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MHD Block 3: Gram Positive Cocci > Staphylococcus > Flashcards

Staphylococcus Flashcards

1
Q

How does staphylococci gram stian?

A

Gram Positive

Cocci in grape like clusters

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2
Q

What are the general characteristics of staphylococci?

A

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

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3
Q

What are the important species of staphylococci?

A

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

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4
Q

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

A

Off-white cream color

Zone of B-hemolysis

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5
Q

Where are S.Aureus found?

A

Environment

SKin/Mucous membranes (Especially anterior nares)

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6
Q

What can predispose to S.Aureus infections?

A 
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
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7
Q

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

A

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

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8
Q

What is pyoderma and what causes it?

A

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

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9
Q

What are furuncles?

A

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

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10
Q

What are carbuncles?

A

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

Most common on back and nape of neck

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11
Q

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

A

Scalded Skin Syndrome: neonates and children

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12
Q

What can happen when S.Aureus disseminates in blood?

A 
Pneumonia
Bacteremia
Endocarditis
Osteomyelitis
Septic Arthritis
Septic Embolization
Metastatic Infections
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13
Q

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

A

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

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14
Q

What are virulence factors causing hemolysis?

A

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

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15
Q

What are Exofliatins?

A

Epidermolytic toxins that cause staphylococcal scalded skin syndrome

Dissolves mucopolysachardie matrix of epidermis -> separation of skin layers

Mostly neonates and children

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16
Q

What are enterotoxins?

A

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

Resolution within 24-48 horus

17
Q

What are the enzymatic virulence factors of S.Aureus?

A

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

18
Q

What are superantigens?

A

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

19
Q

What are the superantigen virulence factors?

A

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

20
Q

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

A

Coagulase + (Improtnatn for determining S.Aureus)

21
Q

What is the latex agglutination test?

A

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

22
Q

What is staph epidermidis?

A

Coagulase Negative
Novobiocin Sensitive

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

23
Q

What are the characteristics of Staph Saprophyticus?

A

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

24
Q

What are hte unique characteristics of Staph Lugdunensis?

A

Similar disease problems of S.Aureus

PYR and Ornithine positive
Coagulase Neg

25
Q

Who gets staph/MRSA most often?

A

Patient si hospitals or healthcare facilities iwth weakened immune systems

26
Q

What are the most important reservoirs of MRSA in hospitals?

A

Colonized/Infected patients

27
Q

How do hospital personnel play a role in MRSA transmission?

A

Serve as a link for transmission between colonized/infected patients

28
Q

What are community acquired MRSA?

A

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

29
Q

What is the mecA gene?

A

Encodes for ALTERED PBP2a

30
Q

How does mecA play a role wiht MRSA?

A

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

31
Q

What are SSTI?

A

Skin and soft tissue infections

32
Q

When shoudl MRSA be considered in the differential diagnosis?

A 
Sepsis
Osteomyelitis
Necrotizing Pneumonia/Fascitis
Septic Arthritis
SSTI
33
Q

What can be done to control MRSA?

A 
Hand hygiene for all patient interactions
Standard contact/droplet precautions
Effective cleaning of patient rooms
Clean equipment
Appropriate use of abx
34
Q

How do we screen for MRSA?

A

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

35
Q

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

A

A

36
Q

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

A

E

MHD Block 3: Gram Positive Cocci (3 decks)

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