Lateral plasmid transfer with various combinations of strains and plasmids in colony biofilm culture.

Frequency of plasmid transfer (mean, n = 3) in each combination is presented in decimal ranges as follows: ++++++, 1E–4 to 1E–5; +++++, 1E–5 to 1E–6; +++, 1E–7 to 1E–8; ++, 1E–8 to 1E–9; +, 1E–9 to 1E–10; – : below detection limit; n.d., not determined or unable to examine because of coincidence of the same antibiotic resistance between strains and plasmids. Samples with plasmid transfer frequency >1E–6 are indicated by .