Streptococci Flashcards
Overview of Streptococci
A) Gram positive cocci B) seen as Chains or diplococci C) Non-spore forming D) Facultative anaerobes ----Grow with/without oxygen E) Catalase negative
what is a Lancefield group?
Serological classification based on major cell-wall carbohydrate antigens
Groups lettered A-U, but some streptococci cannot be assigned to any group
how are streptococci species classified?
Metabolic reactions in culture media
what does culturing Strep in a blood agar medium show us?
Hemolysis pattern
what are the Hemolysis patterns?
a = partial hemolysis and green discoloration of hemoglobin b = clear zone of complete hemolysis g = no zone of clearing
Group A Streptococcal Diseases
A) Acute pharyngitis B) Pyoderma (skin/soft tissues) C) Group A streptococcal pneumonia D) Necrotizing fasciitis E) food-born outbreaks
what is another name for group A strep? (GAS)
S. pyogenes
what illnesses are S. pyogens (GAS) responsible for?
Streptococcal acute pharyngitis (strep throat) Scarlet fever (strep throat + red skin rash)
Acute Rheumatic Fever (ARF)
A) Fairly common until mid-20th century
B) Nonsuppurative sequelae (non-pus forming secondary results)
C) Pharynx is the only site of infection that is followed by ARF
D) Completely prevented by treating strep throat with full course of penicillin
Acute Post-Streptococcal Glomerulonephritis (APSGN)
A) Active inflammation in the glomeruli of the kidneys
B) Urine smoky due to proteins, leukocytes and erythrocytes, renal failure
C) Caused by only a few types of GAS
Group A Infections – Encounter
A) Live on skin and mucous membranes
B) Person to person transmission
- Infected respiratory droplets
- Hand-to-hand-to-mouth
- Food
- Skin/wound infections
can group a infections penetrate the skin?
NO- must find cut/lesion/bite/wound to enter thru
group A Bacteria bind to epithelial cells using
adhesins
Adhesins
Lipoteichoic acid (LTA)
- Cell wall of Gram positive bacteria
- Makes streptococci sticky
- Binds to fibronectin on epithelial cell surfaces (coats oropharynx cells)
Besides Lipoteichoic acid, what are the other 2 adhesins used by group A strep?
Protein F – high affinity fibronectin binding protein
M protein – keratinocytes (outer skin) adhesin
how does Group A streptococci spread?
Depends on how infection was acquired
A) On skin or mucous membranes, usually remains localized
B) Deeper tissue infections- rapid spread
Streptokinase
binds to, and activates host plasminogen
A) plasminogen breaks down blood clots
how does streptococci avoid phagocytosis?
1) M protein – rod-shaped molecule
Most important antiphagocytic factor
2) Central to pathogenesis and required for virulence
3) Hyaluronic acid capsule – mucoid capsule
4) C5a Peptidase – inactivates phagocyte chemotaxin
Hyaluronic Acid Capsule
Makes strep “slippery”, interfering with phagocyte attachment
Streptococcal Pyrogenic Exotoxins (SPEs)
1) GAS invokes intense inflammatory response in tissues
2) Superantigens activate macrophages and cause T cells to release of cytokines
- three types- SpeA, SpeB, SpeC
what is responsible for the red rash of scarlet fever
Superantigens (SPEs)
which superantigen causes streptococcal shock syndrome?
mainly SpeA
Group B Streptococci (GBS)
A) Inhabit lower GI and female genital tracts
B) cause cellulitis, arthritis, and meningitis in adults with chronic diseases
C) Polysaccharide capsule that is antigenic
–Unlike hyaluronic acid capsule of GAS
Other b-hemolytic Streptococci
1) Mainly Groups C, G, and F
2) Implicated in AGN but not ARF
Group D Streptococci
A) a- or g-hemolytic
B) Enterococci and nonenterococci
C) Normal flora of GI and genitourinary tracts
Low virulence
—usually accompany other bacterial infections
Enterococci
A) “World’s Toughest Pathogenic Bacteria”
B) Antibiotic synergism required for effective killing
Vancomycin resistant enterococci (VREs)
A) low virulence, but UNTREATABLE
Nonenterococcal Group D Streptococci
A) S. bovis – most common for human disease
B) Subacute bacterial endocarditis
C) Does not grow in high salt
D) Most strains are killed by penicillin
Viridans Streptococci
1) a-hemolytic
2) oropharyngeal flora- low virulence
3) Most common cause of subacute bacterial endocarditis
4) Produce dextrans- Adherence
Viridans Streptococci – “mutans” group
1) Responsible for dental caries
2) Surface proteins bind salivary glycoproteins on teeth (pellicle)
3) Ferment sugar to lactic acid (demineralizes enamel)
