Microbiology to know for AKT Flashcards
(62 cards)
Should an asymptomatic person who tests positive for MRSA (nasal swab) while in hospital receive treatment?
Yes. The patient should receive eradication with shampoos/nasal creams to protect those around him, and to prevent him from becoming sick with
overgrowth of his current MRSA should his immune system become compromised by
another illness or if antibiotic treatment removes competing commensals.
Which of the following statements best describes a Staphylococcus Aureus infection?
a. S. aureus is not a commensal organism.
b. S. aureus is a coagulase negative bacterium.
c. Ricardo ideally should be moved into a
side room, and the bay he was sleeping in
previously should be deep cleaned.
d. If he does not approach any of the other patients, Ricardo cannot pass on the infection.
e. S. aureus has adhesin proteins, which bind the Fc region of IgG (Fab) to disrupt their function and Protein A, which helps the bacterium adhere to host proteins as well as evade the immune system.
a. S. aureus is not a commensal organism. Incorrect. 30% of the population have S.
aureus on their skin; 10% of this is MRSA.
b. S. aureus is a coagulase negative bacterium. Incorrect. Staph Aureus is Coagulase
positive. Coagulase stimulates clotting and plays a role in immune evasion.
c. Ricardo ideally should be moved into a side room, and the bay he was sleeping in
previously should be deep cleaned. Correct. It is important that the chain of infection
is broken. Cleaning items which may act as fomites will prevent indirect transmission
to other patients. In practice, this rarely due to lack of side rooms and patients are
barrier nursed.
d. If he does not approach any of the other patients, Ricardo cannot pass on the
infection. Incorrect. He can still pass it on by indirect transmission. Therefore, he
needs to be moved into a side room or barrier nursed so that he is not touching items
that other patients will then be handling.
e. S. aureus has adhesin proteins, which bind the Fc region of IgG (Fab) to disrupt their
function and Protein A, which helps the bacterium adhere to host proteins as well as
evade the immune system. Incorrect. S aureus has both; however, the functions are
reversed.
Staph aureus is coagulase
positive
What action does coagulase have in bacteria?
Coagulase stimulates clotting and plays a role in immune evasion.
What do adhesion proteins do, such as those found in Staph aureus?
Adhesion proteins help the bacterium adhere to host proteins as well as
evade the immune system.
What the function of Protein A in Staph aureus bacteria?
Protein A binds the Fc region of IgG (Fab) to disrupt their function.
Time elapsed between exposure to a pathogen
and developing symptoms.
Incubation period
The presence of bacteria on a body surface
without causing harm.
Bacterial colonisation
A symbiotic relationship in which one population
derives benefit and the other is neither harmed
nor benefits.
Commensalism
Molecules produced by a pathogen that
increase its’ effectiveness at causing disease.
Virulence factors
An infection that does not produce symptoms
unless activated but may still be transmissible.
Latent infection
An infection caused by multiplication of an
organism that was already present in the body.
Endogenous infection
The mechanism by which latent infections begin
to multiply and spread.
Reactivation
An infection caused by invasion by a bacterium
from the environment.
Exogenous infection
A commensal bacteria of anterior nares
Staph aureus
Which type of bacteria forms “golden colonies” on blood agar?
Staph aureus
Microscopic appearance/staining of Staph aureus?
Gram positive cocci in clusters
What percentage of the population are carriers of Staph aureus?
20-60%
What virulence factors of S.aureus provide (host) tissue adherence and immune evasion “cloaking?”
Adhesion proteins
Elastin-binding protein, collagen-binding protein, and fibronectin binding protein are examples of
Adhesion proteins
Surface proteins such as adhesion proteins are associated with which growth phase of bacteria?
Exponential (log) growth phase
Secreted proteins of S. aureus are associated with which growth phase of the bacteria?
Stationary phase
How does the capsule of S. aureus play a role in evading the immune system (preventing opsonisation?)
It blocks antibodies from binding to antigens such as the peptidoglycan layer, and also by binding of cell wall opsonins to complement receptors and Fc region of antibodies blocks opsonisation
Commonest cause of bacteraemia?
Staph aureus
