Staphylococci and Relate Gram+ Cocci Flashcards
Epidemiology of staphylococcal infection
Recovered from environment or commensals inhabiting skin and mucus membranes (or nares, skin folds, perineum, axillae, vagina)
Normally found on humans, we are our own reservoirs
Poor host defense, skin injuries (burns, surgical incisions, eczema, sports injuries), foreign bodies, infections with other agents (flu, measles), chronic disease (malignancy, alcoholism, heart disease) can create opportunity for pathogenic infection
Sites of infection: skin, nose and throat, GI tract, urethra, vagina
Identify species of staphylococci that are coagulase and slide latex +
S. AUREUS
List six settings that have been associated with community-acquired MRSA outbreaks
Sports Correctional facilities Military recruits Daycare Newborn nurseries Men who have sex with men
List five severe disease syndromes in which MRSA should be considered in the differential diagnosis
Sepsis syndrome Osteomyelitis Necrotizing pneumonia Septic arthritis Necrotizing fasciitis
Describe effective infection prevention measures to control MRSA infections in the hospital
Compulsive hand hygiene Contact/droplet precautions Screen every patient Effective cleaning of environment/shared equipment Appropriate use of antibiotics
Key characteristics of staphylococci
Gram+ cocci, arranged single cells, pairs, tetrads, and short chains, but appear predominantly in grape-like clusters
Non-motile
Non-spore-forming
Catalase+
Facultative anaerobes: can grow aerobicall or anaerobicall (except s. aureus, anaerobius and saccharolyticus)
Virulence factors associated with S. aureus
Capsules
Prevent ingestion of organisms by PMNs
Virulence factors associated with S. aureus
Protein A
Binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs
Virulence factors associated with S. aureus
Panton-Valentine Leukocidin (PVL)
An enzyme that alters cation permeability of leukocytes resulting in white cell destruction
Virulence factors associated with S. aureus
Coagulase
Binds to prothrombin catalyzing conversion of fibrinogen to fibrin, which in turn acts to coat bacterial cells with fibrin, rendering them more resistant to opsonization and phagocytosis
Virulence factors associated with S. aureus
Hemolysins
ALPHA: lyses RBCs, dermonecrotic, leukocyte toxicity
BETA: sphingomyelinase, varying lysis of RBCs, produces hot-cold lysis (ie hemolysis enhanced at low temperature after 35C incubation)
DELTA: surfactant to disrupt cell membrane, coagulase- staph can use this to cause nectrotizing entrocolitis in neonates)
GAMMA: causes lysis of a variety of cells
Virulence factors associated with S. aureus
Toxins
Exfoliatins/epidermolytic toxins (scalded skin syndrome in babies)
Enterotoxins: heat-stable toxins causing staph food poisoning
Virulence factors associated with S. aureus
Fibrinolysins
Break down fibrin clots and facilitate spread of infection to other tissues
Virulence factors associated with S. aureus
Hyaluronidase
Hydrolyzes ICM to spread infection to adjacent tissues
Virulence factors associated with S. aureus
Phospholipase C
PLC causes tissues to be damaged by complement components
