Chapter 93 - Gram-positive infections

Question 1

Where (in healthy animals) is a gram-positive normal microflora mainly found ?

Answer 1

Skin
Mucous membranes
Gastrointestinal tract

Question 2

Who are the patients at increased risk for gram-positive bacteria?

Answer 2

• Hospitalized patients

- Critically ills

Question 3

Describe the morphology of gram-positive bacteria

Answer 3

• Cell wall: thick, coarse structure that serves as an exoskeleton
• Single cytoplasmic membrane
• Cytosol

Question 4

Name three gram-positive bacteria protective mechanisms against the environment or antibiotics

Answer 4

• Thick wall cell
• Outer capsule or biofilm, interfacing with the external environment
• Beta-lactamases (enzymes) within the cytoplasmic membrane, preventing antibiotics from binding to PBPs

Question 5

What are the two major cell wall structural components with pro-inflammatory activities once released into the circulation?

Answer 5

Peptidoglycan

Question 6

Name 3 gram-positive cocci genus

Answer 6

Streptococcus
Enteroccocus
Staphylococcus

Question 7

There is 2 ways to classify Streptococcus into different groups. What are the criteria used for each of these classification? Give the most pathogenic groups for each classification?

Answer 7

Blood agar plate hemolysis
- Non hemolytic
- alpha-hemolytic
- beta-hemolytic (generally pathogenic)
Carbohydrate cell wall antigens
- From A to L
Group G (streptococcus canis) > C

Question 8

Give the most commonly efficacious antibiotics used against Streptococcus

Answer 8

• Penicillin G
• Ampicillin
• Erythromycin
• Clindamycin
• TMP-SMZ
• Cephalosporins

(generally not susceptible to aminoglycoside and fluoroquinolone)

Question 9

What is the most common source for infection in animals with Streptococcal toxic shock syndrome (STSS)? What is the prognosis?

Answer 9

Lungs

Poor prognosis

Question 10

What is the recommended treatment for a necrotizing fasciitis and myositis (NFM)? What is the prognosis?

Answer 10

Aggressive surgical resection and clindamycin

Good prognosis with appropriate treatment

Question 11

Does Enterococcus release pro-inflammatory toxins?

Answer 11

No (unlike Streptococcus and Staphylococcus)

Question 12

What are the most common infections seen with Enterococcus?

Answer 12

Post-operative and urogenital infections

Question 13

What is the particularity of Enterococcus regarding its sensitivity to antibiotics?

Answer 13

Intrinsically resistant to numerous antibiotics

Development of multi-drug resistance in hospitals

Question 14

What are the thoughts on the use of ampicillin alone against bacteria susceptible to this antibiotics?

Answer 14

It is inappropriate as enterococci are often only inhibited by ampicillin (and not killed) and production of beta-lactamases may be induced in bacteria exposed to ampicillin

Question 15

What is the standard of care for serious enterococcal infections in critically ill patients and in those with osteomyelitis, endocarditis, sepsis and joint infections?

Answer 15

Co-administration of gentamicin with a cell wall-active agent such as ampicillin

Question 16

What are the three most clinically relevant Staphylococcus in companion animals?

Answer 16

S. pseudointermedius, aureus, schleiferi ssp.coagulans

Question 17

What are the most common infections associated with Staphylococcus?

Answer 17

Skin and ear

Question 18

What do MRSP and MRSA stand for? What are the precautions to take when facing those bacteria?

Answer 18

Methicillin-Resistant S. Pseudointermedius , and Methicillin-Resistant S. Aureus.
Those infections emerge as an important zoonotic and veterinary disease -> hospitalization in isolation, barrier contact with the patients and all associated materials, hand-washing, warning the owner and his family

Question 19

What are the antibiotics usually effective for treating staphylococcal infections?

Answer 19

Clindamycin, TMP-SMZ, doxycycline, aminoglycosides

Question 20

What are the recommendations for empiric antibiotic strategies?

Answer 20

Culture, prompt administration of injectable broad-spectrum antibiotics (such as ampicillin +/- beta-lactam, cephalosporin) pending the culture results, +/- adapted to known nosocomial infections in the hospital
Exceptions: new infections in a patient already receiving an antibiotic / critically ill patients with known history of recent antibiotics treatment
=> Use of broader-spectrum antibiotics such as carbapenem

Question 21

What is the maximal dose of enrofloxacin in cats? What are the risks associated to the use of this antibiotics at higher doses in cats

Answer 21

5 mg/kg/d

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