Staphyloccocus Flashcards

(34 cards)

1
Q

Name the 7 Staphylococcus species

A
  1. S. aureus
  2. S. epidermis - surgical implantation infections
  3. S. lugdunensis SluG - S. aureus like
  4. S. saprophyticus -UTI
  5. S.pseudointermedius - dogs and cats
  6. S. haemolyticus
  7. S. schleiferi -dog ears
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2
Q

List the general characteristics for Staphylococcus SPECIES

A

Gram‐positive, nonmotile, non‐spore‐forming

single cocci, in pairs, as tetrads, or as short chains

Usually all catalase positive, but few rare spp are negative

grow in the presence of 10% NaCl - MSA +

facultative anaerobes

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3
Q

Who is known as coagulase positive?

FREE COAGULASE

AND

BOUND COAGULASE (clumping factor)

A

S. aureus

ALL produce free coagulase
(tube +)

85-90% produce clumping factor (bound coagulase) detected on Staphaurex. SpaA also detected by Staphaerux

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4
Q

Who is known as coagulase negative

and how are the CoNS distinguished?

A

novobiocin‐susceptible

S. epidermis group

  1. S. lugdunensis
  2. S. pseudointermedius
  3. S. scheiferi
  4. S. haemolyticus

novobiocin‐resistant
1. S. saprophyticus (like a STI)

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5
Q

What is the difference between the 2 types of coagulases?

A

FREE coagulase is SECRETED reacts with a globulin plasma factor (coagulase-reacting factor) to form staphylothrombin. Staphylothrombin then catalyzes the breakdown of fibrinogen to insoluble fibrin.
(no bacteria seen here) = TEST TUBE +

Bound coagulase (attached to bacterial cell wall) converts fibrinogen into fibrin (clot formation). Latex agglutination assays used to detect bound coagulase of S. aureus on the bench. = SLIDE OR STAPHAERUEX +. Latex agglutination assay (with fibrinogen and IgG)
Beads coated with fibrinogen and IgG

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6
Q

Which non-S aureus strains produce free or bound coagulase?

Name the 3 species and how they differ

A

SLUG and S. schlefeiri = have clumping factor (BOUND) but DON’T secrete FREE COUAGULASE

Veterinary S. intermedius secrete free coagulase!! TEST TUBE POSITIVE

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7
Q

Name the non-S. aureus strains that can be beta hemolytic and cause similar disease to S. aureus (3) “LIS”.

And how to to distinguish them from S. aureus with biochemicals

A

S. lugdenensis - PYR and Ornithine decarboxylase POSITIVE (S. aureus is negative) BOTH POSITIVE = RED

S. intermedius group (S. intermedius, pseudointermedius, delphini) - Voges-Proskauer (VP) test detect the production of acetoin (also known as acetylmethylcarbinol) from glucose fermentation POSITIVE = RED

S. schleiferi - PYR + = red
Ornithine decarboxylase negative = yellow

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8
Q

What are the culture characteristics of S. aureus? (5)

What color is it on Mannitol sal agar?

A
  1. GPC in clusters
  2. Beta hemolytic (most strains) , usually yellow/white colonies
  3. CATALASE + (all Staph)
  4. Tube and slide COAGULASE +
  5. Mannitol fermentation (produces acid which lowers pH) and high salt (7.5%) - MSA plate = S. aureus yellow
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9
Q

What are the MOST COMMON diseases caused by S. aureus? (8)

A

SKIN

  1. Scalded Skin Syndrome - no bacteria or leukocytes seen in would; only superficial peeling of skin toxin mediated; (exfoliative toxins A and B)
  2. Toxic Shock Syndrome (Fever, macular erythematous rash, skin peeling (sunburn like rash), hypotension) Differential : RMSF, Leptospirosis, Rubeola (negative titers); toxin mediated (TSST-1)
  3. Folliculitis, carbuncles, furuncles - no need to cx unless severe
  4. Impetigo - crustys around mouth or other parts; need to order a Cx for ruling out S. aureus vs. Strep pyogenes
  5. Osteomyelitis - bone infection
  6. Septic arthritis - #1 cause; Lyme, Kingella (<2 YO), and other differentials ; septic = “infectious” rather autoimmune
  7. Food poisoning - last less than 24h and doesn’t cause fever; toxin mediated (enterotoxin)
  8. Endocarditis
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10
Q

Describe Staphylococcal Scalded Skin Syndrome

A

Superficial infection only on the epidermis, mediated by exfoliative toxins A and B (occurs in kids 5-6 years old)

The disease is usually followed by upper resp infections, otitis media (in children) or after abscess, arteriovenous fistula infection, or septic arthritis (in adults).

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11
Q

Describe impetigo caused by S. aureus

A

Impetigo - yellow crusts
superficial skin infection (also caused by GAS)

itchy sores or blisters to form on exposed skin

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12
Q

Describe abscesses caused by S. aureus

A

Abscesses - enclosed bacteria and Polymorphonuclear neutrophils (PMNs) cells (Neutrophils, eosinophils, and basophils) inside of a fibrous capsule

Types:

Furuncle-abscess that forms in hair follicle or sweat gland

Carbuncle - a group of furuncles under the skin

Treated by incision and drainage

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13
Q

What are the key symptoms of ACUTE endocarditis and the risk factors of the disease?

A

Hemorrhaging in the fingers, nails, and eyes (busted blood vessels)

Risk factors:

  1. Prosthetic medical devices (heart valves)
  2. congenital heart formation
  3. diabetes,
  4. IVDU
  5. HIV
  6. Older age
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14
Q

What diseases are caused by HEMATOGENOUS spread of S. aureus? (5)

A

HEMATOGENOUS SPREAD

  1. ACUTE endocarditis
    *inflammation in the heart valves by vegetation formations
  2. VAP (ventilator associated pneumonia)
    *this may lead to empyema (infection between the lung and the pleural membrane)
    *risk factor is recent influenza infection
  3. Cystic fibrosis associated infections
    *(more common in CF patients <34 yr)
    *small colony variants that are thymidine auxotrophs (do not grown on MH plates for susceptibility testing)
  4. Community acquired pneumonia (linked to recent influenza infection) Less common than VAP

5) Bone and joint infections

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15
Q

Describe Toxic Shock Syndrome caused by S. aureus

A

Caused by the toxic shock syndrome toxin (may also be caused by S. pyogenes)

Symptoms include: fever, hypotension, diffuse rash

Desquamation on the palms and soles

This is mediated by the toxin, bacteria culture may be negative

Associated with tampons too

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16
Q

Described food poisoning by S. aureus

A

Very rapid symptom onset (30 mins - 8h)
and quick resolution (<1 day)

Not treated with antimicrobials

17
Q

How is MRSA methicillin resistant?

A

mecA encodes PBP2a

betal lactam cannot bind transpeptidase due to confomational change

resistant to all bet lactams EXCEPT ceftaroline

18
Q

How is MRSA cultured, diagnosed, and treated?

MRSA surveillance

A

The nare are swabbed

Swabs are streaked on Blood agar and
Mannitol salt (MSA) agar plates + oxacillin and cefoxitin resistance

Diagnosed by PCR and PBP2a for mecA

Positive patients are decolonized with mupirocin and/or chlorohexidine prior to antibiotic treatment

19
Q

How is MRSA screened for methicillin susceptibility/resistance?

A

Using a Disk diffusion test or test on the AST systems

cefoxitin and oxacillin are used to induce the mecA gene

PBP2a lateral flow

20
Q

Is S. aureus the only spp that is resistant to methicillin?

A

No!

Any strain can have resistance

Staphylococci have species-specific breakpoints for oxacillin and cefoxitin

21
Q

How is PBP2A detected?

2 methods in lab

*ADD PIC of mecA table **

A

1) PBP2a antigen test

*Lyze the colony cells
*add strip to liquid with lyzed cells
*sample migrate through strip that has the PBP2a antibodies

2) PCR for mecA insertion

Primers for the Staphylococcal Chromosomal Cassette (SCCmec)

1) insertion site (is there a SSmec?)
2) mecA primers (resistance to methicillin?)
3) spa primers (is this S. aureus?)

** all 3 most be positive for MRSA**

Coagulase negative Staph can also encode mecA
If spa is the only positive then it means MSSA
If mecA and spa are the only positive it means CoNS and MSSA

22
Q

How is Staph aureus diff from S. epidermidis?

A

S. epidermis:
1) does not grow on MSA agar
2) coagulase negative
3) non hemolytic

23
Q

Diseases associated with s. epidermidis?

A

Rare in healthy people, only causes disease in debilitated patients

SUBACUTE endocarditis

Prosthetic device infections; wounds

Maybe hard to diagnose because CoNS are considered skin contaminants; require multiple positive blood cultures

24
Q

Describe Staphylococcus lugdunensis and its associated disease

(SLUG)

A

Commensal of the perineal and the groin areas

1) skin and soft tissue infections
2) subacute endocarditis
3) shunt and joint infections
4) otitis media (1 yr olds)

Only in debilitated hosts

25
Describe Staphylococcus intermedius group and associated diseases
S. intermedius S. pseudointermedius S. delphini 1) commensal in dog and cats skin 2) may cause abscesses 3) skin and soft tissue infections PYR positive (red color) (S. aureus is negative; yellow) Only in debilitated hosts
26
Describe Staphylococcus schleiferi and its associated disease
Commensal of dog ears 1) skin and soft tissue infections 2) rare bone infections Only in debilitated hosts
27
Describe Staphylococcus haemolyticus and its associated disease
Normal flora of humans and dogs/cats. colonizes axillary, perineal and inguinal areas 1) skin and soft tissue infections 2) rare bone infections Only in debilitated hosts
28
Describe Staphylococcus saprophyticus and its associated disease
Sexual activity related acquired UTI pathogen Novobiocin resistant Does not reduce nitrate to nitrites, so dipstick may be negative Treated with Nitrofurantoin or trimethoprim/sulfamethoxazole (Bactrim)
29
How to report a Staph spp that is S to oxacillin but R to cefoxitin and what is the mechanism?
mecC cassette (bovine MRSA homolog) OR low level of meta expression Uncommon phenotype Report as Oxacillin resistant MRSA
30
How to report a Staph spp that is R to oxacillin but S to cefoxitin and what is the mechanism?
PBP changes or hyper production of Beta lactamase Rare but reported as resistant MRSA
31
How to treat Small Colony Variants according to CLSI?
Must be tested for PBP2s antigen test or mecA only
32
How do you explain Methicillin resistance in strains that do not have a detecable mecA? 2 mechanisms
BORSA- borderline oxacillin resistance caused by over expression of blaZ; mecA not detected but resistant phenotype mecC - oxacillin S and Cefoxitin R
33
Vancomycin resistance in Staph is mediated by what?
Plasmid VanA from E. faecalis Very rare in the US ETEST is preferred method ; must incubate for a full 24h before reading results Still susceptible to Daptomycin
34
Vancomycin Intermediate Staph Aureus
High Daptomycin MICs Low Oxacillin MICs Thick cell wall