Staphylococcus

Question 1

Staphylococci

Answer 1

Gram Positive cocci

Occur in singles, pairs, tetrads, short chains, but most commonly as irregular clusters

Suppurative (Pus-forming) infections

Members of the group Pyogenic Cocci

More than 50 species and subspecies

Most common is S. aureus

Question 2

Catalase Test

Answer 2

Production of oxygen form hydrogen peroxide

Is used to distinguish Staphylococcus (Positive) from Streptococcus (negative)

Question 3

Pathogenic Species

Answer 3

S. aureus

S. pseudintermedias

S. hyicus

Question 4

Double Zone Hemolysis

Answer 4

On blood agar S. aureus and S. pseudintermedius produce two zones of hemolysis.

A narrow zone of complete hemolysis (a-hemolysis)

Wider zone of partial or incomplete hemolysis (B-hemolysis)

Question 5

Staphylococcus aureus

Answer 5

“golden yellow” colored collonies

Grows well in medium containing 7.5-10% NaCl

Mannitol Salt agar is routinely used to selectively isolate S. aureus and distinguish from S. epidermidis.

Opportunistic and nosocomial pathogen.

Causes enteritis (Food poisoning; intoxication)

Question 6

MRSA

Answer 6

Methicillin resistant S. aureus

Major clinical and epidemiological problem in human hospitals.

Also present in animals and are of zoonotic significance

Question 7

Habitat

Answer 7

Occur in commensals of the skin of humans and animals.

Rugged cell wall allows them to withstand environmental insults such as drying, heat, high concentrations of salts.

Question 8

Virulence Factors

Answer 8

Most of them have been studied.

Cell-Associated Components,

Exoenzymes and Exotoxins

Question 9

Virulence Factors:

Cell-Associated Components:

Protein A

Answer 9

Surface protein that binds to Fc region of IgG molecules, disrupts opsonization and phagocytosis

Question 10

Virulence Factors:

Cell-Associated Components:

Capsular Polysaccharides

Answer 10

11 serologically distinct capsule types in S, aureus of Humans and Cattle

Interfere with host defense mechanisms by inhibiting attachement of antibodies, induce the release of cytokines, and mediate binding to epithelial and endothelial cells

Question 11

Virulence Factors:

Cell-Associated Components:

Peptidoglycan and Lipoteichoic Acid

Answer 11

Cell wall components function as virulence factors probably by stimulating cytokine release

Question 12

Virulence Factor:

Cell-Associated Components:

Adhesins

Answer 12

Proteins of the cell surface promote attachement to host proteins, such as fibronectin. (Fibronectin-Binding Protein responsible for attachement to blood clots)

Besides binding to host matrix proteins, the adhesins are responsible for the formation of Biofilm

Question 13

Virulence Factor:

Exoenzymes:

Coagulase

Answer 13

Enzyme binds to prothrombin to form a complex called Staphylothrombin.

Protease activity is activated in the complex, leads to conversion of fibrinogen to fibrin

Localized clotting protects bacterial cells from phygocytic and immune defenses

Question 14

Virulence Factor:

Exoenzymes:

Lipase

Answer 14

Enzyme hydrolyzes lipid molecules that the host produces in response to infections.

Act as surfactants and disrupt bacterial cell membranes, especially when an abscess is formed

Question 15

Virulence Factor:

Exoenzyme:

Hyaluronidase

Answer 15

Enzyme digest hyaluronic acid present in connective tissue and promotes spread of the infection

Question 16

Virulence Factor:

Exoenzymes:

Proteases

Answer 16

Best described staphylococcal protease is a serine protease (V8 protease)

Cleaving and inactivating antibodies, antimicrobial peptides, and to obtain nutrients.

Contribute to tissue protein destruction and enhance invasiveness

Question 17

Virulence Factor:

Exotoxins:

Toxic Shock Syndrome Toxin (TSST-1)

Answer 17

Superantigen activity

Stimulate T cells nonspecifically without normal antigenic recognition resulting in a strong stimulation of T cells, which respond with proliferation and massive cytoline release

Question 18

Virulence Factors:

Exotoxins:

Enterotoxins

Answer 18

toxins are responsible for diarrhea and vomiting when ingested in fodd poisoning caused by S. aureus.

May also have Superantigen activity

Major cause for food-borne disease

Toxin is resistant proteases, heat stable, and not inactivated by cooking. The toxin in ingested with the food, and in the stomach the toxin stimulates vagus nerve endings to induce vomiting and abdominal pain.

Question 19

Virulence Factor:

Exotoxin:

Exofoliative or Epidermolytic Toxins

Answer 19

Cause a spectrum of skin diseases, ranging from bullous impetigo to the scaled skin syndrome in humans.

S. hyicus causes exudative or exfoliative dermatitis (greasy pig disease)

Question 20

Virulence Factors:

Extotoxins:

Hemolysis

Answer 20

• Alpha Toxin
  
  • most potent membrane-damaging pore-forming toxin.
  • Narrow zone of complete hemolysis surrounding the colony on sheep or cattle blood agar
• Beta Hemolysin
  
  • Sphingomyelinase, damages membranes rich in sphingomyelin lipid.
  • Responsible for incomplete hemolysis of sheep or cattle erythrocytes
• Gamma Toxin
  
  • Leukotoxin, toxic to leukocytes.
  • Important virulence factor in necrotizing lesions.
  • genes located on a prophage
• Delta Toxin
  
  • small peptide.
  • Role in disease not known
  • Pro-inflammatory toxin

Question 21

Antibiotic Resistance

Answer 21

• Beta-lactamase
  
  • enzyme that hydrolyzes b-lactam ring of penicillins ans cephalosporins
• Penicillin-binding Protein 2a (PBP2a)
  
  • confers resistance to penicillins and cephalosporins-class of antibiotics.

Question 22

Pathogenesis and Pathogenic Mechanism

Answer 22

Pyogenic bacteria that cause suppurative lesions.

Minor injury to the skin or immune suppression is a predisposing factor for the development of infections.

Pathogenic effects can range from minor local infections to life-threatening septicemic conditions

Question 23

Mastitis in Dairy Cows

Answer 23

accounts for 25-30% of mastitic infections,