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.
What is a primary prevention method for nosocomial infections involving S. aureus?
Elimination of nasal carriage, especially in medical professionals.
Fill in the blank: Mannitol salt agar is used to culture _______.
Staphylococcus aureus.
True or False: Foodborne transmission of S. aureus is common.
False.
What bacterium is commonly associated with deep lesions?
Staphylococcus aureus
True or False: S. aureus infections can lead to abscess formation.
True
Which of the following is a potential complication of S. aureus deep lesion infections? (A) Osteomyelitis (B) Hypertension (C) Asthma
A) Osteomyelitis
True or False: S. aureus is a Gram-negative bacterium.
False
What is the primary treatment for S. aureus infections?
Antibiotics
Fill in the blank: S. aureus can form __________, making it resistant to certain antibiotics.
biofilms
What is the main route of entry for S. aureus to cause deep tissue infections?
Through breaks in the skin
What is the incubation period for S. aureus infections?
Typically 1 to 10 days
True or False: S. aureus can be found on the skin of healthy individuals.
True
What condition can be caused by S. aureus in deep lesions that affects bone?
Osteomyelitis
Fill in the blank: __________ is a severe skin infection caused by S. aureus.
Necrotizing fasciitis
What diagnostic test is commonly used to identify S. aureus?
Culture and sensitivity testing
A “culture and sensitivity” test, often abbreviated as “C&S,” is a laboratory procedure used to identify the specific bacteria causing an infection and determine which antibiotics are most effective in treating it by growing a sample of the bacteria in a controlled environment and then exposing it to different antibiotics to see how sensitive it is to each one; essentially, it helps a doctor choose the best antibiotic for a particular infection based on the identified bacteria’s susceptibility to different medications. A positive culture indicates the presence of bacteria causing an infection, while the sensitivity results tell the doctor which antibiotic is most likely to be effective in treating the infection.
True or False: S. aureus is always pathogenic.
False
What type of toxin can S. aureus produce that contributes to its pathogenicity?
Exotoxins
Fill in the blank: The presence of __________ is a key factor in the virulence of S. aureus.
Protein A: Protein A (SpA) is a surface protein on Staphylococcus aureus bacteria that helps the bacteria evade the immune system. It’s a key virulence factor that helps the bacteria spread and cause infections.
What serious condition can arise from untreated S. aureus infections (in general)?
Sepsis: a life-threatening condition that occurs when the body’s immune system overreacts to an infection, leading to widespread inflammation and organ damage.
True or False: S. aureus can cause food poisoning.
True
What is the role of pus in S. aureus infections?
Pus indicates the presence of infection and immune response.
Fill in the blank: __________ is a common sign of inflammation in deep S. aureus infections.
Erythema: redness of the skin
What laboratory method is used to differentiate S. aureus from other staphylococci?
Coagulase test
True or False: All strains of S. aureus are resistant to penicillin.
False
What type of surgical intervention may be necessary for severe S. aureus infections?
Drainage of abscesses
What type of immune response is primarily involved in fighting S. aureus infections?
Humoral immunity: a branch of the adaptive immune system that involves the production of antibodies by B lymphocytes (B cells) in response to specific antigens. Antibodies are proteins that circulate in the bloodstream and neutralize or destroy pathogens, such as bacteria, viruses, and toxins.
True or False: S. aureus can enter the bloodstream and cause bacteremia.
True.
Bacteremia is a condition where bacteria are present in the bloodstream. It can occur when bacteria from an infection elsewhere in the body, such as the lungs, urinary tract, or skin, enter the bloodstream.
What is the significance of the capsule produced by S. aureus?
It helps the bacterium evade the immune system.
True or False: Vaccines are available to prevent S. aureus infections.
False
What is a common laboratory sign of S. aureus infection?
Elevated white blood cell count
Fill in the blank: __________ is a chronic skin condition that can be exacerbated by S. aureus.
Eczema
True or False: S. aureus can cause toxic shock syndrome.
True
What is the role of the skin’s normal flora concerning S. aureus?
They help prevent overgrowth of pathogenic bacteria.
True or False: S. aureus can survive on surfaces for long periods.
True
