Staphylococci

Question 1

Are staphylococci catalase positive or negative?

Answer 1

Catalase POSITIVE

Question 2

Are staphylococci motile?

Answer 2

No

Question 3

What is the aerobic status of staphylococci?

Answer 3

Facultative anaerobes.

They undergo aerobic respiration but are capable of growing under the absence of oxygen by undergoing fermentation.

Question 4

What is the general appearance of staphylococci described as?

Answer 4

Bunch of grapes

Question 5

Where is staphylococci generally found?

Answer 5

• External environment
• Anterior nose
• Perineum
• Axillae
• Vagina

Question 6

What are factors that can predispose a person to serious staphylococci infection?

Answer 6

• 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

Question 7

What are the usual sites of staphylococci infection?

Answer 7

• Skin
• Nose and Throat
• GI Tract/Urethra/Vagina

Question 8

Pyoderma

Answer 8

Pyoderma means any skin disease that is pyogenic.

Question 9

Furuncle

Answer 9

Furuncle (or boil) skin disease caused by infection of hair follicles, resulting in localized accumulation of pus and dead tissue.

Question 10

Carbuncle

Answer 10

Carbuncle is an abscess larger than a boil, usually with one or more openings draining pus onto the skin.

Question 11

What are the virulence facts of S. aureus?

Answer 11

– Capsules
– Protein A 
– Panton-Valentine Leukocidin (PVL) 
– Coagulase
– Hemolysins

Question 12

What is the function of capsules in virulence?

Answer 12

Prevent ingestion of organism by PMNs

Question 13

What is the function of Protein A in virulence?

Answer 13

Binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs

Question 14

What is the function PVL of in virulence?

Answer 14

An enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction

Question 15

What is the function of coagulase in virulence?

Answer 15

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

Question 16

What is the function of hemolysis in virulence?

Answer 16

Lyse RBCs and/or act as toxins

Question 17

α-hemolysin

Answer 17

• Lyses RBCs of several animals
• Dermonecrotic on subcutaneous injection
• Leukocyte toxicity

Question 18

ß-hemolysin

Answer 18

• 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)

Question 19

∂-hemolysin

Answer 19

• 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

Question 20

𝛄-hemolysin

Answer 20

Only in some S. aureus and can lyse a variety of cells

Question 21

Exfoliatins or Epidermolytic Toxins

Answer 21

Responsible for “staphylococcal scalded skin syndrome,” dissolves the mucopolysaccharide matrix of epidermis, causing separation of skin layers; rare in adults

Question 22

Enterotoxins

Answer 22

Heat stable molecules that cause staphylococcal food poison and is the most common cause of food poisoning with a quick onset and quick recovery.

Question 23

Fibrinolysins

Answer 23

Fibrinolysins - break down fibrin clots and facilitate

spread of infection to contiguous tissues

Question 24

Hyaluronidase

Answer 24

Hyaluronidase - hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue

Question 25

Phospholipase C

Answer 25

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.

Question 26

What are the characteristics of super antigens?

Answer 26

* Pyrogenicity * Superantigenicity * Enhance lethal effects of minute amounts of endotoxin

Question 27

What do super antigens all induce?

Answer 27

Polyclonal T-cell proliferation

Question 28

What are examples of super antigens?

Answer 28

* Toxic shock syndrome toxin-1 (TSST-1) of S. aureus * Streptococcal pyrogenic exotoxins (SPE) * Streptococcal superantigens

Question 29

What is the use of coagulase in the lab?

Answer 29

Quick determination of S. aureus - it will cause coagulation as coagulase is traditionally associated with S. aureus

Question 30

What are the tests for coagulase?

Answer 30

- Tube Coagulase | - Latex Agglutinization (fast)

Question 31

What is the most clinical significant coagulase negative staphylococci?

Answer 31

Staphylococcus epidermidis

Question 32

What are Staphylococcus epidermidis infections related to?

Answer 32

Indwelling devices like catheters, etc. Removal of the foreign body is necessary for cure of infection.

Question 33

What is Staphylococcus saprophyticus the main cause of?

Answer 33

Acute UTI in young women and cystitis

Question 34

How is Staphylococcus saprophyticus identified?

Answer 34

Identification based on negative coagulase and resistance to novobiocin

Question 35

What does Staphylococcus lugdunensis generally colonize?

Answer 35

Human inguinal area

Question 36

What diseases does Staphylococcus lugdunensis cause?

Answer 36

WIDE range of diseases just like S. aureus

Question 37

How is Staphylococcus lugdunensis identified?

Answer 37

Only species that is both PYR and Ornithine positive

Question 38

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 ```

Answer 38

E Staphylococcus saprophyticus

Question 39

What are six settings that area associated with MRSA outbreaks?

Answer 39

– 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

Question 40

Why did the rate of MRSA increase so much?

Answer 40

MRSA moved from a hospital only infection to a community infection that led to a doubling of the rate.

Question 41

What makes S. aureus methicillin resistant?

Answer 41

They acquire the mec A gene

Question 42

What is the function of the mecA gene?

Answer 42

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

Question 43

Where is mecA found?

Answer 43

mecA is carried on a mobile genetic element called “staphylococcal cassette chromosome mec” (SCCmec)

Question 44

What are five severe disease syndromes in which MRSA should be considered in the differential diagnosis?

Answer 44

``` – Sepsis syndrome – Osteomyelitis – Necrotizing pneumonia – Septic arthritis – Necrotizing fasciitis ```

Question 45

What is the most effective measure to control the spread of MRSA?

Answer 45

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

Question 46

What is the most effective lab technique for MRSA detection?

Answer 46

Real Time PCR as it allows for results VERY quickly

Question 47

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

Answer 47

A Colonized or infected patients