Streptococci, enterococci, pneumococci Flashcards
What does streptococcus pyogenes do?
pus-forming
What streptococci are typically seen
as diplo-cocci?
Streptococcus pneumoniae
___-hemolysis on blood-agar plates causes clearing at and around colonies in Streptococcus pyogenes
B (beta)
___-hemolysis shows greening due to partial lysis of erythrocytes in S.mitis and S.pneumoniae
a (alpha)
What degrades hemoglobin and causes green on blood plates?
pneumolysin
Green color sheen has given the name ________ to many α-hemolytic Streptococcilike the caries-causing: S.mutans, S.mitis, S.salivarius, S.sanguis
viridens
What are the two main B-hemolysis bacteria in the streptococcal family?
S. pyogenes
S. galactiae
What is the M protein?
cell wall component, >100 serotypes, membrane-anchored: is an important virulence factor for streptococci
What bacteria is M protein, G protein, capsule, streptolysins, and superantigens a main virulence factor for?
streptococci
What does the M protein do?
- anti-M antibodies prevent infection of S.pyogenes but many serotypes. So protective immunity is type-specific
- M protein binds keratinocytes, the main cell type in outer skin layer
- M protein binds fibrinogen, blocking surface from complement system components
- M protein binds complement control proteins
- Inhibits formation of opsonins by complement cascade
What do capsules do?
prevent phagocytosis
- antibodies are ineffective against them
M protein shows adhesion for what?
fibronectin and strong adhesion to keratinocytes (skin)
M protein anti-complement action through Factor ___
H
Capsular _______________ destroys opsonizing C3b complement opsonization
C3 peptidase
What do G proteins do?
binds Fc of IgG, preventing phagocytosis based on FcReceptors
C5a peptidase in Group ___ Streptococci
A
- group A = S. pyogenes
What does C3b peptidase do?
cleaves the complement component into inactive fragments
What is a microbial anticomplement strategy involving inactive complement chemotaxin C5a?
- inactive complement chemotaxin C5a from group A activates a surface plasminogen to plasmin
- cleaves C3b
What does streptococcus pyogenes do?
- accumlates pus
- inserts into membranes and forms pores that allow fluids to enter
What are strptolysins S and O?
lysis of erythrocytes (direct lysis; basis of β-hemolysis) and of phagocyte lysosomal membranes (indirect lysis of leukocytes)
What does the superantigen strain of streptococcus pyogenes do?
- fever, vomiting, diarrhea, muscle aches, rash, low bp
- systemic toxic effects due to massive release of cytokines
What diseases do streptococcus pyogenes cause?
- causes pharyngitis and other infections
What diseases do superantigen streptococcus pyogenes cause?
- streptococcal toxic shock, streptococcal pyrogenic exotoxins (SPE)
What bacteria causes scarlet fever?
streptococcus pyogenes
What is the virulence factor for scarlet fever?
superantigen SPE (streptococcal pyrogenic exotoxins)
What can pyrogenic SPE cause (Streptococcal Pyrogenic Exotoxins)?
- scarlet fever
- impetigo
- erysipelas
What causes this flesh eating disease?
strept. pyogenes
- streptococcal gangrene
What does “flesh-eating” strept. pyogenes (Necrotizing fasciitis) cause?
Progression to deep, systemic
infection leads to multi-organ
failure and death
What type of reaction is glomerulonephritis?
type III hypersensitivity
What type of reaction is rheumatic fever?
type II hypersensitivity
What can come with acute rheumatic fever?
myocarditis and arthritis
What bacteria causes rheumatic heart disease?
streptococci
What are the symptoms of acute rheumatic fever?
- non-suppurative sequela with some strains
- <10% of population is susceptible
- fever is non-responsive to penicillin because disease is autoimmune
- high frequency of reoccurrence
What are the characteristics of streptococcus agalactiae?
Group B
β-hemolytic (<2% non-hemolytic)
chain-like growth
aerobic
polysaccharide capsule
What does streptococcus agalactiae do?
- Normal occurrence in the lower gastrointestinal tract
- Does not cause disease in healthy people
- pneumonia in neonates
- bacteremia and meningitis in neonates
- urinary infections in pregnant women
How does the maternal antibodies prevent infection of neonates against streptococcus agalactiae?
Neutralizing antibodies against group B polysaccharide Ag develop quickly and protect
What is the epidemiology of enterococcus faecalis?
- more common in elderly
- more common in those with long hospitalization (high nosocomial risk and antibiotic resistance)
What is the level of antibiotic resistance in enterococcus faecalis?
high, multiple antibiotic resistances (plasmid and chromosomal)
What are the characteristics of streptococcus pneumoniae?
- α-hemolytic
- Gram+ diplococci
What can streptococcus pneumoniae cause?
Pneumococcal pneumonia
What type of strains of streptococcus pneumoniae are virulent
only encapsulates strains (smooth colonies)
What are the characteristics of pneumococcal pneumonia?
- high carrier rates for S. pneumoniae
- capsular vaccine avaliable
What are the characteristics of Mycoplasmal pneumonia?
- no vaccine
What are the characteristics of Klebsiella pneumonia?
- Klebsiella pneumoniae (enterobacterium)
- often resistant to antibiotics
- fatal nosocomial pneumonias
- No vaccine
What are the virulence factors for S. pneumoniae?
- a-hemolysis
- capsule
- secretory IgA protease
What bacteria causes meningitis?
S. pneumoniae
