MID 1 - Staph / Strep / Infective Endocarditis

Question 1

What are the four steps in the Gram stain procedure?

Answer 1

1) crystal violet
2) gram’s iodine
3) decolorizer (alcohol)
4) safranin red

Question 2

What class of bacteria are visualized using an acid-fast stain?

Answer 2

mycobacteria (includes species responsible for TB and leprosy).

Question 3

What are the three categories of exotoxins secreted by bacteria?

Answer 3

1) A-B toxins (cholera, tetanus)
2) membrane disrupting toxins (hemolysins, alpha toxin)
3) superantigens (toxic shock syndrome toxins)

Question 4

Who makes spores?

Answer 4

Gram positive (not gram negative)

Question 5

Categorize staphlococci in terms of:

1) pus-forming
2) coagulase
3) sporulation
4) gram stain
5) growth pattern
6) catalase

Answer 5

1) pyogenic
2) S. aureus is coagulase positive; others are coagulase negative
3) nonsporulating, nonmotile (can cause metastatic seeding to joint spaces)
4) gram positive
5) grow in clusters, on agar s. aureus tends to become golden
6) positive

Question 6

What is the primary site of colonization for S. aureus?

Answer 6

anterior nares (present in 20-40%)

Question 7

What are the primary staphylococcal toxin diseases?

Answer 7

toxic shock syndrome; food poisoning; scalded skin syndrome

Question 8

What causes staphylococcal food poisoning and what is the mode of action?

Answer 8

enterotoxins; stimulate vagus nerve and CNS vomiting center and increase peristalsis.

Question 9

What are the important features of staphylococcus epidermidis

Answer 9

1) relatively avirulent
2) part of normal skin flora
3) most common coagulase negative species
4) often found at site of prosthetic implantation sites.

Question 10

What are the most common pathogens that cause infective endocarditis?

Answer 10

s. aureus, followed by viridans group strep, enterococcus and coagulase-negative staph.

Question 11

What are the primary risk factors for IE?

Answer 11

1) Dental procedures / poor dental hygiene, particularly for viridans.
2) prosthetic valves (if first 2-3 months, staph most likely cause.)
3) GI / genitourinary procedures (enterococci)
4) nosocomial (s. aureus, gram-, candida)

Question 12

What is the major pathogen in subacute IE?

Answer 12

viridans strep.

Question 13

What is the definition of septic shock?

Answer 13

severe sepsis + hypotension despite fluid resusitation (BP below 90mmHg or drop of 40 mmHg)

Question 14

What is the definition of sepsis?

Answer 14

Infection plus 2+ SIRS criteria

Question 15

What is the definition of severe sepsis?

Answer 15

sepsis + organ dysfunction, such as lactic acidosis, oliguria, altered mental status.

Question 16

What is the most common pathway for sepsis?

Answer 16

LPS targets macrophages (via CD14 receptor) and endothelial cells (via LPS-sCD14 complex receptor). Can also target TLR4/2, leading to NFkB translocation, activation of TNF.

Question 17

What are three mechanisms of vasodilatory shock?

Answer 17

1) activation of ATP-sensitive K channels (smooth muscle can’t contract)
2) activation of inducible for of NO synthase
3) deficiency of vasopressin.

Question 18

What is the most common mode of staphylococcus aureus inoculation?

Answer 18

auto-innoculation - humans are primary reservoir of the organism.

Question 19

What groups are at increased risk for a Staph Aureus infection?

Answer 19

low-WBC, S. Aureus carriers, IV drug users, dialysis patients, diabetics.

Question 20

What is the primary host response to a Staph Aureus infection?

Answer 20

PMN infiltration, vascular thrombosis, tissue necrosis leading to abscess formation.

Question 21

What is the cause of shock in patients with menstruation-associated toxic shock?

Answer 21

> 95% Toxic-shock syndrome toxin.

Question 22

What is the mode of action for staph aureus food poisoning?

Answer 22

heat-stable enterotoxin activates vagus nerve and CNS vomiting center.

Question 23

Categorize streptococci in terms of:

1) pus-forming
2) gram stain
3) growth pattern
4) catalase

Answer 23

1) pyogenic
2) gram positive
3) grow in chains
4) catalase negative

Question 24

What is an important mechanism for differentiating S. pyogenes, viridans strep, and enterococci?

Answer 24

hemolysis on blood agar plates.

S. pyogenes -> beta hemolytic
viridans strep -> alpha hemolytic
enterococci -> gamma hemolytic

Question 25

What distinguishes virulent from a-virulent S. pyogenes (Group A strep)?

Answer 25

presence / absence of M protein., which is anti-phagocytic (inhibits activation of alternate pathway of complement cascade)

Question 26

What findings are suggestive of Gp A strep, and what findings are not suggestive of Gp A strep?

Answer 26

suggestive: sore throat, sudden onset, pain with swallowing, headache, lymphadenitis, tonsillar exudates, soft palate petechiae. not suggestive: conjunctivitis (pink eye), coryza (nasal discharge), cough, diarrhea.

Question 27

How does strep A spread?

Answer 27

primarily by droplets, nasal secretions, can also be food borne.

Question 28

How does one diagnose rheumatic fever?

Answer 28

Jones criteria: 1) must have evidence of antecedent strep infection. 2) major criteria: carditis, polyarthritis, erythema marginatum, subcutaneous nodules, chorea (involuntary jerky movements).

Question 29

What is the treatment of choice for Strep. pyogenes?

Answer 29

1) penicillin | 2) surgical debridement of any soft tissue infection.

Question 30

Categorize streptococcus pneumoniae in terms of: 1) gram stain 2) growth pattern 3) capsule status 4) hemolysis 5) unique protein present

Answer 30

1) gram positive 2) diplococci 3) encapsulated 4) alpha hemolytic 5) Teichoic acid containing phosphorylcholine C polysaccharide.

Question 31

What factors increase risk of pneumococcal disease?

Answer 31

defective antibody or complement formation, antecedent viral respiratory infection, smoking, HIV infection, COPD.

Question 32

What is the pathogenesis of pneumococcal pneumonia?

Answer 32

strep. pneomoniae colonizes epithelium using adhesins such as phosphorylcholine. capsule is anti-phagocytic. During invasion stage, pneumolysin is released (cytotoxin that activates inflammation and CD4 T cell recruitment).

Question 33

What is the primary cause of infective endocarditis?

Answer 33

gram positive bacterial pathogens, particularly staph strains (historically, veridens strep was most often seen)

Question 34

What are some cutaneous manifestations of endocarditis?

Answer 34

1) splinter hemorrhages 2) osler's node (painful lesions on tips of fingers and toes, seen in subacute manifestations) 3) janeway lesion (seen more commonly in acute endocarditis on palms and soles of feet).

Question 35

Who is at highest risk for infective endocarditis?

Answer 35

prosthetic valve; complex congenital heart disease; previous endocarditis; cardiac transplantation with valvulopathy.

Question 36

What strep strain is susceptible to optochin?

Answer 36

Strep pneumoniae

Question 37

What is the primary cause of bacterial meningitis?

Answer 37

Strep. pneumoniae infection, spreads to the CNS via bacteremia.

Question 38

What should a patient diagnosed with strep. bovis endocarditis be screened for?

Answer 38

colon cancer

Question 39

What are the systemic Inflammatory Response Syndrome symptoms?

Answer 39

T above 100.4 or below 96.8 HR above 90 RR above 20 or pCO2 below 32mmhg WBC above 12K or below 4K or above 10% Bands.