9. Bacterial Diseases , Lecture Exam 2 (Add to full set when done)

What are the general characteristics of Staphylococcus aureus as a bacterial pathogen?

S. aureus is a gram-positive, facultative anaerobic, non-motile coccus that is part of normal microbiota but can act as an opportunistic pathogen.

What is the cellular morphology and arrangement of Staphylococcus aureus?

It appears as gram-positive cocci arranged in irregular, grape-like clusters.

In what locations on the human body is S. aureus commonly found?

It is commonly found on the skin and in the nasal passages of healthy individuals.

Through what mechanisms is S. aureus transmitted between individuals?

It is transmitted through direct contact, respiratory droplets, contaminated fomites, and healthcare-associated spread.

What are fomites in the context of infectious disease transmission?

Fomites are inanimate objects, such as towels or razors, that can carry and transmit pathogens.

What enzymes produced by S. aureus contribute to its ability to invade and spread in host tissues?

Coagulase (clots blood), hyaluronidase (spreads through tissues), DNase (degrades DNA), lipase (breaks down lipids), and penicillinase (confers antibiotic resistance).

What toxins produced by S. aureus contribute to disease development and what are their effects?

Hemolysins (destroy RBCs), leukocidin (kills WBCs), enterotoxin (causes food poisoning), exfoliative toxin (causes skin peeling), and TSST-1 (causes toxic shock syndrome).

What is staphylococcal food poisoning and how does it occur?

It is a food intoxication caused by ingestion of preformed enterotoxins produced by S. aureus in contaminated food.

How does food intoxication differ from food infection in terms of mechanism and symptoms?

Intoxication involves ingestion of toxins with rapid onset and no fever, while infection involves bacterial growth in the host with slower onset and often fever.

Which specific virulence factor of S. aureus is responsible for food poisoning symptoms?

The enterotoxin is responsible for causing vomiting and gastrointestinal symptoms.

How is S. aureus food poisoning typically transmitted?

Through consumption of improperly handled or contaminated food after toxin production.

What types of skin and soft tissue infections are commonly caused by S. aureus?

Folliculitis, furuncles, carbuncles, impetigo, cellulitis, and scalded skin syndrome.

What is folliculitis in the context of a bacterial skin infection?

It is a superficial infection of hair follicles.

What is a furuncle and how does it differ from folliculitis?

A furuncle is a deeper, pus-filled infection (boil) that extends beyond the hair follicle.

What is a carbuncle and how does it form?

A carbuncle is a cluster of interconnected furuncles that form a larger, deeper infection.

What is toxic shock syndrome and which toxin is responsible for it?

It is a systemic, life-threatening condition caused by TSST-1, a superantigen toxin.

What are the hallmark symptoms of toxic shock syndrome?

High fever, diffuse rash resembling sunburn, hypotension (shock), and potential organ failure.

What are the general characteristics of Streptococcus pyogenes?

It is a gram-positive coccus found in chains, commonly inhabiting the respiratory tract and transmitted via droplets.

What major diseases are caused by S. pyogenes?

Strep throat, scarlet fever, rheumatic fever, and necrotizing fasciitis.

What are the most characteristic symptoms associated with these diseases?

Scarlet fever causes a strawberry tongue and rash; necrotizing fasciitis causes rapid tissue destruction; rheumatic fever affects the heart.

Which three bacterial genera are the most common causes of bacterial meningitis?

Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae.

What are the classic symptoms associated with bacterial meningitis?

Fever, stiff neck, and severe headache.

What are neurotoxins and how do they affect the human body?

Neurotoxins interfere with nerve signaling, leading to paralysis or muscle dysfunction.

How does Clostridium tetani enter the body and initiate infection?

It enters as endospores through puncture wounds and germinates in anaerobic conditions.

What toxin is produced by C. tetani and how does it affect the nervous system?

Tetanospasmin blocks inhibitory neurotransmitters, causing continuous muscle contraction.

What are the characteristic symptoms of tetanus infection?

Lockjaw (trismus), muscle rigidity, and painful spasms.

How can tetanus be prevented?

Through vaccination with the tetanus toxoid vaccine.

What is the causative agent of botulism and how is the toxin acquired in adults?

Clostridium botulinum produces a neurotoxin acquired through ingestion of improperly canned foods.

What effect does botulinum toxin have on the nervous system?

It blocks acetylcholine release, causing flaccid paralysis.

Why are infants particularly susceptible to botulism?

Their normal microbiota is not fully developed, allowing bacterial growth in the intestine.

What organism causes Lyme disease and how is it transmitted?

Borrelia burgdorferi is transmitted through the bite of infected ticks.

What is the characteristic early symptom of Lyme disease?

A bull’s-eye rash (erythema migrans).

What disease is caused by Corynebacterium diphtheriae and how is it transmitted?

It causes diphtheria and is spread via respiratory droplets.

What is the hallmark clinical feature of diphtheria infection?

Formation of a thick pseudomembrane in the throat.

What are the defining characteristics of Mycobacterium tuberculosis?

It is an acid-fast bacterium with a waxy cell wall that resists staining.

How is tuberculosis transmitted and what organ is primarily affected?

It is transmitted via airborne droplets and primarily infects the lungs.

What are tubercles in tuberculosis infection?

They are granulomas formed by the immune system to contain the bacteria.

(granulomas: immune cell clusters that contain infections the body can’t eliminate)

Which bacterium is the leading cause of diarrhea worldwide and what are its characteristics?

Campylobacter jejuni is a gram-negative, spiral-shaped bacterium transmitted through contaminated food and water.

What organism causes cholera and what is its morphology?

Vibrio cholerae is a curved, gram-negative rod.

What is the hallmark symptom of cholera infection?

Profuse “rice-water” diarrhea.

How does cholera toxin contribute to disease symptoms?

It causes massive fluid and electrolyte loss from intestinal cells.

What condition predisposes patients to C. difficile infection?

Disruption of normal microbiota due to antibiotic use.

What diseases are associated with C. difficile infection?

Antibiotic-associated diarrhea and pseudomembranous colitis.

What types of infections can Escherichia coli cause in humans?

Urinary tract infections, gastrointestinal infections, and neonatal meningitis.

Which strain of E. coli is responsible for traveler’s diarrhea?

Enterotoxigenic E. coli (ETEC).

What is syphilis and which organism causes it?

Syphilis is a sexually transmitted infection caused by Treponema pallidum, a spirochete bacterium.

How is T. pallidum transmitted between individuals?

Through sexual contact or from mother to fetus (congenital transmission).

What are the three stages of syphilis and their distinguishing features?

Primary: painless chancre; Secondary: rash and systemic symptoms; Tertiary: severe organ and neurological damage.

What are the life stages of ticks in Lyme disease transmission?

Larva → Nymph → Adult

Which tick stage is MOST responsible for transmitting Borrelia burgdorferi to humans?

Nymph stage

What type of vector are ticks in Lyme disease?

Biological vector (pathogen develops inside the vector).

What illness do early symptoms of Lyme disease resemble?

Flu-like illness.

What type of care is required for severe infections caused by Clostridium tetani and Clostridium botulinum?

Supportive care (especially respiratory support/ventilator).

What specific treatment is used to neutralize toxins in tetanus and botulism?

Antitoxin.

Is botulinum toxin an enterotoxin?

No — it is a neurotoxin.

What are the general characteristics of Corynebacterium?

Gram-positive, club-shaped rods arranged in 'Chinese letters'.

What are the defining features of Mycobacterium?

Acid-fast bacteria with waxy mycolic acid cell wall.

Why are Mycobacterium species hard to treat?

Waxy cell wall → resistant to staining, antibiotics, and immune response.

What diseases are caused by neurotoxins and what do they do?

Tetanus – toxin causes spastic paralysis (muscle contraction); Botulism – toxin causes flaccid paralysis (muscle relaxation).

What diseases are caused by enterotoxins and what do they do?

Staphylococcal food poisoning – rapid vomiting & diarrhea; Cholera – severe 'rice-water' diarrhea.

What disease is caused by a superantigen toxin?

Toxic shock syndrome (TSST-1) – causes massive immune response → fever, rash, shock.

What toxin causes skin peeling and what disease is it associated with?

Exfoliative toxin → Scalded skin syndrome.