L1 MHD: Staph Flashcards
Key Characteristics of
STAPHYLOCOCCI:
- Gram (+ or - ) ?
- How are they arranged?
- Motile? (Y/N)
- Spore forming? (Y/N)
- Catalse (+ or -)
- Facultative anaerobes except for which species? What else is unique about these particular anaerobes?
- Gram positive
- Cocci in single cells, pairs, tetrads & short chains
= GRAPE LIKE CLUSTER - Not motile
- Not spore forming
- Catalase POSITIVE
- S.Aureus subspecies
Anaurobius & S. Saccharolyticus
(these two are also catalase negative)
What are the 4 important staph species?
- S. Aureus
- S. Epidermidis
- S. Lugdunensis
- S. Saprophyticus
Habitat:
Where is STAPH AUREUS predominantly found?
- ANTERIOR NARES
- 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
- at Loyola, every patient gets a nasal swab sent to the lab for detection of STAPH AUREUS
What are the 8 predisposing factors for serious Staph Aureus infection?
- Defects in leukocyte Chemotaxis
- Congenital (Wiskott-Aldrich syndrome, Down’s syndrome, Job’s syndrome, Chediak-Higashi syndrome)
- Acquired (Diabetes mellitus, rheumatoid arthritis) - 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 membrane bound OXIDASE system - SKIN INJURIES (burns, surgical incision, eczema, sports injuries
- Presence of foreign bodies
(sutures, IV lines)
- Infection with other agents
(VIRUSES -influenza, measles) - Chronic underlying disease
- Use of antibiotics that S. Aureus not susceptible to
Staph Aureus:
Site of infection
- Usual sites of infection are those in which the organism is part of ______.
State some examples of infections that S. Aureus causes in the following areas:
- Skin
- Nose & throat
- GI tract, urethra, vagina
- normal flora
SKIN:
1. folliculitis, IMPETIGO , FARUNCLES, CARBUNCLES, postsurgical wound infections
NOSE & throat
2.sinusitis, peritonsillar abscesses, mastoiditis, bronchitis and staphylococcal pneumonia (following influenza infection
GI tract, urethra, Vagina:
3.enterocolitis, cystitis, prostatitis, cervicitis, salpingitis, pelvic abscess
______ means any skin disease that is pyogenic. Causes may be infectious, such as Staphylococcal infections, or possibly autoimmune, such as pyoderma gangrenosum
Pyoderma
-Pyogenic = PUS FORMING organisms
______ skin disease caused by infection of hair follicles, resulting in localized accumulation of pus and dead tissue.
Red, pus-filled lumps that are tender, warm, and extremely painful.
A yellow or white point at center of lump can be seen when boil is ready to drain
Furuncle (or boil)
A _____ is an abscess larger than a boil, usually with one or MORE openings draining pus onto the skin.
Where are they most common?
Carbuncle
- Carbuncles may develop anywhere, but they are most common on the back and the nape of the neck.
FARUNCLE GONE WILD = carbuncle
What are 3 toxin mediated infections of S. Aureus?
- Scalded skin syndrome
- Toxic Shock Syndrome (super antigen)
- Food poisoning (quick recovery- 24/28 hours)
- symptoms at 6-8 hours
The following are examples of what?Caused by which bacteria?
Pneumonia Bacteremia Endocarditis Osteomyelitis Septic arthritis Septic embolization Metastatic infections
Disseminating infections of Staph. Aureus
What are 4 components of Staph Aureus that interfere with phagocytosis (virulence factors)? How?
- Capsules
- prevent ingestion of organism by PMNs - Protein A
- 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
What virulence factor of Staph Aureus does the following:
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
COAGULASE
+
Describe how the following hemolysins of S. Aureus (function).
- Alpha - Hemolysin
- Beta- hemolysin
(which enzyme is responsible)
- Alpha (green)
- Lyses RBCs of several animals
- Dermonecrotic on subcutaneous injection
- Leukocyte toxicity - Beta - Hemolysin
(yellow/cream)
- “golden staph of moses”
- 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)
Describe how the following hemolysins of S. Aureus.
- Delta - Hemolysin
- Gamma - Hemolysin
Which acts as a surfactant that disrupts cell membrane?
- 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 in neonates
- Gamma -hemolysin: found in some S. aureus strains, also causes lysis of variety of cells
______ toxin is responsible for “staphylococcal scalded skin syndrome,” dissolves the mucopolysaccharide matrix of epidermis, causing separation of skin layers; rare in adults
_____ heat-stable molecules responsible for clinical features of staphylococcal food poisoning, probably most common cause of food poisoning in U.S.
- EXFOLIATING EPIDERMOLYTIC TOXINS
- Enterotoxin
- Toxin produced in contaminated food by toxigenic strains, vomiting with or without diarrhea (2-8 hrs), quick recovery (24-48 hrs)
[ unlike salmonella/shigella in which symptoms do not appear for 2 days]
TX: make sure they stay hydrated, enterotoxin is self-limiting and do not need antibiotics to eradicate
What 3 enzymes are described by the following: (which bacteria produces these)
- ____described in patients with ARDS and DIC. Tissues affected by this enzyme become more susceptible to damage and destruction by bioactive complement components and products during complement activation.
- ______break down fibrin clots and facilitate spread of infection to contiguous tissues
- ______hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue
STAPH AUREUS
- Phospholipase C
- Fibrinolysins
- Hyaluronidase
ARDS = acute respiratory distress syndrome
DIC - disseminating intravascular coagulation
The following are _____:
- Toxic shock syndrome toxin-1 (TSST-1) of S. aureus
- Streptococcal pyrogenic exotoxins (SPE)*
- Streptococcal superantigens
What do all of them induce? What 3 biological characteristics do they posses?
SUPER ANTIGENS
- induce Polyclonal T cell proliferation
1) Pyrogenicity
2) Superantigenicity
3) Enhance lethal effects of minute amounts of endotoxin
How can Staph Aureus be best identified in the lab? (which test)
COAGULASE +!!!!
- Tube coagulase - free coagulase.
- Reacts with substance in plasma called coagulase-reacting factor that converts fibrinogen to FIBRIN (clots)
- Rare S. aureus may be coagulase-negative and some animal isolates (S. intermedius, S. hyicus, S. delphini, S. schleiferi subsp. coagulans) may be tube coagulase-positive
What is an alternate test for Staph Aureus besides the Coagulase test?
Ig molecules on the beads detect ______ which specifically binds IgG in the Fc region.
Latex Agglutination!!
- latex beads coated with plasma.
- Fibrinogen bound to latex detects clumping factor.
2. PROTEIN A
(staphylococcal cell-wall protein that binds IgG by the Fc region)
STAPH EPIDERMIDIS
- Coagulase (+ or -)
- Associated with infections of _____ devices
- Virulence is related to what specific structural component?
- What is often necessary for resolution of this infection?
- Coagulase NEGATIVE
- INDWELLING DEVICES
( enemy of ortho’s –> impedes hardware in artificial joints, indwelling catheters, artificial heart valves) - ADHERENT BIOFILM
- also protects organisms from antimicrobial agents, - removal of foreign bodies often necessary for resolution of infection
(jnt, catheter etc..)
Staph Epidermis = PLUMBER (novobiocin sensitive)
How can staph aureus be treated? What about methicillin resistant staph aureus? (MRSA)
- Penicillin
(Nafcillin: Naph for Staph) - VANCOMYCIN for MRSA (IV)
What is the treatment for Staph Epidermidis?
Vancomycin
- removal of joint/foreign body
The following describes which form of staph:
- Acute UTI in young women(sexually active)
- 2nd most common cause of CYSTITIS (after E.Coli)
- Coagulase Negative
- Novobiocin RESISTANT
Staph. Saprophyticus!
On the office’s “staph” retreat there was NO StRESs
NOvobiocin:
- Saprophyticus Resistant
- Epidermidis SENSITIVE
The following describes which type of staph:
- Colonizes INGUINAL area
- both PYR positive
- Ornithine Positive
Staph. LUGDUNENSIS
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.
An organism identified as gram-positive cocci in clusters is isolated from the urine of a 21 year female with symptoms of acute cystitis. The laboratory reports that the organism is coagulase-negative, furozolidone susceptible and novobiocin resistant. What is the most likely identification of this bacterium?
A Staphylococcus aureus
B Staphylococcus epidermidis
C Staphylococcus lugdunensis
D Staphylococcus pyogenes
E Staphylococcus saprophyticus
E Staphylococcus saprophyticus
- What is the only drug that treats MRSA?
2. Where do staph infections most frequently occur?
- VANCOMYCIN
- need to administer via IV - occur most frequently among patients in hospitals and healthcare facilities (such as nursing homes and dialysis centers) who have weakened immune systems
- Healthcare-associated MRSA (HA-MRSA) infections include:
Surgical wound infections Urinary tract infections Bloodstream infections Pneumonia Central venous catheter line infections
- In hospitals, the most important reservoirs of MRSA are ______
- _______ can serve as a link for transmission between colonized or infected patients
- What is the main mode of transmission?
- colonized or infected patients
- Hospital personnel
- The main mode of transmission is via hands (especially healthcare workers’ hands) contaminated by contact with colonized or infected patients; colonized or infected body sites of the personnel themselves; or devices, items, or environmental surfaces contaminated with infected body fluids.
MRSA infections that are acquired by individuals who have not been recently (within the past year) hospitalized or had an invasive medical procedure are known as _______ infections
MRSA infection is becoming more common in the community setting
1.CA-MRSA
CA- MRSA Outbreaks:
- Often first detected as clusters of abscesses or ______
- Various settings. State some examples.
- “spider bites”
- Sports participants: football, wrestlers, fencers - MPSM
Correctional facilities:
Military recruits
Daycare and other institutional centers
Newborn nurseries and other healthcare
settings
Men who have sex with men - MSM
- What gene is acquired in MRSA?
- What does it encode for?
- Has decreased binding affinity for what? What is the result of this?
- mecA gene
- carried on a mobile genetic element called
“Staphylococcal Cassette
Chromosome mec” - Encodes for altered “penicillin-binding protein 2a” (PBP2a)
- Has decreased binding affinity for ß-lactam antibiotics
- allows peptidoglycan synthesis even in the presence of B-lactam antibiotics
[ B- lactam antibiotics usually work by attaching to PBPs and shutting down the protein –> holes in cell wall –> cell BURSTS]
What bacteria belongs in the differential diagnosis of SKIN & SOFT TISSUE infections compatible with Staph. Aureus? (state the 3 infections it should be included with)
Should also be included in what severe diseases compatible with S. Aureus infection?? (5)
MRSA
- Abscesses, pustular lesions
- “boils”
- “Spider bites”
Cellulitis
2. Sepsis syndrome Osteomyelitis Necrotizing pneumonia Septic arthritis Necrotizing fasciitis
Both ____ and ____ patients contaminate hospital environment with same relative frequency
- Infected
- Colonized
- BEDRAILS
Contamination of equipment that is shared, clothing (white coats and uniforms) and hands occurs from both infected and colonized patients
What can be done to control MRSA? (5)
- Careful, compulsive hand hygiene for all patient interactions (behavioral change)
WASH YOUR DAMN HANDS!!! - 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
MRSA Cannot Be Eradicated Without ______ ____
Active Surveillance
Screening for MRSA: how?
Swab Anterior nares
- microbiology culture
- Real Time PCR
- GeneXpert Real Time PCR
What are potentially interfering substances in Xpert MRSA Assay? (3)
- Whole blood
- Mucus
- Nasal Spray
Running tests in the excessive presence of these substances can generate errors or invalid results
- What was the result of Universal Surveillance of the Nosocomial MRSA infection?
(Nosocomial = originating in the hospital)
MRSA infection is becoming more common in the _____ setting
79% sustained reduction in nosocomial MRSA infections (0.48 -> 0.16)
-Active Surveillance of hospitalized patients can REDUCE MRSA infections and associated morbidity and mortality
CONCLUSION:
MRSA is NO LONGER exclusively a nosocomial pathogen
- -> Skin and soft tissue infections
- -> Necrotizing pneumonia, severe sepsis syndrome
- community
What is the most effective method for detection of MRSA from patient specimens?
Real time PCR is the most effective method for detection of MRSA from patient specimens
What is the most important reservoir of methicillin resistant Staphylococcus aureus (MRSA) in hospitals?
A Colonized or infected patients
B Colonized or infected medical staff
C Clothing worn by patient care personnel
D Child visitors who attend day care centers
E Medical equipment
A Colonized or infected patients
What bacteria undergo Alpha - hemolysis? (2)
What bacteria undergo Beta hemolysis? (4)
Form a green ring around colonies on blood agar.
- Strep Pneumoniae (catalase -, optochin sensitive)
- Viridans Strep (catalase -, optochin resistant)
BETA HEMOLYSIS:
- Staph. Aureus - (catalase & coagulase +0
- Strep Pyogenes (group A strep; Catalase -, Bacitracin Sensitive)
- Strep Agalctiae -Group B ( catalse -, bacitrasin resistant)
- Listeria Monocytogenes (tumbling motility, meningitis in newborns, unpasteurized milk)
