🦠 The “Lesser Enterococci”: E. casseliflavus & E. gallinarum — What FRCPath Candidates Must Know

Published on: July 26, 2025

Author: Team FRCPathPrep

Category: Uncommon Pathogens, Antimicrobial Resistance, FRCPath Exam Topics

🧬 Who Are They?

When we think of enterococci, the usual suspects are Enterococcus faecalis and Enterococcus faecium.But there's a third group—often forgotten in textbooks but critical in exams and practice:

• Enterococcus casseliflavus

• Enterococcus gallinarum

These species belong to the motile enterococci and carry intrinsic low-level vancomycin resistance, often confusing even experienced microbiologists.

🔍 Key Characteristics

Feature	E. casseliflavus	E. gallinarum
Motility	Positive 🏃	Positive 🏃
Pigment	Yellow pigment 🟡	None
Vancomycin resistance	VanC phenotype (VanC2/3)	VanC1 phenotype
MIC to Vancomycin	4–32 mg/L (low-level)	4–32 mg/L (low-level)
Resistance Type	Intrinsic, chromosomal	Intrinsic, chromosomal
Teicoplanin MIC	Sensitive	Variable
Clinical Role	Rare bloodstream infections, more common in polymicrobial or gut translocation	Same as E. casseliflavus

💡 VanC Phenotype: The Catch

• VanC resistance is not transferable via plasmids (unlike VanA/VanB).

• Hence, these species are not a major outbreak risk, but they do appear in bacteraemia cases.

• May be mistaken as VRE in routine testing, leading to confusion in infection control and treatment.

🧠 Why This Matters for FRCPath

📌 Part 1 MCQ Points:

• Know the difference between VanA/B (acquired, high-level resistance) vs VanC (intrinsic, low-level).

• Be able to match van gene to species:

  • E. faecium/faecalis = VanA/VanB

  • E. gallinarum = VanC1

  • E. casseliflavus = VanC2/3

📌 Part 2 OSPE/SAQ Clues:

• You may be shown a vancomycin-intermediate enterococcus with a motility test positive and asked for interpretation.

• Always interpret species ID carefully when deciding whether isolation or contact precautions are required.

• Understand that treatment may still include ampicillin if the isolate is susceptible.

🔬 Lab Identification Clues

Test	Result
Bile esculin	Positive
6.5% NaCl	Growth
Motility	Positive (rare among enterococci)
PYR test	Positive
Vancomycin E-test	Intermediate (MIC 8–16)
Pigment (casseliflavus)	Yellowish colony hue

⚠️ Clinical Pearls

• Usually not highly virulent — often found in polymicrobial intra-abdominal infections or gut translocation in neutropenic patients.

• Rarely cause monomicrobial bacteraemia, but such cases should not be ignored.

• Infection control measures do not require isolation as for VanA/VanB VRE.

📖 Summary Table

Feature	VanA/B Enterococci	VanC Enterococci (E. gallinarum, casseliflavus)
Resistance Mechanism	Acquired, plasmid-borne	Intrinsic, chromosomal
Vancomycin MIC	>64 mg/L	4–32 mg/L
Teicoplanin Susceptibility	VanA = resistant VanB = sensitive	Usually susceptible
Outbreak Risk	High	Low
Contact Precautions	Yes	No
FRCPath Importance	High (MCQ + SAQ + OSPE)	High (often forgotten trap in OSPEs)

📘 Final FRCPathPrep Tip

“If it moves and resists vancomycin modestly — think casseliflavus or gallinarum.Don’t panic — it’s VanC.”

✅ What to Do Now?

• 🔍 Review van gene mechanisms (VanA to VanE)

• 📖 Practice OSPE stations on VRE interpretation

• 🎯 Attempt MCQs covering enterococcal resistance and species ID

👨‍⚕️ Want visual aids or flashcard pack on Van genes and enterococci?🧪 Access them in our FRCPathPrep Microbiology Toolkit!

👉 Visit www.FRCPathPrep.com for more resources and updates.