S.Pyogenes

Question 1

What shape is S.Pyogenes?

Answer 1

Round shaped

Question 2

What is the lancefield classification?

Answer 2

Group A Strep

Question 3

How does S.Pyogenes stain

Answer 3

Gram positive

Question 4

What type of anaerobes are S.Pyogenes

Answer 4

Facultative anaerobe;

Question 5

What result does S.pyogenes give in catalase test

Answer 5

Catalase negative

Question 6

What type of hemolysis does S.Pyogenes show in blood agar?

Answer 6

Beta hemolysis. This is because of streptolysins produced by S.Pyogenes

Question 7

How can you distinguish between S.Pyogenes and S.Agalctiae

Answer 7

Bacitracin is added to the agar. S.Pyogenes is bacitracin sensitive so the colony will die off where as for S.agalactiae, they remain intact.

Question 8

What are the components of the S.Pyogenes capsule

Answer 8

Adherence proteins, Streptococcus fibronectin binding protein and M protein which attach to skin or pharyngeal mucosa

Question 9

How does hyaluronidase work?

Answer 9

Destroys hyaluronic acid

Question 10

How does hyaluronidase work?

Answer 10

Destroys hyaluronic acid. A cement substance that keeps cells of the connective tissue tightly linked. This results in local inflammation and enables bacteria to enter the blood stream where it releases streprolysin O and S which cause hemolysis

Question 11

Name the super antigens produces by S.Pyogenes

Answer 11

Streptococcal pyrogenic Extotoxin A and C (SpeA and Spec)

Question 12

How do S.Pyogenes super antigens work?

Answer 12

They interact with Class 2 MHC molecule on the surface of the macrophage forming a super antigen MHC complex. This then stimulates 30% of the entire T-cell population stimulating release of many inflammatory cytokines, causing a cytokine storm which leads to Toxic shock syndrome, a widespread systemic vasodilation making blood pressure drop and causing poor perfusion of other organs

Question 13

What disease does S.Pyogenes cause in the lungs?

Answer 13

Pneumonia and lung abscesses.

Question 14

What disease does S.Pyogenes cause in the heart?

Answer 14

Clumps called vegetations on the heart valves causing Infective endocarditis

Question 15

What disease does S.Pyogenes casuse in the CNS?

Answer 15

Brain abscesses or meningitis

Question 16

Which areas of the body are peacefully colonized by S.Pyogenes?

Answer 16

Skin
Mucosa of pharynx
Vagina
Rectum

Question 17

Who is under greater risk of infection by S.Pyogenes?

Answer 17

Infants
Elderly
Hiv patients
Diabetics
Maliginancies

Question 18

How does S.Pyogenes enter the blood stream?

Answer 18

It can enter through a breach in the skin

Question 19

What is the most common disease caused by S.Pyogenes

Answer 19

Strep pharyngitis, inflammation of the pharyngeal mucosa and tonsils

Question 20

Explain what happens when S.Pyogenes invades the epidermis, Upper dermis, Lower dermis, and muscle fascia respectively

Answer 20

Epidermis: Impetigo, superficial skin lesions that look like honey clusters

Upper dermis: Erysipelas, skin infection

Lower Dermis: Cellulitis, acute, painful quick spreading infection of lower dermis and subcutaneous tissue

Muscle fascia:Necrotizing fasciitis, when muscle fascia and subcutaneous tissue are destroyed by necrosis

Question 21

Explain Post infectious sequaelae

Answer 21

Complications that arise after bacteria has been eliminated from the body

Question 22

Explain post streptococcal glomerulonephritis

Answer 22

Acute inflammation of the kidneys glomerulis usually seen after impetigo. Usually happens after 2 to 4 weeks after initial infection due to type 3 sensitivity reaction. This means the streptococcal antigens that remained in the blood bind to antibodies forming antibody antigen complexes that are deposited in the basement membrane of the glomerulus. This can activate the complement system attracting neutrophils to glomeruli resulting in kidney damage

Question 23

What are the symptoms of Pharyngitis?

Answer 23

Fever, panful swallowing and swollen red tonsils that may have pus on them

Question 24

What are the symptoms of Impetigo

Answer 24

Itchy honey coloured scabs on skin that can become fluid filled blisters.

Question 25

What are the symptoms of Erysipelas?

Answer 25

Warm painful lesions on the skin with raised edges

Question 26

What are the symptoms of Necrotizing fasciitis?

Answer 26

Fever and the skin over affected part becomes painful and purple coloured

Question 27

What are the symptoms of scarlet Fever?

Answer 27

Fever, bright red skin rash, tongue may have a sandpaper feel

Question 28

What are the symptoms of Acute rheumatic fever?

Answer 28

Joints inflammation
Heart damage causing heart murmers. Subcutaneous nodules seen on elbows knees and forearm. Erythema marginatum, a rash with thick red margins. Sydenhams chorea, rapid involuntary movement of the face and hands.

Question 29

What are the symptoms of post streptococcal glomerulonephritis?

Answer 29

Mainly facial edema and dark red urine because glomerular damage allows red blood cells to pass in the urine

Question 30

How do you diagnose strep pharyngitis?

Answer 30

It can be done with rapid strep test or RST which looks for bacterial antigens in a throat swab. This however may give a false positive so a culture from a throat swab may be required

Question 31

How do you diagnose skin infections and systemic infections?

Answer 31

For skin infections, cultured can be made from the fluid inside the blisters or from debrided tissue. Blood cultures can be done for systemic infections

Question 32

What is the treatment for strep pyogenes?

Answer 32

Penicillin

Question 33

What is an alternative treatment?

Answer 33

Cephalosporins such as ceftriaxone and macrolides such as azithromycin

Question 34

What titre can be used to detect recent S.Pyogenes infection?

Answer 34

Anti-streptolysin O titre

Question 35

Which virulence factor of S.Pyogenes converts plasminogen to plasmin

Answer 35

Streptokinase

Question 36

A 30-year-old man comes to his primary care physician for evaluation of progressive fatigue and dyspnea for several months. He does not smoke, drink alcohol
, or use illicit drugs. Family history is unremarkable. He traveled to South America one year ago but does not recall any subsequent illnesses. Temperature is 37.0 °C (98.6 °F), pulse is 75/min, and blood pressure
is 131/80 mmHg. On physical examination, the patient appears visibly dyspneic. A systolic murmur
is auscultated over the cardiac apex. Pulmonary auscultation reveals diffuse rales over both lung
fields. The patient undergoes cardiac biopsy. What is the most likely etiology of this patient’s clinical condition?

Answer 36

Acute rheumatic fever. An early sequela of untreated group A streptococcal throat infection that usually occurs two weeks following untreated group A Streptococcus
(GAS) pharyngitis. Clinical manifestations include arthritis, carditis, chorea, erythema marginatum, and subcutaneous nodules. Cardiac involvement typically involves all layers of the heart (pancarditis).

Damage to cardiac valves often becomes chronic and progressive, leading to mitral (most common), aortic, and, rarely, tricuspid valve damage. Rheumatic heart disease may manifest years after the initial episode of GAS pharyngitis. Regurgitation is the most common complication, but it may progress to stenosis. Pathogenesis involves antibody production and subsequent T cell response against myosin that shares similar epitopes with the M protein virulence factor of the bacteria (type II hypersensitivity)

Question 37

A 34-year-old man presents to the emergency department for evaluation of pain in the right lower extremity. The patient was running on the beach without shoes over the past weekend and sustained a small laceration to the bottom of the foot. Over the past 24 hours, he has been experiencing severe pain and swelling of the foot to the point that he is unable to bear weight. He is otherwise healthy and does not
smoke
, consume
alcohol
, or use illicit substances. Temperature is 38.6°C (101.5°F),
pulse
is 109/min, respirations are 22/min, and
blood pressure
is 131/72 mmHg. On physical examination, a 3 cm x 3 cm area of erythema is noted on the underside of the right foot. The patient is exquisitely tender to palpation over the entire aspect of the right foot extending to the mid
tibia
. A radiograph of the right foot is obtained and demonstrates the following finding

Answer 37

This patient has right foot cellulitis
, pain out of proportion to physical exam findings, and radiograph demonstrating air in the soft tissue
. Together, these findings are consistent with necrotizing fasciitis
, which must be treated emergently with surgical debridement of devitalized tissue.

Necrotizing fasciitis
is a rare but serious infection of deep soft tissues
that results in rapid, progressive destruction of muscle
fascia and overlying subcutaneous fat
. Typically, bacteria (usually anaerobes or Streptococcus pyogenes
) with appropriate toxin-carrying capabilities enter through broken skin
and spread along the myofascial plane. Pyrogenic
exotoxins induce cytokine
production, contributing to tissue destruction and subsequent production of methane and CO2
. Ultimately, this process causes bullae
formation, crepitus
, and gas
within soft tissue
.

Necrotizing fasciitis
carries a high rate of morbidity and mortality. Therefore, prompt recognition and treatment are paramount. Clues to the diagnosis include pain out of proportion to physical exam findings, erythema without sharp margins, as well as skin
bullae
and necrosis
. Definitive treatment includes debridement of devitalized tissue for source control, as well as empiric antibiotics
that include either carbapenem
or piperacillin-tazobactam
plus vancomycin
and clindamycin
. This combination is effective against both Gram positive and anaerobic pathogens. Furthermore, clindamycin
helps inhibit bacterial toxin production.

Question 38

A 9-year-old girl comes to the office because of 2 days of sore throat and fevers of 38.9°C (102°F). Physical exam shows an erythematous pharynx with a white, creamy
exudate covering the left tonsil. Palpation of the neck shows an extremely tender left submandibular lymph node. Throat cultures are taken and show beta-hemolytic colonies on blood agar. Susceptibility analysis show
growth is inhibited by bacitracin
. What is the mostly likely causal organism?

Answer 38

Streptococcal pharyngitisis the most common form of pharyngitis and caused by group A Streptococcus (GAS), or Streptococcus pyogenes. GAS is a gram-positive cocci with a hyaluronic acid capsule. It is beta-hemolytic, meaning that growth on sheep blood agar plates will show a golden clearning around each colony due to complete breakdown of heme. GAS
is additionally bacitracin-sensitive, a feature that distinguishes it from Group B Streptococcus. GAS
pharyngitis is characterized by an exudative pharyngitis accompanied by fever, vomiting, tender cervical lymph nodes, palatal petechiae, and scarlatiniform rash. It can be diagnosed with throat culture. Penicillin is the first-line treatment.

Question 39

A 7-year-old girl is brought to the urgent care clinic by her mother after she developed a rash on her shoulders, neck, and upper chest in the past 24 hours. The rash followed a fever and a severe sore throat for 2 days duration. The mother states that other children in the patient’s class have had similar symptoms. Physical examination of the patient shows a flushed and ill-appearing child with erythematous macules on her shoulders and chest. Throat examination shows a white tongue with inflamed papillae (see image below) and tonsillar inflammation. What is the most likely agent causing the patient’s symptoms considering it is susceptible to bacitracin?

Answer 39

The patient in this question is showing symptoms of scarlet fever, a illness caused by Group A Streptococcus. Scarlet fever tends to be preceded by febrile streptococcal pharyngitis for a couple of days before the onset of an erythematous maculopapular rash that begins on the upper trunk and spreads to the extremities. Other significant symptoms include a “strawberry” tongue—a whiteish appearance with red, inflamed papillae, and a flushed face. Scarlet fever
can lead to acute poststreptococcal glomerulonephritis
as well as rheumatic fever. Many classes of gram positive organisms may be distinguished by their sensitivity to particular agents. Among the beta-hemolytic, catalase-negative organisms, one can tell apart group A streptococcus (S. pyogenes) from group B streptococcus (S. agalactiae) by Bacitracin
treatment in culture. Group A is sensitive to it, while Group B is resistant.

Question 40

How do the M proteins work?

Answer 40

M proteins are a virulence factors which break down complement proteins and delay breaking down. This prevents phagocytosis