J M García-Lobo

Facultad de Medicina, Madrid, Madrid, Spain

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Publications (10)21.84 Total impact

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    C Martin, R Gomez-Lus, J M Ortiz, J M Garcia-Lobo
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    ABSTRACT: A DNA segment originally found in an epidemic plasmid of Escherichia coli encoding an aminoglycoside-(3)-N-acetyltransferase gene (aacC5) and a TEM-type beta-lactamase gene was characterized. The two genes were adjacent and constituted a single transcriptional unit. In addition, these genes were simultaneously mobilized through the action of an insertion sequence related to IS26, IS140, and IS15-delta. This DNA segment is a composite transposon which has been called Tn2922.
    Antimicrobial Agents and Chemotherapy 09/1987; 31(8):1266-70. · 4.57 Impact Factor
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    J León, J M García-Lobo, J Navas, J M Ortíz
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    ABSTRACT: Escherichia coli cells carrying fosfomycin-resistance plasmids show high levels of resistance towards this drug. However, the plasmid-carrying strains exhibited a transient lytic phase induced by fosfomycin when grown in rich liquid media. This lytic phase was not observed if the cells were grown in liquid minimal media. Fosfomycin-induced lysis depended on the accumulation of drug inside the bacteria, presumably as a result of the saturation of the fosfomycin modification system. Growth recovery after lysis was not due to drug inactivation in the culture medium and could be explained by selection of mutants showing impaired fosfomycin transport when high concentrations of fosfomycin were used. However, there was no selection of mutants with low drug concentrations.
    Journal of general microbiology 01/1986; 131(12):3255-60.
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    J León, J M García-Lobo, J Navas, J M Ortiz
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    ABSTRACT: Escherichia coli cells carrying fosfomycin-resistance plasmids modify fosfomycin intracellularly. The product of this modification (fosfomycin-derivative) differs from fosfomycin in chromatographic mobility, but the chemical nature of the modification is not yet known. Fosfomycin-derivative appears to have a cytoplasmic location and lacks antibiotic activity. The modification system can be saturated by an excess of fosfomycin in the incubation media.
    Journal of general microbiology 08/1985; 131(7):1649-55.
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    J Navas, J M García-Lobo, J León, J M Ortíz
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    ABSTRACT: The fosfomycin resistance transposon Tn2921 is flanked by directly repeated sequences homologous to the Tn10-related insertion sequence IS10. The nonrepeated DNA sequences of Tn2921 can be deleted without affecting the transposition ability of the element, showing that at least one of the direct repeats is an active insertion sequence. Transposition of Tn2921 seems to occur through direct transposition, since cointegrates have not been observed. The evolutionary relatedness of Tn2921 and IS10 is discussed.
    Journal of Bacteriology 07/1985; 162(3):1061-7. · 3.19 Impact Factor
  • J M García-Lobo, J León, J Navas, J M Ortiz
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    ABSTRACT: The fosfomycin resistance determinant of the transposon Tn2921 has been localized and cloned into the plasmid pBR322. A DNA fragment of 1 kb contains all the information required for full expression of the resistance. The level of resistance was unaffected by the plasmid copy number and by the orientation in which the fragment was cloned. Studies in minicells showed that this 1-kb fragment directed the synthesis of a single polypeptide with a molecular mass of 16 kDa.
    Plasmid 06/1984; 11(3):243-7. · 1.76 Impact Factor
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    ABSTRACT: A revised physical map of the alpha-haemolysin plasmid pHly152 has been constructed. The known position of the hly genes in the restriction map of pHly152 allowed us to locate in it a direct repeat of IS elements flanking the hly genes of pHly152. These elements are IS92L, which is a derivative of the previously characterised element IS91 (1.85 kb) by insertion of a sequence of 1.2 kb, and IS92R, an element related to IS91 by a deletion of 0.7 kb and substitution of a 0.2 kb sequence of IS91 by a 1.2 kb heterologous sequence. IS92L is, in turn, flanked by an inverted repetition of sequences of 1.4 kb. These and previously published data strongly suggest that the hly genes spread at some time in evolution by means of the recombinational activity of IS91-like elements.
    MGG - Molecular and General Genetics 02/1984; 197(1):90-7.
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    J León, J M García-Lobo, J M Ortiz
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    ABSTRACT: The target enzyme for fosfomycin antibiotic action, enolpyruvyl transferase, was synthesized in similar amounts and with similar kinetic and inhibition constants for phosphoenolpyruvate and fosfomycin, respectively, by an Escherichia coli strain containing the fosfomycin resistance plasmid pOU900 and by plasmid-free strains. Neither phosphoenolpyruvate level nor murein synthesis was altered by pOU900.
    Antimicrobial Agents and Chemotherapy 09/1983; 24(2):276-8. · 4.57 Impact Factor
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    J M García-Lobo, J M Ortiz
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    ABSTRACT: The determinant of resistance to fosfomycin of the Serratia marcescens plasmid pOU900 was transposed into the plasmid ColE1 and into the plasmid RP4 in the absence of the RecA function of the host. In each case, the acquisition of fosfomycin resistance was correlated with the presence of a discrete piece of DNA, uniform in size and in restriction pattern, This new, 7.5-megadalton transposable element encoding resistance to fosfomycin has been called Tn2921. A preliminary map of the transposon is presented.
    Journal of Bacteriology 08/1982; 151(1):477-9. · 3.19 Impact Factor
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    J León, J M García-Lobo, J M Ortiz
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    ABSTRACT: Escherichia coli cells carrying fosfomycin resistance plasmids were able to take up fosfomycin from the medium to the same extent as plasmid-free bacteria. The antibiotic entered the plasmid-harboring cells by means of the glpT and uhp transport systems, as is the case with susceptible bacteria. Active fosfomycin could be detected in soluble extracts of cells which had previously been incubated in the presence of the antibiotic. Furthermore, fosfomycin resistance plasmids did not confer on E. coli cells resistance to the novel antibiotic FR-31564, which is incorporated by the same transport systems as fosfomycin. We conclude that, in contrast to chromosomal resistance mutants, altered transport does not play a role in the plasmid-encoded fosfomycin resistance mechanism.
    Antimicrobial Agents and Chemotherapy 05/1982; 21(4):608-12. · 4.57 Impact Factor
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    JAVIER L EON, JUAN M. GARCIA-LOBO, JESUS NAVAS, JOSE M. ORTIZ