What is the gram stain of staph?
Gm + clusters
What pattern of hemolysis does Staph show?
Why is it called Staph aureus?
-grows yellow on culture Aureus = gold
Is S. aureus coagulase positive or negative?
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?
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
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
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