Staph + related gram pos. organisms Flashcards
Is staph gram positive or negative?
Gram positive
What does staph appear like in culture?
Grape like clusters
Is staph catalase positive or negative?
Catalase positive
List 4 important species of staphylococci.
S. aureus
S. epidermidis
S. lugdunensis
S. saprophyticus
Name as many conditions as you can that can be caused by a serious staph infection.
- Pyoderma
- Faruncle/carbuncle
- Toxin-mediated infections
What are the 3 toxin-mediated infections a/w staph?
- Scalded skin syndrome
- Toxic-shock syndrome
- Food poisoning
What age range is most susceptible to scalded skin syndrome?
Neonates and children under age of four
similar to bad sunburn, separates skin layers
Name as many virulence factors as you can a/w staph (8+)
- Capsules (blocks PMNs)
- Protein A (binds Fc)
- PVL (leukocidin)
- Coagulase (coats bacteria w/fibrin, easing opsonization)
- Hemolysins (alpha, beta, gamma, delta)
- Toxins (exfoliatins, epidermolytic, enterotoxins)
- Enzymes (fibrinolysin, hyaluronidase, PLC)
- Superantigens (TSST-1, SPE)
What staph virulence factor is responsible for staphylococcal scalded skin syndrome?
Exfoliatins or epidermolytic toxins
What virulence factor is responsible for staphylococcal food poisoning?
Enterotoxin
How does fibrinolysin act as a virulence factor for staph?
Break down fibrin clots and facilitate spread
How does hyaluronidase act as a virulence factor for staph?
Hydrolyzes ICM in tissue to spread
How does PLC act as a virulence factor for staph?
Tissues affected by this enzyme become more susceptible to damage/destruction by complement components/products
What are the consequences of superantigens a/w staph, such as TSST-1 (toxic shock syndrome toxin 1) and SPE (streptococcal pyogenic exotoxin)? (3)
- Pyrogenicity – cause extreme fever
- Superantigenicity – cause immune system to overreact
- Enhance lethal effects of minute amounts of endotoxin
Is S. aureus coagulase-neg or pos?
Coagulase positive
Is S. epidermidis coagulase-neg or pos?
Coagulase negative
S. epidermidis infections are a/w _____________.
Indwelling devices
Is S. saprophyticus coagulase-neg or pos?
Coagulase negative
Besides being coagulase negative, what other test is used to differentiate S. saprophyticus from other types of staph?
*Novobiocin resistance
this abx is now only used in lab
What demographic is S. saprophyticus most commonly seen in?
What condition do they usually present with?
- Young women
- UTI
Is S. lugdunesis coagulase-neg or pos?
Coagulase negative
What tests would indicate that one is positive for S. lugdunesis, rather than another type of staph?
They are PYR and orthnithine positive
The diseases caused by S. lugdunesis are similar to those caused by __________.
S. aureus
List 6 settings that have been associated with community-acquired (CA-) MRSA outbreaks.
- Men who play sports w/men - MPSM
- Prisons, jails
- Military recruits
- Daycare + other institutional centers
- Newborn nurseries + other healthcare settings
- Men who have sex with men - MSM
List 5 severe disease syndromes in which MRSA should be considered in the
differential diagnosis.
- Sepsis
- Osteomyelitis
- Necrotizing PNA
- Septic arthritis
- Necrotizing fasciitis
In hospitals, the most important reservoirs of MRSA are ________________.
Colonized or infected pts
Both infected and colonized patients contaminate hospital environment with same relative frequency
What is the name of the gene a/w MRSA?
What does it encode?
How did it evolve?
mecA
- Encodes PBP2a
- Nlly PCN binds PBP, thus inhibiting bacterial cell wall expansion and growth. MecA evolved to encode for a new protein that does the same thing (PBP2a)
MecA is carried on a mobile genetic element called:
staphylococcal cassette chromosome mec (SCCmec)
What sx are usually first noticed w/MRSA? (3)
- Abscesses, pustular lesions, “boils”
- “Spider bites”
- Cellulitis
Describe effective infection prevention measures to control MRSA infections in the
hospital. (objective, but it’s obvious)
- Compulsive hand hygiene for all pt interactions (behavioral change)
- Contact/Droplet precautions: gowns, gloves, masks
- Effective cleaning of the pt care environment: clean shared/dedicated equipment, stethoscopes, BP cuffs, thermometer, TV remotes
- Appropriate use of abx
True or false: Installing hand cleanser dispensers inside and outside all patients’ rooms failed to produce a statistically significant decrease in MRSA bacteremia.
False. (didn’t get drop until we started testing everyone via real-time PCR and then isolating them in hospital)
Running tests in the excessive presence of these 3 substances can generate errors or invalid results in PCR testing of MRSA:
- Whole blood
- Mucus
- Nasal Spray
Describe the typical habitat of staph.
What’s the most common body site that it’s found in that can easily be cultured?
Found in external environment Found on skin and mucous membranes - *Anterior nares - 20-40% of adults have it there - Intertriginous skin folds - Perineum - Axillae - Vagina
Significant opportunistic pathogen under appropriate conditions
What are some factors that can pre-dispose to staph infection?
- Defects in leukocyte chemotaxis
- Opsinization/AB defects
- Defects in intracellular killing (membrane bound oxidase system)
- Skin injuries (e.g. burns)
- Foreign bodies (e.g. prosthetics)
- Viral infections
- Underlying dz’s
- Abx use which staph isn’t susceptible to
What are the “usual” sites of staph infection? (3, but they’re combined)
- Skin
- Nose + throat
- GI tract, urethra, vagina
Define pyoderma.
- What are 2 possible causes
Any skin disease that is pyogenic (pus).
- Infectious (e.g. staph)
- Autoimmune (e.g. pyoderma gangrenosa)
Define furuncle.
How does it differ from carbuncle? (next slide)
- Furuncle (or boil) skin dz caused by infection of hair follicles, resulting in localized pus accumulation + dead tissue
- A carbuncle is an abscess larger than a boil, usually with 1+ openings draining pus (most common at nape of neck)
