glycocalyx

By coating itself in this extracellular polysaccharide, a bacterium adheres to catheters, prosthetic valves, joint replacements, pacemaker leads, and shunts, then builds a biofilm within which cells are metabolically slowed and physically shielded. This has two decisive consequences: antibiotics penetrate poorly and act less effectively against slow-growing organisms, and phagocytes cannot reach the embedded bacteria. Device-related infection therefore frequently requires removal of the hardware for cure, no matter how appropriate the antibiotic. S. epidermidis is the paradigm — a coagulase-negative, novobiocin-sensitive, catalase-positive skin commensal that is the leading cause of prosthetic valve endocarditis and central line infection, and also the commonest blood culture contaminant, so the distinction rests on multiple positive cultures and clinical context. Viridans streptococci use dextran, a glycocalyx polymer, to adhere to both tooth enamel and damaged heart valves. Pseudomonas aeruginosa produces alginate biofilm in the cystic fibrosis airway, giving mucoid colonies and effectively untreatable chronic colonization.