Staphylococcus

Question 1

Staphylococcus

Answer 1

• gram positive, cocci, nomotile
• pairs; short chains;clusters
• facultative anaerobes; diversity

Question 2

Indigenous bacteria

Answer 2

establish residence on surface tissue or alimentary tract; especially the anterior nares

-Staphylococci are part of the normal flora, problem in controlling infection

Question 3

Coagulase

Answer 3

a biochemical test that differentiates S. aureus form other Staph contributes to the clotting of plasma (converts fibrinogen to fibrin)

S aureus is coagulase positive (major pathogen) and Staph epidermidis is coagulasenegative

Question 4

Is staphylococcus catalase positive or negative

Answer 4

• staphylococcus is catalase positive

- streptococcus is catalase negative, this help distinguish between the two

Question 5

catalsae

Answer 5

different gram positive bacteria do or don’t produce catalase under aerobic conditions

Question 6

Protein A

Answer 6

• unique to staphylococcus aureus
• major protein component of cell wall that is covalently bound to peptidoglycan
• with IgG molecules bound in the “wrong” orientation (in relation to normal antibody function, the igG disrupts opsonization and phagocytossis

Question 7

Toxins produced by S. aureus

Answer 7

different strains possess different toxins, producing unique diseases

• Hemolysins (a, b, g)
• Leukotoxins
• Enterotoxins (superantigens): toxic shock syndrome
• Exfoliative toxins

Question 8

Hemolysins

Answer 8

• RBC membrane damaging proteins

- they contribute to pathogenicity by producing tissue damage after the establishment of a focus of infection

Question 9

Leukotoxin

Answer 9

a two protein toxin, attacks Polymorphonuclear leukocytes (PMNs aa neutrophils) and macrophages

Question 10

Enterotoxins

Answer 10

large family of Staphylococcus toxins, superantigens
-superantigens cause diarrhea and emesis (vomiting)
-intoxication of preformed enterotoxin, not an infection
-source of enterotoxin is from S. aureus contaminated foods (usually by food-handler)
-symptoms occur within 2-6 hours after ingestion and include cramping, nausea, vomiting, diarrhea with rapid recovery 6-8 hour
heat stable
-Includes Toxic Shock Syndrome

Question 11

Enterotoxins and TSST bind to

Answer 11

Enterotoxins and TSST bind directly MHC class II and TCR independent of antigen stimulate about 20% of all T cells

Question 12

What does massive cytokine production lead to

Answer 12

systemic toxicity of host/ suppression of the adaptive immune response

Question 13

Name two superantigens

Answer 13

Staph enterotoxins (SE) and TSST are superantigens

Question 14

Exfoliative toxins

Answer 14

2 forms, ETA/ETB proteases
-stimulate lysis of the intracellular attachment between cells of the epidermis

ex: Scalded Skin Syndrome (exclusively a peds illness)

Question 15

Describe the epidemiology of Staphylococcus

Answer 15

Staphylococcus are normal component of human indigenous flora and are carries asymptomatically at several body sites, especially the anterior nares

Question 16

Transmission of Staphylococcus

Answer 16

• direct contact by hands is the most important route of transmission
  ex: hospital personnel with mild Staph lesion. air borne transmission is possible

Question 17

Infection of Staph chaacteristics

Answer 17

• typically localized
• intact skin is a major barrier to infection (meaning that cuts make you susceptible)
• skin is the primary site of infection

Question 18

What are the different infections Staph can cause (and where are they located? 5)

Answer 18

1. Folliculitis-hair follicle
2. Boil-subcutaneous tissue
3. Impetigo-skin infection mixed infection (staph/strep) higly infectious
4. Scalded skin syndrome-exfoliative toxins
5. Pneumonia-compromised host (CF)
   * influenza patients
   * antibiotic therapy
   * chemotherapy
   * immunosuppressants
   - other site of infection are osteomyelitis (bone) and arthritis

Question 19

Treatment of Staphylococcus aureus infections

Answer 19

-No vaccine
-Therapy based treatment:
*drainage of wound
*removal of foreign objects
*antibiotic therapy
-but test for antibiotic sensitivity as there are multiple drugs resistant isolates
75% are methicillin resistant
10% are vancomycin resistant

Question 20

MRSA

Answer 20

Methicillin Resistant Sthapylococcus aureus (MRSA)
-MR of SA is due to the selection of SA with mutation within the Penicillin Binding Proteins (PBP) that have low affinity for Penicillin

-Vancomycin is used to treat MRSA infections

Question 21

How do you treat MRSA infections

Answer 21

Vancomycin

Question 22

Vancomycin resistance in SA

Answer 22

• Staph aureus is resistant to intermediate, but clinically relevant levels of staph aureus. VIRSA
• VIRSA resistance is due to changes in the cell wall, NOT enterococcal mechanism

Question 23

Community Acquired MRSA

Answer 23

transmitted more easily and cause more skin infections than Hospital Acquired MRSA

• HA-MRSA infection is easily transmitted in hospital infections
• CA-MRSA infection spreads through those living in close contact, such as military barracks, dormitories nd gyms

Question 24

Staphylococcuus in the normal flora

Answer 24

• other staphylococcus pathogens (coagulase negative)
  1. S. epidermidis
  2. S. saprophyticus

Question 25

S. epidermidids

Answer 25

• low virulence
• hospital acquired infection, contamination of surgical site binds to plastics (valves, catheter, prosthetic devices)
• treatment, problem multi-drug resistance so use an antibiogram (analysis of antibiotic sensitivyt locally)

Question 26

S. saprophyticus

Answer 26

• responisble for urinary tract infections selectively binds to cells of the urinary tract (tropism)
• S. saprophyticus does NOT possess virulence factors found in S. aureus, such as coagulase, enterotoxins, exoenzymes, and extracellular matrix binding proteins