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Questions and Answers
Staphylococcus aureus is a Gram negative bacteria.
Staphylococcus aureus is a Gram negative bacteria.
False
Staphylococcus epidermidis is a catalase-negative species.
Staphylococcus epidermidis is a catalase-negative species.
True
Enterococcus faecium is a Gram negative cocci.
Enterococcus faecium is a Gram negative cocci.
False
Staphylococcus saprophyticus is not associated with genitourinary tract infections.
Staphylococcus saprophyticus is not associated with genitourinary tract infections.
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Staphylococcus epidermidis can cause severe infections in immunosuppressed patients.
Staphylococcus epidermidis can cause severe infections in immunosuppressed patients.
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Streptococcus pyogenes is part of the Enterococcus genus.
Streptococcus pyogenes is part of the Enterococcus genus.
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Staphylococcus aureus can produce IgA proteases to destroy IgA antibodies.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
