Transconjugants were
placed on Luria-bertani (LB) agar (Difco,
BD Diagnostic Systems, Detroit, ME)
supplemented with 32 μg/ml of rifampicin
and one of the following antibiotics:
streptomycin (80 μg/ml), gentamicin
(100 μg/ml) or trimethroprim (10 μg/ml).
Transconjugants were confirmed to be E.
coli by growth on MacConkey agar (Difco)
and transfer of class 1 integrons was confirmed
using PCR as described above.