Colonies of Pseudomonas aeruginosa bacteria protect themselves from antibiotics and other insults by grouping together and secreting adhesive polysaccharides, forming what is known as a biofilm.
"From the clinical perspective, biofilms are a major problem, since these structures display greatly increased resistance to physical and chemical insults, 7 which is probably a major reason why they form in the first place! Crucially, biofilms are much more resistant to antibiotic treatment than their planktonic counterparts, making them particularly difficult to eliminate from patients and contaminated surgical equipment…One of the main problems with P. aeruginosa infections is that the organism is resistant intrinsically to the action of many antibiotics, a situation that is exacerbated when it forms biofilms." (Welch et al., 2005:197, 199)
Learn more about this functional adaptation.