Gram Positive Cocci

Question 1

Catalase Positive Genera

Answer 1

• Micrococcus and related genera
• Staphylococcus
• Rothia (Stomatococcus) mucilaginosus

Staphylococcus genera are primary clinical significance

Question 2

Micrococcus, Rothia, and related Genera Characteristics

Morph, habitat, transmission, clinical

Answer 2

G+ cocci in tetrads
Grow on routine media
Colonies may be pigmented
Habitat: skin, mucosa, oropharynx
Transmission: endogenous
Clinical significance: rarely complicated, low virulence

Question 3

Staphylococcus General Characteristics

Morph, atmosphere, habitat, transmission, clinical

Answer 3

G+ cocci in clusters
Grow on routine media
Type: facultative anaerobe
Habitat: nares, axillae, vagina, pharynx, skin surfaces
Transmission: spread of endogenous flora, person to person
Clinical significance: virulence factors, species variation

Question 4

S. Epidermidis

Predisposing factors? virulence?

Answer 4

Most frequently encountered staph. - moist body surfaces

Predisposing factors: catheters, medical implants, prosthetics, immune status

Major virulence factor: biofilm

Other: a lot are healthcare-acquired, bloodstream, endocarditis

Question 5

Biofilm

What problems?

Answer 5

• Biofilm cells are more resistant to antibiotics
• More resilient to phagocytosis than free floating bacteria
• Many diseases associated with biofilms

Question 6

Catheter Associated Infection

Answer 6

• Microbe moves from catheter skin entry side to catheter tip within bloodstream
• Inside the catheter hub into the body
• Hematogenous spread

Question 7

Staphylococcus lugdunensis

Where, problems, virulence, special test?

Answer 7

• Lower body, axillae
• Community and healthcare infections
• Skin, soft tissue
• Endocarditis, bacteremia, prosthetic devices

Major virulence factor: biofilm
Extracellular clumping factor positive

Question 8

Staphylococcus saprophyticus

Where, clinical, virulence

Answer 8

GI tract - age season dependent
- UTIs in young, sexually active women
Major virulence factor: adhere to epithelial cells in urogenital tract

Question 9

Staphylococcus hominis, Staphylococcus haemolyticus

where,what is special about this? Virulence?

Answer 9

Colonize axillae and pubic areas
S. haemolyticus second most common coag- associated with infections: most virulent coag- staphs

Major virulence factor: biofilm or adhesion

Question 10

Staphylococcus capitis

Where, virulence

Answer 10

Colonize scalp, forehead after puberty
Major virulence factor: biofilm or adhesion

Question 11

Staphylococcus aureus General

The apex! Raaagh

Answer 11

Most significant staph species
- Mild to life-threatening infections
- Can be on almost any specimen
- Healthcare associated infection
- Increasing antimicrobial resistance problem

Question 12

S. aureus: Virulence Factors

Answer 12

• Structural components
• Exotoxins
• Enzymes
• Biofilm

Question 13

S. aureus: Structural Components

Virulence factors, 4 things

Answer 13

Capsule: slime layer, resists chemotaxis, phagocytosis, and facilitates adherence to other bodies
Peptidoglycan: resists phagocytosis
Teichoic acid/lipoteichoic acid: binds to fibronectin, ahesion to human cells
Protein A: binds IgG, inhibits antibody mediated clearance

Question 14

S. aureus: Exotoxins

Virulence factor, 4 of them

Answer 14

Enterotoxins: superantigens that stimulate T cells and release cytokines, heat stable, involved in food poisoning
- interfere with adaptive immune system, not processed by antigen presenting cell, activates T cell directly, cytokine storm = fever and shock
- Cytolytic toxins: lyses different human cells (RBCS, WBCs, tissue damage)
- Exfoliative toxins: epidermolytic, epidermal cells slough off
- Toxic shock syndrome toxin: superantigen, penetrate mucosal barriers, systemic effects

Question 15

S. aureus: Enzymes

Answer 15

Hyaluronidase: digest hyaluronic acids in host tissue, spreads microbes
Staphylokinase (fibrinolysin): dissolves fibrin clots, spreads microbes
Lipases: hydrolyzes lipids, microbe can survive in sebaceous areas, spread more

Question 16

S. aureus Infection: Impetigo

Answer 16

• Intraepidermal vesicles with exudate, leaking and crusting lesion
• Common in children
• Moist areas, warm, highly contagious
• Clears on its own or with antibiotics

Question 17

S. aureus Infection: Folliculitis

Answer 17

• Inflammation/infection of hair follicles
• Small papule lesions, pustulates with white/yellow centers
• At points of friction like thighs, groin

Question 18

S. aureus Infection: Furuncles

Boils

Answer 18

• Spreads from follicle to follicle, tissue around it too
• Redness, firm, painful with drainage
• Neck, face, breasts, buttocks, friction and sweat

Question 19

S. aureus Infection: Carbuncle

Multiple boils

Answer 19

• Infection a lot deeper, into fat, has multiple drainage sites
• Fever and chills maybe
• Don’t really heal by itself, drain and antibiotic treatments

Question 20

S. aureus Infection: Cellulitis

Answer 20

• Acute inflammatory, subcutaneous tissue, redness, heat, tenderness
• Lower body, legs, skin
• Over 90% of cases are because of S. aureus
• Develop rapidly (24-48 hours) from minor injury to severe septicemia

Question 21

S. aureus Infection: Scalded Skin Syndrome

Toxin mediated!!

Answer 21

“Ritter disease”
- Abrupt onset, redness, inflammation around mouth and spreads over whole body in 2 days
- Blisters soon after
- Young children, 5% mortality
- Spontaneous recovery, 7 day period of infection

Question 22

S. aureus Infection: Toxic Shock Syndrome

Toxin mediated!!!

Answer 22

• Rare, may be fatal
• Localized growth in vagina or wound, then releases toxins
• Fever, chills, rash
• 5-65% fatality if incorrect antibiotic is given

Question 23

S. aureus Infection: Food Poisoning

Toxin mediated!!!!

Answer 23

• Quick onset, 1-6 hours
• Heat stable: reheating food won’t get rid of toxin even after bacteria dies
• Poor food handling
• Vomiting, nausea, cramps, diarrhea

Question 24

Antibiotic Resistance in S. Aureus

Answer 24

• Methicillin-resistant S. aureus (MRSA)
• Vancomycin-intermediate S. aureus (VISA)
• Vancomycin-resistant S. aureus (VRSA)
• Coag- staphs can be resistant to a variety of antimicrobials

Question 25

Community Acquired Methicillin Resistant S. aureus (CA-MRSA)

How do you get it?

Answer 25

• Person who hasn’t been recently hospitalized or had a procedure
• Skin infections, otherwise healthy people
• Athletes, military, children, MLM, prisoners
• Skin contact, crowded conditions, openings in skin, bad hygiene
• Contaminated surfaces
• Drug injections

Question 26

Distinguishing CA-MRSA from Healthcare MRSA

Answer 26

• Location during/before diagnosis (hospital or outpatient?)
• No history of MRSA or colonization
• No medical history recently
• No catheters or things breaking skin

Question 27

Strain Characteristics of CA-MRSA

Answer 27

Virulence factors:
- susceptible to wider range of antibiotics than HA-MRSA
- Exotoxin Pantone-Valentine leucocidin (PVL) = skin and soft tissue infection and necrotizing pneumonia

Question 28

Treatment and Prevention

Answer 28

• Antibiotics for Staphylococcs
• Surgical removal
• Good hygiene
• Food safety
• Healthcare precautions

Question 29

Laboratory Diagnosis

Methods

Answer 29

• Microscopy
• Culture, biochemical
• Instrumentation

Question 30

Bloodstream Infections: Diagnosis and Results

What to do, diff between contaminant and pathogen?

Answer 30

Collection
- Collection appropriate amount for age
- Prior to antibiotics/at fever spikes
Results
Contaminant: normal skin flora, multiple organisms, blood culture organism not the same as infection site
Pathogen: same organism growing at differen collections, S. aureus, S. pyogenes, S. agalactiae, A. pneumoniae, E. coli, Candida