Staphylococcus Flashcards
There are two types of gram positive cocci and they are
catalase positive (clusters): Staph
Catalase negative (chains): Strep
staphylococci can be divided into two groups
coagulase positive: Staph Aureus
Coagulase negative: Staph
coagulase negative Staph can be devided to two groups
Novobiocin Sens: Staph Epidermidis
Novobiocin Res: Staph Saprophyticus
All Staphylococci are catalase
positive
Staph Aureus’s basic habitat
is the nares (nose)
30% of people carry the bacteria
Staphy Aureus produces
a yellow pigment ( Aureus: golden)
staphy Aureus: Protein A virulence factor
Blocks Fc-IgG interaction
prevents phagocytosis and complement activation
Since Staph Aureus is coagulase positive
it forms fibrin clots
Staph Aureus causes
Toxin diseases and infectious diseases
Toxin diseases that Staph Aureus causes
Toxic shock Syndrome (TSST-1)
Food poisoning ( Staph Aureus enterotoxin)
scalded skin syndrome ( Exfoliatin )
Infectious diseases caused by Staph Aureus
Skin infections ( Impetigo )
Pneumonia
Endocarditis
Osteomyelitis
Abscesses
classic scenarios for Toxic shock syndrome
Being exposed to staph + packing
women using tampons
Surgical wound with packing
Toxic shock Syndrome is caused by
Toxin ( TSST-1)
Symptoms are: fever, shock (hypotension), red rash
Diffuse, red erythroderma (resembles sunburn)
After weeks :desquamation of palms /soles
Diarrhea is common
Multi-organ system failure often results
Staph Food Poisoning
Food handler contaminates food
Food left at room temperature several hours .
Picnic is classic scenario
Bacteria grow in food > produce enterotoxin
Ingestion of preformed toxin causes disease
Gl illness develops ~3 to 6 hours later
Nausea, vomiting (diarrhea rare) ,Abdominal cramps Look for multiple sick people after eating at a picnic Classic food is mayonnaise in potato or egg salad
Scalded Skin Syndrom
Newborn disease Caused by S. Aureus exfoliative toxin (Exfoliatin) ○Classically occurs 3 to 7 days of age
Fever, difuse 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
Bullous Impetigo is caused by Staph Aureus
Impetigo = skin infection Caused by Group A strep or Staph Aureus, honey colored, crusted lesions
Bullae = fluid-filled sacs similar to blisters
Bullous impetigo caused by S. Aureust Classically occurs in children Easily spread one child to another
S. Aureus exfoliative toxin strains
Bullous Impetigo is Caused by Staph Aureus
Impetigo = skin infection Caused by Group A strep or Staph Aureus .Honey colored, crusted lesions
Bullae = fluid-filled sacs similar to blisters
Bullous impetigo caused by S. Aureus Classically occurs in children Easily spread one child to another
S. Aureus exfoliative toxin strains
Staph is rare cause of
lobar pneumonia
Classically occurs as “post-infectious””
Bacterial pneumonia following influenza
Staph Aureus is a classic cause of
ACUTE endocarditis
Rapid onset of symptoms, Very ill patient -often no pre-existing valve disease (ie. mitral valve prolapse)
Contrast with subacute > Strep Viridans
Slower onset of symptoms, Less sick patient
Prior valve abnormality
Staph Aureus can be passed through
Intravascular devices
“Central lines”
Common cause of staph bacteremia
Most important preventative measure is sterile
technique: Wash hands, Gloves, Sterile insertion practices
Osteomyelitis is a rare infection but a common cause is
Staph Aureus
Children: Usually long bones (femur, tibia, fibula) Adults: Usually spine
Mechanisms: Hematogenous spread, Spread from skin/soft tissues ,Trauma (surgery)
Symptoms uusually localized pain +/- fever
Diagnosis made by imaging (CXR, CT scan, MRl)
Osteomyelitis Classic Causes
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
Cellulitis
Infection of deep dermis and subcutaneous fat
Mostly caused by B-hemolytic streptococci
S Aureus can also cause
Antibiotics must cover Staph
