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MHD #3 > Streptococci and Enterococci > Flashcards

Streptococci and Enterococci Flashcards

1
Q

Name the species of streptococci associated with Lancefield groups A and B

A

group A: Streptococcus pyogenes

group B: Streptococcus agalactiae

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2
Q

Describe the structural and functional characteristics that distinguish streptococci from staphylococci

A

Staphylococci:

  • Catalase positive
  • Cocci in clusters
  • Grows in minimal media
  • Grows best 35-37 C
  • Prefers aerobic atmosphere
  • white colonies

Streptococci

  • Catalase negative
  • Cocci in pairs and chains
  • Requires complex media
  • Grows best 35-37 C
  • Prefers anaerobic or carbon dioxide atmosphere
  • clear colonies
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3
Q

List six clinical manifestations of Streptococcus pyogenes infection.

A 
Acute Pharyngitis
Impetigo
Erysipelas
Scarlet Fever
Necrotizing Fasciitis
Toxic Shock-like Syndrome
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4
Q

Name two diseases that occur as sequelae to streptococcal infections

A

Rheumatic Fever

Acute Glomerulonephritis

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5
Q

Name four virulence factors associated with Streptococcus pyogenes and the mechanisms by which they enhance infection

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

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6
Q

Describe the limitations of Rapid Group A Detection kits

A

the sensitivity is only 70% therefore there will be many false negatives. (high specificity so no false positives)

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7
Q

Explain the role of S. agalactiae in causing neonatal disease and how neonatal disease may be prevented.

A
  • N.B. is exposed to maternal colonization of vagina or rectum at delivery
  • the N.B. lacks of protective maternal antibody
  • Sialic acid on polysaccharide capsule inhibits C’ allowing organisms to multiply

prevention:

  • cultures should be performed on vaginal/rectal swabs collected at 35 to 37 weeks gestation
  • Prophylaxis of culture positive pregnant women during labor with penicillin / ampicillin to prevent neonatal disease
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8
Q

Name the species included in the Strep Milleri Group

A

S. anginosus,
S. constellatus,
S. intermedius

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9
Q

List the two major species of Enterococus causing infection in humans and explain their association with penicillin (or ampicillin) susceptibility and resistance.

A

E. faecalis “pertaining to feces”
E faecium “of feces”

Inherently resistant to may commonly used antibiotic

E. faecalis susceptible to pen / amp
E. faecium resistant to pen / amp

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10
Q

List 3 most common infections caused by Enterococci

A

Urinary tract
Mixed bacterial wound infections and decubiti
Sepsis, endocarditis

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11
Q

Identify the key morphologic and phenotypic tests used for identification of S. pneumoniae

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.

alpha hemolytic

0.5 and 1.25 micrometers in diameter.

may have a runny appearance or circular with an indented center

Catalase Negative
Bile Soluble
Inhibited by ethylhydrocupreine (Optochin)

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12
Q

what is the catalase test

A

scrape a colony off a plate and put in a drop of hydrogen peroxide.

If it bubbles it is catalase positive

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13
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

strep throat

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14
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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15
Q

Erysipelas

A
  • Spreading erythema with well demarcated edge on the face
  • Fever and lymphadenopathy
  • Lesions often on face and often with accompanying steptococcal pharyngitis
  • historically most common on the face but now seen mostly on the legs
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16
Q

Scarlet Fever

A
  • Complication of streptococcal pharyngitis
  • Caused by erythrogenic exotoxin (SPE)
  • 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
    spares the face (although some circumoral pallor is characteristic)

Characterized by:

  • Sore throat
  • Fever
  • **Bright red tongue with a “strawberry” appearance
  • The rash begins to fade three to four days after onset and desquamation begins.
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17
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 (pain is often disproportional to how it looks)
  • requires surgery
  • Systemic toxicity, mortality exceeds 50%
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18
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
19
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

20
Q

Rheumatic Fever clinical presentation

A
  • Nonsuppurative (no pus) inflammatory disease occurs 1-5 weeks after strep pharyngitis (if strep is not treated)
  • Fever, carditis, subcutaneous nodules, chorea, polyarthritis
  • Attacks reoccur into adulthood
  • Characteristic cardiac lesions = Aschoff bodies and valvular damage leads to possible endocarditis later in life
21
Q

Acute Glomerulonephritis clinical presentation

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 ( caused by the bodies response to the organism not by the organism itself)
22
Q

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

M protein of Streptococcus pyogenes

A
  • Binds to epidermal cells
  • allows bacteria to survive
  • Strains without M protein are avirulent
  • Antiphagocytic
    • Degrades complement C3b
    • Antibodies to M protein activate complement and kill the bacteria
24
Q

Hemolysins possessed by Streptococcus pyogenes

A 
Streptolysin S (oxygen stable, non-antigenic)
Streptolysin O (oxygen labile, ASO antibodies)

Streptolysins and streptokinase allow spread of bacteria in tissues

25
Q

Treatment of S. pyogenes

A

Drug of Choice = Penicillin /ampicillin/amoxacillin
- No resistance worldwide

Pen allergic pt = Cephalosporins or Erythromycin

26
Q

clinical presentations of GBS infections

Streptococcus agalactiae

A

Neonatal pneumonia, sepsis, meningitis
Skin and wound infections in adult diabetic patients
Endocarditis
Part of normal flora in throat, vaginal and GI tract

27
Q

Early onset vs late onset Streptococcus agalactiae

A

Early Onset neonatal disease

  • First week of life
  • Bacteremia, pneumonia, or meningitis

Late onset neonatal disease

  • 1 week to 3 months of age
  • Bacteremia with meningitis
28
Q

treatment of S. agalactiae

A

Penicillin / ampicillin = drug of choice

  • No resistance worldwide
  • Add gentamicin to enhance killing

Prophylaxis of culture positive pregnant women during labor with penicillin / ampicillin to prevent neonatal disease
- Clindamycin for pen allergic

29
Q

prevention of S. agalactiae

A

To prevent perinatal GBS disease, cultures should be performed on vaginal/rectal swabs collected at 35 to 37 weeks gestation

Lab Plays Important Role
- Combined vaginal/rectal swab
- Use of selective enrichment broth (LIM)
Report all GBS in urine regardless of colony count

30
Q

name the species in the and Nutritionally deficient Strep Group

A

Abiotrophia
Granulicatella

require another organism that is producing vitamin B-6 to grow

31
Q

Viridans 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
Important cause of endocarditis

includes Bovis Group – consists of non-enterococcal group D streptococci

32
Q

Bovis Group – Clinical Significance

A

S. bovis causes bacteremia, meningitis, and both native- and prosthetic-valve endocarditis

Isolation of S. bovis from blood is associated with carcinoma of colon**

33
Q

Streptococcus Milleri Group

A

Produce pinpoint colonies (small colony Streptococcus)
May require CO2 for isolation - sometimes mistaken for anaerobic streptococci
Have characteristic caramel (butterscotch) odor when cultured on agar plates

Usually commensals isolated from mouth, oropharynx, GI tract and vagina
Reported to cause deep-seated pyogenic infections of cardiac, abdominal, skin and CNS tissues
Have been isolated from 56-81% of brain abscesses either in pure or mixed culture

34
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

Rheumatic fever

35
Q

Streptococcus pneumoniae can cause

A

Normal flora of human upper respiratory tract
Can cause pneumonia, usually lobar type
Paranasal sinusitis
Otitis media
Meningitis, which is usually secondary to one of the former infections
Also causes osteomyelitis, septic arthritis, endocarditis, peritonitis, cellulitis and brain abscesses.

36
Q

Streptococcus pneumoniae important virulence factor is

A

Polysaccharide capsule

37
Q

Commonest cause of community acquired acute bacterial pneumonia

A

Streptococcus pneumoniae

38
Q

Most common cause of bacterial meningitis in the U.S

A

Streptococcus pneumoniae

Highest rate of meningitis among children younger than 2 years

39
Q

Recommended Treatments for Pneumococcal Infections

A

Penicillin if susceptible
Cefotaxime or ceftriaxone if susceptible

Alternative agents

  • Macrolides: Erythromycin, Clarithromycin, Azithromycin
  • Fluoroquinolones: Levofloxacin, Moxifloxacin

requires a lower MIC to be susceptible in the spinal cord than other areas

40
Q

Enterococcus Characteristics

A

Gram positive cocci in pairs and short chains
Alpha, beta or gamma hemolytic
Group D antigen pos.
PYR pos.

41
Q

Enterococcus Epidemology

A

Originates from patient’s bowel flora
Transferred from patient to patient
Acquired through consumption of contaminated food or water

42
Q

Enterococcal are resistant to

A

Intrinsically resistant to all cephalosporins, trimethoprim-sulfa, aminoglycosides

E. faecalis susceptible to pen / amp
E. faecium resistant to pen / amp
Some strains vancomycin resistant (VRE)

43
Q

enteroccocal treatment

A

Systemic infections require ampicillin plus aminoglycoside for synergy

Linezolid (oxazolidinone: unique class of synthetic antibiotic) effective in treating VRE

44
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

An Enterococcus species

VRE

MHD #3 (11 decks)

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