Staphylococcus

Question 1

How does staphylococci gram stian?

Answer 1

Gram Positive

Cocci in grape like clusters

Question 2

What are the general characteristics of staphylococci?

Answer 2

Non-motile
Non Spore Forming
Catalase Positive
Facultative Anaerobes (except: S.Anaerobius and Saccharolyticus)

Question 3

What are the important species of staphylococci?

Answer 3

S. Aureus
S. Epidermidis
S.Saprophyticus
S.Lugdunensis

Question 4

What are some characteristics of S.Aureus when grown on agar plates?

Answer 4

Off-white cream color

Zone of B-hemolysis

Question 5

Where are S.Aureus found?

Answer 5

Environment

SKin/Mucous membranes (Especially anterior nares)

Question 6

What can predispose to S.Aureus infections?

Answer 6

Leukocyte Chemotaxis defects
Opsonization defects
Acquired Hypogammaglobulinemia
Complement defect
Defective intracellular killing of bacteria (Inability to activate membrane bound oxidase system)
Skin Injuries (Burns, incisions, sports injuries)
Presence of foreign bodies
Viral infections
Chronic Underlying Diseases

Question 7

Where are the usual sites of infections for S.Aureus?

Answer 7

Skin: Impetigo, Furuncles, Carbuncles, Post Surgical wound infections
Nose and Throat
GI Tract
Urethra/Vagina

Question 8

What is pyoderma and what causes it?

Answer 8

Pyogenic skin disease caused by infections (ex: S.Aureus), or autoimmune (ex: pyoderma gangrenosum)

Question 9

What are furuncles?

Answer 9

Boils on skin caused by infeciton of hair follicles leading to localized accumulation of pus and dead tissue with white head in center of lump later

Question 10

What are carbuncles?

Answer 10

Abscess larger than a boil with one or more openings that drain pus onto skin

Most common on back and nape of neck

Question 11

What are the toxin mediated infections caused by S.Aureus?

Answer 11

Scalded Skin Syndrome: neonates and children

Question 12

What can happen when S.Aureus disseminates in blood?

Answer 12

Pneumonia
Bacteremia
Endocarditis
Osteomyelitis
Septic Arthritis
Septic Embolization
Metastatic Infections

Question 13

What are the virulence factors of S.Aureus that interfere with phagocytosis? What do they do?

Answer 13

Capsules:prevent ingestion by PMNs

Protein A: binds Fc region of IgG -> prevent opsonizaiton and ingestion by PMNs

PVL: enzyme that alters cation permeability of leukocytes-> WBC destruction

Coagulase: binds prothrombin-> catalyze fibrinogen to fibrin -> coat bacterial cells wiht fibrin -> resistance to opsonization and phagocytosis

Question 14

What are virulence factors causing hemolysis?

Answer 14

a-hemolysin: lyse RBCS and leukocyte toxicity

B-hemolysin: shows clearning around colony on agar plate due to killing of RBCs (Seen with S.Aureus)

d-hemolysin: Surfactant that disrupts cell membrane and forms channels to leak cellular contents

y-hemolysin: lysis of cells

Question 15

What are Exofliatins?

Answer 15

Epidermolytic toxins that cause staphylococcal scalded skin syndrome

Dissolves mucopolysachardie matrix of epidermis -> separation of skin layers

Mostly neonates and children

Question 16

What are enterotoxins?

Answer 16

Causes staphylococcal food poisoning
Toxins produced causes sickness within 2-8 hours => most likely staph aureus

Resolution within 24-48 horus

Question 17

What are the enzymatic virulence factors of S.Aureus?

Answer 17

Fibrinolysins: break down fibrin clots -> infection to tissues
Hyaluronidase: hdyrolyze matrix of mucopolysaccharides-> promote spread
PLC: Make tissue more susceptible to damage and destruction by complement components

Question 18

What are superantigens?

Answer 18

Pyogenic Toxin superantigens that induce polyclonal T cell proliferation and are pyrogenic

Question 19

What are the superantigen virulence factors?

Answer 19

TSST-1 (S.Aureus)
SPE (Streptococcal pyrogenic exotoxins)
Streptococcal superantigens

Question 20

What does it mean in a lab if a bacteria strain with serum and plasma causes clots?

Answer 20

Coagulase + (Improtnatn for determining S.Aureus)

Question 21

What is the latex agglutination test?

Answer 21

Alternative Coagulase test
Fibrinogen bound to latex to detect clumping factor
Smooth suspension: coag neg
Clumping: Coag pos

Question 22

What is staph epidermidis?

Answer 22

Coagulase Negative
Novobiocin Sensitive

Associated with infections of indwelling devices
Biofilm production and adherence to surfaces of foreign bodies

Question 23

What are the characteristics of Staph Saprophyticus?

Answer 23

Cause of acute UTI infection in sexually active young woemn
2nd most common cause of uncomplicated cystitis in child bearing age women

Coagulase Negative
Novobiocin Resistant

Question 24

What are hte unique characteristics of Staph Lugdunensis?

Answer 24

Similar disease problems of S.Aureus

PYR and Ornithine positive
Coagulase Neg

Question 25

Who gets staph/MRSA most often?

Answer 25

Patient si hospitals or healthcare facilities iwth weakened immune systems

Question 26

What are the most important reservoirs of MRSA in hospitals?

Answer 26

Colonized/Infected patients

Question 27

How do hospital personnel play a role in MRSA transmission?

Answer 27

Serve as a link for transmission between colonized/infected patients

Question 28

What are community acquired MRSA?

Answer 28

MRSA infections acquired by people who have not been recently hospitalized or had an invasive medical procedure

Question 29

What is the mecA gene?

Answer 29

Encodes for ALTERED PBP2a

Question 30

How does mecA play a role wiht MRSA?

Answer 30

altered PBP2a -> decreased binding affinity for B-lactam abx -> allows peptidoglycan synthesis even with abx S.Aureus wiht mecA gene -> resistance to B-lactam drugs like Penicillin

Question 31

What are SSTI?

Answer 31

Skin and soft tissue infections

Question 32

When shoudl MRSA be considered in the differential diagnosis?

Answer 32

``` Sepsis Osteomyelitis Necrotizing Pneumonia/Fascitis Septic Arthritis SSTI ```

Question 33

What can be done to control MRSA?

Answer 33

``` Hand hygiene for all patient interactions Standard contact/droplet precautions Effective cleaning of patient rooms Clean equipment Appropriate use of abx ```

Question 34

How do we screen for MRSA?

Answer 34

Screen everyone on admission via swab on both nostrils on anterior nares -> LAB (Culture, RT-PCR)

Question 35

What is the most important reservoir of MRSA in hospitals? A.Colonized or infected pts 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 35

A

Question 36

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 coagulasenegative, 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 36

E