Staphyloccocus Flashcards
(34 cards)
Name the 7 Staphylococcus species
- S. aureus
- S. epidermis - surgical implantation infections
- S. lugdunensis SluG - S. aureus like
- S. saprophyticus -UTI
- S.pseudointermedius - dogs and cats
- S. haemolyticus
- S. schleiferi -dog ears
List the general characteristics for Staphylococcus SPECIES
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
Who is known as coagulase positive?
FREE COAGULASE
AND
BOUND COAGULASE (clumping factor)
S. aureus
ALL produce free coagulase
(tube +)
85-90% produce clumping factor (bound coagulase) detected on Staphaurex. SpaA also detected by Staphaerux
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 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) = 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
Which non-S aureus strains produce free or bound coagulase?
Name the 3 species and how they differ
SLUG and S. schlefeiri = have clumping factor (BOUND) but DON’T secrete FREE COUAGULASE
Veterinary S. intermedius secrete free coagulase!! TEST TUBE POSITIVE
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
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
What are the culture characteristics of S. aureus? (5)
What color is it on Mannitol sal agar?
- GPC in clusters
- Beta hemolytic (most strains) , usually yellow/white colonies
- CATALASE + (all Staph)
- Tube and slide COAGULASE +
- Mannitol fermentation (produces acid which lowers pH) and high salt (7.5%) - MSA plate = S. aureus yellow
What are the MOST COMMON diseases caused by S. aureus? (8)
SKIN
- Scalded Skin Syndrome - no bacteria or leukocytes seen in would; only superficial peeling of skin toxin mediated; (exfoliative toxins A and B)
- Toxic Shock Syndrome (Fever, macular erythematous rash, skin peeling (sunburn like rash), hypotension) Differential : RMSF, Leptospirosis, Rubeola (negative titers); toxin mediated (TSST-1)
- Folliculitis, carbuncles, furuncles - no need to cx unless severe
- Impetigo - crustys around mouth or other parts; need to order a Cx for ruling out S. aureus vs. Strep pyogenes
- Osteomyelitis - bone infection
- Septic arthritis - #1 cause; Lyme, Kingella (<2 YO), and other differentials ; septic = “infectious” rather autoimmune
- Food poisoning - last less than 24h and doesn’t cause fever; toxin mediated (enterotoxin)
- Endocarditis
Describe 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
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?
MRSA surveillance
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
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
PBP2a lateral flow
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
*ADD PIC of mecA table **
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
How is Staph aureus diff from S. epidermidis?
S. epidermis:
1) does not grow on MSA agar
2) coagulase negative
3) non hemolytic
Diseases associated with s. epidermidis?
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
Describe Staphylococcus lugdunensis and its associated disease
(SLUG)
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
