Streptococci and Enterococci

Question 1

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

Answer 1

group A: Streptococcus pyogenes

group B: Streptococcus agalactiae

Question 2

Describe the structural and functional characteristics that distinguish streptococci from staphylococci

Answer 2

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

Question 3

List six clinical manifestations of Streptococcus pyogenes infection.

Answer 3

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

Question 4

Name two diseases that occur as sequelae to streptococcal infections

Answer 4

Rheumatic Fever

Acute Glomerulonephritis

Question 5

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

Answer 5

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

Question 6

Describe the limitations of Rapid Group A Detection kits

Answer 6

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

Question 7

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

Answer 7

• 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

Question 8

Name the species included in the Strep Milleri Group

Answer 8

S. anginosus,
S. constellatus,
S. intermedius

Question 9

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

Answer 9

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

Question 10

List 3 most common infections caused by Enterococci

Answer 10

Urinary tract
Mixed bacterial wound infections and decubiti
Sepsis, endocarditis

Question 11

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

Answer 11

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)

Question 12

what is the catalase test

Answer 12

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

If it bubbles it is catalase positive

Question 13

Acute Pharyngitis

Answer 13

• 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

Question 14

Impetigo

Answer 14

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

Question 15

Erysipelas

Answer 15

• 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

Question 16

Scarlet Fever

Answer 16

• 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.

Question 17

Necrotizing Fasciitis

Answer 17

• 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%

Question 18

Toxic Shock-like Syndrome

Answer 18

• 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

Question 19

Puerperal Sepsis

Answer 19

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

Question 20

Rheumatic Fever clinical presentation

Answer 20

• 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

Question 21

Acute Glomerulonephritis clinical presentation

Answer 21

• 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)

Question 22

Streptococcal pyrogenic exotoxins (SPE)

Answer 22

• 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”

Question 23

M protein of Streptococcus pyogenes

Answer 23

• 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

Question 24

Hemolysins possessed by Streptococcus pyogenes

Answer 24

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

Streptolysins and streptokinase allow spread of bacteria in tissues

Question 25

Treatment of S. pyogenes

Answer 25

Drug of Choice = Penicillin /ampicillin/amoxacillin - No resistance worldwide Pen allergic pt = Cephalosporins or Erythromycin

Question 26

clinical presentations of GBS infections | Streptococcus agalactiae

Answer 26

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

Question 27

Early onset vs late onset Streptococcus agalactiae

Answer 27

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

Question 28

treatment of S. agalactiae

Answer 28

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

Question 29

prevention of S. agalactiae

Answer 29

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

Question 30

name the species in the and Nutritionally deficient Strep Group

Answer 30

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

Question 31

Viridans Streptococci

Answer 31

``` 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

Question 32

Bovis Group – Clinical Significance

Answer 32

S. bovis causes bacteremia, meningitis, and both native- and prosthetic-valve endocarditis Isolation of S. bovis from blood is associated with carcinoma of colon**

Question 33

Streptococcus Milleri Group

Answer 33

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

Question 34

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:

Answer 34

Rheumatic fever

Question 35

Streptococcus pneumoniae can cause

Answer 35

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.

Question 36

Streptococcus pneumoniae important virulence factor is

Answer 36

Polysaccharide capsule

Question 37

Commonest cause of community acquired acute bacterial pneumonia

Answer 37

Streptococcus pneumoniae

Question 38

Most common cause of bacterial meningitis in the U.S

Answer 38

Streptococcus pneumoniae Highest rate of meningitis among children younger than 2 years

Question 39

Recommended Treatments for Pneumococcal Infections

Answer 39

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

Question 40

Enterococcus Characteristics

Answer 40

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

Question 41

Enterococcus Epidemology

Answer 41

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

Question 42

Enterococcal are resistant to

Answer 42

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)

Question 43

enteroccocal treatment

Answer 43

Systemic infections require ampicillin plus aminoglycoside for synergy Linezolid (oxazolidinone: unique class of synthetic antibiotic) effective in treating VRE

Question 44

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:

Answer 44

An Enterococcus species | VRE