Gram-Positive Bacteria – Exam 3 Review

A comprehensive set of question-and-answer flashcards covering key concepts, pathogens, toxins, clinical features, and comparative points for Gram-positive bacteria (Firmicutes and Actinobacteria) as presented in the lecture notes.

What are the two main gram-positive bacterial phyla distinguished by genome G+C content?

Low G+C Firmicutes and High G+C Actinobacteria

Which phylum contains low G+C gram-positive bacteria (<60 % G+C)?

Phylum Firmicutes

Which phylum contains high G+C gram-positive bacteria (>60 % G+C)?

Phylum Actinobacteria

What structural change defines Tenericutes (class Mollicutes) within Firmicutes?

They lost their cell wall and underwent genome reduction, adopting an intracellular/parasitic lifestyle.

Why do some Firmicutes stain gram-negative even though they are genetically gram-positive?

They have a thin peptidoglycan layer covered by a pseudo-outer membrane that prevents retention of crystal violet.

What additional cell-wall component helps many Actinobacteria survive harsh environments?

Long-chain mycolic acids that thicken and protect the cell wall.

Which metabolic reaction do proteolytic Clostridia use to generate ATP?

The Stickland reaction (paired oxidation-reduction of amino acids).

Name the four clinically important Clostridium species highlighted in the lecture.

Clostridium tetani, C. perfringens, C. difficile, and C. botulinum.

What vaccine prevents tetanus, and how often is a booster recommended?

The toxoid vaccine (DTaP/Tdap); booster every 10 years.

Which neurotransmitters are blocked by tetanospasmin?

GABA and glycine.

Why are puncture wounds particularly prone to tetanus infection?

They are deep, narrow, become sealed off, and quickly become anaerobic—ideal for germination of C. tetani spores.

At the molecular level, how does tetanospasmin act?

It is a zinc endopeptidase that travels retrograde to the CNS and cleaves SNARE proteins in inhibitory interneurons, preventing GABA/glycine release.

What type of paralysis is produced by tetanus?

Spastic paralysis (rigid muscles, lockjaw).

Which Clostridium species produces alpha toxin that causes gas gangrene?

Clostridium perfringens.

List key clinical features of gas gangrene.

Rapid tissue destruction, gas production in tissue, foul odor, intense pain, and possible systemic shock.

Which toxin is responsible for C. perfringens food poisoning?

C. perfringens enterotoxin.

When does C. difficile overgrowth typically become a problem?

After prolonged or broad-spectrum antibiotic therapy that disrupts normal gut flora.

Name the two major toxins produced by C. difficile.

Toxin A and Toxin B.

What is considered the most potent natural toxin known?

Botulinum toxin produced by Clostridium botulinum.

How does botulinum toxin cause flaccid paralysis?

It cleaves SNARE proteins in peripheral cholinergic nerves, blocking acetylcholine release at neuromuscular junctions.

Why should infants under one year old not be fed honey?

Honey can contain C. botulinum spores that may germinate in the infant gut, causing “floppy baby syndrome.”

Compare the type of paralysis caused by tetanus and botulism.

Tetanus causes spastic (rigid) paralysis; botulism causes flaccid (limp, descending) paralysis.

Are Bacillus species usually communicable between people?

No; infections arise from environmental spores, not person-to-person spread.

Name two antibiotics naturally produced by some Bacillus species.

Bacitracin and polymyxin.

Which Bacillus species is the agent of anthrax?

Bacillus anthracis.

What are the four clinical forms of anthrax?

Cutaneous, inhalation (pulmonary), gastrointestinal, and injectional anthrax.

Which form of anthrax is most common?

Cutaneous anthrax.

Which form of anthrax is most lethal?

Inhalation anthrax.

Name the two principal exotoxins of Bacillus anthracis.

Edema toxin and lethal toxin.

Where on the body are Staphylococci most commonly found?

On the skin, in sweat glands, and on mucous membranes such as the nasal passages.

Which enzyme distinguishes coagulase-positive Staphylococcus aureus?

Coagulase, which causes fibrin clot formation.

List three virulence factors of Staphylococcus aureus.

Coagulase, β-hemolysin, and DNase (others include protein A, etc.).

What does MRSA stand for?

Methicillin-Resistant Staphylococcus aureus.

Why is MRSA a serious concern in hospital settings?

It carries multiple antibiotic resistance genes, making nosocomial infections difficult to treat.

Which populations are at highest risk for Listeria infection?

Pregnant women, neonates, the elderly, and immunocompromised individuals.

Which bacterium causes listeriosis?

Listeria monocytogenes.

Name food products frequently linked to Listeria outbreaks.

Unpasteurized milk and cheeses, deli meats, cooked meats and gravies, ice cream, and improperly refrigerated produce.

What metabolic end product makes Lactobacillus valuable in food fermentation?

Lactic acid.

What small antimicrobial peptides are produced by many Lactobacillus species?

Bacteriocins.

Which Streptococcus species causes strep throat?

Streptococcus pyogenes (Group A β-hemolytic).

When S. pyogenes carries erythrogenic toxin genes, what illness can develop?

Scarlet fever.

What hemolysis pattern is exhibited by Streptococcus pyogenes on blood agar?

β-hemolysis (complete lysis).

Which Streptococcus species commonly causes lobar pneumonia?

Streptococcus pneumoniae.

Which enterococcal species is a frequent cause of UTIs and endocarditis?

Enterococcus faecalis.

Approximately what percentage of known antibiotics come from Actinomycetes?

About 70 %.

What soil odorant is produced by Streptomyces species?

Geosmin, responsible for the “earthy” smell of soil.

Name three antibiotics derived from Streptomyces.

Erythromycin, neomycin, and streptomycin (others include ivermectin derivatives).

Which Streptomyces metabolite was modified to create the antiparasitic drug ivermectin?

Avermectin.

What chronic opportunistic disease of the face and jaw is caused by Actinomyces?

Actinomycosis (characterized by chronic abscesses/sulfur granules).

What hallmark lesion forms in diphtheria caused by Corynebacterium diphtheriae?

A grayish pseudomembrane across the throat and tonsils.

The diphtheria toxin gene is carried by which mobile genetic element?

A lysogenic bacteriophage (β-phage).

Which 1925 event emphasized the urgency of delivering diphtheria antitoxin to Alaska?

The Serum Run to Nome, commemorated by the Iditarod Trail Sled Dog Race.

What waxy cell-wall component characterizes Mycobacterium species?

Mycolic acid.

Which Mycobacterium species causes tuberculosis?

Mycobacterium tuberculosis.

What live attenuated vaccine, derived from M. bovis, is used against TB in many countries?

The BCG (Bacille Calmette–Guérin) vaccine.

What term describes TB strains resistant to at least isoniazid and rifampin?

Multi-drug-resistant TB (MDR-TB); extensively drug-resistant TB (XDR-TB) if additional drugs fail.

Which Mycobacterium species causes leprosy?

Mycobacterium leprae.

Which fermentation product of Propionibacterium freudenreichii gives Swiss cheese its holes and aroma?

Propionic acid (and accompanying CO₂ bubbles).

Which microorganism forms the active probiotic in Activia yogurt?

Bifidobacterium species.

Overgrowth of which bacterium can lead to bacterial vaginosis?

Gardnerella vaginalis.