is essential for bacterial growth?

Moisture Signup and view all the answers

What type of bacteria are described as having a thin peptidoglycan cell wall?

Gram-negative bacteria Signup and view all the answers

Which of the following describes the components of a bacterial cell wall?

Peptidoglycan Signup and view all the answers

In bacteria classification, what does 'Streptococcus salivarius' represent?

Genus and Species Signup and view all the answers

What field utilizes Gram staining to classify bacterial species?

Dentistry Signup and view all the answers

Which structure is NOT found in bacterial cells?

Nucleus Signup and view all the answers

What is a common method of asexual reproduction found in fungi?

Budding Signup and view all the answers

Which of the following is a characteristic of fungi?

Composed of chitin Signup and view all the answers

What shape characterizes a spirochete?

Spiral-shaped Signup and view all the answers

What is an example of direct transmission of infectious agents?

Kissing Signup and view all the answers

Which of the following is classified as a vector in the transmission of infectious diseases?

Insects Signup and view all the answers

Which method of disease transmission involves the entry of pathogens through the respiratory tract?

Droplets from coughing Signup and view all the answers

What distinguishes indirect transmission through vehicles from direct contact?

Involves non-living intermediaries Signup and view all the answers

Which of the following is NOT a common vehicle for indirect transmission of diseases?

Kissing Signup and view all the answers

Which of the following best describes how typhoid is transmitted?

Through insect bites and feces Signup and view all the answers

What is the primary vector responsible for malaria transmission?

Mosquitoes Signup and view all the answers

Which term describes the spread of infections through soil contact?

Vehicle transmission Signup and view all the answers

Which of the following pathogens is commonly associated with fecal-oral transmission?

Salmonella Signup and view all the answers

In the context of infection transmission, which statement is true about fomites?

They can carry pathogens through physical contact with contaminated surfaces Signup and view all the answers

What is a common consequence of inadequate hand-washing for food handlers?

It causes contamination of food with pathogens Signup and view all the answers

Which of the following diseases is NOT typically spread by mosquitoes?

Typhoid Signup and view all the answers

Which of the following correctly describes the concept of horizontal transmission?

Spread of infection between individuals of the same generation Signup and view all the answers

Which component is NOT part of the transmission chain required for the spread of infection?

Symptom Signup and view all the answers

What defines vertical transmission in the context of disease transmission?

Transmission from mother to child Signup and view all the answers

Which mode of transmission involves pathogens being spread through an intermediary agent?

Indirect transmission Signup and view all the answers

In the context of the transmission of disease, which example best illustrates a reservoir?

Contaminated water Signup and view all the answers

Which of the following best characterizes horizontal transmission?

Any non-maternal person-to-person contact Signup and view all the answers

Which of the following options is considered a vehicle in disease transmission?

Food contaminated with bacteria Signup and view all the answers

Which of these steps is included in Koch's postulates related to pathogen identification?

The pathogen must be isolated from the infected host Signup and view all the answers

Which mechanism relates to the host's ability to prevent disease ingress?

Germicidal handwashing Signup and view all the answers

Which condition is typically NOT needed for microbial growth?

Extreme temperatures Signup and view all the answers

What is a major distinguishing feature of prokaryotes compared to eukaryotes?

Always unicellular Signup and view all the answers

How do microorganisms contribute positively to human health?

By aiding digestion and synthesizing vitamins Signup and view all the answers

What mechanism describes how microorganisms cause disease?

By entering and replicating within host cells Signup and view all the answers

Which statement best describes the establishment of the microbiome in humans?

Microbial introduction begins at birth and is influenced by various factors Signup and view all the answers

In which of the following scientists' theories do pathogenic microorganisms play a crucial role?

Germ theory of disease Signup and view all the answers

Which feature is NOT associated with eukaryotic microorganisms?

Nucleoid region Signup and view all the answers

What ecological role do microorganisms play in relation to human health?

Create barriers to infection Signup and view all the answers

Which factor is most critical for microbial growth in terms of hydration?

Water content Signup and view all the answers

How does the level of light influence the growth of parasitic microorganisms?

They grow best in darkness. Signup and view all the answers

How does temperature affect bacterial growth rates?

Bacterial growth rates vary with different temperature ranges. Signup and view all the answers

Which nutrient is essential for bacteria and plays a crucial role in microbial growth?

Sulfur Signup and view all the answers

What distinguishes the moisture tolerance of Staphylococci and Treponema pallidum?

Staphylococci thrive in dry conditions while Treponema pallidum dies quickly. Signup and view all the answers

Which of the following best describes the impact of nutrients on microbial growth?

Specific nutrients can enhance growth while inhibitors can retard it. Signup and view all the answers

Why can X-rays be used as a sterilization method for medical supplies?

They damage microbial DNA effectively. Signup and view all the answers

What environmental condition is generally lethal to parasitic microorganisms?

Exposure to ultraviolet light Signup and view all the answers

What role do enzymes play in microbial invasiveness?

They suppress the host's immune response. Signup and view all the answers

Which of the following best describes the origin of exotoxins compared to endotoxins?

Exotoxins are released by living bacteria while endotoxins are part of the bacterial cell wall. Signup and view all the answers

What is a significant consequence of the metabolites produced by Streptococcus mutans?

They lead to the dissolution of enamel. Signup and view all the answers

Which statement accurately reflects the role of endotoxins in disease?

Endotoxins are composed of lipopolysaccharides from the bacterial cell membrane. Signup and view all the answers

How does age potentially influence microbiome diversity?

Microbiome diversity decreases with age due to reduced metabolic activity. Signup and view all the answers

Which component is essential in understanding how microorganisms cause disease?

The products released by microorganisms play a critical role. Signup and view all the answers

What defines a key functional difference between microbial enzymes and traditional enzymes?

Microbial enzymes facilitate bacterial metabolism and invasiveness. Signup and view all the answers

Which of the following correctly identifies a characteristic of microbial growth conditions?

Oxygen levels can significantly affect the growth of certain microbes. Signup and view all the answers

What are the two types of viral proteins that play a role in viral assembly?

Structural and Non-structural Signup and view all the answers

During which phase of viral replication does the host cell continue to survive while the virus is present?

Lysogenic replication Signup and view all the answers

Which term best describes the ability of a virus to remain dormant within a host cell?

Viral Latency Signup and view all the answers

What is a common characteristic of persistent viral infections?

The virus may exhibit silent and productive infection stages. Signup and view all the answers

Which of the following viruses is commonly associated with persistent infections in humans?

Hepatitis B virus Signup and view all the answers

What is the primary distinguishing characteristic of RNA viruses compared to DNA viruses?

Higher mutation rates Signup and view all the answers

What does the eclipse phase refer to in viral replication?

The period after penetration when the virus is undetectable Signup and view all the answers

Which mechanism allows a virus to penetrate the host cell?

Endocytosis Signup and view all the answers

What best describes viral tropism?

The selection of a virus to infect specific host cells or tissues Signup and view all the answers

Which of the following viruses is typically associated with dental implications?

HIV Signup and view all the answers

Which of the following viruses is known to have a persistent infection stage?

Herpes virus Signup and view all the answers

In what step does a virus become uncoated and its nucleic acid is freed for replication?

Uncoating Signup and view all the answers

What is one method by which non-enveloped viruses penetrate the host cell?

Translocation through the membrane Signup and view all the answers

What type of nucleic acid do viruses possess?

Either DNA or RNA, but never both Signup and view all the answers

Which of the following classifications accurately describes a virus based on its structure?

Viruses can be classified as filamentous, icosahedral, or head-tail Signup and view all the answers

What describes the concept of viral tropism?

The specific types of cells or tissues a virus can infect Signup and view all the answers

In the context of dental health, which virus is known for its dental implications?

Herpes simplex virus Signup and view all the answers

What does the term 'viral persistence' refer to?

The continual presence of virus in the body without causing symptoms Signup and view all the answers

What are the stages of viral replication?

Attachment, entry, replication, assembly, release Signup and view all the answers

How do viruses spread within the host organism?

Through bloodstream and lymphatic system once released Signup and view all the answers

What is the difference between viral latency and viral persistence?

Latency involves temporary inactivity; persistence is indefinite Signup and view all the answers

What type of microorganism lacks chlorophyll and usually has a single circular DNA chromosome?

Bacteria Signup and view all the answers

Which structural component is found in fungi cell walls but not in bacteria cell walls?

Chitin Signup and view all the answers

What method of reproduction is commonly seen in most fungi?

Asexual spore release Signup and view all the answers

Which bacteria are classified based on their reactions to Gram staining?

Gram-positive and Gram-negative Signup and view all the answers

Which type of fungi is primarily unicellular?

Yeast Signup and view all the answers

What is a common symptom associated with Mumps infection?

Painful swelling of the parotid gland Signup and view all the answers

Which of the following viruses is most commonly associated with oral hairy leukoplakia?

Epstein-Barr Virus Signup and view all the answers

Which condition can cause significant long-term consequences if left untreated?

Mumps infection Signup and view all the answers

What is a potential trigger for the reactivation of herpes labialis?

Immunosuppression Signup and view all the answers

What is the maximum duration of contagiousness after a viral infection can still be present according to the provided content?

8 weeks Signup and view all the answers

What defines whether a virus is classified as a 'naked virus'?

Absence of a lipid envelope Signup and view all the answers

What type of symmetry is characteristic of icosahedral viruses?

Polygon with 20 triangular facets Signup and view all the answers

Which enzyme activity is significant in the viral replication process?

Transcription of the viral genome to mRNA Signup and view all the answers

What condition is commonly associated with the reactivation of the Varicella-Zoster virus?

Trauma or immunosuppressive drugs Signup and view all the answers

What factor influences viral tissue tropism?

Presence of cellular receptors on the host cell Signup and view all the answers

In which specific location does the Varicella-Zoster virus remain dormant?

Dorsal root ganglia Signup and view all the answers

Which structural feature is NOT found in viruses?

Cell wall Signup and view all the answers

What symptom is commonly associated with Ramsay Hunt syndrome caused by shingles?

Unilateral facial palsy Signup and view all the answers

Study Notes

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.

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Explore the fascinating world of fungi, focusing on yeasts as unicellular organisms. Learn about their structural characteristics, growth environments, and their significance in health and disease. This quiz will deepen your understanding of the role fungi play in both ecology and medicine.