Gram positive infections: bench to bedside (word document) Flashcards by Brock Wilde

What are the gram positive cocci?

staphylococcus, streptococcus, enterococcus

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What are the gram positive bacilli?

corynbacterium, listeria

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What are the gram stain pattern of the following aerobic gram positive cocci: staphylococcus, streptococcus, enterococcus

Staphylococcus – Gram positive cocci in clusters

Streptococcus – Gram positive cocci in pairs OR Gram positive cocci in chains
Enterococcus – Gram positive cocci in pairs and chains

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What are the staphylococcal species associated with human infections?

o	Staphylococcus aureus
o	Coagulase negative Staphylococcus – term used to describe a group of bacteria
•	Staphylococcus epidermidis
•	Staphylococcus saprophyticus
•	Others

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What does the catalaze test show for the three gram positive cocci?

Positive = staphylococci

catalaze negative = Streptococci, Enterococci

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How do you differnetiate between staph. aureus and both staphylococcus epidermis, and staphylococcus saprophyticus and others?

Coagulase: Enzyme converts fibrinogen ⇒ fibrin
o Positive = Staphylococcus aureus
o Negative = Staphylococcus epidermidis, Staphylococcus saprophyticus, others

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What local infections does staphylococcus aureus produce?

o Skin and soft tissue – cellulitis, impetigo, folliculitis/furuncles/carbuncles, mastitis, necrotizing fasciitis

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What invasive infections are produced by staphylococcus aureus?

o Bacteremia
o Endocarditis
o Osteomyelitis/septic arthritis

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What toxin mediated infections - toxin producing strains of S. aureus - are produced by staphylococcus aureus?

o Toxic shock syndrome
o Staphylococcal scalded skin syndrome
o Food poisoning

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For coagulase negative staphylococcus infections, what are the local and invasive infections produced?

Local infections
o Urinary tract infection – S. saprophyticus
Invasive infections – associated with foreign devices (prosthetic joint, prosthetic valve)
o Bacteremia
o Endocarditis
o Osteomyelitis/septic arthritis

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What are the streptococcus species associated with human infection?

Streptococcus pneumoniae
- Group A Streptococcus (GAS) – Streptococcus pyogenes
- Group B Streptococcus (GBS) – Streptococcus agalactiae
- Group C (GCS) and Group G Streptococcus (GGS)
- Viridans group Streptococci – encompasses large group of streptococci
  that live in oropharyngeal and GI tract

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How do you differentiate between streptococcal species?

hemolytic pattern on blood agar
- alpha-hemolytic: incomplete hemolysis of blood agar – zone of green
around bacterial colony on blood agar
- Streptococcus pneumonia, Viridans group streptococci
- beta-hemolytic: complete hemolysis of blood agar – zone of clear around
bacterial colony on blood agar
- GAS, GBS, GCS, GGS
- gamma-hemolytic: no hemolysis of blood agar
- Viridans group streptococci
- Lancefield group – method of grouping beta-hemolytic bacteria based on carbohydrate composition of cell walls (Group A, B, C, etc)

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What are the local and invasive infections caused by streptococcus pneumonia?

-	Local infections
o	Otitis media
o	pneumonia
-	Invasive infections
o	meningitis

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What is Group A streptococcus also known as and what are the local, invasive, and toxic infections caused by it?

Group A Streptococcus (S. pyogenes): Infections
- Local infections
o Skin and soft tissue – cellulitis, impetigo, folliculitis/furuncles/carbuncles, mastitis, necrotizing fasciitis
o Tonsillopharyngitis / paratonsillar abscess / retropharyngeal abscess
- Invasive infections
o Bacteremia
o Osteomyelitis/septic arthritis
- Toxin mediated infections – toxin producing strain
o Toxic shock syndrome

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Bacteremia - peripartum sepsis (maternal or neonatal) is caused by what type of streptococcus?

Group B Streptococcus (S. agalactiae): Infections
- Invasive infections
o Bacteremia – peripartum sepsis (maternal or neonatal)

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What is the local infection caused by Group C and Group G streptococcus?

o Tonsillopharyngitis / paratonsillar abscess / retropharyngeal abscess

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What are the infections caused by the viridans group streptococcus?

Viridans group Streptococcus: Infections
- invasive infections
o bacteremia
o endocarditis

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What are the enterococcus species associated with human infections?

Enterococcal species associated with human infections

- Enterococcus faecalis
- Enterococcus faecium

What are the local infections caused by enterococcus?

Urinary tract infection

What are the corynebacterium species associated with human infections?

C. diphtheria – covered in Toxin mediated infections

What is the listerial species associated with human infections? and it’s infections?

L. monocytogenes
- Invasive infections
o Neonatal sepsis – bacteremia, meningitis, pneumonia

What is the laboratory diagnosis of gram positive infections?

Specimen - pus, blood, CSF, pleural fluid, synovial fluid, urine
- gram stain and culture

What are the principles of treatment for impetigo, and folliculitis?

Topical therapy: mupirocin, fucidic acid

What are the principles of treatment for other infections?

localized, not extensive, not toxin mediated: po antibiotics sufficient
extensive localized infections, abscess, invasive, septic shock: IV abx, may need surgery for debridement of devitalized tissue

If an abcess is present what should you do?

drain abscess + antibiotics

If there is toxin mediated: septic shock, staphylococcal scalded skin syndrome, what should you do?

- Supportive therapy - IV antibiotic - IVIG – when septic shock present

If there is toxin mediated: food poisoning, what should you do?

– self limited illness, no treatment required

If there is a neonatal infection, what should you do?

requires inpatient treatment with parenteral antibiotics

For MSSA (methicillin susceptible S. aureus) what antibiotic should you give?

o penicillinase resistant penicillins – Cloxacillin (po, IV) o First generation cephalosporins – Cephalexin (po), Cefazolin (IV) o Clindamycin (po, IV)

For the Streptococci – Viridans group Streptococci, GAS, GBS, GCS, GGS what antibiotic should you give?

o Penicillin – penicillin V (po), penicillin G (IV) | o First generation cephalosporins – Cephalexin (po), Cefazolin (IV)

For the Streptococci – S. pneumoniae, what antibiotic should you give?

o 2nd and 3rd generation cephalosporins

For the enterococci, what antibiotic should you give?

o ampicillin susceptible – ampicillin | o ampicillin resistant – vancomycin

For listeria, what type of antibiotic should you give?

ampicillin

for methicillin resistant S. aureus (MRSA) what should you give for antibiotics?

- resistance to beta-lactam antibiotics: tested by resistance to methicillin - d/t mecA gene – altered PBP2a (penicillin binding protein 2a) - antibiotic – vancomycin, other antibiotics as indicated by susceptibility pattern

What are hospital associated MRSA risk factors?

- prolonged or multiple hospitalizations - multiple courses of antibiotics - presence of indwelling line or tracheal tube - contact with MRSA positive individual

What are community associated MRSA risk factors?

- athletes - crowded living situations – homeless shelters, jails, army - Aboriginal - Tattoos - IVDU

What are the vancomycin resistant Enterococci (VRE)?

- resistance to: vancomycin - d/t production of peptidoglycan precursors that have decreased affinity for vancomycin - antibiotic options limited

What are the VRE risk factors?

- prolonged or multiple hospitalizations - multiple courses of antibiotics - presence of indwelling line or tracheal tube - immunosuppression

What are the prevention and control measures for skin and soft tissue infections?

a. Skin and soft tissue infections - Hand washing - Standard precautions: Wear gloves when examining skin

What are the prevention and control measures for respiratory infections?

- Hand washing | - Droplet precautions: Gloves, gown, mask for healthcare workers

What are the prevention and control measures for patient colonized/infected with MRSA or VRE?

- Nasal/groin swab to detect colonization - Hand washing before entering room and after exiting - Private room - Gloves, gown for HCW - Gloves, gown for patient when not in room

For the gram stains, what is special about gram negative organisms?

Gram negative organisms (Red): higher lipid content of cell walls - Increased permeability to acetone (decolorizer) - Lose crystal violet and take up safranin

For the gram stains, what is special about the gram positive organisms?

Gram positive organisms (Blue/Violet): increased number of cross-linked teichoic acid in cell wall - Decreased permeability to acetone - Retain crystal violet and take up safranin

What is the coagulase test?

Coagulase: converts fibrinogen to fibrin - Rabbit plasma inoculated with Staphylococcal bacteria - Positive – serum coagulates, forms clot - Negative – serum remains liquid