Dear Alla, biofilm formation on surfaces by bacteria protect them against antibiotics, disinfectants and immune cell attacks. They produce a protective layer glycocalyx.
"The glycocalyx is a polysaccharide and protein film that surrounds bacterial cells. It may be found surrounding individual cells or colonies, and it forms part of the complex organization of bacterial biofilms"
The following references can help you.
1. Costerton, J.W. et al. (1999) Bacterial biofilms: a common cause of
persistent infections. Science 284, 1318–1322
2. Survival strategies of infectious biofilms
TRENDS in Microbiology Vol.13 No.1 January 2005
3. Jan A. Hobot, in Molecular Medical Microbiology (Second Edition), 2015.