Staphylococci Flashcards
True or False: Micrococci are usually associated with disease and are considered clinically significant when isolated from human specimens.
False: Micrococci are not typically associated with disease and not considered clinically significant when isolated from human specimens
Staphylococci are usually recovered from the ______ _______ or as commensals inhabiting the ________ and _______ ______.
Staphylococci are usually recovered from the external environment or as commensals inhabiting the skin and mucous membranes.
Staphylococcus aureus is commonly found in the ______ ______ of 20 - 40% of adults, as well as the _________, __________, _________.
Staphylococcus aureus is commonly found in the anterior nares of 20 - 40% of adults, as well as the Perineum, Axillae, Vagina.
In general, Staph aureus most commonly infects sites where the organism is ______________.
Sites where the organism is a part of the normal flora.
Specifically, what sites on the body are most commonly infected by Staph aureus? (Name them)
Skin , nose/throat, GI tract, urethra, vagina
What general conditions are caused by S. aureus skin infection?
Furuncles, carbuncles, folliculitis, cellulitis
Describe the cause and implications of a furuncle:
A skin disease caused by infection of the hair follicle that results in localized accumulation of pus and dead tissue.
Describe the appearance of a furuncle, include:
- Color?
- Tender?
- Temperature?
- Purulent?
- Pain?
Furuncle Appearance:
- 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
Define a carbuncle:
An abscess larger than a boil, usually with one or more openings draining pus onto the skin
Most common sites of carbuncles?
May develop anywhere, but are most common on the back and the nape of the neck
What are the 4 general virulence factors of S. aureus?
- Adhesin (Protein A)
- Lysins (Hemolysins)
- Enzymes “-ases”
- Cytotoxins
Describe the function of Protein A as a driver of virulence for S. aureus.
Protein A on the surface of Staph aureus organisms binds the Fc region of the antibody so that it is no longer recognized by the phagocyte, preventing opsonization and phagocytosis of S. aureus by PMNs
Describe the function of each hemolysin as a driver of virulence for S. aureus. (4 types)
Lysins lyse RBCs and leukocytes
α-hemolysin: Pore former; most closely associated with tissue damage
β-hemolysin: Sphingomyelinase
Gamma-hemolysin: Pore former
Delta-hemolysin: Surfactant that disrupts cell membranes
Describe the function of enzymes (“-ases”) as a driver of virulence for S. aureus. (4 types)
Each of these enzymes assists in cell to cell spread
Coagulase – conversion of fibrinogen to fibrin to form a clot
Fibrinolysin - breaks down fibrin clots
Hyaluronidase - hydrolyzes intercellular matrix connective tissue
Lipase – survival in sebaceous material
What are the 3 cytotoxins that drive virulence for S. aureus.
Exfoliatins or Exfoliative Toxins
Enterotoxins
Superantigen: Toxic shock syndrome toxin-1 (TSST-1)
Describe the function of Exfoliatins as a driver of virulence for S. aureus.
Exfoliatins or Exfoliative Toxins
- Dissolves the mucopolysaccharide matrix of epidermis
- Causes separation of skin layers
Describe Enterotoxins as a driver of virulence for S. aureus.
Enterotoxins
- Heat-stable toxin that causes food poisoning
- Not produced by ingested Staphylococcus
What 5 factors predispose an individual to S. aureus infection?
- Congenital or acquired defects in leukocyte chemotaxis
- Defects in opsonization by antibodies
- Defects in intracellular killing of bacteria following phagocytosis
- Skin injuries
- Presence of foreign bodies
List severe disease syndromes in which Staphylococcus aureus should be considered in the differential diagnosis.
Septic arthritis and osteomyelitis
Sepsis syndrome
Necrotizing pneumonia
Necrotizing fasciitis
Who is affected in staphylococcal scalded skin syndrome?
Neonates and young children
What are the 4 hallmark clinical manifestations of staphylococcal scalded skin syndrome?
No bacteria or leukocytes are present in the fluid
Erythema spreads from around mouth to cover entire body
Large cutaneous bullae (blisters) form followed by sloughing off of the skin layer (desquamation of the epithelium)
Bullae contain clear fluid
What S. aureus virulence factors cause scalded skin syndrome?
Exfoliatins or Exfoliative Toxins
What are the hallmark clinical manifestations of staphylococcal food poisoning?
Severe vomiting, nausea, diarrhea, abdominal cramping, headache, but not fever
True or False: Staphylococcal food poisoning is caused when an individual ingests Staph aureus. Explain.
False: Staphylococcal food poisoning is caused by intoxication with a Staph toxin, but not infection by the organism.
True or False: To determine the organism that causes Staph food poisoning, it is good to culture the organism from the food.
False. It is unlikely to recover the organism from the food. Cell culture would not be helpful in this case.
Incubation period for staph aureus food poisoning?
Very rapid, 4 hour incubation period
Foods associated with Staph aureus food poisoning?
Associated with processed meats, custard-filled pastries, potato salad, ice cream
What virulence factor(s) are responsible for Staphylococcal food poisoning?
Enterotoxins
True or False: Heating food will prevent Staphylococcal food poisoning.
False. Enterotoxins in the food are heat-labile. Heating may kill the organism, but the toxin will cause symptoms.
What are the 6 hallmark clinical manifestations of Staphylococcal Toxic Shock Syndrome?
Multi-organ toxicity
Febrile and hypotensive
Diffuse erythematous rash over entire body
Disseminated intravascular coagulation (DIC) and severe thrombocytopenia
Entire skin desquamates
Vomitting and watery diarrhea
Population in which Staphylococcal Toxic Shock Syndrome is usually observed?
Often observed in young women using tampons
What virulence factor(s) are responsible for Staphylococcal Toxic Shock Syndrome?
Toxic shock syndrome toxin-1 (TSST-1)
How does Toxic shock syndrome toxin-1 (TSST-1) cause disease?
It is a super-antigen that causes non-specific activation of T-cells (MHC class II), followed by polyclonal T-cell proliferation, and massive cytokine release.
What are the 2 hallmark clinical manifestations of Staphylococcal cellulitis/abscess? Required inoculum?
Large, pyogenic lesions surrounded by erythema
Pain, edema, and accumulation of purulent material
High inoculum required in immunocompetent host
What event(s) are typically responsible for the onset of Staphylococcal cellulitis/abscess?
Staphylococcal cellulitis/abscess often occurs following trauma or introduction of a foreign body
Which staphylococcal species is most likely associated with acute urinary tract infection in young women?
Staphylococcus saprophyticus
What is the 2nd most common cause of uncomplicated cystitis (after E. coli) among women of college and child-bearing age?
Staphylococcus saprophyticus
How is Staphylococcus saprophyticus differentiated from other Staph species?
Identification of Staphylococcus saprophyticus is based on a negative coagulase test and resistance to novobiocin
Name 3 ways Staphylococcus lugdunensis is differentiated from other Staph species.
Colonizes human inguinal area
More virulent than other coagulase-negative Staph
Most commonly associated with native-valve, prosthetic-valve, and pacemaker-associated endocarditis
What are the hallmark clinical manifestations of Native Valve Endocarditis caused by Staphylococcus lugdunensis?
Acute onset weakness of right extremity
10 weeks of fever, chills, malaise, shortness of breath
tachycardia, hypotension, fever, pansystolic murmur
Multiple positive blood cultures
Name 2 ways Staphylococcus epidermidis is differentiated from other Staph species.
Most often associated with infections of indwelling devices (i.e. catheters)
Biofilm production
Describe the virulence mechanism of Staphylococcus epidermidis.
Virulence is related to production of extracellular slime that promotes adherence to surfaces of foreign bodies forming biofilm. The biofilm protects S. epidermidis from antimicrobial agents.
Hemolysis of S. aureus?
beta-hemolytic - Complete hemolysis of the RBC
Morphology of S. aureus?
Golden beta-hemolytic colonies
Gram positive cocci in clusters
Name4 tests for lab identification of S. aureus.
Beta Hemolysis on blood agar
Mannitol Salt Agar
CHROMagar
Coagulase test
S. aureus result on Mannitol Salt agar?
Organisms are salt tolerant and use mannitol as a sugar/energy source
S. aureus result on CHROMagar?
Turns organism a characteristic color that identifies it
Describe the “slide coagulation” technique via latex agglutination assay.
Fibrinogen is attached to a small bead that contains a monoclonal antibody to protein A. The beads act by binding protein A and interacting with coagulase (converts fibrinogen to fibrin) on the surface of S. aureus to cause agglutination. Only occurs if the organism is coagulase positive.
Methicillin Resistant Staphylococcus aureus (MRSA) is responsible for __________ and ___________ Staph infections.
Methicillin Resistant Staphylococcus aureus (MRSA) is responsible for hospital-associated and community-associated Staph infection
Methicillin Resistant Staphylococcus aureus (MRSA) is resistant to all ____________ antibiotics.
Methicillin Resistant Staphylococcus aureus (MRSA) is resistant to all beta-lactam antibiotics.
What confers methicillin resistance to Staph aureus?
The mecA Gene
What is the mechanism of resistance conferred by mecA?
mecA encodes for altered “penicillin-binding protein 2a” (PBP2a), which alters the cell wall such that beta-lactam antibiotics no longer have binding affinity at penicillin-binding proteins. Thus, peptidoglycan synthesis proceeds even in the presence of antibiotics
How is mecA acquired?
mecA is carried on a mobile genetic element called “staphylococcal cassette chromosome mec” (SCCmec)
2 groups that are most susceptible to MRSA Infections?
Patients in hospitals and healthcare facilities
Patients who have weakened immune systems
In hospitals, the most important reservoirs of MRSA are _________________.
In hospitals, the most important reservoirs of MRSA are colonized or infected patients
Both __________ and _________ patients contaminate the hospital environment with MRSA at the same relative frequency
Both infected and colonized patients contaminate hospital environment with MRSA at the same relative frequency
How does septic arthritis and osteomyelitis present?
spider-bite cellulitis
pain and fever
joints feel like “jelly”
How does cellulitis progress to septic arthritis and osteomyelitis?
Hematogenous dissemination or secondary infection
Groups outside of the hospital that are at risk of MRSA?
MPSM MSM Correctional inhabitants Military Recruits Daycares and nurseries
Staph aureus: catalase
Catalase positive (bubbling reaction)
Staphylococci: morphology
Gram-positive Cocci in clusters
Staphylococci: media
Grows in minimal media
Staphylococci: oxygen requirement
Prefers an aerobic environment
Name the catalase negative Staph organisms:
Staph saprophyticus, epidemidis, and ludunensis
First step in resolving an S. epidermidis infection?
Removal of infected foreign bodies
