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?
Staphylococci and streptococci are motile and capable of forming spores.
Staphylococci and streptococci are motile and capable of forming spores.
False
Which of the following is a characteristic difference between staphylococci and streptococci?
Which of the following is a characteristic difference between staphylococci and streptococci?
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?
Signup and view all the answers
Which of these species of Staphylococcus are important human pathogens?
Which of these species of Staphylococcus are important human pathogens?
Signup and view all the answers
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?
Signup and view all the answers
What is the most common cause of bacterial conjunctivitis?
What is the most common cause of bacterial conjunctivitis?
Signup and view all the answers
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?
Signup and view all the answers
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.
Signup and view all the answers
What is the primary reservoir for staphylococci?
What is the primary reservoir for staphylococci?
Signup and view all the answers
Which of the following is a common site of Staphylococcus aureus colonization?
Which of the following is a common site of Staphylococcus aureus colonization?
Signup and view all the answers
Handwashing is an ineffective method for reducing the transmission of staphylococci.
Handwashing is an ineffective method for reducing the transmission of staphylococci.
Signup and view all the answers
Where is Staphylococcus epidermidis primarily found?
Where is Staphylococcus epidermidis primarily found?
Signup and view all the answers
Where is Staphylococcus saprophyticus primarily found?
Where is Staphylococcus saprophyticus primarily found?
Signup and view all the answers
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?
Signup and view all the answers
Match the Staphylococcus species with their typical disease manifestations.
Match the Staphylococcus species with their typical disease manifestations.
Signup and view all the answers
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?
Signup and view all the answers
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?
Signup and view all the answers
Signup and view all the answers
Study Notes
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+
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the key characteristics and medical significance of gram-positive cocci, focusing on genera like Staphylococcus and Streptococcus. Learn about their microscopic appearance, biochemical properties, and the diseases caused by Staphylococcus aureus. This quiz will provide essential insights into these important pathogens.
