Antibiotic sensitivity in Rhizobium and Agrobacterium

The resistance of 81 Rhizobium strains and 11 Agrobacterium strains to 16 antibiotics was investigated. Most strains were resistant even to high concentrations of lincomycin.

All the strains of the species Rhizobium meliloti, Rhizobium phaseoli, Rhizobium japonicum and the genus Agrobacterium reacted relatively homogeneously to all the antibiotics, unlike Rhizobium trifolii, Rhizobium leguminosarum and Rhizobium spp.

The majority of the fast-growing species of Rhizobium tested was found to be resistant to > 32 μg/ml penicillin and to < 1 μg/ml tetracyclin. On the other hand, most of the slow-growing species of Rhizobium were susceptible to penicillin concentrations < 16 μg/ml while they were resistant to tetracyclin concentrations > 1 μg/ml.

The majority of the Agrobacterium strains tested were resistant to streptomycin concentrations > 32 μg/ml, allowing them to be distinguished from strains of R. meliloti which were rarely resistant to such high concentrations.