Streptococci + Enterococci Flashcards
Name the species of streptococci associated with Lancefield groups A and B.
Streptococcus pyogenes = Group A
Streptococcus agalactiae = Group B
What test is the major differentiator b/w staph and strep?
Staph is catalase positive, strep is catalase negative
Contrast how strep and staph appear in culture.
- Staph are cocci that grow in clusters
- Strep are cocci that grow in pairs and chains
Differentiate amongst the alpha, beta, and gamma hemolytic classes.
- Alpha: incomplete hemolysis
- Beta: complete hemolysis
- Gamma: No hemolysis
Are strep and staph alpha, beta, or gamma-hemolytic?
Both beta
*List 6 (there are actually 7) clinical manifestations of Streptococcus pyogenes infection. (there will be more questions detailing them, but these AREN’T objectives)
- Acute pharyngitis
- Impetigo
- Erysipelas
- Scarlet fever
- Necrotizing fasciitis
- Toxic-shock-LIKE syndrome
- Puerperal Sepsis
Besides group A & B strep, provide 4 other groups we should know. (not an objective but good overview)
- Other Beta hemolytic streptococci
- Viridans group streptococci
- Nutritionally Deficient streptococci
- Streptococcus pneumoniae
What are the sx of acute pharyngitis?
What demo gets it?
- Fever, sore throat, headache, swollen lymph nodes
- 5-15 year old
(5% asymptomatic carriers. Transmitted by respiratory droplets)
How does acute pharyngitis resolve?
Why does it reoccur? (be specific)
- Resolves on its own (self-limiting)
- Recurs because there are 80 forms of M protein (AB only adds one at a time)
What is impetigo (describe dz)?
What demo gets it?
- Localized skin disease: pustule with yellow crust; appears on face or extremities (a/w trauma, insect bites)
- 2-5 y/o children
What is erysipelas/what sx are associated w/it?
What body area is most affected?
- Spreading erythema with well demarcated edge on the face
- Fever and lymphadenopathy
- Lesions often on face and often with accompanying steptococcal pharyngitis
- Legs most often affected
What causes Scarlet fever (be specific)?
Describe the signs/sx.
- Caused by erythrogenic exotoxin (complication of streptococcal pharyngitis)
- Fever, followed by rash (12-48 hrs later) first appears as tiny red bumps on the chest and abdomen: fine, red, and rough-textured blanches upon pressure. Generally starts on the chest, armpits, and behind the ears
- Spares the face (although some circumoral pallor is characteristic)
- Rash fades (desquamation) 3-4 days after appearance
- Bright red tongue with a “strawberry” appearance
What tissue layer does necrotizing fasciitis affect?
How dangerous is it?
What’s an important sign to recognize it?
- Deep subQ tissue
- Mortality exceeds 50%
- Pain exceeds appearance of what it should be
Toxic shock toxin syndrome 1 is often caused by the bacteria ___________, while toxic shock-like syndrome is often caused by the bacteria ___________.
- Staph. aureus
- Group A strep
What demo typically suffers from puerperal sepsis?
What kind of conditions can it lead to? (don’t memorize)
- 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
Name two diseases that occur as sequelae to streptococcal A infections.
- Rheumatic fever
2. Acute glomerulonephritis
What type of dz is rheumatic fever?
When does it occur w/r/t strep pharyngitis?
Associated sx?
How is it related to the heart?
- Nonsuppurative inflammatory disease
- Occurs 1-5 weeks after strep pharyngitis
- 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
Why does acute glomerulonephritis sometimes occur s/p strep A infections?
Associated sx?
- Certain M types are “nephritogenic”- Ag + AB + C’ deposited in glomeruli
- Edema, HTN, hematuria, proteinuria
Name 4 virulence factors associated with Streptococcus pyogenes (and try to think of up to 10).
- Streptococcal pyrogenic exotoxins (SPE)
- M protein
- Streptolysins
- Streptokinase
- Capsular polysaccharide
- Lipoteichoic acid
- Hemolysins
- Hyaluronidase
- Nucleases
- C5a peptidase
- Streptokinase
What do SPEs work as strep A virulence factors?
Streptococcal pyrogenic exotoxins
- Superantigens that stimulate cytokine response leading to shock and organ failure
- A, B, and C types
Differentiate b/w exo and endotoxin.
Endotoxin: released from gram-pos
Exotoxin: part of LPS (lipid A) of gram-neg
How does M protein work as a strep A virulence factor?
- Binds to epidermal cells, allows bacteria to survive (strains without M protein are avirulent)
- Antiphagocytic (degrades complement C3b) (ABs to M protein activate complement and kill the bacteria)
How does streptolysin serve as a strep A virulence factor?
What are the 2 types?
As a hemolysin
- Streptolysin S (oxygen stable, non-antigenic)
- Streptolysin O (oxygen labile, ASO antibodies)
What are the 3 drugs of choice for streptococcus pyogenes?
PCN, ampicillin, amoxicillin
- Cyclosporins could also work
What are 3 antimicrobials we’ve learned so far that have no resistance worldwide?
PCN, ampicillin, amoxicillin (they do have allergies, though)
If a pt is allergic to PCN, what might you given them to treat S. pyogenes?
Erythromycin
What infections are a/w Streptococcus agalactiae? (no objective)
- *Neonatal pneumonia, sepsis, meningitis
- Skin and wound infections in adult diabetic patients
- Endocarditis
(Part of normal flora in throat, vaginal and GI tract)
What bacteria is a/w perinatal GBS (group B strep) disease?
Streptococcus agalactiae (GBS = group B strep)
When should cultures be performed for perinatal GBS dz, and what should be swabbed?
Vaginal/rectal swabs collected at 35-37 weeks gestation
What are the 3 types of perinatal GBS disease, and the sx a/w each?
- Early-onset neonatal disease (1st week of life): bacteremia, PNA, or meningitis
- Late-onset neonatal disease (1 week to 3 months age): bacteremia w/ meningitis
- Pregnant women: UTI’s and carrier
Explain the role of S. agalactiae (Strep B) in causing neonatal disease. (pathogenesis)
- Maternal colonization of vagina or rectum exposes baby at delivery
- Lack of protective maternal antibody
- Sialic acid on polysaccharide capsule inhibits C’ allowing organisms to multiply
What is the drug of choice to fight S. agalactiae?
What could you add to enhance killing?
Penicillin or ampicillin
- Gentamycin
Describe the limitations for Rapid Group A Detection kits.
What happens if someone is negative on rapid strep?
Not that sensitive: best sensitivity only close to 85%
- Everyone who is negative therefore gets cultured
What’s a group of Viridians streptococci that we should know?
Bovis group
Isolation of Strep Bovis (Viridians) Group from blood is strongly associated w/ __________.
Carcinoma of colon
Name the species included in the Strep Milleri Group. (3)
- S. anginosus
- S. constellatus
- S. intermedius
Name the species included in the Nutritionally-deficient Streptococci Group. (3)
- Abiotrophia
- Granulicatella
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: Toxic shock-like syndrome Rheumatic fever Scarlet fever Puerperal fever Acute glomerulonephritis
Rheumatic fever
Is strep pneumoniae gram-pos or negative?
Gram-positive
Most common cause of community acquired acute bacterial pneumonia
Describe the shape of s. pneumoniae on culture?
- 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.
When cultured on blood agar, s. pneumoniae are ______ (alpha/beta/gamma) hemolytic.
Alpha (incomplete)
Is s. pneumonia catalase pos or neg?
Is it bile soluble or insoluble?
*What is it inhibited by? (special lab test)
- Catalase negative
- Bile soluble
- Inhibited by ethylhydrocupreine (Optochin)
What are the recommended tx’s for s. pneumoniae? (no treatments are on objectives, part of pharm)
- Penicillin if susceptible
- Cefotaxime or ceftriaxone if susceptible
- Alternative agents: Macrolides: Erythromycin, Clarithromycin, Azithromycin. Fluoroquinolones: Levofloxacin, Moxifloxacin
List the two major species of Enterococus causing infection in humans.
- E. faecalis susceptible to pen / amp
2. E. faecium resistant to pen / amp
List the 3 most common infections caused by Enterococcus species.
(Do you heart trees?)
- Urinary tract
- Mixed bacterial wound infections and decubiti
- Sepsis, endocarditis
When cultured on blood agar, this alpha-hemolytic pathogen shows up as “dime-shaped” colonies w/sinking centers.
S. Pneumoniae
Enterococcus are formally known as group ___ streptococci.
D
Explain the penicillin (or ampicillin) susceptibility and resistance for E. faecalis and E. faecium.
*What other abx are some strains resistant to?
- E. faecalis susceptible to pen / amp
- E. faecium resistant to pen / amp
- Vancomycin (VRE)- Vancomycin-resistant enterococcus, becoming more common
What’s an important test that we should know for detecting enterococcus? (are they pos or neg?)
PYR (they are PYR positive)
