Streptococci and Enterococci Flashcards
Name the species of streptococci associated with Lancefield groups A and B
group A: Streptococcus pyogenes
group B: Streptococcus agalactiae
Describe the structural and functional characteristics that distinguish streptococci from staphylococci
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
List six clinical manifestations of Streptococcus pyogenes infection.
Acute Pharyngitis Impetigo Erysipelas Scarlet Fever Necrotizing Fasciitis Toxic Shock-like Syndrome
Name two diseases that occur as sequelae to streptococcal infections
Rheumatic Fever
Acute Glomerulonephritis
Name four virulence factors associated with Streptococcus pyogenes and the mechanisms by which they enhance infection
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
Describe the limitations of Rapid Group A Detection kits
the sensitivity is only 70% therefore there will be many false negatives. (high specificity so no false positives)
Explain the role of S. agalactiae in causing neonatal disease and how neonatal disease may be prevented.
- 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
Name the species included in the Strep Milleri Group
S. anginosus,
S. constellatus,
S. intermedius
List the two major species of Enterococus causing infection in humans and explain their association with penicillin (or ampicillin) susceptibility and resistance.
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
List 3 most common infections caused by Enterococci
Urinary tract
Mixed bacterial wound infections and decubiti
Sepsis, endocarditis
Identify the key morphologic and phenotypic tests used for identification of S. pneumoniae
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)
what is the catalase test
scrape a colony off a plate and put in a drop of hydrogen peroxide.
If it bubbles it is catalase positive
Acute Pharyngitis
- 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
Impetigo
- 2-5 year old child with localized skin disease
- Associated with trauma / insect bites
- Pustule with yellow crust
- Appears on face or extremities
Erysipelas
- 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
Scarlet Fever
- 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.
Necrotizing Fasciitis
- 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%
Toxic Shock-like Syndrome
- 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
Puerperal Sepsis
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
Rheumatic Fever clinical presentation
- 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
Acute Glomerulonephritis clinical presentation
- 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)
Streptococcal pyrogenic exotoxins (SPE)
- 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”
M protein of Streptococcus pyogenes
- 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
Hemolysins possessed by Streptococcus pyogenes
Streptolysin S (oxygen stable, non-antigenic) Streptolysin O (oxygen labile, ASO antibodies)
Streptolysins and streptokinase allow spread of bacteria in tissues
Treatment of S. pyogenes
Drug of Choice = Penicillin /ampicillin/amoxacillin
- No resistance worldwide
Pen allergic pt = Cephalosporins or Erythromycin
clinical presentations of GBS infections
Streptococcus agalactiae
Neonatal pneumonia, sepsis, meningitis
Skin and wound infections in adult diabetic patients
Endocarditis
Part of normal flora in throat, vaginal and GI tract
Early onset vs late onset Streptococcus agalactiae
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
treatment of S. agalactiae
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
prevention of S. agalactiae
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
name the species in the and Nutritionally deficient Strep Group
Abiotrophia
Granulicatella
require another organism that is producing vitamin B-6 to grow
Viridans Streptococci
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
Bovis Group – Clinical Significance
S. bovis causes bacteremia, meningitis, and both native- and prosthetic-valve endocarditis
Isolation of S. bovis from blood is associated with carcinoma of colon**
Streptococcus Milleri Group
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
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:
Rheumatic fever
Streptococcus pneumoniae can cause
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.
Streptococcus pneumoniae important virulence factor is
Polysaccharide capsule
Commonest cause of community acquired acute bacterial pneumonia
Streptococcus pneumoniae
Most common cause of bacterial meningitis in the U.S
Streptococcus pneumoniae
Highest rate of meningitis among children younger than 2 years
Recommended Treatments for Pneumococcal Infections
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
Enterococcus Characteristics
Gram positive cocci in pairs and short chains
Alpha, beta or gamma hemolytic
Group D antigen pos.
PYR pos.
Enterococcus Epidemology
Originates from patient’s bowel flora
Transferred from patient to patient
Acquired through consumption of contaminated food or water
Enterococcal are resistant to
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)
enteroccocal treatment
Systemic infections require ampicillin plus aminoglycoside for synergy
Linezolid (oxazolidinone: unique class of synthetic antibiotic) effective in treating VRE
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:
An Enterococcus species
VRE
