Streptococci Flashcards
(29 cards)
streptococcus species - overview
*gram POSITIVE coccus
*grows aerobically and facultative anaerobically
*differentiated by hemolytic pattern
*short and long CHAINS
*CATALASE NEGATIVE
which strep strains are BETA hemolytic
*Group A (strep. pyrogenes)
*Group B
which strep strains are alpha hemolytic
*strep viridans
*strep pneumoniae
which strep strains are GAMMA hemolytic
*enterococcus strep
strep pyrogenes (Group A Strep - GAS) overview
*colonizes oropharynx, esp of children
*can cause suppurative and nonsuppurative infections
*infections range from minor (pharyngitis) to life threatening (necrotizing fasciitis)
strep pyogenes - virulence factors
*lipotechoic acid
**M protein
*capsule
*streptococcal pyrogenic exclusions (Spe)
*streptolysins & streptokinase
*DNases A to D
streptococcal pyrogenic exclusions (Spe) - virulence factor of S. pyogenes
*exotoxins & superantigens
*produced by lysogenic strains
*responsible for the rash of scarlet fever, toxic shock, and necrotizing fasciitis
DNases A to D - virulence factor of S. pyogenes
depolymerize free DNA that is present in pus
strep pyogenes - pathophysiology
*acquired through respiratory droplets, direct contact, or fomite
*colonizes and attaches to oropharyngeal mucosa or other mucous membranes
*IMMUNITY through M protein specific immunoglobulin
what is the best host defense (immune response) against strep pyogenes
antibodies against the M protein!
strep pyogenes - suppurative clinical infection
-pharyngitis
-scarlet fever
-pyoderma
-erysipelas
-cellulitis
-necrotizing fasciitis
-streptococcal toxic shock syndrome
-bacteremia & septic shock
necrotizing fasciitis (s. pyogenes)
deep infection of skin that involves destruction of muscle and fat layers
streptococcal toxic shock syndrome
multiorgan systemic infection resembling staph toxic shock syndrome, but pts are bacteremic and have evidence of fasciitis
*Spe gets T cells so revved up that cytokine production can’t maintain homeostasis
strep pyogenes - non-suppurative infections
-rheumatic fever
-post-strep glomerulonephritis
non-suppurative infection: rhematic fever & strep pyogenes
*complication following streptococcal PHARYNGITIS
*antibody against M protein cross-reacts with host cell structural proteins (antigenic mimicry)
*can cause inflammation of heart structures, joints, CNS, subcutaneous tissues
diagnosis of rheumatic fever & post-streptococcal glomerulonephritis
anti-DNAase, - ASO or hyaluronidase antibodies
non-suppurative infection: post-streptococcal glomerulonephritis & strep pyogenes
*complication following streptococcal CELLULITIS
*antigen-antibody complexes deposit in the glomeruli, causing renal dysfunction
diagnosis of strep pyogenes
*culture & gram stain (looking for beta hemolysis and gram + cocci in chains)
strep agalactiae (Group B Strep - GBS)
*robust capsule (type-specific capsular polysaccharides)
*gram positive in chains
*beta hemolytic
*catalase negative
group B strep - virulence factors
***polysaccharide capsule (most important - helps avoid opsonization, interferes with phagocytosis, etc)
group B strep - epidemiology
*normal flora of lower human intestine and vagina
*colonization of neonates upon birth, which can cause disease in the babies
what is the most common cause of meningitis in babies in the first month of life
group B strep
group B strep infection in adults
*usually in older adults with comorbidities
*presents as pneumonia, bacteremia, etc
prevention of Group B Strep
*screen ALL pregnant women (vaginal PCR or culture)
*if positive, we treat mom and baby with antibiotics
