bacteria

Question 1

Coagulase negative vs positive staphylococci examples? virulence?

Answer 1

Coagulase-negative staphylococci - Staph epidermidis
positive - staph aureus

coagulase negative is less virulent - pathogenicity only likely if underlying immune system dysfunction or foreign material (prosthetic valve/joint, IV line, PD catheter, pacemaker)

Question 2

Different presentations of coagulase positive staphylococcus?

Answer 2

1. Toxin release causes disease distant from infection. Includes: Scalded skin syndrome (bullae and desquamation due to epidermolytic toxins
   (no mucosal disease, less skin loss compared to toxic epidermal necrolysis)
   preformed toxin in food - sudden D+V
   toxic shock: fever, confusion, rash, diarrhoea, low BP, AKI, multiorgan dysfunction.
   Tampon associated or occurs with (minor) local infection.
2. Local tissue destruction: impetigo, cellulitis, mastitis, septic arthritis, osteomyelitis,
   abscess, pneumonia, UTI.
3. Haematogenous spread: bacteraemia, endocarditis, ‘metastatic’ seeding.

Question 3

Symptoms of toxic shock? Causative organism

Answer 3

fever, confusion, rash, diarrhoea, low BP, AKI, multiorgan dysfunction.

coagulase positive staph

Question 4

How is staph aureus resistance defined?

Answer 4

by stability to meticillin, ie meticillin-resistant Staph. aureus (MRSA)

Question 5

How is vancomycin resistance classified in staph aureus?

Answer 5

classified according to the amount of vancomycin needed to inhibit
bacterial growth: vancomycin-intermediate Staph. aureus (VISA) and vancomycin-
resistant Staph. aureus (VRSA).

Question 6

Risk factors for MRSA colonisation?

Answer 6

antibiotic exposure, hospital stay, surgery, nursing home residence.

Question 7

MRSA infection treatment?

Answer 7

vancomycin (for MRSA), teicoplanin

Question 8

oral agents with activity against MRSE?

Answer 8

clindamycin, co-trimoxazole, doxycycline, linezolid

Question 9

What are the major classes of gram positive cocci?

Answer 9

staphylococci
streptococci
enterococci

Question 10

How are streptococci grouped?

Answer 10

by haemolytic pattern (alpha, beta,

or non-haemolytic), by Lancefield antigen (A–G), or by species.

Question 11

Which strep bacteria are beta haemolytic group A and beta haemolytic group B?

Answer 11

Streptococcus pyogenes (beta-haemolytic group A)
Streptococcus agalactiae (beta-haemolytic group B):

Question 12

Range of infection of strep pyogenes? Complication and symptoms/signs? Post-infectious complications? Tx?

Answer 12

tonsillitis, pharyngitis, scarlet fever, impetigo, erysipelas,
cellulitis, pneumonia, peripartum sepsis, necrotizing fasciitis

All can lead to streptococcal
toxic shock = sudden-onset low BP, multiorgan failure

Post-infectious complications
rare: rheumatic fever, glomerulonephritis

Treatment: penicillin

Question 13

Streptococcus agalactiae infection? risk factors of invasive disease? Tx?

Answer 13

neonatal and peurperal infection,
skin, soft tissue.
Invasive disease (bacteraemia, endocarditis, osteomyelitis,
septic arthritis, meningitis)
risk factors: DM, malignancy, chronic disease.

Treatment: penicillin, macrolide, cephalosporin, chloramphenicol.

Question 14

Streptococcus milleri sign.? Tx?

Answer 14

if found in blood culture look for an abscess—mouth, liver,

lung, brain. Treatment: penicillin

Question 15

Strep pneumoniae infection? Tx? When to vaccinate?

Answer 15

pneumonia, otitis media, meningitis, septicaemia.

Treatment: penicillin. Vaccination: childhood, hyposplenism, >65y

Question 16

What does viridans strep cause?

Answer 16

commonest cause of oral/dental origin endocarditis

Question 17

Strep bovis infection?

Answer 17

Bacteraemia –> endocarditis. Look for colon/liver disease

Question 18

Where are enterococci found? Which antibiotics are they resistant to? Most common?

Answer 18

Gut commensal

Resistant to quinolones and cephalosporins

most common is Enterococcus faecalis: if found in blood
culture, assume endocarditis until proven otherwise.