Flashcards in Streptococci Deck (48)
What are the main features of streptococci that differentiate them from staphylococci?
– Catalase negative
– Cocci in pairs and chains
– Requires complex media
– Prefers anaerobic or carbon dioxide atmosphere
What is a catalase test?
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
What are the 3 groups of streptococci?
What is Lancefield Group A?
What is Lancefield Group B?
What are the six possible clinical manifestations of streptococcus agalactiae?
-Toxic Shock Like Syndrome
– 5-15 year old with fever, sore throat, headache, swollen lymph nodes
– 5% asymptomatic carriers
– Transmitted by respiratory droplets
– Reoccurs due to lack of type specific antibody to M protein
– 2-5 year old child with localized skin disease
– Associated with trauma / insect bites
– Pustule with yellow crust
– Appears on face or extremities
– Speading erythema with well demarcated edge on the face
– Fever and lymphadenopathy
– Lesions often on face and often with accompanying steptococcal pharyngitis
– 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%
• 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
– 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
-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
What are common post-streptococcal sequelae of untreated strep infections?
Hospital acquired infection
– 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
– Edema, hypertension, hematuria, proteinuria
– Occurs after skin / respiratory infection
– Certain M types are “nephritogenic”
￼– Antigen + antibody + C’ deposited in glomeruli seen on kidney biopsy
What are the 4 virulence factors of S. pyogenes?
• 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
What is the function of 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”
What is the main factor in the pathogenesis of S. pyogenes?
Adherence via its M protein.
- Binds to epidermal cells
- Allows bacteria to survive
- Strains without M protein are avirulent
What is the main treatment for S. pyogenes?
What is the main target population in pathogenesis of Streptococcus agalactiae?
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
How are Group B bacterial infections prevented?
• 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%
What is Streptococcal agalctiae treated with?
What is used to treat Streptococcal pyogenes in patients with penicillin allergy?
What is used to treat Streptococcal agalctiae in patients with penicillin allergy?
What are the limitation of Rapid Group A Detection Tests?
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.
What are the characteristics of viridian's 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
What is isolation of S. bovis from blood associated with?
Carcinoma of the colon
What are the species in the S. milleri group?
How can the S. milleri group be determined from the agar plate?
Have characteristic caramel (butterscotch) odor when cultured on agar plates
What are the species in the Nutrient Deficient Group?
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
B. Rheumatic fever (heart murmur)
Where is S. pneumoniae normally found?
• Normal flora of human upper respiratory tract
• Gram-positive bacteria
What are the virulence factors of S. pneumoniae?
• sIgA protease – prevents IgA-mediated binding of pneumococcal cells to mucus
• Teichoic acid/peptidoglycan – activates complement by alternative pathwaymediates inflammation
￼￼￼– Precipitates C-reactive protein (CRP)
What is the commonest cause of community acquired
acute bacterial pneumonia?
What does S. pneumoniae look like under the microscope?
• 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.
What are the main pathogenic Enterococcus species?
• E. faecalis “pertaining to feces”
• E. faecium “of feces”
What are the 3 most common Enterococcal infections?
• Urinary tract
• Mixed bacterial wound infections and decubiti
• Sepsis, endocarditis
What are the features of Enterococcus?
• Alpha, beta or gamma hemolytic
• Group D antigen positive
• PYR positive
How are S. pneumoniae determined using an agar plate?
What are the metabolic indications of S. pneumoniae?
• Catalase Negative
• Bile Soluble
• Inhibited by ethylhydrocupreine
What are the reactions of E. faecalis and E. faecium to penicillins?
• E. faecalis susceptible to pen / amp
• E. faecium resistant to pen / amp
What is the intrinsic resistance of Enterococcus?
Intrinsically resistant to all cephalosporins, trimethoprim-sulfa, aminoglycosides