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Staphyloccocus Flashcards

1
Q

Name the 7 Staphylococcus species

A
  1. S. aureus
  2. S. epidermis
  3. S. lugdunensis
  4. S. saprophyticus
  5. S.pseudointermedius
  6. S. haemolyticus
  7. S. schleiferi
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2
Q

List the general characteristics for Staphylococcus spp

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%

facultative anaerobes

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3
Q

Who is known as coagulase positive?

A

S. aureus

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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 are the 2 types coagulases produced by most S. aureus?

A

Free and Bound Coagulases

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6
Q

What is the difference between the 2 types of coagulases?

A

Free coagulase 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)

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.

Latex agglutination assay (with fibrinogen and IgG)
Beads coated with fibrinogen and IgG
Bound coagulase binds and converts fibrinogen into fibrin
Protein A of Staph binds to the constant region of IgG antibodies
False positives can occurs, if other Staph (Not S. aureus produce coagulase)

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7
Q

Can other non-S aureus strains produce free or bound coagulase?

A

yes!
False positives on Latex Agglutination Assays may occur

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8
Q

Name the non-S. aureus strains that can be beta hemolytic and cause similar disease to S. aureus

A

S. lugdenensis
S. intermedius group (S. intermedius, pseudointermedius, delphini)
S. schleiferi

LIS

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9
Q

What are the culture characteristics of S. aureus? (4)

A
  1. GPC in clusters
  2. Beta hemolytic (most strains) , usually yellow/white colonies
  3. Catalse positive (all Staph)
  4. Tube and slide coagulase positive
  5. Mannitol fermentation and high salt (7.5%) - MSA plate
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10
Q

What SKIN diseases are caused by S. aureus? (5)

A

SKIN

  1. Impetigo
  2. Abscesses
  3. Furuncles or carbuncles
  4. Staphylococcal Scalded Skin Syndrome
  5. Toxic Shock Syndrome
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11
Q

Describe Staphylococcal Scalded Skin Syndrome

A

Staphylococcal Scalded Skin Syndrome- 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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12
Q

Describe impetigo caused by S. aureus

A

Impetigo - superficial skin infection (also caused by GAS)

itchy sores or blisters to form on exposed skin

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13
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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14
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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15
Q

What diseases are caused by HEMATOGENOUS spread of S. aureus? (3)

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
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16
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

17
Q

Name the diseases caused by S. aureus toxins (3)

A
  1. Staphylococcal Scalded Skin Syndrome
  2. Toxic Shock Syndrome
  3. Food poisoning - enterotoxin

Toxins may be heat stable, not mediated by the organism

18
Q

Described food poisoning by S. aureus

A

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

Not treated with antimicrobials

19
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

20
Q

How is MRSA cultured, diagnosed, and treated?

A

The nare are swabbed

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

Diagnosed by PCR and lateral assays for mecA

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

21
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

22
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

23
Q

How is PBP2A detected?

2 methods in lab

A

1) Immunochromatographic assays

Labeled antibody (bind analyte)

Primary antibody (binds the analyze + labeled antibody) ONLY IF ANALYTE IS PRESENT

Secondary antibody (always binds the labeled antibody)

2) PCR

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

24
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

25
Q

Diseases associated with s. epidermidis?

A

Rare in healthy people, only causes disease in debilitated patients

SUBACUTE endocarditis

Prosthetic device infections

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

26
Q

Describe Staphylococcus lugdunensis and its associated disease

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

27
Q

Describe Staphylococcus intermedius group and associated diseases

A

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 (S. aureus is negative)

Only in debilitated hosts

28
Q

Describe Staphylococcus schleiferi and its associated disease

A

Commensal of dog ears

1) skin and soft tissue infections
2) rare bone infections

Only in debilitated hosts

29
Q

Describe Staphylococcus haemolyticus and its associated disease

A

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

30
Q

Describe Staphylococcus saprophyticus and its associated disease

A

Sexual activity related
acquired UTI pathogen

Does not reduce nitrate to nitrites, so dipstick may be negative

Treated with Nitrofurantoin or trimethoprim/sulfamethoxazole (Bactrim)

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