Bacteriology 8: Streptococcus/Enterococcus Flashcards
Streptococcus morphology
Gram (+)
Cocci
Most arranged in chains (except S.pneumomiae)
Most members of the Streptococcus family commonly are found where?
As a normal flora of the mouth and gut EXCEPT S.pyogenes
lol
How does streptococcus differentiate from staphylococcus with the catalase test and salt test
Staphylococci = all of them are catalase (+) therefore must do a coagulase test to exclude S.aureus. All of them are also salt tolerant in the mannitol-salt test.
Streptococci = all of them are catalase (-) and not salt tolerant
Therefore we can distinguish staph and strep with a catalase test and a mannitol-salt test
How are most streptococci classified in the lancefield group
Based on a carboyhydrate antigen found on the cell wall
Group A Streptococci (GAS): Includes Streptococcus pyogenes, which causes strep throat, scarlet fever, and rheumatic fever.
Group B Streptococci (GBS): Includes Streptococcus agalactiae, which is a major cause of neonatal infections
Cell wall = peptidoglycan layer
Not all streptococci can be classified by this system, though; for example, Streptococcus pneumoniae don’t fit into the Lancefield groups.
Alpha-hemolytic streptococcus species
Can be further classified with optochin-sensitive vs. optochin-resistant
optochin-sensitive
-streptococcus pneumoniae
optochin-resistant
-Group D and viridans streptococci
Beta-hemolytic streptococcus species
Can be further classified b/w bacitracin-sensitive and bacitracin-resistant
bacitracin-sensitive
-group A streptococci (Streptococci Pyogenes)
bacitracin-resistant
-group B, C streptococci
Virulence factors- surface antigens for GAS
M-protein
More than 100 stereotypes of M protein = pathogenic
The more pathogenic forms can cause serious sequelae of strep throat like rheumatic fever (b/c autoimmune rxn)
M-protein
-inhibit phagocytosis
-inactivates the complement system
-Antigenic
sticking out of the capsule in bacteria like Protein F, protein G and the M protein and lipoteichoic acid (b/c gram (+))
Virulence factors- surface antigens for GAS
Protein G
Binds to the Fc portion of antibodies, thereby interfering with/ opsonization
sticking out of the capsule in bacteria like Protein F, protein G and the M protein and lipoteichoic acid (b/c gram (+))
Virulence factors- surface antigens for GAS
protein F
Responsible for attachment to host cells
sticking out of the capsule in bacteria like Protein F, protein G and the M protein and lipoteichoic acid (b/c gram (+))
Virulence factors- surface antigens for GAS
Hyaluronic acid capsule
Inhibits phagocytosis
(We know this… capsule = virulence factor)
Virulence factors- surface antigens (GAS)
Group A carbohydrate
Protection against lysozyme
(We know that the lysozyme is an enzyme that will cleave the peptidoglycan cell wall- specifically the glycosidic bond b/w NAG-NAM carbohydrate backbone)
Therefore group A carbohydrate surface antigen must be imbedded w/n the cell wall to protect against lysozymes.
It anchors on top of the the cytoplasmic membrane (inner membrane)
Which surface antigens (virulence factors) are found outside the capsule for possible antibody interaction on GAS?
Protein G
Protein F
M protein
The hyaluronic acid = capsule
Group A carbohydrate = from outer surface of inner membrane to top layer of cell wall (peptidoglycan layer)
Virulence factors - toxins (GAS)
Streptococcal pyrogenic exotoxins (SPE)
Erythrogenic toxins b/c they cause the skin to redden
-they cause the red rash that isass. w/ scarlet fever
-superantigen ass. w/ toxic shock syndrome**
Virulence factors - toxins (GAS)
Streptolysin O
Causes lysis of RBCs, leukocytes, and platelets but only under anaerobic conditions
Virulence factors - toxins (GAS)
Streptolysin S
Causes lysis of RBCs, leukocytes, and platelets but under both under anaerobic conditions and aerobic
Virulence factors - enzymes (GAS)
-streptokinase
Dissolves blood clots
(We know this… kinases will dissolve the blood clots created by a coagulase enzyme for virulence factor)
Virulence factors - enzymes (GAS)
C5a peptidase
Degrades C5a from the complement cascade and prevents the recruitment of neutrophils
Virulence factors - enzymes (GAS)
-hyaluronidase
The primary function of hyaluronidase is to degrade hyaluronic acid, a key component of the extracellular matrix, particularly in connective tissues.
Hyaluronidase is an enzyme produced by several types of bacteria, including Streptococcus, Staphylococcus, and Clostridium species, as well as some other organisms.
Name all the virulence factors describes as toxins, enzymes, and surface antigens under a streptococcus bacteria (GAS)
Surface antigens
-M protein
-Protein G
-Protein F
-Hyaluronic acid capsule
-Group A carbohydrate
toxins
-SPE
-streptolysin O
-Streptolysin S
enzymes
-streptokinase
-C5a peptidase
-hyaluronidase
URS infection caused by streptococcus group A (GAS)
Strep. Pharyngitis
GAS = S.pyogenes
Skin infection caused by streptococcus group A (GAS)
Impetigo
Soft tissue infections caused by streptococcus group A (GAS)
Skin trauma/infection spreads into surrounding lymph nodes and tissues
Erysipelas
-involves the epidermis and upper dermis
cellulitis
-involves both the superficial and deep layers of the skin (dermis and subcutaneous fat)
can progress to deeper tissues or sepsis in the very young, very old, and immunocompromised
Necrotizing Fasciitis
-“flesh-eating disease”
-necrotizing fasciitis is a severe and rapidly progressing soft tissue infection. It primarily affects the fascia, which is a layer of connective tissue that surrounds muscles, nerves, and blood vessels.
-starts as a minor infection or break in the skin, then progresses rapidly in the fascia, resulting in the destruction of muscle/fat tissue due to a variety of enzymes and toxins.
therefore it invades the CT and muscle
