Gram Positive Bacteria Part 1

Question 1

Which component of Sterp pyogenes is responsible for most of the pathology in Acute Rheumatic Fever?

Answer 1

M protein (via molecular mimicry)

Question 2

A baby was brought to your clinic with a history of diffuse erythematous rash and is now presenting with blistering of the skin. No recent intake of medications were elicited. What’s your initial impression? On histology, on which layer will separation be seen? Which protein is cleaved?

Answer 2

This is SSSS (aka Ritter Disease) This is caused by EXFOLIATIN which cleaves desmoglein causing separation at Stratum Granulosum so the mucuos membranes are spared (vs TEN where separtion occurs at dermo-epidermal junction)

Question 3

Which pattern of blood hemolysis does S. aureus exhibit?

Answer 3

Beta-hemolytic

Question 5

Which Staphylococcal toxin causes marked necrosis of the skin and hemolysis?

Answer 5

Alpha Toxin

Question 6

Which test differentiates S. aureus from other Staphylococcus species?

Answer 6

Coagulase test (S. aureus coagulates blood)

Question 7

A patient presents with erythematous rashes and blistering of the skin. You suspecta staphylococcal infection. Which exotoxin is probably responsible?

Answer 7

Exfoliatin

Question 8

Which pigment is responsible for the “golden” color of Staph aureus?

Answer 8

Staphyloxanthin

Question 8

A patient presents with painful pea-sized lumps under the arm pits some of which broke open drainin foul-smelling pus. This condition is probably called? Which organism is responsible?

Answer 8

Hidradenitis Suppurativa caused by Staph aureus

Question 9

How will you diffrentiate S. saphrophyticus and epidermidis?

Answer 9

Novobiocin sensitivity. Saphrophyticus is Resistant, epidemidis is sensitive

Question 11

What test differentiates Group A from Group B Strep?

Answer 11

Bacitracin Sensitivity test. A is Sensitive B is Resistant (B-BRAS)

Question 12

What do you call a sequestered focus of osteomyelitis arising in the metaphyseal area of the bone? Which organism is responsible?

Answer 12

Brodie abscess; Staph aureus

Question 13

A 56 year-old man who recently had a prosthetic valve operation suddely develops endocarditis. Which organism is the most likely culprit? What treatment will you give?

Answer 13

Staphylococcus epidermidis. Over 50% are methicillin resistant so treatment requires VANCOMYCIN and removal of the device. It is also most commonly implicated in prosthetic joints and ventriculoperitoneal shunt.

Question 14

What is the difference between ASO and anti-DNASE B in terms of documenting recent strep infections?

Answer 14

ASO for PHARYNGITIS and Anti-DNASE B for recent SKIN infection (since ASO is inhibted by cholesterol in skin lipids)

Question 15

Staphylococcus predominantly resides in whicr part of the body?

Answer 15

Anterior nares

Question 17

A 23 year old female comes to your clinic complaining of burning pain, dysuria and hypogastric pain. You requested for urine culture which showed whitish, non-hemolytic colonies on blood-agar. What is the offending organism?

Answer 17

Staphylococcus saprophyticus. It is the second most common cause of UTI after E. coli.

Question 18

Which medically important virulence enzyme of Strep pyogenes activates plasminogen?

Answer 18

Streptokinase (used in reperfusion therapy for certain embolic cases)

Question 19

Erysipelas, a superficial infection extending into dermal lymphatics is most commonly caused by?

Answer 19

Strep pyogenes

Question 20

A 4 year old child presents to your clinic with fever and centifugal rash which is “sandpaper-like”. What’s your diagnosis and the bacteria involved?

Answer 20

Scarlet fever caused by Strep pyogenes. Other findings include Pastia’s lines (along the axilla) and strawberry tongue. Dick Test for sussceptibility.

Question 21

Enumerate the JONES criteria

Answer 21

JONES - Joints (migratory polyarthritis) O my heart (pancarditis) Nodules (subcutaneous nodules) Erythema Marginatuma ansd Sydenham chorea

Question 22

This virulence factor is responsible for necrotizing fasciitis caused by Strep pyogenes.

Answer 22

Exotoxin B (Another exotoxin produced by S pyogenes is Pyrogenic EXOTOXIN A which is similar to S aureus’ TSST-1, both are superantigens)

Question 23

The drug of choice for Acute Rheumatic Fever prophylaxis is?

Answer 23

Penicillin G

Question 24

LIM broth grows which organism which is also the most common cause of neonatal sepsis and meningitis?

Answer 24

Strep agalactiae (Group B strep). It is CAMP positive, bacitracin resistant, beta-hemolytic and hydrolyzes hippurate.

Question 25

Viridans group of Strep and Strep pneumoniae both show ALPHA-HEMOLYTIC pattern on blood culture. Which tests will differentiate the two?

Answer 25

Bile and Optochin tests. V I R idans is both Insoluble to bile and Resistant to optochin

Question 26

Which organism is the most common cause of Subacute and Native Valve endocarditis?

Answer 26

Strep sanguis (belongs to VIRIDANS group)(most commonly affects the MITRAL VALVE)

Question 27

The PYR test differentiates between positive and negative reactors among Streptococcus species. Which is the only two species that will yield a positive PYR (red compound) test?

Answer 27

Strep pyogenes (Group A) and Group D strep

Question 29

How is GBS infection prophylaxis given?

Answer 29

IV Penicillin or Ampicillin 4 hours prior to delivery (GBS screening is done 35-37 weeks AOG)

Question 30

Group D Strep exhibits which pattern of hemolysis?

Answer 30

Gamma Hemolysis (nonhemolytic)

Question 31

S. aures will most likely cause a problem in which valve among IV drug abusers?

Answer 31

Tricuspid valve (S. aureus is the most common cause of ACUTE ENDOCARDITIS)

Question 31

A 3 year old child was brought to your clinic with perioral blistered lesions with honey-colored crust. On histology, which skin layer will you find neutrophil accumulation? Which organism is responsible?

Answer 31

This is Impetigo Contagiosa most commonly caused by Strep pyogenes. Neutophils are found beneath the STRATUM CORNEUM

Question 32

A patient presented with acute bouts of cough with “rust-colored” sputum and pleuritic chest pain. Culture revealed “lancet-shaped” cocci in pairs. Which pattern of pneumonia would you most likely see in the x-ray film?

Answer 32

This is Streptococcus pneumonia, the most common cause of CAP. Most common pattern of pneumonia is LOBAR.

Question 33

4 hours after eating a reheated mayonnaise-based salad, a patient presents with vomiting and diarrhea. Which toxin is probaly responsible?

Answer 33

HEAT-STABLE ENTEROTOXIN produced by S. aures

Question 33

Endocarditis among patients with colorectal cancer is associated with?

Answer 33

Streptococcus bovis

Question 33

Endocarditis in patients who underwent GIT surgery is usually caused by?

Answer 33

Enterococcus faecalis

Question 35

A patient confined in the ICU for 3 weeks was ordered an X-ray which revealed a cavity in the lung parenchyma filled with air. Which organimsm is most likely the cause of the x-ray finding?

Answer 35

The radio finding is a PNEUMATOCELE which is probably a complication of NECROTIZING PNEUMONIA which is frequently caused by Staph aureus among hospitalized patients. S. aures is also notorious for causing POST-VIRAL pneumonia)

Question 35

A 43 yo patient who recently had a sino-nasal surgery presents with high fever, hypotension and desquamating rash. What is your intial impression?

Answer 35

This is most likely TSS caused by the nasal packing after the surgery. This is caused by TSST-1 causing fever, hypotension and STRAWBERRY TONGUE among other systemic symptoms. Blood CS is usually negative.