Staphlococci

Question 1

Staph Aureus Special Features

1. Basic habitat is ___
2. Produces a ___ pigment (aureus = __)
3. ___-hemolytic
4. Coagulase___
5. ___ virulence factor - does these 2 things
6. Produces several ____

Answer 1

1. Basic habitat is the nares (nose) • 30% of people carry the bacteria
2. Produces a yellow pigment (aureus = golden)
3. Beta-hemolytic
4. Coagulase (+) • Forms fibrin clot
5. Protein A virulence factor • Blocks Fc-IgG interaction • Prevents phagocytosis & complement activation
6. Produces several toxin-related diseases

Question 2

Staph Aureus Infections

3 toxin diseases:

5 infectious diseases

Answer 2

Toxin disease

Toxic Shock Syndrome (TSST-1) • Food poisoning (Staph aureus enterotoxin) • Scalded skin syndrome (Exfoliatin) •

Infectious diseases

Skin infections (Impetigo) • Pneumonia(rare-“post-infectious” meaning Bacterial pneumonia following influenza) • Endocarditis • Osteomyelitis • Abscesses

Question 3

Staph Food Poisoning sequence of events

Answer 3

Food handler contaminates food → Food left at room temperature [Picnic is classic scenario] → Bacteria grow in food → produce enterotoxin → Ingestion of preformed toxin causes disease • GI illness develops ~3 to 6 hours later QUICK!

Nausea, vomiting (diarrhea rare) • Abdominal cramps

Look for multiple sick people after eating at a picnic

Classic food is mayo in potato or egg salad

Question 4

Scalded Skin Syndrome

age affected:

caused by:

symptoms:

Answer 4

NEWBORN disease (Classically occurs 3 to 7 days of age )

Caused by S. Aureus exfoliative toxin (Exfoliatin)

Fever, diffuse erythema starting at the mouth • Sloughing of skin

Toxin destroys keratinocyte attachments in stratum granulosum only

Damage intraepidermal: Heals completely (no scar) •

Nikolsky’s sign: skin slips off with gentle tug

Question 5

type of Impetigo caused by Staph Aureus

Answer 5

Bullous Impetigo

Classically occurs in children • Easily spread one child to another • S. Aureus exfoliative toxin strains

Question 6

Endocarditis- compare and contrast staph vs group a strep

Answer 6

Classic cause of ACUTE endocarditis • Rapid onset of symptoms • Very ill patient • Often no pre-existing valve disease (i.e. mitral valve prolapse)

Contrast with subacute → Strep Viridans • Slower onset of symptoms • Less sick patient • Prior valve abnormality

Question 7

Common cause of staph bacteremia prevented by sterile tecnique:

Answer 7

Intravascular devices • “Central lines”

Question 8

Osteomyelitis

S. Aureus is ___ cause of osteomyelitis

Children: ___ Adults:___

Mechanisms: (3)

Symptoms __

Diagnosis made ___

Answer 8

S. Aureus is common cause of osteomyelitis

Children: Usually long bones (femur, tibia, fibula) • Adults: Usually spine

Mechanisms: • Hematogenous spread • Spread from skin/soft tissues • Trauma (surgery)

Symptoms usually localized pain +/- fever

Diagnosis made by imaging (CXR, CT scan, MRI)

Question 9

Osteomyelitis Classic Causes

Child :

Sickle Cell patient :

TB patient :

Diabetic :

Bedbound patients :

Answer 9

Child • Staph aureus (hematogenous spread)

Sickle Cell patient • Salmonella (hematogenous spread)

TB patient • Pott’s disease (vertebrae/spine)

Diabetic • Polymicrobial from foot ulcer

Bedbound patients • Polymicrobial from pressure sores

Question 10

Cellulitis Mostly caused by

Answer 10

Mostly caused by β-hemolytic streptococci but s aureus can also be guilty

Question 11

Skin abscesses commonly caused by :

Answer 11

• Skin abscesses commonly caused by S. Aureus!!!
• Mainstay of treatment is incision and drainage

Question 12

Staph Aureus Antibiotics

Most strains of Staph resistant to:

3 drug options:

Answer 12

Most strains of Staph resistant to penicillin b/c they Produce beta-lactamases. that inactivate penicillin

1. ) Antistaphylococcal penicillins • Dicloxacillin, Nafcillin, Oxacillin
2. )First generation cephalosporins • Cephalexin
3. )Beta lactam plus inhibitor • Amoxicillin/clavulanate

Question 13

MRSA

Resistant to ___ because:

treat with:

Answer 13

Resistant to all beta lactams b/c of Altered penicillin binding proteins (PBPs)

Important hospital-acquired bacteria • Sometimes community acquired

treat with: Vancomycin or daptomycin: antibiotics of choice • (Can also use Linezolid)

Question 14

Staph Epidermidis

Normal skin flora; two clinical implications

resistance to:

treatment:

Answer 14

1: Blood culture contaminant • Needle/IV contaminated by S. epi

Normal skin flora; two clinical implications

Often methicillin resistant

Treatment: Vancomycin

Question 15

Staph Saprophyticus

Cause of __ especially :

2 key features

treatment:

Answer 15

Cause of UTIs especially in sexually active women- Most caused by E. Coli (~90%) • Other bugs: Proteus, Klebsiella, S. Saprophyticus

Key features: • Sexual activity (honeymooner’s cystitis)

Nitrite negative on urine dipstick

Treated by UTI antibiotics • Fluoroquinolones • SMX-TMP • Nitrofurantoin