Edaphic factors as determinants for the distribution of intrinsic antibiotic resistance in a cowpea rhizobia population |
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| Authors: | G R Xavier L M V Martins M C P Neves N G Rumjanek |
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| Institution: | EMBRAPA/Centro Nacional de Pesquisa de Agrobiologia Ant. Rod. Rio – S?o Paulo, Km 47, Seropédica, RJ, 23851-970, Brazil e-mail: rumjanek@cnps.embrapa.br Fax: +021-6821230, BR
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| Abstract: | A large collection of cowpea rhizobia strains was obtained from soil samples collected from either a semi-arid or a tropical
rain forest area located at about the same latitude in the north-eastern region of Brazil and evaluated for their intrinsic
antibiotic resistance to eight commercial antibiotics. The aim of this study was to correlate antibiotic resistance of native
rhizobia strains to edaphic-climatic factors as a way to establish suitable inoculants for specific areas. A large diversity
regarding intrinsic antibiotic resistance was found, and 17 clusters were identified as varying from sensitive to gradually
resistant up to 500 μg·ml–1 of the antibiotics tested. Clustering analysis did not show any pattern related to the geographic region where isolates have
been obtained. On the other hand, an increase in the antibiotic-resistant rhizobia population was associated with an increase
in soil P and Al contents. lsolates which were sensitive to spectinomycin, ampicillin, streptomycin, chloramphenicol and tetracycline
were present at higher rates in soils devoid of Al. Rhizobia bacteria producing mucus type I (fluid and capable of spreading
over the solid media) were found preferentially in soil with Al concentrations up to 36 mg·kg–1, diminishing quickly at higher levels.
Received: 2 May 1997 |
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| Keywords: | Rhizobia Cowpea Antibiotic resistance Phosphorus Aluminium |
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