Aerobic and Facultatively Anaerobic Gram-Positive Cocci


Enterococcus faecalis and Enterococcus faecium are gram-positive cocci that belong to the genus Enterococcus. They are facultatively anaerobic, meaning they can grow in the presence or absence of oxygen. They are also catalase-negative, meaning they do not produce the enzyme catalase that breaks down hydrogen peroxide. They are part of the normal flora of the human gastrointestinal tract, but they can also cause opportunistic infections in various sites of the body.

Enterococcus faecalis and Enterococcus faecium are among the most common causes of nosocomial infections, which are infections acquired in hospitals or other healthcare settings. They are responsible for about 10% of all bloodstream infections and 16% of all urinary tract infections in hospitalized patients. They can also cause peritonitis, endocarditis, wound infections, intra-abdominal abscesses, and meningitis. These infections are often difficult to treat because enterococci have intrinsic resistance to many antibiotics and can acquire additional resistance genes through horizontal gene transfer.

Enterococcus faecalis is more prevalent and more virulent than Enterococcus faecium. It accounts for about 80% of all enterococcal infections and has a higher mortality rate than Enterococcus faecium. However, Enterococcus faecium is more resistant to antibiotics and has emerged as a major cause of vancomycin-resistant enterococci (VRE) infections. VRE are strains of enterococci that are resistant to vancomycin, which is a last-resort antibiotic for treating serious gram-positive infections. VRE infections pose a serious threat to public health and require strict infection control measures to prevent their spread.

Enterococcus faecalis and Enterococcus faecium have relatively low virulence compared to other gram-positive pathogens such as Staphylococcus aureus or Streptococcus pyogenes. They do not produce many toxins or enzymes that damage host tissues or evade host defenses. However, they have several factors that contribute to their pathogenicity, such as adhesins, biofilm formation, aggregation substance, cytolysin, gelatinase, and enterococcal surface protein. These factors enable enterococci to adhere to host cells and surfaces, form protective communities, exchange genetic material, lyse host cells, degrade extracellular matrix, and evade phagocytosis.

Enterococcus faecalis and Enterococcus faecium are important pathogens that cause significant morbidity and mortality in hospitalized patients and immunocompromised individuals. They have a remarkable ability to adapt to different environments and acquire resistance to multiple antibiotics. Therefore, it is essential to understand their clinical features and virulence factors in order to prevent and treat their infections effectively.