Staphylococci Flashcards
Are staphylococci catalase positive or negative?
Catalase POSITIVE
Are staphylococci motile?
No
What is the aerobic status of staphylococci?
Facultative anaerobes.
They undergo aerobic respiration but are capable of growing under the absence of oxygen by undergoing fermentation.
What is the general appearance of staphylococci described as?
Bunch of grapes
Where is staphylococci generally found?
- External environment
- Anterior nose
- Perineum
- Axillae
- Vagina
What are factors that can predispose a person to serious staphylococci infection?
- Defects in leukocyte chemotaxis
- 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
- Skin injuries
- Presence of foreign bodies
- Infection with other agents - viruses
What are the usual sites of staphylococci infection?
- Skin
- Nose and Throat
- GI Tract/Urethra/Vagina
Pyoderma
Pyoderma means any skin disease that is pyogenic.
Furuncle
Furuncle (or boil) skin disease caused by infection of hair follicles, resulting in localized accumulation of pus and dead tissue.
Carbuncle
Carbuncle is an abscess larger than a boil, usually with one or more openings draining pus onto the skin.
What are the virulence facts of S. aureus?
– Capsules – Protein A – Panton-Valentine Leukocidin (PVL) – Coagulase – Hemolysins
What is the function of capsules in virulence?
Prevent ingestion of organism by PMNs
What is the function of Protein A in virulence?
Binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs
What is the function PVL of in virulence?
An enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction
What is the function of coagulase in virulence?
It 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 is the function of hemolysis in virulence?
Lyse RBCs and/or act as toxins
α-hemolysin
- Lyses RBCs of several animals
- Dermonecrotic on subcutaneous injection
- Leukocyte toxicity
ß-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)
∂-hemolysin
- 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
Only in some S. aureus and can lyse a 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 that cause staphylococcal food poison and is the most common cause of food poisoning with a quick onset and quick recovery.
Fibrinolysins
Fibrinolysins - break down fibrin clots and facilitate
spread of infection to contiguous tissues
Hyaluronidase
Hyaluronidase - hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue
Phospholipase C
Phospholipase C - 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.
What are the characteristics of super antigens?
- Pyrogenicity
- Superantigenicity
- Enhance lethal effects of minute amounts of endotoxin
What do super antigens all induce?
Polyclonal T-cell proliferation
What are examples of super antigens?
- Toxic shock syndrome toxin-1 (TSST-1) of S. aureus
- Streptococcal pyrogenic exotoxins (SPE)
- Streptococcal superantigens
What is the use of coagulase in the lab?
Quick determination of S. aureus - it will cause coagulation as coagulase is traditionally associated with S. aureus
What are the tests for coagulase?
- Tube Coagulase
- Latex Agglutinization (fast)
What is the most clinical significant coagulase negative staphylococci?
Staphylococcus epidermidis
What are Staphylococcus epidermidis infections related to?
Indwelling devices like catheters, etc. Removal of the foreign body is necessary for cure of infection.
What is Staphylococcus saprophyticus the main cause of?
Acute UTI in young women and cystitis
How is Staphylococcus saprophyticus identified?
Identification based on negative coagulase and resistance to novobiocin
What does Staphylococcus lugdunensis generally colonize?
Human inguinal area
What diseases does Staphylococcus lugdunensis cause?
WIDE range of diseases just like S. aureus
How is Staphylococcus lugdunensis identified?
Only species that is both PYR and Ornithine positive
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 are six settings that area associated with 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
Why did the rate of MRSA increase so much?
MRSA moved from a hospital only infection to a community infection that led to a doubling of the rate.
What makes S. aureus methicillin resistant?
They acquire the mec A gene
What is the function of the mecA gene?
Encodes for altered “penicillin-binding protein 2a” which has decreased binding affinity for ß-lactam antibiotics and allows peptidoglycan synthesis even in the presence of B-lactam antibiotics
Where is mecA found?
mecA is carried on a mobile genetic element called “staphylococcal cassette chromosome mec” (SCCmec)
What are five severe disease syndromes in which MRSA should be considered in the differential diagnosis?
– Sepsis syndrome – Osteomyelitis – Necrotizing pneumonia – Septic arthritis – Necrotizing fasciitis
What is the most effective measure to control the spread of MRSA?
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
What is the most effective lab technique for MRSA detection?
Real Time PCR as it allows for results VERY quickly
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
