Gram+ Cocci and Bacilli Flashcards
All of these are properties of Staphylococci bacteria EXCEPT:
A. they are exclusively nonmotile and nonspore forming
B. they are facultative aerobes/anaerobes
C. they may be either catalase-positive or -negative but are always coagulase positive
D. they demonstrate weak to beta-hemolytic activity
E. to cause disease, they must produce both a superantigen and a cytolysin
C.
All staph are catalase-positive, which distinguishes them from steptococci. They may be either coagulase-positive (S. aureus) or coagulase-negative (other strains of staph).
Which of the following statements about S. aureus is FALSE?
A. it contains protein A, a surface antigen that binds the Fc receptor of IgG and causes an antiphagocytic effect
B. it is a multdimensional organism with differentially regulated virulence factors
C. it uses MSCRAMMS such as LPXTG for host attachment
D. it makes the superantigens TSST-1, SEB and SEC
E. SCCmec is a mobile genetic element that encodes PBP2A for methicillin resistance, which makes S. aureus much more toxic
E.
SCCmec does not make Stapholococcus bacteria more toxic; rather, more difficult treat.
Which of the following secreted staph virulence factors is incorrectly matched with its mechanism of action?
A. alpha hemolysin: homo-heptamer necrotic to human skin
B. beta hemolysin: sensitive to cold temperature
C. gamma hemolysin: hetero-octomer pore former
D. delta hemolysin: blocks nerve repolarization
E. coagulase protein: activates clotting cascade
D.
delta hemolysin acts as a surfactant to solubilize host cell membranes. Alpha hemolysin, in addition to its dermonecrotic properties also blocks nerve repolarization
This is the Staph aureus global regulator whose ultimate effect is to increase RNA synthesis and secretion of virulence factors
AgR
(This is accomplished via the staph respiratory response system and the turning off of cell adhesion proteins.)
Why have vaccines to S. aureus failed?
Antibodies formed from vaccination help the bacteria aggregate, and wall itself off from immune cells
Which of the below statements regarding S. aureus pathogenesis is FALSE?
A. S. aureus forms boils and soft tissue abscesses by walling itself off from the host immune response via cell surface virulence factors.
B. Scalded skin syndrome is a non-inflammatory illness caused by S. aureus exfoliative exotoxins.
C. S. aureus produces alpha-toxin, which typically causes wide zones of alpha-hemolysis in blood agar.
D. Strains of S. aureus that infect the mucous membranes are less inflammatory than those that infect skin, but produce more superantigen.
E. S. aureus is the number one cause of infective endocarditis.
C.
Alpha-toxin causes wide zones of beta-hemolysis in blood agar.
This illness is defined by:
- fever >102ºF
- systolic BP < 90
- macular erythroderma
- peeling of the skin
- 3 multi-organ changes
toxic shock syndrome (TSS)
What are the 3 primary superantigens produced by Staphylococcus aureus in TSS?
- TSST-1 (causes virtually all menstrual TSS and half of “other” TSS)
- SEB and SEC (staphylococcal enterotoxin - causes the other half of “other” TSS)
Which of the following coagulase-negative staph organisms is matched incorrectly with its associated disease?
A. S. hominis: occasional cause of skin infection
B. S. lugdunensis: occasional cause of infective endocarditis
C. S. epidermidis: upper respiratory infection
D. S. saprophyticus: urinary tract infections
C.
S. epidermidis is the #1 cause of blood stream infections and is not a common cause of URIs (which are most commonly associated with S. pneumoniae and H influenzae).
Note: Coagulase-negative staphylococci are normal flora microbes and only a few cause human infections, usually in immunocompromised persons.
Which of the following statements about group A strep is FALSE?
A. it is also knowns as Streptococcus pyogenes and exhibits delayed sequelae
B. it is an unencapsulated mucoid organism
C. it produces the superantigen SPEC which is the primary cause of scarlet fever
D. it has beta-hemolytic activity
E. it is bacitracin sensitive
B.
Group A strep is a highly encapsulated (hyaluronic acid capsule) mucoid organism.
What cancer is associated with infections by Streptococcus bovis?
colorectal cancer (additionally, it is an occasional cause of infective endocarditis)
Which of the following is NOT an accurate descriptor of Streptococci?
A. They are chain-forming cocci
B. They are gram negative & alpha, beta, or gamma hemolytic
C. They are catalase negative
D. They use superoxide dismutase to survive aerobically
E. They are classified into groups by their acid extractable C carbohydrate
B.
They are gram positive organisms.
some strains of streptococcal bacteria, like group A strep, display this antiphagocytic component on their cell surface
M protein
this hemolytic exotoxin is responsible for the beta-hemolytic activity of group A strep
streptolysins O (in anaerobic conditions) and S
Which of the following cell-surface virulence factors is not associated with Streptococcus pyogenes?
A. SCCmec
B. fibronectin and Fc binding proteins
C. M protein
D. C5a peptidase
E. hyaluronic acid capsule
SCCmec is a mobile genetic element of Staphylococci that confers methicilin resistance.
M protein prevents the proper deposition of complement and is antiphagocytic. C5a peptidase cleaves C5a to prevent PMN influx. The hyaluronic acid capsule mimics self and repels phagocytes with its high negative charge. Binding proteins act as adhesins, allowing bacteria to attach themselves and gain entry to host cells.
This is part of the Group A Strep delayed sequelae and is characterized by the development of rose-petal shaped lesions in genetically susceptible persons
Guttate psoriasis
This is a type III hypersensitivity reaction that is part of the Group A Strep delayed sequelae, and is characterized by painful nodular lesions on arms and legs due to immune complex disease
Erythema nodosum
common histological finding associated with rheumatic fever
Aschof body “granuloma”
Which of the following statements about Bacillus anthracis is INCORRECT?
A. It is highly susceptible to all antibiotics
B. Its enzymatically active components are a pore-forming homo-heptamer with protein kinase protease activity, and an edema-causing adenylate cyclase.
C. Spores from the organism are carried to the cervical spine where they germinate and proliferate
D. Causes gram-positive shock with septicemia when ingested or breathed
E. Causes intoxication locally by direct contact
C.
After a 1-2 day incubation period, spores are carried to the mediastinum by phagocytic cells where they germinate and proliferate. Pulmonary anthrax is the most severe form of infection and is diagnosed via chest xray
