This electron micrograph depicted the biofilm formation found inside the lumen of an indwelling catheter being secreted by Staphylococcus aureus
bacteria. The biofilm secretions are primarily composed of polysaccharides, and by covering the bacteria, render the bacteria resistant to attacks they may face from antimicrobial agents. S. aureus
, often referred to simply as "staph," are bacteria commonly carried on the skin, or in the nose of healthy people. Approximately 25% to 30% of the population is colonized, i.e., when bacteria are present, but not causing an infection, in the nose with staph bacteria.