Bacterial lawn or biofilm are terms used by biologists to describe the appearance of bacterial colonies when all the individual colonies on a petri-dish merge together to form a mat of bacteria.
Biofilms are common in nature, as bacteria commonly have mechanisms by which they can adhere to surfaces and to each other. Dental plaque is a biofilm, for example. Bacteria living in a biofilm can have singificantly different properties from free-floating bacteria, as the dense and protected environment of the film allows them to cooperate and interact in various ways. In industrial environments, biofilms can develop on the interiors of pipes and lead to clogs and corrosion. In medicine, biofilms spreading along implanted tubes or wires can lead to pernicious infections in patients. Biofilms on floors and counters can make sanitation difficult in food preparation areas.
Bacteria organized in biofilms are highly resistant to detergents and antibiotics, as only the bacterial layer directly exposed to the harmful agent dies, the layers below remain unaffected for some time.
Biofilms can also be harnessed for constructive purposes. For example, many sewage treatment plants include a treatment stage in which waste water passes over biofilms grown on filters, which extract and digest harmful organic compounds.