Podcast
Questions and Answers
What are the two medically important genera of gram-positive cocci?
What are the two medically important genera of gram-positive cocci?
- Streptococcus and Salmonella
- Staphylococcus and Streptococcus (correct)
- Streptococcus and Bacillus
- Staphylococcus and Escherichia
Staphylococci and streptococci are motile and capable of forming spores.
Staphylococci and streptococci are motile and capable of forming spores.
False (B)
Which of the following is a characteristic difference between staphylococci and streptococci?
Which of the following is a characteristic difference between staphylococci and streptococci?
- Streptococci degrade hydrogen peroxide
- Staphylococci appear in grapelike clusters (correct)
- Staphylococci are found in chains
- Streptococci are catalase-positive
What is the name of the enzyme that staphylococci produce, which degrades hydrogen peroxide?
What is the name of the enzyme that staphylococci produce, which degrades hydrogen peroxide?
Which of these species of Staphylococcus are important human pathogens?
Which of these species of Staphylococcus are important human pathogens?
Which of the following is NOT a common cause of infection by Staphylococcus aureus?
Which of the following is NOT a common cause of infection by Staphylococcus aureus?
What is the most common cause of bacterial conjunctivitis?
What is the most common cause of bacterial conjunctivitis?
Which species of Staphylococcus is known to cause prosthetic valve endocarditis and prosthetic joint infections?
Which species of Staphylococcus is known to cause prosthetic valve endocarditis and prosthetic joint infections?
Staphylococcus saprophyticus is primarily found in the gastrointestinal tract and is a common cause of gastrointestinal infections.
Staphylococcus saprophyticus is primarily found in the gastrointestinal tract and is a common cause of gastrointestinal infections.
What is the primary reservoir for staphylococci?
What is the primary reservoir for staphylococci?
Which of the following is a common site of Staphylococcus aureus colonization?
Which of the following is a common site of Staphylococcus aureus colonization?
Handwashing is an ineffective method for reducing the transmission of staphylococci.
Handwashing is an ineffective method for reducing the transmission of staphylococci.
Where is Staphylococcus epidermidis primarily found?
Where is Staphylococcus epidermidis primarily found?
Where is Staphylococcus saprophyticus primarily found?
Where is Staphylococcus saprophyticus primarily found?
Which of the following is NOT a type of pathogenesis associated with Staphylococcus aureus?
Which of the following is NOT a type of pathogenesis associated with Staphylococcus aureus?
Match the Staphylococcus species with their typical disease manifestations.
Match the Staphylococcus species with their typical disease manifestations.
Which of the following is a clinical finding that can be caused by Staphylococcus aureus?
Which of the following is a clinical finding that can be caused by Staphylococcus aureus?
What are the two main groups that the clinical manifestations caused by Staphylococcus aureus can be divided into?
What are the two main groups that the clinical manifestations caused by Staphylococcus aureus can be divided into?
Flashcards
Staphylococci
Staphylococci
Spherical, gram-positive bacteria arranged in clusters resembling grapes. They produce catalase, an enzyme that breaks down hydrogen peroxide.
Staphylococcus aureus
Staphylococcus aureus
A common cause of skin infections like boils, folliculitis, and impetigo. It can also cause serious conditions such as pneumonia, endocarditis, and toxic shock syndrome.
Staphylococcus epidermidis
Staphylococcus epidermidis
A common inhabitant of human skin, usually harmless but can cause infections, especially in those with compromised immune systems. It's often associated with infections in prosthetic devices like heart valves and joints.
Staphylococcus saprophyticus
Staphylococcus saprophyticus
A causative agent of urinary tract infections, particularly cystitis (bladder infection). It's more common in young, sexually active women.
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Abscess
Abscess
A collection of pus caused by an infection. It can occur in various parts of the body, usually caused by bacteria like S. aureus.
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Pyogenic Infections
Pyogenic Infections
Infections characterized by the formation of pus. Examples include boils, carbuncles, and cellulitis.
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Endocarditis
Endocarditis
Inflammation of the inner lining of the heart, often caused by bacteria, commonly by S. aureus and viridans streptococci.
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Osteomyelitis
Osteomyelitis
Inflammation of the bone and bone marrow. It can be caused by S. aureus, commonly affecting the long bones in children.
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Septic Arthritis
Septic Arthritis
Inflammation of a joint, usually caused by infection. S. aureus is a common culprit.
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Septicemia
Septicemia
A serious condition caused by bacteria entering the bloodstream. It can lead to organ damage and even death.
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Pneumococcal Pneumonia
Pneumococcal Pneumonia
A bacterial infection of the lungs, often caused by S. aureus. It can be a major complication of other illnesses.
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Pathogenesis
Pathogenesis
The process by which pathogens invade, multiply, and cause disease in the body.
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Streptococci
Streptococci
A group of gram-positive, nonmotile, and nonspore-forming bacteria arranged in chains. They are catalase-negative.
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Hemolysis
Hemolysis
The ability of bacteria to break down red blood cells in blood agar, leading to different zones of hemolysis: alpha (green), beta (clear), and gamma (no hemolysis).
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Streptococcus pyogenes (Group A Streptococcus)
Streptococcus pyogenes (Group A Streptococcus)
A common cause of strep throat (pharyngitis), skin infections like impetigo and cellulitis, and several other conditions.
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Streptococcus agalactiae (Group B Streptococcus)
Streptococcus agalactiae (Group B Streptococcus)
A significant cause of infections in newborns, including sepsis and meningitis.
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Viridans Group Streptococci
Viridans Group Streptococci
Often found in the mouth, these streptococci cause dental caries (cavities) and are a major cause of infective endocarditis, especially following dental procedures.
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Streptococcus pneumoniae (Pneumococci)
Streptococcus pneumoniae (Pneumococci)
A gram-positive, lancet-shaped bacteria commonly found in pairs or short chains. They are known for causing pneumonia, meningitis, otitis media, and other respiratory infections.
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Capsular Polysaccharide
Capsular Polysaccharide
The ability of S. pneumoniae to produce a capsule around their cell wall, making them more resistant to host defenses.
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C-Substance
C-Substance
A substance in the cell wall of S. pneumoniae that reacts with C-reactive protein (CRP), a marker of inflammation.
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IgA protease
IgA protease
An enzyme produced by S. pneumoniae that breaks down IgA antibodies, allowing the bacteria to colonize the respiratory tract more easily.
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Pneumolysin
Pneumolysin
A toxin produced by S. pneumoniae that contributes to its virulence by damaging host cells.
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Antimicrobial Drug Treatment
Antimicrobial Drug Treatment
The use of antibiotics to treat infections. The choice of antibiotics depends on the specific bacteria involved and patient factors.
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13-Valent Pneumococcal Conjugate Vaccine
13-Valent Pneumococcal Conjugate Vaccine
A type of pneumococcal vaccine that uses the capsular polysaccharide of 13 common strains conjugated to a carrier protein, making it more effective in children.
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23-Valent Pneumococcal Vaccine
23-Valent Pneumococcal Vaccine
A type of pneumococcal vaccine that uses the capsular polysaccharide of 23 common strains, recommended for healthy individuals over 50 years old.
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Booster Dose
Booster Dose
A booster dose of pneumococcal vaccine is recommended for individuals with increased risk of severe pneumococcal infections.
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Gram-Positive Cocci
- Gram-positive cocci are medically important bacteria
- Two medically important genera are Staphylococcus and Streptococcus
- Staphylococcus and Streptococcus are nonmotile and do not form spores
- These bacteria are distinguished by microscopic and biochemical criteria
Staphylococcus
- Microscopic Appearance: Staphylococci appear in grape-like clusters
- Biochemical Properties: All staphylococci produce catalase
- Virulence Factor: Catalase degrades hydrogen peroxide, important for virulence
- Important Human Pathogens: S. aureus, S. epidermidis, S. saprophyticus
Staphylococcus Aureus
- Diseases caused by S. aureus include abscesses, pyogenic infections (e.g., endocarditis, septic arthritis, osteomyelitis), food poisoning, scalded skin syndrome, and toxic shock syndrome.
- Common Causes: Hospital-acquired pneumonia, septicemia, surgical-wound infections, skin and soft tissue infections (folliculitis, cellulitis, impetigo), and conjunctivitis
- Transmission: Human's bodies are the reservoir. The nose is the main site of colonization for S. aureus and approximately 30% of people are colonized. The skin, particularly of hospital personnel and patients, is also a common site of S. aureus colonization. Hand contact is an important mode of transmission.
- Pathogenesis: Toxigenic (superantigen) and pyogenic (abscess) infections. Local and disseminated infections. (refer to subsequent slides for specific toxins)
- Clinical findings: Pyogenic and toxin-mediated. Pyogenic infections include abscess, impetigo, furuncles, cellulitis, folliculitis, conjunctivitis, eyelid infections, and septicemia (originates from any localized lesions). Toxin-mediated diseases include food poisoning, toxic shock syndrome, and scalded skin syndrome.
- Treatment: Mostly resistant to penicillin G. Treated with β-lactamase-resistant penicillins (e.g., nafcillin or cloxacillin), some cephalosporins, or vancomycin. Combination therapy using a β-lactamase-sensitive penicillin (e.g., amoxicillin) and a β-lactamase inhibitor (e.g., clavulanic acid) is also useful. Methicillin-resistant S. aureus (MRSA) or nafcillin-resistant S. aureus (NRSA) strains require vancomycin.
- Prevention: Reduce time of tampon use and refrigerate food. Maintain cleanliness and handwashing to reduce nasal carriage. Reduce IV drug use. Handle IV catheters promptly.
Staphylococcus Epidermidis
- Diseases caused by S. epidermidis include prosthetic valve endocarditis and prosthetic joint infections, central nervous system shunt infections, and cause of sepsis in newborns
- Treatment: Penicillins. Prolonged treatment with penicillin.
Staphylococcus Saprophyticus
- Diseases caused by S. saprophyticus: urinary tract infections, especially cystitis
- Treatment: Penicillins.
Streptococcus
- Important Properties: Family of G+ve, nonmotile, non-spore forming, catalase-negative cocci
- Common Facultative Anaerobic Cocci: The most common facultative anaerobic cocci
- Hemolysis: Divided into three groups based on their ability to induce hemolysis on blood agar: α-hemolytic, β-hemolytic, γ-hemolytic
Streptococcus Pyogenes
- Diseases caused by S. pyogenes: Leading bacterial cause of pharyngitis, cellulitis, impetigo, necrotizing fasciitis, streptococcal toxic shock syndrome, rheumatic fever, and acute glomerulonephritis (AGN)
- Transmission: Part of the normal flora of the throat, skin, and intestines, but produce disease when accessing tissues or blood. Found in the pharynx in small numbers, but also skin.
- Pathogenesis: Pyogenic, toxigenic, immune-mediated (post-streptococcal)
- Clinical findings: Pharyngitis (sore throat, inflamed throat, and tonsils), Otitis media, mastoiditis, sinusitis, and meningitis
- Treatment: Penicillin G or Amoxicillin. Penicillin V for mild cases, Erythromycin or Azithromycin for penicillin-allergic patients.
Streptococcus Agalactiae
- Diseases caused by S. agalactiae: Leading cause of neonatal sepsis and meningitis
- Transmission: Found in the vagina and colon
Streptococcus Pneumoniae
- Important Properties: Gram-positive lancet-shaped cocci, arranged in pairs (diplococci) or short chains
- Diseases caused by S. pneumoniae: Pneumonia, bacteremia, meningitis, otitis media, mastoiditis, sinusitis
- Transmission: Part of the normal flora in the oropharynx
- Pathogenesis: Capsular polysaccharide, lipoteichoic acid, pneumolysin
- Clinical findings: Sudden chill, fever, cough, pleuritic pain, red or brown sputum (“rusty” sputum). Bacteremia occurs in 15-25% of cases. Spontaneous recovery in 5-10 days. Leading cause of sepsis in patients without a functional spleen.
- Treatment: Penicillins and Erythromycin. In penicillin-allergic patients, Erythromycin or Azithromycin (long-acting derivatives) are used. In severe cases, penicillin G is preferred; in mild cases, oral penicillin V might suffice. Vancomycin is used for penicillin-resistant pneumococci. Ceftriaxone or levofloxacin for less severely ill patients.
- Prevention: Vaccination with 13-valent pneumococcal conjugate vaccine (important for immunocompromised and young children). Unconjugated 23-valent pneumococcal vaccine for healthy adults age 50+
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