Staph.Lecture 1 Flashcards
What are the key characteristics of staphylococci
- gram + arranged in single cells , pairs, tetrads, and short chains, but appear predominantly in grape-like clusters
- non-motile
- non-spore-forming
**4. catalase POSITIVE (very useful to separate strep from staph!)
- facultative anaerobes (except: S. aureus, subsp. anaerobius and S. saccharolyticus–these two are also catalase NEGATIVE).
4 important staphylococci species
- S. aureus (ohreeus)
- S. epidermidis (ehpeedurmiss)
- S. saprophyticus (saprofitikus)
- S. lugdunensis (lugdone.eesis)
S. aureus KEY characteristics
- grape like clusters
- uniform, equal size
- round
- gram POSITIVE
- on blood agar plates: grow large, 48hrs, off white, cream, sometimes gold.
- clearing zone=beta hemolysis
S. aureus HABITAT
- external environments
- skin and mucous membranes
- anterior nares (20-40% adults)
- intertriginous skin folds
- perinuem
- axillae
- vagina
- significant opportunistic pathogen under appropriate conditions
S. aureus FACTORS predisposing to SERIOUS INFECTION (8)
- defects in leukocyte chemotaxis
- congenital: Wiskott-Aldrich syndrome, Down’s syndrome, Job’s syndrome, Chediak-Higashi syndrome)
- acquired: DM, RA
- defects in opsonization by antibodies secondary to congenital or acquired hypogammaglobulinemias or complement component
- defects in intracellular killing of bacteria following phagocytosis due to inability to activate the membrane bound oxidase system (CGD-chronic granulomar disease, lymphoblastic leukemia, acute and chronic myelogenous leukemia)
- skin injuries (*burns, surgical incisions, eczema, sports injuries-falling on turf)
- presence of foreign bodies (sutures, IV lines, prosthetic devices)
- infections with other agents, particularly viruses (eg influenza, measles)
- -sometimes with influenza wont die from virus, die from secondary pneumonia infection.
- chronic underlying diseases (e.g. malignancy, alcoholism, heart disease)
- use of antibiotics to which the infecting S. aureus is not susceptible (MRSA staph…)
OBJECTIVE 2: S. aureus VIRULENCE FACTORS-Components that interfere with phagocytosis (1/4)–CPPC
- Components that interfere with phagocytosis
- CAPSULES-interfere with phagocytosis, prevent ingestion of organism by PMNs
- PROTEIN A-binds Fc region of IgG, interfering with opsonization an dingestion of organism by PMNs
- PANTON-VALENTINE LEUKOCIDIN (PVL)-an enzyme that alters cation permeability of rabbit an human leukocytes resulting in white cell destruction
- COAGULASE-forms a clot; binds to prothrombin catalyzing conversion of fibrinogen to fibrin, which in turn acts to coat bacterial cells with fibrin, rendering them ore resistant to opsonization and phagocytosis
S. aureus-serious infection sites
usually those in which the organism is part of normal flora.
- SKIN: folliculitis, impetigo, furuncles and carbuncles, post-surgical wound infections
- NOSE AND THROAT-sinusitis, peritonsillar abscesses, mastoiditis, bronchitis and **STAPHYLOCOCCAL PNEUMONIA (usually involving infection with influenza)
- GI TRACT, URETHRA, VAGINA-enterocolitis, cystitis, prostatitis, cervicitis, salpingitis, pelvic abscess
S. aureus-serious infection-child with pyoderma
PYODERMA=pyogenic (pus forming) skin dz. causes may be infectious, such as staphylococcal infections, or possible AUTOIMMUNE (pyoderma gangrenosum)
S. aureus-serious infection-furuncle (or boil)
- skin dz caused by infection of hair follicles, resulting in localized accumulation of pus and dead tissue
- red, pus-filled lumps that are tender, warm, extremely painful
- a yellow or white point at center of lump can be seen when boil is ready to drain
S. aureus-serious infection-carbuncle (foruncle gone wild)
- abscess larger than a boil, usually with one or more openings draining pus onto the skin
- may develop anywhere, but they are most common on the back and the nape of the neck
S. aureus-serious infection-Toxin-mediated Infections
- scalded skin syndrome: neonates and children under 4
- Toxic-shock syndrome
- food poisoning
S. aureus-serious infection-Disseminated infections
During localized infection metastasis via blood (to other distant sites) may result in:
- pneumonia
- bacteremia
- endocarditis
- osteomyelitis
- septic arthritis
- septic embolization
- metastatic infections
OBJECTIVE 2: S. aureus VIRULENCE FACTORS-Hemolysins (2/4)
- HEMOLYSINS (LYSINS, TOXINS)
–LYSINS–
ALPHA HEMOLYSIN
-lyses RBCs of several animals
-dermonecrotic (causes necrosis of the skin) on subcutaneous injection
BETA HEMOLYSIN
-sphingomyelinase will cause varying lysis of RBCs from different animals due to difference in membrane sphingomyelin content (test with sheep blood)
-produces “hot-cold” lysis (hemolysis enhance at low temp after 35 C incubation)
DELTA 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 (necrotizing enterocolitis) in neonates
GAMMA HEMOLYSIN
-found in some S. aureus strains, also causes lysis of variety o cells
–TOXINS–
EXFOLIATINS or EPIDERMOLYTIC TOXINS
-responsbile for “STAPHYLOCOCCAL SCALDED SKIN SYNDROME”
-toxin 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
-most common cause of food poisoning in the US
-toxin produced in contaminated food by toxigenic strains, vomiting with or without diarrhea (2-8hrs-because you are ingesting the toxin itself when you eat the food) + quick recovery (24-48 hrs)
{salmonella or shigella will show up a day or two later. avoid giving AB, should let it pass by itself}
OBJECTIVE 2: S. aureus VIRULENCE FACTORS-Enzymes (3/4)
- ENZYMES
FIBRINOLYSINS
-break down fibrin clots and facilitate spread of infection to contiguous tissues
HYALURONIDASE
-hydrolyze intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue
PHOSPHOLIPASE C
-described in patients with ARDS (acute respiratory distress syndrome) and DIC (disseminated intravascular coagulation-rare life threatening condition prevents blood from clotting normally)
-tissues affected by the E become ore susceptible to damage and destruction by bioactive complement components and products during complement activation
OBJECTIVE 2: S. aureus VIRULENCE FACTORS-
- SUPERANTIGENS
Group of toxins known as pyrogenic toxin superantigens, these include:
-toxic shock syndrome toxin-1 (TSST-1) of S. aureus
-streptococcal pyrogenic exotoxins (SPE)-toxic-shock-LIKE-syndrome
-streptococcal superantigens
All posses THREE biologic characteristics: - pyrogenicity
- superantigenicity
- enhance lethal effects of minute amounts of endotoxin
All induce polyclonal T-cell proliferation
S. aureus-Lab Identification-COAGULASE (VIRULENT FACTOR)
Tube coagulase-free coagulase reacts with substance in plasma called coagulase-reacting factor that converts fibrinogen–> fibrin. (rare S. aureus ma be coagulase-NEG and some animal isolate {S. intermedius, S. hyicus, S. delphini, S. schleiferi, subsp. coagulans} may be tube coagulase-POSITIVE. COAGULASE POSITIVE = STAPH AUREUS
S. aureus-Lab Identification-Alternative Coagulase Test, Latex Agglutination
- quick test in lab
- latex beads coated with plasma
- fibrinogen bound to latex detects clumping factor
- Ig molecules also on beads detect Protein A (staphylococcal cell-wall protein that binds IgG by the Fc region)
- CLUMPING=COAGULATIVE POSITIVE
S. epidermidis
- most frequently isolated clinically significant coagulase-NEG staphylococci (NON pathogenic)
- catalase POSITIVE
- associated with infections of indwelling (line, catheter) devices
- common cause of UTI in sexually active females
- virulence related to production of extracellular slime that promotes adherence of organism to surfaces of foreign bodies forming biofilm
- biofilm also protects organism from antimicrobial agents, therefore removal of foreign bodies is often necessary for resolution of infection
S. saprophyticus
- cause of acute urinary tract infection in young women (20-30 yo)
- 2nd most common cause of uncomplicated cystitis (after E. coli) among women of college and child-bearing age
- Identification based on NEGATIVE coagulase and resistance to novobiocin (separates saprophyticus from others)
NB and FX disc-Staphylococcus
S. saprophyticus is SENSITIVE to Furozolidone (halo will form). But, RESISTANT (insensitive) to Novobiocin, it cannot be stopped by Novobiocin.
NB and FX disc-Micrococus
Micrococcus is RESISTANT to FX, SENSITIVE to NB.
S. lugdunensis
-coagulase NEGATIVE
-colonizes human inguinal area
-only species that is both PYR and ORNITHINE POSITIVE
-causes variety of human infections including:
%native-valve, prosthetic-valve, and pacemaker associated endocarditis
%meningitis
%skin and soft tissue abscesses
%cellulitis
%peritonitis
%infected prostheses
%osteomyelitis
%vertebral diskitis
%vascular line infection
%oral infections
%septic arthritis
%UTI
Who gets Staph or MRSA infections?
-pts in hospitals and healthcare facilities (nursing homes, dialysis centers) who have weakened immune systems
CA-MRSA
- community acquired MRSA
- staph MD, need VANCOMYCIN therapy given iv, so need to stay in hospital
- once it moved into the community there was a doubled rate of infections
What do healthcare-associated MRSA (HA-MRSA) infections include:
- surgical wound infections
- urinary tract infections
- bloodstream infections
- pneumonia (weakened immune systems)
- central venous catheter line infections
MRSA transmission in hospitals
- in hospitals COLONIZED/INFECTED PATIENTS=MOST IMPORTANT MRSA RESEROVOIRS
- hospital personnel=link for transmission between colonized or infected patients
What is CA-MRSA
MRSA infections acquired by individuals who havent (in the past yr) been recently hospitalized or had an invasive medical procedure
-12% of clinical MRSA infections are CA-MRSA, vary by region and population
CA-MRSA Outbreaks
often detected as clusters of abscesses or “spider bites”. swollen and PAINFUL
- -various settings–
- sports participants: football, wrestlers, fencers-MPSM
- correctional facilites: prisons, jails
- military recruits
- daycare and other institutional centers
- newborn nurseries and other healthcare settings
- MSM
MRSA-mecA Gene
- mecA Gene codes for altered “penicillin-binding protein 2a” (PBP2a) which can keep making the wall fragments
- has decreased binding affinity for beta-lactam AB and allows peptidoglycan synthesis even in the presence of beta-lactam AB
- mecA is carried on a mobile genetic element called “staphylococcal cassette chromosome mec” (SCCmec), it is acquired
Penicillin Binding Proteins Background
- PBP are in all bacteria an instrumental in building cell wall components
- when bacteria grow bigger the organism makes cuts in the cell wall and new pieces are inserted. PMP makes these new pieces
- Penicillin=ANY beta-lactam drug
- Penicillin will attach itself to PBP and shut it down, B will continue cutting but with no new pieces water will rush in and burst the cell.
MRSA Clinical Considerations-SSTI
MRSA belongs in the differential dx of skin and soft tissue infections (SSTI’s) compatible with S. aureus infection:
- abscesses, pustular lesions, “boils”
- “spider bites”
- cellulitis (inflamm of subcutaneous connective tissue)
MRSA Clinical Considerations-Compatible severe diseases
MRSA should be considered in differential dx of severe dz compatible with S. aureus infection:
- sepsis syndrome
- osteomyelitis (imflamm of bone/marrow usually due to infection)
- necrotizing pneumonia
- (septic arthritis (purrulent invasion of a joint by an infectious agent that produces arthritis)
- necrotizing fasciitis (acute dz in which inflamm of the fasciae of muscle or other organs results in rapid destruction of overlying tissues)
Who contaminates the hospital environment more? Infected OR colonized patients?
BOTH infected and colonized pts contaminate with the SAME RELATIVE FREQUENCY
What can be done to control MRSA
- careful, compulsive hand hygiene for all patient interactions (behavioral change)
- standard and transmission based contact/droplet precautions (masks, gowns, gloves)
- effective cleaning of the pt care environment (clean ALL devices that the pt might touch)
- clean shared/dedicated equipment (stethoscope, BP cuffs, thermometer, TV remotes)
- appropriate use of AB
What caused a 75% DECREASE in MRSA bacteremia in ICUs and a 67% DROP hospital-wide?
MRSA testing of ALL patients entering ICUs and contact precautions for all patients testing positive.
What does patient screening entail?
Rim the end of the nose, both nares. can reduce MRSA infections and associated M&M
What are the different surveillance methods?
- microbioloy cultures
- conventional realtime PCR
- GeneXpert realtime PCR (get results in 1hr)
Interfering Substances
The following substances were tested in the Xpert MRSA assay:
- whole blood
- mucus
- nasal spray
* *running test in the excessive presence of these substances can generate errors and invalid results in nucleic acid amplification.
MRSA is only found in hospital settings, right?
WRONG! It is NO LONGER exclusively a nosocomial pathogen.
What is the most effective method for detection of MRSA from patient specimens?
REAL TIME PCR
