Bacteria: Staphylococcus Aureus Flashcards
What type of bacteria is Staphylococcus aureus?
Gram-positive cocci in clusters
Staphylococcus aureus is a type of bacteria that forms clusters and is classified as gram-positive.
What does it mean that Staphylococcus aureus is a facultative anaerobe?
It can make ATP by aerobic respiration if oxygen is present but can switch to fermentation if oxygen is absent.
What is the purpose of the coagulase test?
To distinguish S. aureus from other staph species; S. aureus is coagulase positive.
What is coagulase?
An enzyme that causes blood to clot.
What type of hemolysis does S. aureus exhibit on blood agar plates?
Beta-hemolytic: able to completely hemolyze (Hemolysis is the process of red blood cells breaking down, releasing hemoglobin, and spilling their contents) the blood which produces a clearing around and under the colony on a blood agar plate
What does hemolysis refer to?
The process of red blood cells breaking down, releasing hemoglobin.
What is alpha hemolysis?
Partial damage of red blood cells reducing hemoglobin to methemoglobin.
What is the appearance of beta hemolysis on blood agar?
Produces a clear zone around and under the colony.
What is the significance of the anterior nares in S. aureus epidemiology?
Common site of colonization.
Alpha vs Beta vs Gamma
Hemolysis
Alpha hemolysis represents a partial damage of the red blood cells which reduces the hemoglobin to methemoglobin. Methemoglobin is a form of hemoglobin that cannot carry oxygen. It is formed when the iron atom in hemoglobin is oxidized from its ferrous (Fe2+) state to its ferric (Fe3+) state. Alpha hemolysis produces a greenish or brownish zone around the bacterial colony, while beta hemolysis produces a clear zone and gamma hemolysis produces no visible change. Beta hemolysis is the complete breakdown of red blood cells, while gamma hemolysis is the lack of red blood cell breakdown
How can transmission of S. aureus be stopped?
Handwashing.
What is an enterotoxin?
A substance that is harmful to the digestive system, produced by certain bacteria.
What can cause symptoms such as cramps, nausea, vomiting, or diarrhea?
Consumption of food contaminated with enterotoxins.
What is a furuncle?
A superficial skin infection that usually develops in a hair follicle (aka boil)
What is a carbuncle?
When multiple boils combine.
What is bullous impetigo?
Blisters containing many staphylococci in the superficial layer of the skin.
What serious condition can acute osteomyelitis caused by S. aureus lead to?
Infection of the bone.
Can be caused by the infection of S. aureus in deep lesions.
What is scalded skin syndrome caused by?
Exfoliatin-producing strains of S. aureus.
What are the early findings of toxic shock syndrome?
Fever, vomiting, diarrhea, and muscle pain.
What is the drug of choice for treating MRSA?
Vancomycin.
What is the mechanism of action of the protease in scalded skin syndrome?
Causes cleavage of desmosomes, leading to the scaly appearance of the skin.
Which antibiotics are some S. aureus strains resistant to?
Penicillin and other beta-lactam antibiotics.
What method is used to test for catalase in bacteria?
Mixing bacteria with hydrogen peroxide.
What indicates a catalase positive result?
Formation of bubbles when mixed with hydrogen peroxide.