Gram-positive cocci

Question 1

Where are Staphylococci found?

Answer 1

Skin/nasal commensals in 80% of adults

Question 2

What are the features of staphylococci?

Answer 2

• Gram-positive cocci
• Facultative anaerobes
• Produce catalse
• Coagulase positive or negative

Question 3

What diseases does Staph. Aureus cause?

Answer 3

• Local tissue destruction: Impetigo, cellulutis, septic arthritis, osteomyeliti, abscesses, pneumonia, UTI
• Haematogenous spread: Infective endocarditis

Question 4

What does the toxin in Staph Aureus do?

Answer 4

1. Toxic shock syndrome

Diagnostic criteria:

• fever >38.9
• hypotension (SBP<90)
• diffuse erythematous rash
• desquamation of rash esp. of palms and soles
• involvement of 3 or more organ systems (GI D/V, mucous membrane erythema, renal failure, hepatitis, thrombocytopenia, CNS involvement such as confusion)
• NB: Tampon associated or occurs with (minor) local infection.

2. Scalded skin syndrome: bullae and desquamation due to epidermolytic toxins

Preformed toxin in food—sudden D&V

Question 5

Is Staph. Aureus coagulase +ve or -ve?

Answer 5

Positive

A –> positive grade

Question 6

Describe the features of Staph. Epidermis

Answer 6

• Less virulent
• Only affects if immune system dysfunction or foreign material present e.g. prosthesis where it can form biofilms, central lines etc.

Question 7

Describe the features of Streptococci

Answer 7

Gram +ve cocci

Alpha or beta haemolytic

Question 8

How are streptococci classified?

Answer 8

Question 9

Describe Strep. Pneumonia

Answer 9

• Alpha haemolytic (partial haemolysis)
• Causes: Pneumonia, otitis media, meningitis, septicaemia.
• Treatment: penicillin.
• Vaccination: childhood, hyposplenism, >65y

Question 10

Describe Strep.Viridans

Answer 10

• Alpha haemolytic (partial haemolysis)
• Commonest cause of oral/dental origin endocarditis

Question 11

Describe Strep. pyogenes

Answer 11

• Group A, beta haemolytic (complete haemolysis) that colonizes throat, skin, anogenital tract.
• Range of infection: tonsillitis, pharyngitis, scarlet fever, impetigo, erysipelas, cellulitis, pneumonia, peripartum sepsis, necrotizing fasciitis.
• All can→ streptococcal toxic shock = sudden-onset ↓bp, multiorgan failure.
• Post-infectious complications rare: rheumatic fever, glomerulonephritis.
• Treatment: penicillin.

Question 12

Describe Strep. agalacticea

Answer 12

Group B, beta haemolytic (complete haemolysis)

causes:

• neonatal sepsis and meningitis
• Invasive disease (bacteraemia, endocarditis, osteomyelitis, septic arthritis, meningitis)
• usually has risk factors: DM, malignancy, chronic disease.

Treatment: penicillin, macrolide, cephalosporin, chloramphenicol.

Question 13

Describe Strep. Bovis

Answer 13

• Group D, gamma haemolytic (no haemolysis)
• Bacteraemia can cause endocarditis.
• Look for colon/liver disease.

Question 14

Describe enterococci

Answer 14

Gut commensal

Causes: intraabdominal sepsis, IE, UTI

Features:

• Inherent Resistance to Cephalosporins and Quinolones  leads to nosocomial colonization and infection
• Most common is Enterococcus faecalis: if found in blood culture, assume endocarditis until proven otherwise.

Vancomycin-resistant enterococci also exist

Question 15

Describe Strep. milleri

Answer 15

If found in blood culture look for an abscess—mouth, liver, lung, brain

Treatment: penicillin.