B1. Gram positives Flashcards
What is the gross appearance of the colonies for staph aureus?
Grape-like clusters
Golden yellow colonies
How do you tell apart staph and strep?
staph are all catalase positive
catalase is enzyme that converts H2O2 to water
How do you tell staph aureus apart from the other staphs?
S. aureus is coagulase positive, all other Staphs are coagulase negative
Coagulase is enzyme that converts fibrinogen to fibrin
What are the five characteristics on a petri-dish that you would see with staph a?
- Gram positive (violet)
- Catalase positive (tells you its staph)
- Coagulase positive (tells you its staph a)
- Beta-hemolytic (hemolysis of blood)
- Ferments mannitol (agar turns yellow)
What is the main virulence factor for staph a?
Protein A
is a component of the cell wall that binds the Fc portion of antibodies, preventing opsonization
What are the nine diseases caused by staph a?
Pneumonia Septic arthritis Skin infections - abscesses Acute bacterial endocarditis Osteomyelitis Scalded-skin syndrome Toxin shock syndrome Staph food poisoning MRSA
What is the appearance on x-ray film of a staph aureus infections?
patchy infiltrate
What is the most common cause of septic arthritis?
Staph aureus
Where does staph aureus like to colonize?
nares
What is the most common cause of osteomyelitis in adults?
staph aureus
What are the toxin-mediated diseases caused by staph aureus?
Scalded-skin syndrome (expholiative toxin)
Toxin shock syndrome (leaving in a foreign body too long, TSS is a superantigen causing overactivation and cytokine storm)
Food poisoning - pre-formed toxin causes acute vomitting due to meats and mayo
What is altered in MRSA?
penicillin binding proteins that are part of cell walls
How do you tx MRSA?
Methicillin-sensitive staph?
MRSA: Vancomycin
Methicillin-sensitive is treated by nafcilin (Naf for Staf)
What is the most common cause of endocarditis of artificial heart valves?
Staph epidermis
How do you treat a staph epidermidis ifx?
vancomycin
What organism is usually linked to infections that arise from prosthetic joints, indwelling catheters
staph epidermidis
Why doe staph epidermidis cause blood culture contamination so much?
Because it’s part of the normal skin flora, so it’s easy for it to contaminate samples (e.g. drawing blood through needle)
How do you tell the difference between staph aureus and staph epidermidis/saprophyticus
Staph aureus is coagulase positive
Staph epidermidis/saprophyticus is coagulase negative
How do you tell the difference between staph epidermidis and saprophyticus
Novobiocin sensitivity
Novobiocin sensitive = S. epidermidis
Novobiocin resistant = S. saprophyticus
Which staph bacteria produces biofilms?
S. epidermidis
What is a common cause of UTIs in sexually active female?
S. saprophyticus
Relate the following characteristics for staph saprophyticus: coagulase, catalse, urease
Catalse + (so it’s staph)
Coagulase - (so it’s not staph a)
Urease + (so it’s s. saprophyticus)
What does urease do?
converts urea to ammonia
What does coagulase do?
Coagulase converts fibrinogen to fibrin
What does catalase do?
Converts H2O2 to water
What does beta-hemolytic mean?
Complete hemolysis of rbc
Fermenting mannitol turns the agar what color?
Yellow
What bacteria is considered to be Group A Strep?
Strep pyogenes
Which strep is encapsulated and contains hyaluronic acid? is it immunogenic?
Group A strep pyogenes
No, not immunogenic
What three skin infections does Group A strep cause?
Impetigo (honey crusted)
Pharyngitis (strep throat)
Erysipela and cellulitis
What is the most common cause of erysepilas
S. pyogenes
What are the three toxin-mediated diseases of Strep pyogenes?
Scarlet fever, toxic shock-like syndrome, necrotizing fasciitis
What are the three characteristics of scarlet fever
- Strawberry tongue
- Pharyngitis
- Wide-spread rash sparring the face
What is necrotizing fasciitis? What causes it?
Necrotizing invades fascia underlying skin and spreads rapidly
Caused by GAS (SPE-B)
What are SPE-A, SPE-B, SPE-C? What do they cause?
SPE = strep pyrogenic exotoxin
A, C cause Toxic shock-like syndrome
B causes necrotizing fasciitis
M Protein, which bac? What does it do?
What does it lead to?
Found in GAS (pyrogenes)
Main virulence factor
Interferes with opsonization = antiphagocytic
Induces strong humoral response = autoantibody production against cardiac myosin, leading to damaged heart valves
THIS IS RHEUMATIC FEVER
What valve is most likely damaged with a staph aureus infection?
Tricuspid valve (due to right-sided endocarditis)
What valve is most likely damaged with a strep pyogenes GAS infection?
Mitral valve
What are the symptoms of rheumatic fever?
J - polyarthritis
O - heart problems (valve damage –> murmurs, myocarditis, pericarditis)
N - subcutaneous Nodules
E - erythema marginatum
S - Sydenham’s chorea (rapid involuntary movements of hands and face)
What is Sydenham’s chorea? What infection and condition do you see it with?
Rapid involuntary movements of hands and face
GAS
Rheumatic fever
What bacterial infection do you see PSGN in?
GAS (pyogenes)
How long after a GAS infection do you see PSGN?
2 weeks
What are some clinical features of PGSN?
Dark brown or cola colored urine
facial swelling and puffiness (edema)
What are the two ways to tell RF and PSGN apart?
- RF occurs after pharyngitis, PSGN occurs after pharyngitis or skin infection
- Early dx and tx of strep throat can prevent RF but not PSGN
How do you treat GAS?
Penicillin
What are the three main virulence factors for GAS?
- Stretolysin O
- Stretokinase
- DNase
What does Stretolysin O do? CLinical significance?
Allows bac to lyse RBC and do beta-hemolysis
AB generated against SO. ASO titers reveal strep infection occurred recently
What does stretokinase do? Clinical significance?
Converts plasminogen –> plasmin (which is fibrinolytic)
Given as medication to bust clots. Used in MIs, strokes, etc
How do you tell apart GAS and GBS in terms of antibiotics?
GAS (pyrogenes) is bacitracin SENSITIVE
GBS is bacitracin RESISTANT
What is the enzyme that cross links the dissachs in the CW to make the peptidoglycan layer?
What inactivates this enzyme?
Another name for this enzyme?
Tanspeptidase located in the inner cytoplasmic
membrane
Penicillin binds to
and inhibits it. For this reason the enzyme is
also called penicillin binding protein
What is the importance of teichoic acid?
Polysacch present in gram (+) bacteria
Important for identification of bacteria
Group B strep is what organism?
S. agalactiae
The hippurate test tells you what?
Which organism is positive for the hippurate test?
(+) Hippurate test shows that organism can hydrolyze hippurate
GBS (S. agalactiae)
What is the CAMP test? Which organism is positive for CAMP test?
CAMP test is when you plate organism with S. aureus. (+) CAMP means that the zone of hydrolysis increased w/ S. aureus presence
GBS (agalactiae)
What sets S. agalactiae apart from GAS?
Bacitracin resistant
How do you tell if S. agalactiae is different than strep pneumo and viridans?
S. agalactiae is beta hemolytic
What is the no. 1 cause of meningitis in neonates?
S. agalactiae
S. agalactiae causes which diseases? (3)
- meningitis in neonates
- sepsis
- pneumonia
How does a neonate contact GBS? What is done to prevent this?
During delivery, if mother has GBS in vaginal canal, baby will get GBS infection
Penicillin is given prophylactically
