R.O Lecture 8&9 Flashcards
Virulence Factors
Specialised structures or characteristics that improve the ability of an organism to cause infection and disease.
Adherence
Attachment to host cell’s surfaces; important tool for initiation of infection
Adhesins
- proteins/glycoproteins that bind to complementary surface receptors (usually glyoproteins/sugars) on host cells.
- Found on surfaces of bacterial attachment pili or glycocalyx
- Adhere to membranes of specific cell types
Is aderence alone sufficient to cause infection?
- No, adherence alone is not sufficient to cause infection.
- Microbes must be able to colonise the tissue surface or penetrate it
Types of identified adhesions and their targets
Refer to slide 3
Action of Hyaluronidase in bacterial invasion
- Enzyme that digests hyaluronic acid (a glue-like substance that holds cells together in some tissues)
- Produced by some pneumococci and streptococci species
- Enables passage through the epithelium to deeper tissues
Coagulase
- Enzyme that causes blood clotting; can aid infection by some bacterial species like Staphylococcus aureus; protects them from immune defenses
Streptokinase
Enzyme that dissolves blood clots; allows bacteria trapped within a clot to free themselves and spread the infection
Can organisms such as Mycobacterium tuberculosis and Neisseria gonorrhoeae survive within host cells?
Organisms such as Mycobacterium tuberculosis and Neisseria gonorrhoeaecan survive within host cells –escape destruction and are transported to other tissues
Toxin
A toxin is any substance that is poisonous to other organisms
Toxigenicity
- The capacity of microbes to produce toxins.
- Can produce fever, cardiovascular disturbances, diarrhoea, destroy blood cells/vessels, disrupt the nervous system, inhibit protein synthesis, damage cell membranes etc.
Endotoxins
- Part of the outer membrane of Gram-negative bacteria; released into host tissue when bacteria die or divide.
- Consist of Lipid A portion of Lipopolysaccharide (LPS) complexes
- Relatively weak unless released in large doses
- Non-specific effects: Fever, sudden drop in blood pressure (endotoxic shock)
- Produced by species including Salmonella typhi, Neisseria meningitidis
Exotoxins
- Soluble substances produced by Gram-positive and Gram-negative bacteria that are secretedinto the host tissues
- Produced by species of Clostridium, Bacillus, Staphylococcus, Streptococcus etc.
- Most are polypeptides; some are enzymes.
- Most genes for exotoxins are carried on plasmids/phages
Cytotoxins
Kill host cells/inhibit their functions
Neurotoxins
Interfere with nerve impulse transmission
Enterotoxins
- Affect cells lining the GI tract
- Includes cholera toxin (Vibrio cholerae), heat-labile enterotoxin (E. coli) and Staphylococcal enterotoxin (S. aureus)
- Can cause symptoms by attaching to GI cell membranes and causing them to release fluids, disturbing the electrolyte balance and affecting muscle contractions
- Diarrhea, vomiting
Hemolysins
Lyse red blood cells; produced by Strepto-and Staphylococci; release iron.
- α-hemolysin - Partially break down hemoglobin
- β-hemolysin - Completelybreak down hemoglobin
Botulisim neurotoxin (BoNT)
- Botulism neurotoxin (BoNT) blocks acetylcholine (neurotransmitter) release from excitatory neurons at neuromuscular junctions, preventing muscle contraction (botulism).
Tetanus neurotoxin (TeNT)
blocks acetylcholine (neurotransmitter) release from inhibitory neurons, preventing muscle relaxation (tetanus).
Bacterial Meningitis
- Inflammation of the meninges (membranes covering CNS)
- Causes necrosis, clogging of blood vessels, increased intracranial pressure, decreased CSF flow, impaired CNS function.
- Toxins (pneumolysin) produced by S. pneumonia contribute to disease (cytotoxins)
- Most cases are acute but some can be chronic
Hansen’s disease (leprosy)
- Caused by Mycobacterium leprae.
- Disfiguring chronic disease.
Tetanus
- Severe muscle spasms; caused by Clostridium tetani.
- Tetanus toxin (neurotoxin): affects central nervous system, blocking neurotransmitter release from inhibitory neurons leading to lock jaw, muscle rigidity and muscular spasms.
Botulism
- Botulism-severe muscle relaxation; caused by Clostridium botulinum.
- Neurotoxin blocks the release of acetylcholine at the junction between neurons and muscle cells; thusmuscle stimulation does not occur
What are the three forms of botulism?
- Foodborne (intoxication)
- Infant
- Wound (infection and intoxication)
Erysipelas
lesions form on skin and spread. Caused by haemolytic streptococci
Impetigo
- Highly contagious and caused by staphylococci and/or streptococci.
- Treated with penicillin.
- Almost exclusive to children
Acne
- Affects 80% of teenagers and many adults.
- Propionibacteriumacnes responsible for severe cases
- Feeds on sebum produced by sebaceous glands in skin (overproduction can be hormone stimulated)
Burn infections
- Severe burns can remove much of the body’s protective barrier
- Pseudomonas aeruginosais prime cause of infections
- Treatment difficulties such as antibiotic access issues (topical treatments or debridement) and antimicrobial resistance
Refer to slide 16
Explain the function of lysozyme in tears
- Antimicrobial effect of tears on M. luteus
- Tears also contain other antimicrobial agents. e.g. lipocalin, lactoferrin, sIgA
Ophthalmia neonatorum
- Bacterial eye disease
- Conjunctivitis of the newborn
- Caused by Neisseria gonorrhoeaeand Chlamydia trachomatis (birth canal)
- Can cause inflammation of the cornea (keratitis)
Bacterial conjuctivitis (pink eye)
- Extremely contagious
- Caused by S. aureus, Neisseria gonorrhoeaeand Pseudomonas spp.
- Causes inflammation of the conjunctiva
Trachoma
- Bactieral eye Disease
- Caused by Chlamydia trachomatis
- Infection and destruction of conjuctivia; cause of preventable blindness
Gas gangrene
- In body regions where oxygen concentration is low, spores germinate, multiply, and produce toxins (alpha toxin: cytotoxin) and enzymes.
- As the organisms divide they ferment muscle carbohydrates and produce hydrogen gas.
- These gas bubbles distort and destroy tissue.
- Produces blackening of tissue
Upper respiratory tract infections
- Pharyngitis - sore throat - S.pyrogenes
- Laryngitis - infection of the larynx, loss of voice
- Epiglottitis - infection of the epiglottis
- Sinusitis, bronchitis, tonsillitis
Last 3 - S.pneumoniae and H.influenzae
Name diseases of the lower respiratory tract
- whopping cough (pertussis)
- Pneumonia
- Tuberculosis
Whooping cough (pertussis)
- Main causative agent is Bordetellapertussis (aerobic, encapsulated, Gram negative coccobacillus)
- Inhaled organisms colonise the cilia lining the respiratory tract; produces endotoxin, exotoxins (cytotoxins: pertussis toxin, tracheal toxin) and hemagglutinins (adhesins)
- Disease causes mucus and masses of bacteria to fill the airway leading to violent coughing
Pneumonia
- Inflammation of lung tissue (children and older adults have higher risk)
- Can be caused by bacteria, viruses, fungi, inorganic sources
- Main causative agent is Streptococcus pneumoniae (pneumococcus); can cause fibrin deposits leading to blockage (consolidation) of air spaces and pleurisy
- Disease causes violent chills, fever, chest pain, cough, and sputum-containing blood.
Tuberculosis
- Caused by bacteria from the Mycobacterium tuberculosis complex; aerobic, rod-shaped, long doubling time; replicate inside phagocytes (e.g. neutrophils, macrophages); elicit acute inflammatory response and can produce lesions
- Prior to 1900, one-third of adults died of TB before reaching old age
- BCG vaccine (M. bovis strain)
- Treatment of latent infection with extended course of antibiotics
