Bacterial Pathogens

• Notes cover bacterial structure and function, pathogenesis, virulence factors, and antibiotics.
• Also covers specific bacteria like Staphylococcus, Streptococcus, Bacillus, Listeria, and Corynebacterium.

Gram-Positive vs. Gram-Negative Bacteria

• Gram-positive bacteria feature a thick peptidoglycan layer in their cell wall.
• Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane.
• Both Gram-positive and Gram-negative bacteria contain cytoplasmic membranes and ribosomes.

Bacterial Shapes

• Coccus: Spherical shape
• Bacillus: Rod shape
• Spirillum: Spiral shape

Lipopolysaccharide (LPS)

• LPS is found in Gram-negative bacteria.
• LPS consists of lipid A (endotoxin), the core polysaccharide, and the O antigen.
• LPS triggers strong immune responses in the host.

Gram Stain

• Gram stain differentiates bacteria based on cell wall structure.
• Gram-positive bacteria stain purple.
• Gram-negative bacteria stain pink.

Peptidoglycan

• Peptidoglycan is composed of sugars (NAG & NAM) and peptides.
• Peptidoglycan gives structural support to the bacterial cell wall.

Gram-Negative Outer Membrane

• The Gram-negative outer membrane contains LPS.
• It provides protection against antibiotics.

Mycolic Acid

• Mycolic acid is a waxy substance present in Mycobacteria.
• Mycolic acid makes Mycobacteria resistant to staining and antibiotics.

Bacterial Division

• Binary fission is a form of asexual reproduction in bacteria.

Endospores

• Endospores are extremely resistant, dormant structures.
• Endospores are formed under stress conditions.
• Endospores can be destroyed by autoclaving.

Sporulation vs. Germination

• Sporulation: The process of forming endospores.
• Germination: The return of a spore to active bacterial growth.

Pathogenesis

• Pathogenesis is the process by which bacteria cause disease.

Virulence Factors

• Virulence factors are traits that enhance a pathogen’s ability to cause disease.
• Examples include toxins, adhesion proteins, and immune evasion mechanisms.

Routes of Transmission

• Direct transmission: Person-to-person contact
• Indirect transmission: Via surfaces, food, or vectors

Bacterial Adhesion

• Bacteria use pili, fimbriae, and adhesins to attach to host cells.

Toxins

• Toxins are harmful bacterial products.
• Include both endotoxins and exotoxins.

Endotoxin vs. Exotoxin

• Endotoxin: LPS found in Gram-negative bacteria, causes systemic effects.
• Exotoxin: Secreted proteins, have specific target effects.

A/B Toxins

• A/B toxins consist of two parts: an active (A) subunit and a binding (B) subunit.
• Diphtheria toxin is an example of an A/B toxin.

Endotoxin Concentrations

• Low endotoxin concentrations: Cause fever and immune activation.
• High endotoxin concentrations: Can lead to septic shock.

Toxin Mechanisms

• Toxins disrupt cell function, damage membranes, or trigger excessive immune responses.

Superantigens

• Superantigens cause excessive immune activation.
• This occurs because they over-stimulate T-cells.

Extracellular vs. Intracellular Pathogens

• Extracellular pathogens grow outside host cells.
• Intracellular pathogens evade immune responses by living inside host cells.

Adherence vs. Colonization

• Adherence: Attachment to host cells
• Colonization: Growth and persistence on/in the host

Pathogenicity Islands

• Pathogenicity islands are gene clusters in bacteria.
• They are responsible for virulence.

Antimicrobials vs. Antibiotics

• Antimicrobials target microorganisms
• Antibiotics are naturally derived antimicrobials.

Antibiotic Mechanisms

• Inhibit cell wall synthesis (e.g., penicillins)
• Inhibit protein synthesis (e.g., tetracyclines)
• Inhibit nucleic acid synthesis (e.g., fluoroquinolones)
• Disrupt metabolic pathways (e.g., sulfonamides)

Synergism vs. Antagonism

• Synergism: Two antibiotics work better together
• Antagonism: One antibiotic reduces the effectiveness of the other

Bacteriostatic vs. Bactericidal

• Bacteriostatic: Inhibits bacterial growth
• Bactericidal: Kills bacteria

Broad vs. Narrow Spectrum

• Broad-spectrum: Acts on many bacteria
• Narrow-spectrum: Targets specific species

Antibiotics and Eukaryotic Ribosomes

• Antibiotics don’t affect eukaryotic ribosomes because bacterial (70S) and eukaryotic (80S) ribosomes differ.

Bacterial Resistance

• Bacteria acquire resistance through mutations, efflux pumps, target modifications, and enzyme production.

β-Lactamase

• β-Lactamase is an enzyme that deactivates β-lactam antibiotics (e.g., penicillins).

Penicillin-Binding Proteins (PBPs)

• PBPs are enzymes that antibiotics (like penicillin) target to inhibit cell wall synthesis.

MRSA & VRSA

• MRSA: Methicillin-resistant S. aureus
• VRSA: Vancomycin-resistant S. aureus

S. aureus Habitat

• S. aureus is found on the skin and in the nose.
• It survives dry conditions due to its thick cell wall.

S. aureus Transmission

• Transmission occurs via direct contact, fomites, and respiratory droplets.

S. aureus Infections

• Skin infections, pneumonia, endocarditis, osteomyelitis

S. aureus Toxin Mediated Diseases

• Scalded skin syndrome, food poisoning, toxic shock syndrome

Exfoliative Toxin

• Breaks down desmosomes in skin, leading to peeling.

Cytotoxins, Superantigens, TSST-1

• Damage host cells, trigger a massive immune response

PV Toxins

• Destroy white blood cells

S. aureus Food Poisoning

• Caused by enterotoxin
• Enterotoxin is heat-stable, so cooking doesn't eliminate the toxin

Bacteremia vs. Endocarditis

• Bacteremia: Bacteria in the blood
• Endocarditis: Infection of the heart lining

Nosocomial Infections

• Hospital-acquired infections

Empyema

• Pus in the pleural cavity (lung infection)

S. aureus Virulence Factors

• Capsule, slime layer, Protein A (immune evasion), coagulase (clots blood)

Hemolysis Types

• Alpha: Partial hemolysis (greenish)
• Beta: Complete hemolysis (clear)
• Gamma: No hemolysis

Carbohydrate Groups (A-U)

• Used for classifying Streptococcus

Group A Strep (GAS)

• Found in the throat and skin; spread via droplets/contact.

Group A Strep (GAS) Infections

• Pharyngitis, scarlet fever, cellulitis, necrotizing fasciitis, rheumatic fever

Group A Strep (GAS) Virulence Factors

• M protein (immune evasion), hyaluronidase (tissue invasion), Streptolysins (kill cells)

Group B Strep (GBS)

• Causes neonatal sepsis; transmitted during birth.

Streptococcus pneumoniae

• Virulence depends on the capsule.
• Causes pneumonia and meningitis.

Endogenous Infections

• Originate from the patient’s own microbiota

Streptococcus pneumoniae Vaccine

• Polysaccharide and conjugate vaccines are available.

Enterococcus

• Formerly Group D Streptococcus
• Includes two main species: E. faecalis and E. faecium.

VRE (Vancomycin-Resistant Enterococcus)

• Resistant to vancomycin; spreads in hospitals.

Medically Relevant Bacillus Species

• B. anthracis and B. cereus.

Anthrax Diseases

• Cutaneous, inhalational, gastrointestinal

Anthrax Mortality Rates

• Inhalational anthrax has the highest risk.

Anthrax Bioterrorism Threat

• B. anthracis spores are highly stable and can be weaponized.

Anthrax Toxins

• Protective antigen (PA) + Edema Factor (EF) = edema toxin
• PA + Lethal Factor (LF) = lethal toxin.

Anthrax Toxin Functions

• EF disrupts fluid balance
• LF triggers cell death

Bacillus Virulence Genes

• Found on plasmids

Bacillus Capsule

• Prevents phagocytosis

Bacillus Endospore State

• Dormant form that withstands harsh conditions.

Bacillus Zoonotic Infection

• Spread via animals.

Wool Sorter’s Disease

• Inhalational anthrax from contaminated animal products

Listeria

• Intracellular pathogen causing listeriosis.

Listeria Virulence Factors

• Internalin (entry), ActA (movement), listeriolysin O (escape)

Listeria Transmission

• Contaminated food (e.g., dairy, deli meats)

Listeriosis

• Flu-like in adults and severe in newborns and pregnant women

Listeria Transplacental Spread

• Infection passes to the fetus

Corynebacterium diphtheriae

• Causes diphtheria via diphtheria toxin.

Diphtheria Toxin

• Inhibits protein synthesis

DTaP Vaccine

• DTaP protects against diphtheria, tetanus, and pertussis.

Questions cover bacterial structures, antibiotic resistance, endotoxins, sporulation vs germination, virulence factors, mechanisms of action, A/B toxins, and routes of transmission. Assess knowledge of bacterial characteristics and their impact on host cells.