Staphyloccocus Flashcards
(30 cards)
Name the 7 Staphylococcus species
- S. aureus
- S. epidermis
- S. lugdunensis SluG
- S. saprophyticus -UTI
- S.pseudointermedius
- S. haemolyticus
- S. schleiferi -dog ears
List the general characteristics for Staphylococcus spp
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
facultative anaerobes
Who is known as coagulase positive?
S. aureus
Who is known as coagulase negative
and how are the CoNS distinguished?
novobiocin‐susceptible
S. epidermis group
- S. lugdunensis
- S. pseudointermedius
- S. scheiferi
- S. haemolyticus
novobiocin‐resistant
1. S. saprophyticus (like a STI)
What are the 2 types coagulases produced by most S. aureus?
Free and Bound Coagulases
What is the difference between the 2 types of coagulases?
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)
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)
Can other non-S aureus strains produce free or bound coagulase?
yes!
False positives on Latex Agglutination Assays may occur
Name the non-S. aureus strains that can be beta hemolytic and cause similar disease to S. aureus (3)
S. lugdenensis
S. intermedius group (S. intermedius, pseudointermedius, delphini)
S. schleiferi
LIS
What are the culture characteristics of S. aureus? (4)
- GPC in clusters
- Beta hemolytic (most strains) , usually yellow/white colonies
- Catalse positive (all Staph)
- Tube and slide coagulase positive
- Mannitol fermentation (produces acid which lowers pH) and high salt (7.5%) - MSA plate
What SKIN diseases are caused by S. aureus? (5)
SKIN
- Impetigo
- Abscesses
- Furuncles or carbuncles
- Staphylococcal Scalded Skin Syndrome
- Toxic Shock Syndrome (Fever, rash, skin peeling, low blood pressure)
Describe Staphylococcal Scalded Skin Syndrome
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).
Describe impetigo caused by S. aureus
Impetigo - yellow crusts
superficial skin infection (also caused by GAS)
itchy sores or blisters to form on exposed skin
Describe abscesses caused by S. aureus
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
What are the key symptoms of ACUTE endocarditis and the risk factors of the disease?
Hemorrhaging in the fingers, nails, and eyes (busted blood vessels)
Risk factors:
- Prosthetic medical devices (heart valves)
- congenital heart formation
- diabetes,
- IVDU
- HIV
- Older age
What diseases are caused by HEMATOGENOUS spread of S. aureus? (5)
HEMATOGENOUS SPREAD
- ACUTE endocarditis
*inflammation in the heart valves by vegetation formations - VAP (ventilator associated pneumonia)
*this may lead to empyema (infection between the lung and the pleural membrane)
*risk factor is recent influenza infection - 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) - Community acquired pneumonia (linked to recent influenza infection) Less common than VAP
5) Bone and joint infections
Describe Toxic Shock Syndrome caused by S. aureus
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
Name the diseases caused by S. aureus toxins (3)
- Staphylococcal Scalded Skin Syndrome
- Toxic Shock Syndrome
- Food poisoning - enterotoxin
Toxins may be heat stable, not mediated by the organism
Described food poisoning by S. aureus
Very rapid symptom onset (30 mins - 8h)
and quick resolution (<1 day)
Not treated with antimicrobials
How is MRSA methicillin resistant?
mecA encodes PBP2a
betal lactam cannot bind transpeptidase due to confomational change
resistant to all bet lactams EXCEPT ceftaroline
How is MRSA cultured, diagnosed, and treated?
The nare are swabbed
Swabs are streaked on Blood agar and
Mannitol salt (MSA) agar plates + oxacillin and cefoxitin resistance
Diagnosed by PCR and lateral assays for mecA
Positive patients are decolonized with mupirocin and/or chlorohexidine prior to antibiotic treatment
How is MRSA screened for methicillin susceptibility/resistance?
Using a Disk diffusion test or test on the AST systems
cefoxitin and oxacillin are used to induce the mecA gene
Is S. aureus the only spp that is resistant to methicillin?
No!
Any strain can have resistance
Staphylococci have species-specific breakpoints for oxacillin and cefoxitin
How is PBP2A detected?
2 methods in lab
1) Immunochromatographic assays
*Lyze the colony cells
*add strip to liquid with lyzed cells
*sample migrate through strip that has the PBP2a antibodies
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
How is Staph aureus diff from S. epidermidis?
S. epidermis:
1) does not grow on MSA agar
2) coagulase negative
3) non hemolytic
