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► Med - Pathology > Streptococci > Flashcards

Streptococci Flashcards

1
Q

What are the main features of streptococci that differentiate them from staphylococci?

A

– Catalase negative
– Cocci in pairs and chains
– Requires complex media
– Prefers anaerobic or carbon dioxide atmosphere

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2
Q

What is a catalase test?

A

Hydrogen peroxide is added to the colony and the appearance of O2 indicates the presence of catalase with bubbles and therefore that would be staphylococcus.

No bubbles = Streprococcus

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3
Q

What are the 3 groups of streptococci?

A
  • Pyogenic
  • Pneumococci
  • Viridans
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4
Q

Beta streptococcus

A

Complete hemolysis

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5
Q

Alpha streptococcus

A

Incomplete hemolysis

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6
Q

Gamma streptococcus

A

No hemolysis

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7
Q

What is Lancefield Group A?

A

Streptococcus pyogenes

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8
Q

What is Lancefield Group B?

A

Streptococcus agalactiae

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9
Q

What are the six possible clinical manifestations of streptococcus agalactiae?

A
  • Acute Pharyngitis
  • Impetigo
  • Erysipelas
  • Necrotizing Fasciitis
  • Scarlet Fever
  • Puerperal Sepsis
  • Toxic Shock Like Syndrome
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10
Q

-Acute Pharyngitis

A

– 5-15 year old with fever, sore throat, headache, swollen lymph nodes
– 5% asymptomatic carriers
– Transmitted by respiratory droplets
– Self-limiting
– Reoccurs due to lack of type specific antibody to M protein

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11
Q

-Impetigo

A

– 2-5 year old child with localized skin disease
– Associated with trauma / insect bites
– Pustule with yellow crust
– Appears on face or extremities

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12
Q

-Erysipelas

A

– Speading erythema with well demarcated edge on the face
– Fever and lymphadenopathy
– Lesions often on face and often with accompanying steptococcal pharyngitis


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13
Q

-Necrotizing Fasciitis

A

– Strep infection that occurs deep in the subcutaneous tissues
– Spreads along the fascial planes
– Extensive destruction of the muscle and fat – “flesh eating” bacteria
– Systemic toxicity, mortality exceeds 50%

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14
Q

-Scarlet Fever

A

• Complication of streptococcal pharyngitis
• Caused by erythrogenic exotoxin
• A rash first appears as tiny red
bumps on the chest and abdomen
• fine, red, and rough-textured
blanches upon pressure
• appears 12–48 hours after fever
• generally starts on the chest, armpits, and behind the ears but spares the face
•Bright red tongue with a “strawberry” appearance

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15
Q

-Puerperal Sepsis

A

– Seen in women following delivery or abortion
– Organisms colonizing genital tract or from obstetrical personnel invade the upper genital tract causing endometritis, lymphangitis, bacteremia, necrotizing fasciitis, and streptococcal toxic shock syndrome

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16
Q

-Toxic Shock Like Syndrome

A

– Multisystem organ failure (heart, respiratory tract, kidney)
– SPE toxins are similar to Staph aureus TSST-1
– Unlike patients with staph toxic shock, cultures are usually positive for group A strep

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17
Q

What are common post-streptococcal sequelae of untreated strep infections?

A
  • Rheumatic Fever

- Acute Glomerulonephritis

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18
Q

Nosocomial Infection

A

Hospital acquired infection

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19
Q

Rheumatic Fever

A

– Nonsuppurative inflammatory disease occurs 1-5 weeks after strep pharyngitis
– Fever, carditis, subcutaneous nodules, chorea, polyarthritis
– Characteristic cardiac lesions = Aschoff bodies and valvular damage leads to possible endocarditis later in life

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20
Q

Acute Glomerulonephritis

A

– Edema, hypertension, hematuria, proteinuria
– Occurs after skin / respiratory infection
– Certain M types are “nephritogenic”
– Antigen + antibody + C’ deposited in glomeruli seen on kidney biopsy

21
Q

What are the 4 virulence factors of S. pyogenes?

A

• Ability of the bacteria to adhere to the surface of the host cells
• Invade into the epithelial cells
• Ovoid opsonization and phagocytosis
• Produce a variety of toxins and enzymes

22
Q

What is the function of Streptococcal pyrogenic exotoxins (SPE)?

A

– Three distinct heat labile toxins (A, B, C)
– Called “superantigens” that stimulate cytokine response leading to shock and organ failure
– Strep toxic shock-like syndrome
– Responsible for the rash in scarlet fever “erythrogenic exotoxin”

23
Q

What is the main factor in the pathogenesis of S. pyogenes?

A

Adherence via its M protein.

  • Binds to epidermal cells
  • Allows bacteria to survive
  • Strains without M protein are avirulent
24
Q

What is the main treatment for S. pyogenes?

A

Penicillin/Ampicillin/Amoxacillin

25
Q

What is the main target population in pathogenesis of Streptococcus agalactiae?

A

Neonates who acquire it from mothers who are carriers. Maternal colonization of vagina or rectum exposes baby at delivery, and due to lack of Ab get disease.

Sialic acid on polysaccharide capsule inhibits C’ allowing organisms to multiply

26
Q

How are Group B bacterial infections prevented?

A

• To prevent perinatal GBS disease, cultures should be performed on vaginal/rectal swabs collected at 35 to 37 weeks gestation
– Combined vaginal/rectal swab improves isolation rates by 40% over vaginal swab alone. Alert physician when cervical or vaginal specimens received
– Use of selective enrichment broth (LIM) will increase GBS isolation by 50%

27
Q

What is Streptococcal agalctiae treated with?

A

Penicillin

Ampicillin

28
Q

What is used to treat Streptococcal pyogenes in patients with penicillin allergy?

A

Erythromycin

29
Q

What is used to treat Streptococcal agalctiae in patients with penicillin allergy?

A

Clindamycin

30
Q

What are the limitation of Rapid Group A Detection Tests?

A

The sensitivity is only ~70%. Negative tests will need to have a backup culture.

The specificity is very high though. Positive tests will be Group A.

31
Q

What are the characteristics of viridian’s streptococci?

A

• Alpha or gamma hemolytic
– Lack hemolysins and toxins of beta strep
• Normal flora of upper respiratory tract
• Major cause of dental caries
• Opportunistic pathogen causing sepsis in neutropenic cancer patient

32
Q

What is isolation of S. bovis from blood associated with?

A

Carcinoma of the colon

33
Q

What are the species in the S. milleri group?

A

S. anginosus
S. constellatus
S. intermedius

34
Q

How can the S. milleri group be determined from the agar plate?

A

Have characteristic caramel (butterscotch) odor when cultured on agar plates

35
Q

What are the species in the Nutrient Deficient Group?

A

– Abiotrophia

– Granulicatella

36
Q

A 7-year-old child presents with a fever, pain in his ankles, knees and wrist, and a new heart murmur. His mother said that he complained of a “sore throat” last month, but the symptoms resolved without taking him to the pediatrician. A rapid screening test for strep throat is negative. His most likely diagnosis is:

A. Toxic shock-like syndrome 
B. Rheumatic fever
C. Scarlet fever
D. Puerperal fever
E. Acute glomerulonephritis
A

B. Rheumatic fever (heart murmur)

37
Q

Where is S. pneumoniae normally found?

A
  • Normal flora of human upper respiratory tract

* Gram-positive bacteria

38
Q

What are the virulence factors of S. pneumoniae?

A

• sIgA protease – prevents IgA-mediated binding of pneumococcal cells to mucus
• Teichoic acid/peptidoglycan – activates complement by alternative pathwaymediates inflammation
– Precipitates C-reactive protein (CRP)

39
Q

What is the commonest cause of community acquired

acute bacterial pneumonia?

A

S. pneumoniae

40
Q

What does S. pneumoniae look like under the microscope?

A
  • Gram-positive, lancet-shaped cocci (elongated cocci with a slightly pointed outer curvature).
  • Usually seen as pairs of cocci (diplococci), but they may also occur singly and in short chains.
41
Q

What are the main pathogenic Enterococcus species?

A
  • E. faecalis “pertaining to feces”

* E. faecium “of feces”

42
Q

What are the 3 most common Enterococcal infections?

A
  • Urinary tract
  • Mixed bacterial wound infections and decubiti
  • Sepsis, endocarditis
43
Q

What are the features of Enterococcus?

A
  • Alpha, beta or gamma hemolytic
  • Group D antigen positive
  • PYR positive
44
Q

How are S. pneumoniae determined using an agar plate?

A

Alpha hemolytic

45
Q

What are the metabolic indications of S. pneumoniae?

A
  • Catalase Negative
  • Bile Soluble
  • Inhibited by ethylhydrocupreine
46
Q

What are the reactions of E. faecalis and E. faecium to penicillins?

A
  • E. faecalis susceptible to pen / amp

* E. faecium resistant to pen / amp

47
Q

What is the intrinsic resistance of Enterococcus?

A

Intrinsically resistant to all cephalosporins, trimethoprim-sulfa, aminoglycosides

48
Q

An organism is isolated from the blood of a 65 year-old male patient with a diagnosis of probable bacterial endocarditis. The organism displays streptococcus-like morphology on gram stain and is catalase-negative. On blood agar the colonies appear gamma hemolytic and are PYR positive. Patient was being treated with vancomycin plus an aminoglycoside with no response. This isolate is likely to be:

A. Streptococcus pyogenes
B. An Enterococcus species
C. Group B Streptococcus
D. A member of the "Streptococcus milleri" group 
E. A Staphylococcus species
A

B. An Enterococcus species

► Med - Pathology (203 decks)

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