Bacteria of Skin & Nasopharynx Flashcards by Annie Nebieridze

Where do streptococci reside?

nasopharynx, skin, GI, GU

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What are the two genus of pyogenic gram + bacteria?

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What is the main morphological difference between staphylococci and streptococci?

Staphylocci: clusters
Streptococci: pairs/chains

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What is a catalase test used for?

differentiating between staphylococci and streptococci species

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What does catalase do?

Converts Hydrogen peroxide into water and oxygen

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Which bacteria lack catalase?

Streptococci

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Which bacteria produce catalase?

Staphylococci

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Will a cell culture with H2O2 and streptococci produce Water and oxygen gas?

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Will a cell culture with H2O2 and staphylococci produce Water and oxygen gas?

Yes

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What makes staphylococci a major problem in hospitals? (2)

Resistant to drying/heat and resistant to many antibiotics

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How is staphylococci species usually spread in hospital settings?

nasal and skin carriage

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What are the two species of staphylococci?

staphylococcus aureus

staphylococcus epidermidis

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Which staphylococcus species is less pathogenic?

s. epidermidis, part of normal microbiota

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endocarditis from sharing needles or surgery would be most associated with which staphylococcus species?

staphylococcus epidermidis

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what diagnostic test is used to differentiate between staphylococcus aureus and staphylococcus epidermidis?

coagulase test

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Which species of staphylococcus produces coagulase?

staphylococcus aureus

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prothrombin in combination with coagulase will cause fibrinogen to do what?

convert to fibrin (blood will clot)

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What virulence factors make up the pathogenic capacity of staphylococcus aureus? (3)

Surface molecules
Extracellular factors
Toxins

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List two surface molecules of S. aureus

Fibronectin binding protein

Protein A

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Fibronectin binding protein is what kind of virulence factor?

adhesin

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Which virulence factor of Staph aureus

binds to Fc of IgG1, IgG2, IgG4
linked to peptidoglycan
prevents phagocytosis (opsonization)

protein A

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the surface molecule of S. aureus, fibronectin acts as what?

adhesin

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Give an example of the extracellular factors produced by Staph aureus

Hemolysins “alpha toxin”

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What does the alpha toxin produced by staph aureus do?

pokes holes in the membrane, forming transmembrane channels

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Where do staphylococci reside?

nasopharynx, skin, GI

Why are the transmembrane channels formed by Staph aureus alpha toxin damaging to the cell?

lyses the mammalian cells

How is Staph aureus alpha toxin used diagnostically?

observe whether mixture of red blood cells lyses on contact with bacterial culture (if yes, bacteria contain alpha toxin)

What is the alpha toxin produced by Staph aureus primary virulence function?

lyse white blood cells

What are the three exotoxins associated with Staph aureus?

- TSST-1 - Exfoliative toxins A & B - Enterotoxins

TSST-1 and enterotoxins

Which of the Staph aureus exotoxins cause toxic shock syndrome?

TSST-1

What does exfoliative toxins A & B do? (Staph aureus exotoxin)

Proteases that cleave desmosomal proteins of the skin

Exfoliative toxins A & B produced by Staph aureus were thought to be superantigens but are actually?

proteases

What is the protein that exfoliative toxins A & B of Staph aureus cleave?

desmosomal proteins of the skin

Enterotoxins produced by Staph aureus causes what kind of symptoms?

food poisoning

Why don't the enterotoxins of Staph aureus cause toxic shock syndrome since they are superantigens like TSST-1?

location, enterotoxins occur in the gut producing food poisoning

Where can Staph infections occur? (5)

- endocarditis - genitourinary - muskuloskeletal - skin & soft tissue - Toxin based

List several skin infections caused by Staphylococcus species

- Carbuncle - Folicullitis - Furuncle - Impetigo

Skin infection that Starts as a pus-filled epidermal blister that breaks to leave thick yellowish crust (common in children)

impetigo

What are symptoms of a Furuncle (boil)?

hot, tender, low fever

What is folicullitis?

infection in or around hair follicle and usually confined to that area

Why can furuncles be hard to treat?

the coagulase produced by bacteria can cause clotting wall around bacteria

What is a carbuncle?

confluence of boils which have traversed deep into the dermis entering subcutaneous fat

Suppurative infections can occur on the skin and where else?

surgical/burn wound infections and pneumonia

Scalded skin syndrome is common in?

children (esp <5)

What are symptoms of scalded skin syndrome?

Rash and peeling skin, fever

Are the rash and peeling skin of scalded skin syndrome infected with bacteria?

no, peeling caused by exfoliative toxins

scalded skin syndrome is caused by?

exfoliative toxins A & B from Staph aureus bacteria

What are symptoms associated with Toxic shock syndrome caused by TSST-1?(6)

Fever, rash, respiratory distress, irrational behavior, vomiting, multi-organ failure

What is treatment consist of for toxic shock syndrome (tsst-1)?

supportative measures & antibiotics

Staph food poisoning is different from other staph related infections because?

No infection, only intoxication by staph enterotoxins

What is the common cause of staph food poisoning?

staphylococcal enterotoxin

What is one of the ways to differentiate between intoxication and bacterial infection (of GI)?

time period of when symptoms first appear, bacterial toxins act much quicker (span of hours) while bacterial infection can take up to 48 hours

Why will heating food not make staph aureus infected food safe to eat?

the enterotoxins are heat stable

What is treatment for Staph food poisoning? (2)

- hydration | - monitor/correct electrolytes

What are symptoms of food poisoning? (2)

severe vomiting and diarrhea

Why is there only clinical presentation in diagnosing staph food poisoning?

There is no infection, (no diagnostic test to do), only toxins are causing distress to body

diagnosis of localized & systemic infections of Staph include: (3)

- culture from abscess, lesion, sputum, or blood sample - catalase, coagulase tests - antibiotic sensitivity (bc MRSA!)

What is normal treatment for Staph skin infection? (2)

- Drainage, topical treatment | - Chronic - systemic antibiotic

What is typical treatment for focal & systemic staph infection?

80-90% of Staph aureus strains are have what?

Beta lactamase

Most strains of Staph aureus even though they may have betalactamase are resistant to [...] spectrum of B-lactams

Most strains of Staph aureus even though they may have betalactamase are resistant to limited spectrum of B-lactams

What is methicillin?

betalactam antibiotic that was used some time back

What protein confers resistance to methicillin?

mecA - encodes mutant penicillin binding protein (PBP2a)

HA-MRSA has a high chance of having what kind of resistance to antibiotics?

broad spectrum of antibiotics (MDR) as well as most all first line antibiotics

CA-MRSA is rarely accompanied by resistance to what?

other antibiotics

Hospital Acquired MRSA is typically found where? In whom?

hospitalized, older individuals with immunological deficiencies

HA-MRSA is MDR, list some antibiotics that it is resistant to? (5)

tetracycline, macrolides, fluoroquinolones, aminoglycosides, Tm/sulfa)

Transposable genetic elements that have gotten so big that they no longer able to transpose (large, non-mobile cassette that captures transposons & plasmids)

pathogenicity islands

HA-MRSA is found in hosptialized individuals while CA-MRSA is usually found in whom?

otherwise healthy individuals who have not been in the hospital for at least one year

CA-MRSA is usually found as what kind of infections? (area of body)

skin

What size "pathogenicity island" is found to be in CA-MRSA genomes?

small

the mecA small "pathogenicity island" has lost and gained what functions?

loss of MDR but now it's mobile