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Questions and Answers
Staphylococcus aureus is a Gram negative bacteria.
False
Staphylococcus epidermidis is a catalase-negative species.
True
Enterococcus faecium is a Gram negative cocci.
False
Staphylococcus saprophyticus is not associated with genitourinary tract infections.
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Staphylococcus epidermidis can cause severe infections in immunosuppressed patients.
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Streptococcus pyogenes is part of the Enterococcus genus.
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Staphylococcus aureus can produce IgA proteases to destroy IgA antibodies.
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Staphylococcus epidermidis is known for altering actin filaments of the host cell cytoskeleton using invasins.
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Gram-positive cocci like Staphylococcus aureus can penetrate host cells by using actin filaments.
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Staphylococcus saprophyticus is commonly associated with biofilm formation to resist phagocytes.
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Enterococcus species are known to use siderophores to take iron away from iron transport proteins.
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Most host cell damage by bacteria is caused by the penetration of invasins produced by Staphylococcus aureus and E.coli.
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Staphylococcus aureus produces an enzyme that breaks down fibrin clots to isolate the infection.
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Staphylococcus epidermidis has a capsule that resists the host's defenses by impairing phagocytosis.
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Gram-positive cocci such as Staphylococcus aureus can resist phagocytosis due to the presence of mycolic acid in their cell wall.
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Staphylococcus saprophyticus produces coagulases that help in clotting fibrinogen in blood.
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Enterococcus bacteria are known for producing exoenzymes that assist in the infection process.
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M protein found on the cell surface of Staphylococcus aureus helps in resisting phagocytosis.
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Study Notes
Bacterial Virulence Factors
- Collagenase breaks down collagen, a protein forming connective tissue in muscles and organs.
- Leukocidins destroy White Blood Cells (WBCs), while Hemolysins lyse Red Blood Cells (RBCs).
- IgA proteases are enzymes produced by some pathogens to destroy IgA antibodies.
Penetration into Host Cells
- Actin, a protein in the host cell cytoskeleton, is used by some microbes to penetrate host cells and move through/between them.
- Example: Salmonella and E. coli use invasins to alter actin filaments, causing membrane ruffling and engulfment by the host cell.
Biofilms
- Biofilms resist phagocytes and shield antigens from recognition by the immune system.
- Siderophores take iron away from iron transport proteins.
- Pathogens use host cells for nutrients, producing waste products and eventually causing cell rupture.
Toxins
- Toxins are poisonous substances produced by certain microorganisms.
- Toxigenicity is the capacity of microorganisms to produce toxins.
- Most host cell damage by bacteria is done by toxins.
Types of Toxins
- Exotoxins
- Endotoxins
Gram Positive Bacteria
- Gram Positive Cocci:
- Staphylococcus
- Streptococcus
- Enterococcus
- Gram Positive Bacilli:
- Bacillus
- Clostridium
- Listeria
- Corynebacterium
- Mycobacterium
Staphylococcus
- General features: Gram positive, spherical, and form in grape-like clusters.
- Facultative anaerobic organisms.
- Most are harmless and reside normally on the skin and mucous membranes of humans.
- Grow in the presence of bile salts and 6.5% NaCl (Mannitol Salt agar).
- Can cause a wide variety of diseases through either toxin production or penetration.
Capsule
- The capsule resists the host's defenses by impairing phagocytosis.
- However, the human body can produce antibodies against the capsule, allowing phagocytosis to occur.
Cell Wall Components
- Cell walls of certain bacteria contain chemical substances that contribute to virulence.
- Example: Streptococcus pyogenes produces M protein, which mediates attachment and helps resist phagocytosis.
- Example: Mycobacterium tuberculosis has a waxy lipid (mycolic acid) that increases virulence by resisting digestion by phagocytes.
Production of Extracellular Enzymes (Exoenzymes)
- Many bacteria produce enzymes that play an important role in the infection process.
- Coagulases: clot fibrinogen in blood, protecting the bacterium from phagocytosis.
- Kinases: break down fibrin and digest clots formed by the body to isolate the infection.
- Hyaluronidase (spreading factor): hydrolyzes hyaluronic acid, helping the microorganism to spread.
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Description
Test your knowledge on Gram-positive bacteria by identifying different species of Gram-positive cocci and bacilli. Learn about common bacteria such as Staphylococcus and Streptococcus.
