Gram-Positive Cocci in Medicine

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Questions and Answers

What is the most significant virulence factor of Streptococcus pneumoniae?

Capsule

Besides pneumonia, what are two other common infections caused by Streptococcus pneumoniae?

Acute otitis media, meningitis

What is the primary habitat of Enterococci in humans?

Gastrointestinal tract

What is the leading cause of neonatal sepsis and meningitis?

Streptococcus agalactiae (GBS) Signup and view all the answers

Name two infections, other than UTIs, that are commonly caused by enterococci.

Septicemia, infective endocarditis Signup and view all the answers

Besides secondary infections, what is another potential complication of S.aureus?

Bacteraemia Signup and view all the answers

What specific medical product was significantly linked to the rise of menstrual toxic shock syndrome in the early 1980s?

Super-absorbent tampons Signup and view all the answers

Besides menstruation, what other situation or procedure can be a source of non-menstrual toxic shock syndrome?

Localized infections or surgery Signup and view all the answers

What is the appearance of the rash associated with toxic shock syndrome?

Sunburn-like or erythematous Signup and view all the answers

What is the process that skin goes through after the rash appears in toxic shock syndrome?

Desquamation Signup and view all the answers

What is the name of the toxins produced by S. aureus that function as superantigens?

Enterotoxins, epidermolytic toxins and TSST-1 Signup and view all the answers

What type of immune cell is directly stimulated by superantigens, leading to a large cytokine release?

T cells Signup and view all the answers

What is the first step in the laboratory investigation of an S. aureus infection?

Collecting specimens Signup and view all the answers

What is the primary site of colonization for Staphylococcus aureus?

Anterior nares Signup and view all the answers

Name one condition associated with a higher risk of S. aureus carriage.

Type 1 diabetes, IV drug use, hemodialysis, skin diseases, or working in healthcare. Signup and view all the answers

What is the second most common cause of urinary tract infections in young females?

Staphylococcus saprophyticus Signup and view all the answers

What is the skin infection that is characterized by an infection of the hair follicle?

Folliculitis Signup and view all the answers

What is a deeper infection in and around the hair follicle that may develop from untreated folliculitis?

Furuncle (boil) Signup and view all the answers

Name two arrangements of Streptococcus bacteria.

Pairs and chains Signup and view all the answers

Name one specific infection categorized as an invasive infection caused by S. aureus.

Folliculitis, furunculosis, carbuncle, impetigo, wound infection, cellulitis, abscess, osteomyelitis, septic arthritis, pneumonia Signup and view all the answers

What is a key feature that differentiates streptococci from staphylococci based on a lab test?

Streptococci are catalase negative Signup and view all the answers

What toxin produced by S. aureus is responsible for staphylococcal scalded skin syndrome?

Epidermolytic toxin (exfoliatin) Signup and view all the answers

Name two virulence factors of Streptococcus pyogenes.

M protein, Streptolysin O Signup and view all the answers

Name one skin infection caused by Streptococcus pyogenes.

Impetigo Signup and view all the answers

What is the common source of contamination in staphylococcal food poisoning?

Contaminated food by colonized or infected food handlers. Signup and view all the answers

What is the typical time frame in which symptoms of staphylococcal food poisoning occur after ingestion of contaminated food?

1-6 hours Signup and view all the answers

Besides pharyngitis, what is another disease caused by S. pyogenes characterized by a rash and circumoral pallor?

Scarlet fever Signup and view all the answers

What is the characteristic feature of erysipelas' margins?

Sharply demarcated Signup and view all the answers

What is the typical habitat of viridans streptococci?

Oral cavity and upper respiratory tract Signup and view all the answers

What is the literal Greek origin of the name Staphylococcus?

"bunch of grapes" and "grain or berry" Signup and view all the answers

What is the appearance of Staphylococcus bacteria when gram stained?

gram-positive cocci in grape-like clusters Signup and view all the answers

What are the two major categories of Staphylococcus species based on the coagulase test?

Coagulase-positive and Coagulase-negative Signup and view all the answers

Name the most clinically significant coagulase-positive Staphylococcus species.

Staphylococcus aureus Signup and view all the answers

What are two common coagulase-negative Staphylococcus species?

Staphylococcus epidermidis and Staphylococcus saprophyticus Signup and view all the answers

Describe the typical colony morphology of S. aureus on blood agar.

sharply defined, round, convex, smooth, 1-4 mm diameter, pale yellow to dark orange, complete haemolysis Signup and view all the answers

What is the optimal growth temperature for S. aureus?

37°C Signup and view all the answers

What is the typical colony appearance of Staphylococcus aureus on blood agar, and what type of hemolysis does it exhibit?

White colonies with no complete hemolysis Signup and view all the answers

What is the name of the carotenoid pigment produced by S. aureus that gives it a golden color?

staphyloxanthin Signup and view all the answers

What is a primary habitat for Staphylococcus epidermidis in humans?

Skin and mucous membranes Signup and view all the answers

In what type of patient is Staphylococcus epidermidis a major cause of infection?

Hospitalized, immunocompromised, and those with indwelling foreign bodies Signup and view all the answers

What is a major factor in the pathogenesis of Staphylococcus epidermidis polymer-associated infections?

Biofilm formation Signup and view all the answers

Name two types of infections associated with intravascular catheters that can be caused by Staphylococcus epidermidis.

Bacteremia and peritonitis Signup and view all the answers

Besides intravascular catheters, name two other types of prosthetic devices that Staphylococcus epidermidis can infect.

Prosthetic heart valves and pacemakers Signup and view all the answers

What is the most common type of endocarditis caused by Staphylococcus epidermidis?

Early prosthetic valve endocarditis Signup and view all the answers

How does the clinical presentation of S. epidermidis infections typically differ from S. aureus infections?

Subtle, non-specific and subacute, with a long latent period Signup and view all the answers

Study Notes

Gram-Positive Cocci of Medical Importance

Gram-positive cocci are spherical bacteria that are important for medical reasons
Key genera include Staphylococcus, Streptococcus, and Enterococcus
These bacteria cause a variety of infections

Staphylococcus

Discovered in 1881 by Sir Alexander Ogston
Greek meaning: staphyle = bunch of grapes, kokkos = grain or berry
Microscopic appearance: Gram stain reveals grape-like clusters of gram-positive cocci
Different species classified as coagulase-positive and coagulase-negative
- Coagulase-positive: Staphylococcus aureus
  - Causes various diseases in humans, even in healthy hosts
  - Produces many virulence factors, including cell surface proteins and toxins
  - Examples of diseases caused by Staphylococcus aureus: toxic shock syndrome and Staphylococcal Scalded Skin Syndrome
- Coagulase-negative: Staphylococcus epidermidis and Staphylococcus saprophyticus
  - Staphylococcus epidermidis: Common cause of infection in hospitalised patients with indwelling devices
  - More common cause of nosocomial infections and resistant to many antibiotics
  - Staphylococcus saprophyticus: Common cause of urinary tract infections (UTIs) in young, sexually active women

Streptococcus

Gram-positive oval or spherical cocci occurring in pairs or chains
Catalase-negative
Important species for human infection include Streptococcus pyogenes (GAS), Viridans streptococci, Streptococcus pneumoniae, and Streptococcus agalactiae (GBS)

Streptococcus pyogenes (GAS)

Colonises the nasopharynx and skin
Produces several virulence factors like M protein, Streptolysins O and S, Streptococcal pyrogenic exotoxins (SPEs), and spreading factors (hyaluronidase, deoxyribonuclease, streptokinase)
Causes various infections, including acute pharyngitis/tonsillitis, scarlet fever, impetigo, erysipelas, cellulitis, sepsis, necrotizing fasciitis, toxic shock syndrome, puerperal sepsis, endocarditis, pneumonia (post-viral), and non-suppurative sequelae like acute rheumatic fever and acute glomerulonephritis.

Viridans streptococci

Heterogeneous group
Important species include S. sanguinis, S. mitis, S. mutans, S. anginosus
Normal habitat: oral cavity and upper respiratory tract
Cause dental caries, plaques, periodontal diseases, infective endocarditis, bacteraemia, and deep-seated abscesses

Streptococcus pneumoniae

Also known as pneumococcus
Gram-positive cocci in pairs (diplococci)
Important virulence factor: capsule
Causes pneumonia, acute exacerbations of COPD, acute otitis media, sinusitis, meningitis, and bacteraemia (in splenectomised patients)

Enterococci

Previously grouped with group D streptococci
Enterococcus faecalis and Enterococcus faecium are the most commonly associated with human diseases
Inhabit the gastrointestinal tract of humans and animals
Important cause of nosocomial infections: urinary tract, septicaemia, infective endocarditis, wound, intra-abdominal, and pelvic infections

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Description

Explore the significance of gram-positive cocci, including Staphylococcus, Streptococcus, and Enterococcus. This quiz covers their characteristics, classifications, and the infections they cause in humans. Test your knowledge on the medical importance of these spherical bacteria.