Clinical Micrbology
Enterococcus faecalis: Overview and Cellular Structure
General Description
Enterococcus faecalis is a Gram-positive, facultatively anaerobic bacterium commonly found in the human gastrointestinal tract. While normally part of the gut microbiota, it can act as an opportunistic pathogen, causing infections such as urinary tract infections, bacteremia, endocarditis, and wound infections. It is medically important because of its resistance to many antibiotics, including vancomycin in some strains (VRE – vancomycin-resistant Enterococcus).
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Cell Morphology
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Shape: Cocci (spherical), usually arranged in pairs (diplococci) or short chains.
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Size: About 0.6–2.0 µm in diameter.
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Cell Wall: Thick peptidoglycan layer characteristic of Gram-positive bacteria, providing structural integrity and resistance to osmotic pressure.
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Capsule: Some strains produce a polysaccharide capsule that helps evade the host immune system.
Key Cellular Structures (Organelles/Features)
Since E. faecalis is a prokaryote, it lacks membrane-bound organelles (like a nucleus or mitochondria). Instead, its cellular features include:
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Cytoplasmic Membrane: Phospholipid bilayer controlling transport of nutrients and waste.
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Cytoplasm: Gel-like matrix containing enzymes, metabolites, and ions.
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Nucleoid: Region containing circular double-stranded DNA, not enclosed in a membrane.
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Plasmids: Extra-chromosomal DNA that often carries antibiotic resistance genes.
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Ribosomes (70S): Sites of protein synthesis, smaller than eukaryotic 80S ribosomes.
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Cell Wall Teichoic Acids: Contribute to cell shape, adhesion, and immune interactions.
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Flagella: Most E. faecalis are non-motile, but some strains have flagella for limited motility.
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Pili (Fimbriae): Surface appendages important for adhesion to host tissues and biofilm formation.
Pathogenic Features
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Ability to survive harsh environments (high salt, bile, detergents).
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Biofilm formation on medical devices (catheters, heart valves).
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Production of virulence factors like cytolysin and gelatinase.
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