Staph Flashcards
What is the gram stain of staph?
Gm + clusters
What pattern of hemolysis does Staph show?
B hemolysis
Why is it called Staph aureus?
-grows yellow on culture Aureus = gold
Is S. aureus coagulase positive or negative?
Positive
What are the three layers of the staph capsule?
-microcapsule -capsule -slime (most external)
What layer of the staph capsule is used to serotype them?
-microcapsule
What are microbial surface components recognizing adhesive matrix molecules? (MSCRAMMS)
-structural features on staph held in common between surface proteins
What is protein A in staph?
-incorporated covalently into outer peptidoglycan layer -binds to Fc component of antibodies, except IgG3 -Antiphagocytic
What does coagulase do?
-interacts with fibrinogen D fragment to produce clumping, protects from phagocytosis -used in diagnostic tests to discriminate between S. aureus (+) and coagulase (-) staph in clinical specimens
What toxins are produced by staph?
-alpha, beta, gamma, and delta hemolysin toxins -Enterotoxins A, B, C1-2, D & E -Toxic Shock Syndrome Toxin I (TSST-1) -exofoliatins
What do alpha, beta, gamma, and delta toxins of staph do?
disrupt cell membranes =hemolysin -destroy RBCs, PMNs, and platelets
What are exofoliatins produced by staph do?
-scalded skin syndrome -act on stratum granulosum to produce rash, blisters, & exfoliation -act as superantigens
What do Enterotoxins A, B, C1-2, D & E produced by staph do?
-food poisoning -vomiting
What does Toxic Shock Syndrome Toxin I (TSST-1): produced by staph do?
-Superantigen that causes clonal expansion of resting T-cells & results in massive cytokine release
Who is at greater risk for staph colonization?
-Needle users -skin breaks -diabetics injecting insulin -allergy patients -dialysis -IV drug users
What are Clinical Clues That May Help Determine if a S. aureus Bacteremia is Due to a Complicated Infection and/or Endocarditis?
Younger patient without underlying illnesses; -Community-acquired (e.g., illicit drugs); -No recognizable primary infections; -Skin evidence of systemic infection; -(+) echocardiogram (Transesophageal Echo); -Failure to defervesce (fever break) by 72 hours on therapy; -(+) blood cultures at 48-96 hours on therapy.
What is Staphylococcal Scalded Skin Syndrome?
Characterized by the appearance of large bullae & separation of large areas of the epidermis due to effects of the exfoliatin toxin at the stratum granulosum level of the skin. -more common in newborns
Which of the following individuals is most likely to be chronically colonized with Staphylococcus aureus? a. Allergy patient taking Benadryl b. Diabetic on oral metformin/glipizide c. Hemodialysis patient d. Drug addict that snorts cocaine
c. Hemodialysis patient
A 35-year-old woman who is menstruating presented to the ER with hypotension and the following physical findings: -strawberry tongue -conjunctivitss -blanching rash What toxin is responsible for this? a. TSST-1 b. Panton-Valentine leukocidin c. Enterotoxin C1 d. delta toxin
a. TSST-1
What is true about antibiotic therapy in this woman with toxic shock syndrome? a. Because it is a toxin-induced disorder, caused by colonization and not infection, antibiotics are not beneficial. b. Appropriate antibiotic therapy should be provided in order to attempt to prevent recurrent episodes. c. Antibiotic therapy should not be provided because it may prevent the development of an appropriate humoral immune response. d. Both a & c.
b. Appropriate antibiotic therapy should be provided in order to attempt to prevent recurrent episodes
In June, you attended a family reunion in Hermann Park at which you and 10 other family members ate some of your aunt’s famous potato salad. Unfortunately, your aunt had a small cut on her finger that was colonized with an enterotoxin-producing S. aureus while she prepared the salad. What is the likely clinical scenario that followed? A. Nausea & prominent vomiting within 2-6 hours. B. Fever, abdominal pain & diarrhea within 2-4 hours. C. Fever, abdominal pain & diarrhea 12-24 hours later. D. Nausea & vomiting 12-24 hours later.
A. Nausea & prominent vomiting within 2-6 hours.
Your whole family goes to the ER at Baylor St. Luke’s Medical Center for management of food poisoning caused by staph. Being the bright future MD that you are, which antibiotic do you demand from the ER doc for treatment? A. PO vancomycin, because the infection is in the gut. B. PO dicloxacillin. C. IV vancomycin, because of the possibility of MRSA. D. None of the above choices.
D. None of the above choices. -not caused by infection, caused by toxin
A 29-year-old parenteral drug addict presents to the ER with cough productive of blood-tinged purulent sputum, fever and pleuritic chest pain. Chest CT shows multifocal nodules. What is the likely diagnosis? A. Post-influenza S. aureus pneumonia B. Streptococcus gallolyticus mitral valve endocarditis C. Multifocal Enterococcus faecalis pneumonia D. Tricuspid valve S. aureus endocarditis
D. Tricuspid valve S. aureus endocarditis
MSCRAMMs (Microbial Surface Components Recognizing Adhesive Matrix Molecules) that are components of the staphylococcal cell wall are likely to bind to all of the following except: a. Fibronectin b. Fibrinogen c. Collagen d. All of the above
d. All of the above
A 33-year old man was admitted to Ben Taub with fever. Only 1 set of blood cultures was drawn and it is growing Gram-positive cocci in clusters. In order to determine the significance of this one culture, you ask the laboratory to perform what test? a. Catalase b. SCCmec c. Protein A d. Coagulase
d. Coagulase
You have begun an important research project that requires the production of antibodies to newly identified influenza antigens. Six weeks ago, you immunized rabbits with these antigens and now want to isolate the antibodies. In order to do so, you construct a column using a staphylococcal component to bind the antibody. The component you use is: a. Fibronectin binding protein b. Protein A c. Coagulase d. Lipotechoic acid
b. Protein A
A 32-year-old man walks into the ER at Ben Taub with fever of 104oF and no obvious site of infection. 3 sets of blood cultures grow Gram-positive cocci in clusters. How should he be treated? a. Initially with nafcillin + gentamicin b. Initially with vancomycin c. For 2 weeks duration d. For 4-6 weeks duration e. Both b & d
e. Both b & d Always assume MRSA. Assume deep seeded infection b/c young man w/ no obvious infection.
A 32-year-old man comes to the BTGH Emergency Room with fever. Two sets of blood cultures have grown MRSA. He is started on vancomycin, but no source of infection is found. After 4 days of Rx, he is still bacteremic. How long should he be treated with IV antibiotics? A. 2 weeks B. 4 – 6 weeks C. 1 week with IV and then 3 weeks PO D. Until his bacteremia has cleared
B. 4 – 6 weeks Not a transient bacteremia, probably an infection in heart valve.
What is the major virulence factor for coagulase (-) staph?
-Exopolysaccharide (Slime) -important for resistance to phagocytosis
What are the well documented infections caused by coagulase negative staph?
-UTI’s -Bacteremia in critically ill or immunosuppressed -Native valve endocarditis =unusual & occurs in abnormal valves & IV drug addicts -osteomyelitis (30% of post-op sternal wound infections) -very common cause of infections of prosthetic hardware
One must pose the following 3 questions in an attempt to assess the possibility of true infection by coaguase (-) staph:
- Does the patient have a clinical scenario consistent with a coagulase-negative staphylococcal infection? 2. Are there other likely explanations for fever or is there an infection at another site? 3. Does the patient have >1 positive blood cultures?
How much staph aureus is susceptible to penicillin these days?
only 5-10%
A 28-year-old sexually active woman presents to your office with pain on urination, frequency and suprapubic discomfort. A culture of her urine is growing a non-hemolytic organism with Gram + clusters of cocci. The most likely organism is: a. Staphylococcus aureus b. Staphylococcus epidermidis c. Staphylococcus saprophyticus d. Enterococcus faecalis
c. Staphylococcus saprophyticus
Eight months ago, this 65-year-old man underwent right hip arthroplasty. Over the last 3-4 months, he has experienced increasing pain with ambulation, but no other symptoms. A radiograph shows periprosthetic irregularity of the bone and periosteal elevation suggestive of chronic infection. The most likely causative microorganism is: A. Staphylococcus saprophyticus B. Enterococcus faecalis C. Streptococcus pyogenes D. Staphylococcus epidermidis
D. Staphylococcus epidermidis
A 54-year-old diabetic man comes to the ER at Ben Taub with a swollen, tender foot. I & D is done and the culture grows S. aureus: After I & D and 2 days of vancomycin Rx, what is the most appropriate next step before DC? The patient is sulfa allergic, and the staph is resistant to oxacillin and erythromycin. a. Rx with oxacillin b. Rx with linezolid c. Do a D-test d. Rx with TMP/SMX
c. Do a D-Test Linezolid is too expensive
The mechanism of resistance demonstrated by the S. aureus susceptibility profile shown is: Penicillin R Oxacillin S Vancomycin S Ciprofloxacin S Gentamicin S Erythromycin S Clindamycin S A. Methicillin-resistance B. B-lactamase mediated resistance C. Heteroresistance D. Van A mediated resistance
B. B-lactamase mediated resistance
This 73-yo woman is getting hemodialysis thru a Quinton catheter. She has been admitted with decubitus ulcer & catheter infections multiple times. Now, she is admitted with fever, and 3 sets of blood cultures grow S. aureus with a vancomycin MIC=128 ug/ml. This resistance likely resulted from: a. Overproduction of cell wall precursors that bind up vancomycin. b. SCCmec gene that produces altered binding proteins. c. Altered porins interfering with vancomycin penetration. d. Acquisition of vanA gene by conjugation with resistant strain of Enterococcus.
d. Acquisition of vanA gene by conjugation with resistant strain of Enterococcus.
In 1985, this patient had spine surgery complicated by an infection. The wound ultimately healed by 2o intention. Last week, he developed back pain and drainage over the area. Culture grew S. aureus with the following antibiogram: Penicillin S Oxacillin S Vancomycin S Gentamicin S Linezolid S Clindamycin S The drug of choice is: A. Penicillin B. Nafcillin C. Cefazolin D. Vancomycin E. Linezolid
A. Penicillin Vanc is inferior
You were admitted to the hospital with acute appendicitis. At surgery, they removed an inflamed, but not yet ruptured appendix. The next day, you spiked a fever to 101oF, but rapidly defervesced; one set of 2 blood cultures grew S. epidermidis. The resident is getting ready to start vancomycin; before he does you request that: A. He draw 2 more sets of blood cultures B. Do an echocardiogram C. Start nafcillin instead D. Question whether any antibiotics are necessary. E. Both a & d
E. Both a & d
This 75-year-old man was found to have S. aureus endocarditis on a native bicuspid valve. He is hemodynamically stable. He is begun on nafcillin, because the organism is methicillin-susceptible. However, he is adamant about wanting to go home & receive IV home therapy. What do you do? A. Change to vancomycin because the dosing interval is much longer & it is more convenient. B. Continue with nafcillin, even though it has to be given every 4 - 6 hours. C. Change to oral dicloxacillin + rifampin. D. Use IV ceftriaxone 2 gms. once daily
D. Use IV ceftriaxone 2 gms. once daily ***WE NEVER TREAT ENDOCARDITIS WITH ORAL ABX **never use Vanc when staph is methicillin susceptible
Which staph species is a leading cause of UTI in sexually active young women?
Staph. saprophyticus
What are the diseases that staph aureus causes via exotoxin release?
-Gastroenteritis (food poisoning) -Toxic shock syndrome -Scalded skin syndrome
Why aren’t antibiotics curative in toxic shock syndrome caused by staph aureus?
the exotoxin is causing the disease
What are the main diseases caused by direct organ invasion of staph aureus?
- Pneumonia 2. Meningitis/brain abscesses 3. Osteomyelitis 4. Acute Endocarditis 5. Septic Arthritis 6. Skin infections
What kind of infections are caused by Staphylococcus epidermidis?
-Nosocomial infections (prosthetics, IV sepsis, UTI)
Why should you draw blood from more than one site if a blood culture is positive for Staph epidermidis?
-it is a frequent skin contaminant in blood cultures
How is endocarditis caused by Staph aureus related to the brain?
-embolism of vegetations can travel to the brain (from left valve) *right valve travels to lungs
How do we distinguish a staph infection from a strep infection?
- Staph = Gm + Clusters of cocci 2. Staph = Catalase (+) 3. Staph = golden pigment on sheep blood agar
How do we differentiate staph aureus from other staph?
-Staph aureus is coagulase (+)
What are the symptoms of toxic shock syndrome caused by Staph?
-Fever -Diffuse erythmatous rash -Desquamination of palms and soles -vomiting** -diarrhea** -septic shock
