Microbiology W3-2
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Questions and Answers

Which of the following describes the function of keratin in the skin?

  • It acts as a moisturizer to maintain skin hydration.
  • It facilitates the absorption of nutrients through the skin.
  • It serves as a low pH barrier against pathogens.
  • It forms the structural foundation of hair and nails. (correct)

Which of the following bacterial species is not typically found in normal skin microbial flora?

  • Corynebacterium species
  • Escherichia coli (correct)
  • Propionibacterium acnes
  • Staphylococcus epidermidis

What distinguishes β-hemolytic streptococci from other types?

  • They form clusters in cultures.
  • They produce lactic acid and are catalase-positive.
  • They are primarily anaerobic organisms.
  • They are classified by carbohydrate antigens in their cell walls. (correct)

Which characteristic is true about Streptococcus pyogenes?

<p>It is classified under Lancefield group A. (A)</p> Signup and view all the answers

What is the primary defense function of sebum?

<p>To suppress the growth of pathogenic microorganisms. (A)</p> Signup and view all the answers

Which of the following statements is true regarding the metabolic activity of streptococci?

<p>They are commonly isolated using blood-enriched media. (C)</p> Signup and view all the answers

Which of the following best defines medical microbiology?

<p>The interactions between animals and microorganisms, focusing on diseases. (D)</p> Signup and view all the answers

What type of infection arises from microorganisms originating from external sources?

<p>Exogenous infection (B)</p> Signup and view all the answers

Which type of pathogen is always associated with human disease?

<p>Strict pathogens (C)</p> Signup and view all the answers

In what settings are nosocomial infections typically acquired?

<p>In a hospital environment (B)</p> Signup and view all the answers

Why are opportunistic pathogens particularly concerning for patients with defective immune systems?

<p>They thrive in normal body settings without causing disease. (C)</p> Signup and view all the answers

What is a blood agar plate primarily used for?

<p>To support the growth of fastidious organisms. (B)</p> Signup and view all the answers

Which component in blood agar plates helps in enriching the medium?

<p>Defibrinated blood (C)</p> Signup and view all the answers

What pH range is desired for the nutrient agar in blood agar plates?

<p>7.2 to 7.6 (A)</p> Signup and view all the answers

At what temperature should the mixture be autoclaved for preparing blood agar plates?

<p>121 °C for 15 minutes (B)</p> Signup and view all the answers

What is the primary purpose of Chocolate agar?

<p>To grow fastidious respiratory bacteria (D)</p> Signup and view all the answers

Which type of hemolysis indicates complete lysis and digestion of red blood cells?

<p>β-hemolysis (A)</p> Signup and view all the answers

Which of the following correctly describes γ-hemolysis?

<p>No hemolysis occurring at all (D)</p> Signup and view all the answers

What common mechanism can compromise the skin barrier leading to SSTIs?

<p>Surgical procedures (C)</p> Signup and view all the answers

What structure is found in the dermis layer of the skin?

<p>Nerve endings (C)</p> Signup and view all the answers

In the context of SSTIs, what does the term 'soft tissue' refer to?

<p>Connective and supporting tissues (C)</p> Signup and view all the answers

What is a common clinical challenge related to SSTIs?

<p>Differentiating between severe and less severe cases (D)</p> Signup and view all the answers

What is a characteristic of the epidermis layer of skin?

<p>Formed primarily of keratinocytes (A)</p> Signup and view all the answers

What condition can commonly lead to a break in the skin barrier, resulting in potential SSTIs?

<p>Chickenpox (C)</p> Signup and view all the answers

Which component is NOT typically found in the hypodermis layer of skin?

<p>Keratinocytes (C)</p> Signup and view all the answers

What is the primary characteristic of necrotizing fasciitis?

<p>Deep infection involving destruction of muscle and fat layers. (C)</p> Signup and view all the answers

Which virulence factor is primarily associated with the ability of S. pyogenes to invade host cells?

<p>M protein (C)</p> Signup and view all the answers

Which condition is characterized by localized pain, inflammation, and systemic symptoms related to skin infection?

<p>Erysipelas (A)</p> Signup and view all the answers

Which of the following factors contributes to the virulence of Streptococcus pyogenes by enabling it to evade the immune response?

<p>C5a peptidase (D)</p> Signup and view all the answers

What common characteristic is shared among most species of Staphylococcus?

<p>They are non-motile and grow in clusters. (D)</p> Signup and view all the answers

In compound skin infections, what is a defining feature of cellulitis?

<p>Involvement of subcutaneous tissues. (B)</p> Signup and view all the answers

What is a key clinical presentation of Streptococcal toxic shock syndrome?

<p>Multiorgan systemic involvement with bacteremia. (A)</p> Signup and view all the answers

What is primarily responsible for the yellow or gold color of aureus colonies?

<p>Carotenoid pigments (A)</p> Signup and view all the answers

Which of the following diseases is associated with scalded skin syndrome?

<p>Toxic shock syndrome (C)</p> Signup and view all the answers

What is a recognized virulence factor of Staphylococcus aureus that aids in evading the immune response?

<p>Coagulase enzyme (B)</p> Signup and view all the answers

What type of toxin is responsible for the massive release of cytokines causing hypotension and shock in toxic shock syndrome?

<p>Toxic shock syndrome toxin-1 (C)</p> Signup and view all the answers

Which of the following is NOT a systemic disease associated with Staphylococcus aureus?

<p>Folliculitis (D)</p> Signup and view all the answers

What characteristic of Staphylococcus aureus allows it to survive for extended periods on dry surfaces?

<p>Absence of an outer membrane (B)</p> Signup and view all the answers

Which method is used by the exfoliative toxin of aureus to interact with the immune system?

<p>Binding to MHC II molecules (A)</p> Signup and view all the answers

What does the term 'facultative anaerobe' imply about Staphylococcus aureus?

<p>It can grow with or without oxygen. (A)</p> Signup and view all the answers

Which population is particularly affected by scalded skin syndrome?

<p>Neonates and young children (B)</p> Signup and view all the answers

What is the main reason Pseudomonas aeruginosa is resistant to many antibiotics?

<p>It mutates porin proteins that control antibiotic penetration. (D)</p> Signup and view all the answers

Which of the following environments is NOT typically associated with the presence of Pseudomonas aeruginosa?

<p>Dry soil (B)</p> Signup and view all the answers

What characterizes the growth of Pseudomonas aeruginosa colonies on a blood agar plate?

<p>A green pigmentation with β-hemolysis. (A), A flat colony with a spreading edge and a sweet odor. (C)</p> Signup and view all the answers

What is a significant risk factor for infections caused by Methicillin-resistant Staphylococcus aureus (MRSA)?

<p>Presence of a foreign body. (B)</p> Signup and view all the answers

What is a common disease linked to infections from Pseudomonas aeruginosa?

<p>Burn wound infections. (B)</p> Signup and view all the answers

Which of the following statements best describes the nutritional needs of Pseudomonas aeruginosa?

<p>Has minimal nutritional requirements. (D)</p> Signup and view all the answers

What type of infectious transmission is primarily associated with the spread of MRSA?

<p>Direct contact and exposure to contaminated objects. (A)</p> Signup and view all the answers

What characteristic of Pseudomonas aeruginosa contributes to its classification as an opportunistic pathogen?

<p>It thrives in diverse environments and affects already weakened hosts. (B)</p> Signup and view all the answers

Which of the following is NOT a typical characteristic of Pseudomonas aeruginosa?

<p>It relies on fermentation as its primary energy source. (C)</p> Signup and view all the answers

What range of diameters do aerosols produced by sneezing and coughing typically fall under?

<p>1 to 1000 μm (B)</p> Signup and view all the answers

Which of the following diseases is caused by a bacterial pathogen that can be transmitted through aerosols?

<p>Tuberculosis (B)</p> Signup and view all the answers

What is the primary method to decrease airborne disease transmission?

<p>Wearing a face mask (B)</p> Signup and view all the answers

Which condition is NOT transmitted through aerosols?

<p>Tetanus (C)</p> Signup and view all the answers

What type of colloid describes aerosols?

<p>Suspension (C)</p> Signup and view all the answers

Which of the following examples best illustrates an aerosol?

<p>A suspension of pollen in air (A)</p> Signup and view all the answers

Which part of the respiratory tract is primarily responsible for the passage of air to the lungs?

<p>Bronchi (A)</p> Signup and view all the answers

What factor significantly differentiates the infectious characteristics of the lepromatous and tuberculoid forms of disease?

<p>Infectiousness (A)</p> Signup and view all the answers

Which of the following organisms is least likely to be pathogenic when found in the upper respiratory tract?

<p>Neisseria meningitidis (D)</p> Signup and view all the answers

What is the main function of the mucociliary clearance mechanism in the respiratory tract?

<p>To trap and remove infectious particles (D)</p> Signup and view all the answers

How do goblet cells contribute to the defense mechanisms of the respiratory tract?

<p>By secreting mucus (A)</p> Signup and view all the answers

What characteristic is true about the lower respiratory tract in terms of microorganism presence?

<p>Generally considered sterile (B)</p> Signup and view all the answers

Which type of microorganism is predominantly found in the upper respiratory tract, according to quantity?

<p>Anaerobes (D)</p> Signup and view all the answers

What does the ciliary action in the mucociliary blanket accomplish?

<p>Moves trapped particles toward the throat (C)</p> Signup and view all the answers

Which anatomical component follows the bronchi in the pathway of inhaled air?

<p>Bronchioles (D)</p> Signup and view all the answers

What is the size threshold for infectious particles to be efficiently trapped by the mucociliary blanket?

<p>8-10 μm (B)</p> Signup and view all the answers

What is a primary characteristic of the lepromatous form of leprosy?

<p>Disfiguring skin lesions and thickened dermis (B)</p> Signup and view all the answers

Which of the following best describes Mycobacterium leprae?

<p>Obligate intracellular, weakly gram-positive rod (A)</p> Signup and view all the answers

What is a commonality between the reported cases of leprosy in 2005?

<p>India, Nepal, and Brazil had the highest incidences (A)</p> Signup and view all the answers

How is leprosy primarily transmitted?

<p>Person-to-person contact through respiratory secretions (D)</p> Signup and view all the answers

Which cellular immune response is observed in patients with tuberculoid leprosy?

<p>Strong cellular immune reaction with lymphocytes (A)</p> Signup and view all the answers

What is a defining feature of Mycobacterium leprae that affects its culturing?

<p>It is obligate intracellular and cannot be cultured artificially (D)</p> Signup and view all the answers

In the pathogenesis of leprosy, what characteristic distinguishes lepromatous leprosy from tuberculoid leprosy?

<p>Increased bacterial load in macrophages (B)</p> Signup and view all the answers

Why might leprosy have a low reported incidence despite its historical prevalence?

<p>Widespread use of effective therapy (D)</p> Signup and view all the answers

What type of staining is used to visualize Mycobacterium leprae due to its cell wall composition?

<p>Acid-fast (Ziehl–Neelsen) staining (C)</p> Signup and view all the answers

Which of the following diseases is primarily characterized by inflammation of the tonsils?

<p>Tonsillitis (B)</p> Signup and view all the answers

Which pathogen is known as the causative agent of whooping cough?

<p>Bordetella pertussis (A)</p> Signup and view all the answers

What is a common feature of middle ear infections?

<p>Ear drainage and pressure sensation (A)</p> Signup and view all the answers

Which of the following infections primarily affects infants and young children under two years of age?

<p>Bronchiolitis (A)</p> Signup and view all the answers

Which bacterium is commonly associated with ear infections?

<p>Haemophilus influenzae (B)</p> Signup and view all the answers

What type of respiratory tract infection is characterized by inflammation of the larynx?

<p>Laryngitis (C)</p> Signup and view all the answers

Which pathogen is most likely to cause persistent bacterial infection in the lungs?

<p>Mycobacterium tuberculosis (C)</p> Signup and view all the answers

Inflammation associated with the 'itis' suffix primarily indicates what in a disease context?

<p>Inflammation (C)</p> Signup and view all the answers

What was a significant outcome of the Legionnaires' disease outbreak in 1976?

<p>221 people were infected and 34 succumbed to the disease. (B)</p> Signup and view all the answers

Which of the following pathogens does NOT commonly cause respiratory tract infections?

<p>E. coli (C)</p> Signup and view all the answers

Which of the following accurately describes the bacterium Legionella and its mechanism?

<p>It prevents the fusion of phagolysosomes, aiding in replication. (D)</p> Signup and view all the answers

Why might Legionnaires' disease be mistaken for other illnesses?

<p>Its symptoms share commonality with the flu and common cold. (C)</p> Signup and view all the answers

What is the primary mode of transmission for Legionnaires' disease?

<p>Inhalation of aerosolized water containing the bacteria. (A)</p> Signup and view all the answers

What is a critical implication of failing to correctly diagnose Legionnaires' disease?

<p>It can progress to severe pulmonary complications and death. (B)</p> Signup and view all the answers

Which types of environments are most likely to harbor Legionella bacteria?

<p>Natural bodies of warm water and plumbing systems. (C)</p> Signup and view all the answers

What is the primary feature of the paroxysmal stage of whooping cough?

<p>Repetitive coughing followed by inspiratory whoops (A)</p> Signup and view all the answers

Which treatment is most effective in decreasing the infectious stage of pertussis?

<p>Azithromycin (D)</p> Signup and view all the answers

Why are Legionella considered nutritionally fastidious organisms?

<p>They require L-cysteine for growth (A)</p> Signup and view all the answers

What distinguishes the causative agent of Pontiac fever from other Legionella diseases?

<p>It is nonfatal and resembles mild upper respiratory infections. (B)</p> Signup and view all the answers

Which of the following characterizes the lifecycle of Legionella bacteria?

<p>They can survive in free-living amoebae in the environment (D)</p> Signup and view all the answers

What component in vaccines is crucial for eliciting an effective immune response against pertussis?

<p>Inactivated pertussis toxin (B)</p> Signup and view all the answers

Which statement is true regarding the range of Legionella species?

<p>Approximately half of the identified species are implicated in disease. (C)</p> Signup and view all the answers

In which stage does whooping cough display catarrhal symptoms resembling the common cold?

<p>Catarrhal stage (D)</p> Signup and view all the answers

Which is a lesser-known complication linked to pertussis in adults?

<p>Posttussive vomiting (D)</p> Signup and view all the answers

Which clinical feature is indicative of the convalescence stage of whooping cough?

<p>Gradual reduction of coughing fits (A)</p> Signup and view all the answers

Flashcards

Medical Microbiology

The study of interactions between animals and microorganisms (like bacteria, fungi, viruses) and the diseases these interactions cause, primarily focusing on humans.

Exogenous Infection

Disease caused by microorganisms originating from an external source.

Endogenous Infection

Disease from microorganisms already present in the body (normal flora) that spreads to a different body part, causing disease.

Strict Pathogen

Organism that always causes disease.

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Opportunistic Pathogen

An organism that usually isn't harmful, but can cause disease if the immune system is weak or if it gets into the wrong place in the body.

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Nosocomial Infection

Infection acquired in a hospital or healthcare setting.

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Blood Agar Plate (BAP)

A culture plate with enriched medium and blood, used to grow fastidious bacteria.

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Fastidious Organism

A microorganism that requires complex nutrients to grow.

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Bacterial Classification by Hemolysis

Classifying bacteria based on whether they cause the breakdown of red blood cells in a culture.

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Chocolate agar

A type of blood agar plate used to grow fastidious respiratory bacteria like Haemophilus influenzae, prepared by lysing red blood cells.

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Hemolysis

Breakdown of red blood cells.

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α-hemolysis

Incomplete breakdown of red blood cells.

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β-hemolysis

Complete breakdown of red blood cells.

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γ-hemolysis

No breakdown of red blood cells.

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Skin and soft tissue infections (SSTIs)

Infections involving the layers of skin and underlying soft tissues.

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Soft tissue

Connective tissues supporting and surrounding body structures (muscles, tendons, etc.).

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Skin barrier compromise

A break in the skin's protective layer, increasing vulnerability to infection.

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Epidermis

Outermost layer of skin, primarily made of keratinocytes.

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Hypodermis

Subcutaneous tissue attaching skin to underlying bone/muscle; contains fat.

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Skin's Natural Defense

The skin has multiple layers of protection. It forms a physical barrier, sheds cells to remove microbes, secretes substances like sebum and sweat to inhibit microbial growth and relies on its own microbe flora to compete with harmful bacteria.

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Microbial Flora of Skin

The skin naturally hosts a diverse community of microorganisms, including Propionibacterium acnes, Staphylococcus epidermidis, and various Streptococcus species, which act as a first line of defense against infection.

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Streptococcus: Gram-Positive Cocci

Streptococcus bacteria are spherical (cocci) and appear in chains under a microscope. They are typically found in pairs or chains, in contrast to Staphylococcus, which forms clusters. They are facultative anaerobes, meaning they can grow with or without oxygen.

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Streptococcus: Hemolysis and Grouping

Streptococcus are divided into groups based on their hemolytic activity - how they break down red blood cells: β-hemolytic streptococci (e.g., S. pyogenes) cause complete lysis, α-hemolytic streptococci (e.g., S. pneumoniae) cause partial lysis, and γ-hemolytic streptococci cause no lysis.

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Streptococcus pyogenes: GAS

Streptococcus pyogenes is a rapidly growing, gram-positive bacterium that forms chains. It is a β-hemolytic streptococcus classified as Group A (GAS) due to its specific carbohydrate antigen. It's also identified by its type-specific proteins like the M protein.

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Lancefield Grouping in Bacteria

A method of classifying certain bacteria (like Streptococcus) based on specific carbohydrate antigens found in their cell walls. Each group (A to W) represents a distinct bacterial species.

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Pyoderma

A localized skin infection characterized by fluid-filled blisters (vesicles) that progress into pus-filled bumps (pustules). Importantly, there's no evidence of the infection spreading throughout the body.

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Erysipelas

A localized skin infection that causes pain, redness, and swelling. The infection spreads to nearby lymph nodes, leading to enlarged lymph nodes, and also affects the entire body, causing systemic symptoms.

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Cellulitis

An infection of the skin that extends into the deeper layers of tissue beneath the skin, the subcutaneous tissues.

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Necrotizing Fasciitis

A serious, deep infection of the skin that destroys muscle and fat layers. It's characterized by severe pain and can quickly spread.

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Streptococcal Toxic Shock Syndrome (STSS)

A serious, multi-organ infection that resembles Staphylococcus aureus Toxic Shock Syndrome. Patients often experience bacteremia (bacteria in the blood) and signs of fasciitis.

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M Protein

A key protein in the outer layer of the Streptococcus pyogenes bacteria that plays a crucial role in its virulence. The protein helps the bacteria avoid being destroyed by the body's immune system, adhere to cells, and produce toxins.

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Staphylococcus

A group of gram-positive bacteria that appear in grape-like clusters. They are generally adaptable, able to survive under various conditions, including high salt levels and different temperatures.

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Pseudomonas aeruginosa

A small, gram-negative, rod-shaped bacterium known for its ability to thrive in moist environments and cause various infections. It produces a green pigment and has a characteristic sweet, grapelike odor.

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Mucoid appearance

A characteristic feature of Pseudomonas aeruginosa where the bacteria form a thick, slimy layer due to the presence of a polysaccharide capsule. This makes them appear like mucus.

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Antibiotic Resistance in Pseudomonas

Pseudomonas aeruginosa is inherently resistant to many antibiotics. It can also develop resistance to more antibiotics during therapy due to mutations, especially in porin proteins, which are responsible for antibiotic entry into the bacteria.

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Ubiquitous in nature

Pseudomonas aeruginosa is found in a wide variety of environments, such as water, soil, and even hospital settings.

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Pseudomonas infections: Burn wounds

Burn wounds are a common site for Pseudomonas aeruginosa infections, leading to colonization, tissue damage, and ultimately bloodstream infections.

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Pseudomonas: Diverse infections

Pseudomonas aeruginosa can cause a range of infections, including skin infections, respiratory infections, and even infections in the bloodstream.

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Pseudomonas: Motile

Pseudomonas aeruginosa is motile, meaning it can move independently.

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Pseudomonas: Temperature tolerance

Pseudomonas aeruginosa can withstand a wide range of temperatures, making it very adaptable.

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Staphylococcus aureus

A type of bacteria known for its yellow-gold colonies, often found on human skin and mucosal surfaces. It's a Gram-positive, catalase-positive coccus that grows in clusters. It causes a variety of infections, including skin and soft tissue infections, food poisoning, and toxic shock syndrome.

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Coagulase Positive

Staphylococcus aureus is coagulase positive; meaning it produces an enzyme that causes blood plasma to clot. This clotting effect can help protect Staphylococcus aureus from the host's immune system by forming a barrier around the bacteria.

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Mannitol Fermentation

Staphylococcus aureus can ferment mannitol, a type of sugar, which is a key characteristic used in identifying it in a laboratory setting. The fermentation of mannitol produces acid, which turns the color of the media yellow.

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Scalded Skin Syndrome

A serious skin infection caused by Staphylococcus aureus, especially in infants and young children. It results in large areas of peeling skin, blisters, and a widespread rash.

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Exfoliative Toxin

A powerful toxin produced by Staphylococcus aureus responsible for causing Scalded Skin Syndrome. This toxin disrupts the protein structures holding skin cells together, leading to large areas of skin peeling.

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Superantigens

Certain toxins produced by bacteria, such as the exfoliative toxin and toxic shock syndrome toxin-1, bind to the immune system's T cells in a non-specific way, leading to a massive overreaction of the immune system.

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Toxic Shock Syndrome Toxin-1 (TSST-1)

A potent toxin produced by Staphylococcus aureus which can cause toxic shock syndrome, a serious condition marked by fever, low blood pressure, and organ damage.

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Ubiquitous Normal Flora

Staphylococcus aureus is commonly found on human skin and mucosal surfaces as part of the normal flora. Though it is usually harmless, it can cause infection under certain conditions.

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Peptidoglycan Layer

Staphylococcus aureus has a thick peptidoglycan layer in its cell wall, which helps it to withstand harsh drying conditions.

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Respiratory Tract

The passageway for air from your nose and mouth to your lungs. It's divided into upper and lower sections.

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Upper Respiratory Tract

Includes the mouth, pharynx (throat), and larynx (voice box). This is where air enters the body.

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Lower Respiratory Tract

Includes the trachea (windpipe), bronchi (main air tubes to the lungs), and bronchioles ( smaller branches of air tubes).

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Alveoli

Tiny air sacs in your lungs where oxygen gets transferred to your blood.

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Mucociliary Clearance

The body's defense mechanism in the respiratory tract that traps and removes harmful particles.

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Goblet Cells

Cells in the respiratory tract that produce mucus to trap foreign particles.

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Cilia

Tiny hair-like structures that move mucus upward in the respiratory tract.

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Sterile Lower Airways

Normally, the lower airways are free of bacteria.

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Lepromatous Leprosy

A form of leprosy that is highly infectious.

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Tuberculoid Leprosy

A form of leprosy that is not highly infectious.

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Aerosols

Tiny particles of solid or liquid suspended in air. They can travel long distances and carry pathogens like bacteria and viruses.

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Airborne Disease

An illness that spreads through the air by tiny particles called aerosols containing pathogens.

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Hansen's Disease

Another name for leprosy, a chronic infection caused by Mycobacterium leprae that primarily affects the skin and peripheral nerves.

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Mycobacterium leprae

The bacteria responsible for leprosy. It is weakly gram-positive, strongly acid-fast, and has a lipid-rich cell wall. It is an obligate intracellular bacterium that cannot be cultured in artificial media.

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Acid-fast staining

A staining technique that uses a specific red dye (Ziehl-Neelsen) to identify bacteria that resist decolorization by acid alcohol. This technique is used to identify Mycobacterium leprae.

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Leprosy: Tuberculoid form

A milder form of leprosy characterized by hypopigmented skin macules (patches with less pigmentation). It involves a strong cell-mediated immune response with many lymphocytes and granulomas.

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Leprosy: Lepromatous form

A more disfiguring form of leprosy with nodules, plaques, thickened dermis, and nasal mucosa involvement. It involves a strong antibody response but a defect in the cell-mediated immune response.

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Epidemiology of Leprosy

Leprosy is primarily found in developing countries like India, Nepal, and Brazil. It is spread through person-to-person contact, potentially via respiratory droplets or skin contact.

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Leprosy: Spread

Leprosy is primarily spread through person-to-person contact. The exact mode of transmission is unclear, but it is believed to involve inhalation of respiratory droplets or contact with skin lesions.

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Leprosy: Nasal Secretions

Patients with the lepromatous form of leprosy often have high levels of Mycobacterium leprae in their nasal secretions, making them more infectious.

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Upper Respiratory Tract Infections

Infections that affect the nose, sinuses, and throat. Common examples include the common cold, tonsillitis, sinusitis, laryngitis, and the flu.

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Lower Respiratory Tract Infections

Infections that affect the airways and lungs. Examples include bronchitis, pneumonia, bronchiolitis, and tuberculosis.

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Otitis Media

An infection of the middle ear, commonly known as an ear infection.

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Eustachian Tube

A tube that connects the middle ear to the back of the throat.

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Common RTI Pathogens

Bacteria and other microorganisms commonly responsible for respiratory tract infections.

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Bordetella pertussis

The bacteria that causes whooping cough. It is extremely small, gram-negative, and requires oxygen to survive.

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Streptococcus pneumoniae

A common bacterium that causes pneumonia and other respiratory infections.

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Haemophilus influenzae

A bacteria often causing ear infections and respiratory infections in children.

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Mycobacterium tuberculosis

The bacteria that causes tuberculosis, a persistent lung infection.

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Legionnaires' Disease

A severe pneumonia caused by the bacterium Legionella pneumophila, which is typically transmitted through contaminated water sources like air conditioning systems or cooling towers.

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Legionella pneumophila

A bacterium that causes Legionnaires' disease. It is Gram-negative and thrives in water environments.

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How is Legionnaires' disease spread?

Legionnaires' disease is not spread from person to person. It is spread through contaminated water sources, typically by inhaling droplets containing the bacteria.

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What's the effect of Legionella on the lungs?

Legionella bacteria multiply in the lungs, causing inflammation and fluid buildup, leading to breathing difficulties and potentially deadly complications.

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Pertussis

A highly contagious bacterial infection that causes severe coughing fits, often followed by a whooping sound and vomiting. It is especially dangerous for infants.

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Catarrhal Stage of Pertussis

The initial stage of pertussis, characterized by mild symptoms similar to a common cold, such as runny nose, sneezing, and low-grade fever.

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Paroxysmal Stage of Pertussis

The most serious stage of pertussis, marked by intense coughing spasms, rapid breathing after each cough, and often leading to vomiting.

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Convalescent Stage of Pertussis

The final stage of pertussis, where the coughing episodes become less frequent and less severe, but can take weeks or months to fully recover.

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Pontiac Fever

A milder form of Legionella infection, characterized by flu-like symptoms like fever, muscle aches, and headache.

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Facultative Intracellular Bacteria

Bacteria that can live and multiply both inside and outside of host cells, like Legionella.

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L-Cysteine Requirement in Legionella

Legionella bacteria need the amino acid L-cysteine to grow and survive.

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Study Notes

Medical Microbiology

  • Medical microbiology is the study of interactions between animals (primarily humans) and microorganisms (bacteria, viruses, fungi, and parasites), focusing on diseases caused by these interactions.

Infection Concepts

  • Exposure to an organism can lead to transient colonization, permanent colonization, or disease.
  • Exogenous infections arise from external sources.
  • Endogenous infections originate from the person's own microbes spreading to inappropriate sites.
  • Nosocomial infections are acquired in hospitals.

Pathogen Types

  • Strict pathogens are always associated with human disease (e.g., Mycobacterium tuberculosis).
  • Opportunistic pathogens are normally part of the body's microbial flora but cause disease in compromised individuals (e.g., Staphylococcus aureus, Escherichia coli, Candida albicans).

Bacterial Classification

  • Fastidious organisms require rich media, often containing blood components, to grow.

Blood Agar Plate (BAP)

  • Enriched with mammalian blood (usually sheep or horse), typically at 5-10% concentration.
  • Components: 0.5% Peptone, 0.3% beef extract/yeast extract, 1.5% agar, 0.5% NaCl, distilled water.
  • pH should be from 7.2 to 7.6 (7.4).
  • Autoclave the mixture at 121°C for 15 minutes, let it cool to 45-50°C, and add 5% defibrinated blood.
  • Mix gently.

Chocolate Agar (CHOC)

  • Type of blood agar where red blood cells are lysed by heating to 80°C.
  • Used to grow fastidious respiratory bacteria like Haemophilus influenzae.

Hemolysis

  • Hemolysis is the lysis of red blood cells.
    • Alpha (α)-hemolysis: incomplete hemolysis.
    • Beta (β)-hemolysis: complete lysis and digestion of red blood cell contents.
    • Gamma (γ)-hemolysis: no hemolysis.

Skin and Soft Tissue Infections (SSTIs)

  • Various presentations, etiologies, and severities involving microbial invasion of skin and underlying tissues.
  • Soft tissue includes: muscles, tendons, ligaments, fascia, nerves, fibrous tissues, fat, blood vessels, and synovial membranes.
  • Common entry points are breaks in the skin barrier: lacerations, bite wounds, scratches, instrumentation, pre-existing conditions (e.g., chicken pox, ulcers), burns, and surgery.
  • Diagnosing SSTIs requires differentiating life-threatening cases from less severe ones.

Skin structure

  • Epidermis: outermost layer, containing keratinocytes (95%) and melanocytes.
  • Dermis: contains connective tissue, fibers, glycoproteins, nerve endings, hair follicles, glands, and blood vessels.
  • Hypodermis (subcutaneous tissue): attaches skin to bone and muscle, containing fibroblasts, macrophages, and adipocytes (fat).

Natural Skin Defenses

  • Keratin: a protein forming the basis of horny epidermal tissues (hair, nails).
  • Skin cell shedding and regeneration.
  • Sebum: oily, waxy substance; low pH, high lipid content.
  • Sweat: low pH, high salt, and contains lysozyme (digests peptidoglycan).
  • Normal skin microbiome.

Skin Normal Microbiota

  • Propionibacterium acnes
  • Staphylococci (e.g., Staphylococcus epidermidis, Staphylococcus aureus - in smaller numbers)
  • Streptococci species
  • Corynebacterium species
  • Peptostreptococcus species
  • Acinetobacter species
  • Small numbers of other species (e.g., Pseudomonas aeruginosa, Candida species).

Streptococcus

  • Gram-positive cocci arranged in pairs or chains.
  • Most species are facultative anaerobes with complex nutritional requirements, needing blood or serum-enriched media for isolation.
  • Carbohydrate fermentation results in lactic acid production.
  • Catalase-negative streptococci.
  • Divided into groups (β-hemolytic, α-hemolytic, and γ-hemolytic) based on hemolysis patterns, classified by Lancefield grouping or biochemical testing.

Streptococcus pyogenes

  • Streptococcus pyogenes is a rapidly growing gram-positive coccus arranged in chains.
  • Streptococcus pyogenes causes a variety of diseases, including pharyngitis, skin and soft-tissue infections, bacteremia, rheumatic fever, and acute glomerulonephritis.
  • Streptococcus pyogenes is commonly called "flesh-eating" bacteria due to its necrotic damage to muscle tissue.

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Description

Explore the essential concepts of medical microbiology, focusing on the interactions between humans and microorganisms. Learn about infection types, pathogen classifications, and the significance of various microbial organisms in health and disease.

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