Aerobic Gram-Positive Cocci: Staph Flashcards
- Know the reservoirs of Staph aureus and Staph epidermis.
aureus: normal flora of the anterior nares, skin and various mucosal surfaces
epidermidis: normal inhabitant of skin and mucous membranes
- How are S. aureus and S. epidermis transmitted?
aureus and epidermidis: endogenous flora moved to normally sterile site; by fomites, direct content or respiratory droplets or ingestion of food containing toxin
- Describe the major diseases caused by Staph aureus.
cutaneous infections (abscess): impetigo, cellulitis (subcutaneous fat layer), folliculitis, furuncle, carbuncle, wound infections, mastitis (breast abscess)
Food poising (toxin-mediated)– commonly ham, potato sale and custard-filled pastries
Toxic Shock syndrome, mediated by TSST-1 associated with tampon use or surgical packing and fluid resuscitation is critical
Scalded skin syndrome
bacteremia and endocarditis
pneumonia (ventilator mediated)
osteomyelitis
septic arthritis
- Describe the major diseases caused by S. epidermidis.
hospital acquired bacteremia endocarditis catheter and shunt infections implanted medical device infections surgical site infections
- Discuss which groups of individuals are at increased risk for developing staphylococcal infections and why.
S. aureus: menstruating women (TSS), neonates (SSS), young children (impetigo), patients with intravenous catheters or implanted medical devices, immunocompromised, IV drug abusers, neutrophil dysfunction, burn patients
healthy adults with S. aureus
S. epidermidis: patients with intravenous catheters or prosthetic materials
- What are the virulence factors for Staph aureus v. epidermidis?
aureus: teichoic acid (binding), protein A (inhib. antibody-mediated clearance), TOXINs: cytotoxins (alpha, beta, delta, gamma, Panton-Valentine leukocidin) exfoliative toxins, enterotoxins, Toxic Shock Syndrome Toxin-1; ENZYMES: coagulase, catalase and ANTIBIOTIC RESISTANCE GENES
epidermidis: adherence to medical devices, production of viscous polysaccharide slime or biofilm
- Know the Gram stain reactions and lab tests used to identify S. aureus and S. epidermidis.
S. aureus: gram positive cocci in grape like clusters, colony of golden color, colonies are hemolytic
S. epidermidis: same as above, except, small white colonies that are non-hemolytic; grows on mannitol but does not ferment the mannitol
- Discuss how these infections can be prevented.
hand hygiene, chemoprophylaxis, wound cleaning, refrigerate foods
limit in dwelling catheters, prompt tx. of wounds, chemoprophylaxis of surgical intervention
What is the morphological distinction of staph?
usually found in clusters, some singles, pairs or tetrads and they are all catalase positive as well as facultative
Describe the characteristics of Staph saprophyticus.
coagulase negative staph that colonize the skin and urethral area
can cause UTI in women recently, newly sexually active
Discuss approaches to treating Staph infection, what factors should be considered? (including methicillin resistant Staph aureus (MRSA)
Factors for consideration: drug resistance, site of infection, severity of infection and presence of allergies to antibiotics
40’s resistance to penicillin via beta-lactamase enzymes
70’s first methicilin resistant strains (MRSA); includes resistance to all beta-lactams and semi-synthetic penicillins
00’s vacomycin resistance through changes in peptidoglycan structure (Rare) and community acquired MRSA infections
coagulase-negative Staphylococci have also utilized these drug resistant mechanisms
tx. of MRSA isolates: vancomycin used widely, daptomycin in severe infections that do no include pneumonia; linezolid in soft tissues, clidamycin, trimethoprim-sulfamethoxazole for soft tissue infections
We now assume Staph aureus is MRSA until proven otherwise but list treatments for non-MRSA S. aureus
oxacillin (sever infection) or docloxacillin DOC
cephalosporins
combo beta-lactam/betal lactamase inhibitor drugs
clidamycin for penicillin allergy
vancomycin for severe infection with allergy
