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Introduction
1. Anatomy
2. Microbiology
2.1 General bacteriology
2.2 Introduction to systemic bacteriology
2.3 Gram positive cocci
2.3.1 Staphylococci
2.3.2 Streptococci
2.3.3 Enterococci
2.4 Gram negative cocci
2.5 Gram positive bacilli
2.6 Gram negative bacilli
2.7 Other important bacteria
2.8 Virology
2.9 Parasitology
2.10 Mycology
3. Physiology
4. Pathology
5. Pharmacology
6. Immunology
7. Biochemistry
8. Cell and molecular biology
9. Biostatistics and epidemiology
10. Genetics
11. Behavioral science
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2.3.3 Enterococci
Achievable USMLE/1
2. Microbiology
2.3. Gram positive cocci

Enterococci

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They’re part of the normal intestinal flora of humans. They’ve gained notoriety because many strains are resistant to multiple antibiotics. The medically important species are E. faecalis and E. faecium. Because they react with Group D antisera, they were originally classified as Group D streptococci. They’re now known to be distinct from streptococci.

Morphology

They appear as gram-positive cocci in pairs, tetrads, and small chains. On blood agar, they’re alpha-hemolytic or non-hemolytic.

Classification

Not important for exam :)

Human pathology

They can cause:

  • UTIs, especially following genitourinary instrumentation
  • Endocarditis
  • Bacteremia
  • Wound infections
  • Catheter-related infections

Laboratory diagnosis of enterococcal infections

Gram stain and culture show the typical findings described above. Key laboratory features include:

  • Ability to grow in 6.5% NaCl
  • Ability to hydrolyze esculin in the presence of bile
  • Not killed by Penicillin G
  • Hydrolysis of pyrrolidonyl-beta-naphthylamide (PYR)
  • Production of leucine aminopeptidase
  • Ability to grow at both 10°C and 45°C

General characteristics

  • Normal human intestinal flora
  • Notable for multi-drug resistance
  • Medically important: E. faecalis, E. faecium
  • Formerly Group D streptococci; now distinct genus

Morphology

  • Gram-positive cocci: pairs, tetrads, small chains
  • Blood agar: alpha-hemolytic or non-hemolytic

Human pathology

  • Cause UTIs (post-genitourinary procedures)
  • Endocarditis, bacteremia
  • Wound and catheter-related infections

Laboratory diagnosis

  • Growth in 6.5% NaCl
  • Hydrolyze esculin with bile
  • Resistant to Penicillin G
  • Positive PYR hydrolysis
  • Produce leucine aminopeptidase
  • Grow at 10°C and 45°C

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Enterococci

They’re part of the normal intestinal flora of humans. They’ve gained notoriety because many strains are resistant to multiple antibiotics. The medically important species are E. faecalis and E. faecium. Because they react with Group D antisera, they were originally classified as Group D streptococci. They’re now known to be distinct from streptococci.

Morphology

They appear as gram-positive cocci in pairs, tetrads, and small chains. On blood agar, they’re alpha-hemolytic or non-hemolytic.

Classification

Not important for exam :)

Human pathology

They can cause:

  • UTIs, especially following genitourinary instrumentation
  • Endocarditis
  • Bacteremia
  • Wound infections
  • Catheter-related infections

Laboratory diagnosis of enterococcal infections

Gram stain and culture show the typical findings described above. Key laboratory features include:

  • Ability to grow in 6.5% NaCl
  • Ability to hydrolyze esculin in the presence of bile
  • Not killed by Penicillin G
  • Hydrolysis of pyrrolidonyl-beta-naphthylamide (PYR)
  • Production of leucine aminopeptidase
  • Ability to grow at both 10°C and 45°C
Key points

General characteristics

  • Normal human intestinal flora
  • Notable for multi-drug resistance
  • Medically important: E. faecalis, E. faecium
  • Formerly Group D streptococci; now distinct genus

Morphology

  • Gram-positive cocci: pairs, tetrads, small chains
  • Blood agar: alpha-hemolytic or non-hemolytic

Human pathology

  • Cause UTIs (post-genitourinary procedures)
  • Endocarditis, bacteremia
  • Wound and catheter-related infections

Laboratory diagnosis

  • Growth in 6.5% NaCl
  • Hydrolyze esculin with bile
  • Resistant to Penicillin G
  • Positive PYR hydrolysis
  • Produce leucine aminopeptidase
  • Grow at 10°C and 45°C