Enterococcus faecalis

Enterococcus faecalis is a bacterium in the coccus group, meaning it is round in shape, and it stains purple on Gram stain, which is why it is called gram-positive. It is a facultative anaerobe, that is, it can live with or without oxygen; it forms short chains, and it normally lives in the large intestine, as well as on the skin, in the mouth, in water and in soil.

Its way of causing harm is not the one used by other familiar bacteria. Staphylococci and streptococci make toxins, poisons that damage the body; enterococci do not. Their virulence, meaning their ability to cause disease, comes from endurance: from their durability, their structure and their resistance to antibiotics. It is a bacterium that attacks with patience rather than poison: it sticks and it lasts.

The sticking is literal. It forms biofilm, a sticky layer it uses to adhere to catheters, dental prostheses and heart valves, and that also keeps antibiotics from reaching it. The step before a serious infection is usually colonization of the digestive tract, from which the bacterium crosses the intestinal wall. And there is a practical figure: about 10% of isolates resist vancomycin.