Staphylococcus

Question 1

Define or describe staphylococcus

Answer 1

They are spherical, gram positive coccis arranged in a grape like cluster

Question 2

All staphylococcus produce which enzyme and what is its function

Answer 2

Catalase

It degrades hydrogen peroxide into h2o and o2 (catalase positive)

Question 3

What is the habitat of staphylococcus

And how does it spread

Answer 3

Skin surfaces and mucous membranes

Spreads through air and dust

Question 4

Species of staphylococcus

Answer 4

Aureus
Epidermidis
Saprophyticus

Question 5

Explain staph aureus

Answer 5

It is the main pathogen responsible for Pyogenic infections
It is identified by a coagulate positive test ( coagulate is an enzyme that clots citrated blood)
It is a commensal bacteria in nose, skin( perineum and axilla),throat, gut, mouth(saliva)

Question 6

Explain staph epidermidis

Answer 6

Common member of skin flora
Less common gut and upper respiratory tract flora
-it’s is coagulate negative
-sensitive to novobiocin
- it enters bloodstream and causes hospital acquired infection eg
Metastic infection at the site of implant
.infects iv catheters and prosthetic implants eg prosthetic heart valves(endocarditis), prosthetic joint(arthritis,osteomyelitis), vascular grafts
—major cause of neonatal sepsis
—most common cause of cerebrospinal shunt infection
—peritonitis in renal failur patient undergo peritoneal dialysis through indwelling catheter

Question 7

Explain staphylococcus saprophyticus

Answer 7

Coagulate neg.
Resistant to novobiocin
Cause community acquired infection eg urinary tract infection esp. in young sexually active women after escherichia coli

Question 8

Distinguish aureus from

Others

Answer 8

—It produces coagulase
—it ferments mannitol
—hemolysis of blood

Question 9

Colonial appearance of staph aureus

Answer 9

Staph aureus has golden colonies
Pigmentation varied from orange to white
Staph epidermidis has white colonies

Question 10

Selective media for staph

Answer 10

Tolerates NACL in concentrations of 5-10%

Question 11

Mention Cell components and antigens of staph aureus

Answer 11

Protein A
Teichoic acids
surface receptors for specific staphycoccal bacteriophages

Question 12

Protein A

Answer 12

Major protein in the cell wall
It is a major virulence factor
It binds to the Fc portion of IgG preventing the binding of complement
It is antiohagocytic

Question 13

Explain teichoic acid

Answer 13

They are polymers of ribitol phosphate

Antibodies to these acids develop in certain staohycoccal infections eg endocarditis

Question 14

Explain surface receptors for specific staphylococcal bacteriophages

Answer 14

Permit the phage typing of strains of staph aureus for epidemiological purposes

Question 15

Staph aureus forms a large no of extra cellular toxins and enzymes which may play a role in pathogenicity they are…and mention their uses

Answer 15

-Haemolysin toxins… lyse RBC f various animal species
-coagulase..clots plasma
-fibrinolysin… digest fibrin
-leucucidin…kills leucocytes
-hyaluronidase…breaks down hyaluronic acid which forms the material that binds cells of connective tissue.this tissue facilitate the spread of staph aureus in tissues
-DNAase…hydrolyzes DNA
-lipase…lyse lipids(lipolytic)
-protein A…antiohagocytic
-epidermolytic toxins A and B: they cause epidermal splitting and exfoliation
-enterotoxin:causes vomiting and diarrhea
-toxic shock syndrome:cause shock rash and desquamation
____not all strains of staphylococci produce the whole range of toxins listed above staph epidermidis produces few toxins

Question 16

How does staph cause disease

Answer 16

By producing toxins and multiplying and invading tissues

Question 17

What type of lesions does staph cause

Answer 17

Supporative and necrotic lesions

Question 18

What’s the typical lesion of staph aureus

Answer 18

Is an abscess but the org may spread via blood stream and cause septicemia with metastatic abscesses

It may also cause superficial infection suc as conjunctivitis and wound infection

It also causes deep infection such as septicemia endocarditis pyemia osteomyelitis and pneumonia

It also causes toxic mediated diseases such as food poisoning skin exfoliation and toxic shock syndrome