Staphylococci & Related gram + Flashcards
Describe the epidemiology of staphylococcal infection.
Found in external environment Found on skin and mucous membranes Anterior nares - 20-40% of adults Intertriginous skin folds Perineum Axillae Vagina Significant opportunistic pathogen under appropriate conditions
List virulence factors associated with S. aureus
Capsules Protein A Panton-Valentine Leukocidin (PVL) Coagulase Hemolysins (lysins, toxins) enzymes
Identify species of staphylococci that are coagulase and slide latex positive
S. aureus
List the clinically significant species of coagulase-negative staphylococci and describe the diseases they are associated with
Staphylococcus epidermidis (infections of inter dwelling devices) Staphylococcus saprophyticus ( acute UTIs) Staphylococcus lugdunensis (same as S. aureaus)
List six settings that have been associated with community-acquired MRSA outbreaks
Sports participants: football, wrestlers, fencers - MPSM **
Correctional facilities: prisons, jails
Military recruits
Daycare and other institutional centers
Newborn nurseries and other healthcare settings
Men who have sex with men - MSM **
List five severe disease syndromes in which MRSA should be considered in the differential diagnosis
- skin and soft tissue infections (SSTI’s)
- Sepsis syndrome
- Osteomyelitis *
- Necrotizing pneumonia
- Septic arthritis
- Necrotizing fasciitis *
Describe effective infection prevention measures to control MRSA infections in the hospital
** MRSA testing of all patients entering ICUs and contact precautions for all patients testing positive, produced: A 75% decrease in MRSA bacteremia in ICUs . And a 67% drop hospital wide **
Careful, compulsive hand hygiene for all patient interactions (behavioral change)
Standard and transmission based Contact/Droplet precautions:
Gowns Gloves Masks
Effective cleaning of the patient care environment
Clean shared/dedicated equipment
Stethoscopes BP cuffs
Thermometer TV Remotes
Appropriate use of antibiotics
what diseases are Micrococci associated with
none- not considered clinically significant when isolated from human specimens
Staphylococci Key Characteristics
Gram-positive cocci arranged single cells, pairs, tetrads and short chains, but mostly grape-like clusters
Non-motile
Non-spore-forming
***Catalase positive
Facultative anaerobes, except S. aureus subsp. anaerobius and S. saccharolyticus (these two also catalase negative)
Staphyloccoci are aerobic or anaerobic
Facultative anaerobes,
except S. aureus subsp. anaerobius and S. saccharolyticus (these two also catalase negative)
Staphylococci aureus
gram + with grape like clusters
blood agar plate - grow fairly large in 24 hrs, creme color, and a clearing zone around the colonies
found on skin and mucous membranes
Significant opportunistic pathogen under appropriate conditions
Staphylococcus aureus infections
Pyoderma Furuncle (or boil) carbuncle Scalded skin syndrome Toxic-shock syndrome Food poisoning Disseminated Infections
function of staph aureus’ capsule
prevent ingestion of organism by PMNs
Protein A function in staph aureus
binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs
Panton-Valentine Leukocidin (PVL)
an enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction
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
α-hemolysin
Lyses RBCs of several animals
Dermonecrotic on subcutaneous injection
Leukocyte toxicity
β-hemolysin
Sphingomyelinase, varying lysis of RBCs from different animals due to differences in membrane sphingomyelin content
Produces “hot-cold” lysis (hemolysis enhanced at low temperature after 35 C incubation)
δ -hemolysin
Produced by 97% of S. aureus and 50-70% of coagulase negative Staph
Acts as surfactant that disrupts the cell membrane, interacts with membrane to form channels that increase in size over time resulting in leakage of cellular contents
Some coagulase-negative staphylococci produce enough delta toxin to cause NEC in neonates
γ-hemolysin
found in some S. aureus strains, also causes lysis of variety of cells
Exfoliatins or epidermolytic toxins
responsible for “staphylococcal scalded skin syndrome,” dissolves the mucopolysaccharide matrix of epidermis, causing separation of skin layers; rare in adults
Enterotoxins
heat-stable molecules responsible for clinical features of staphylococcal food poisoning, probably most common cause of food poisoning in U.S. Toxin produced in contaminated food by toxigenic strains, vomiting with or without diarrhea (2-8 hrs), quick recovery (24-48 hrs)
Fibrinolysins
break down fibrin clots and facilitate spread of infection to contiguous tissues
Hyaluronidase
hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue
