{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T09:10:50Z","timestamp":1791277850193,"version":"4.1.0"},"reference-count":25,"publisher":"American Society for Microbiology","issue":"12","license":[{"start":{"date-parts":[[2002,12,1]],"date-time":"2002-12-01T00:00:00Z","timestamp":1038700800000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.asm.org\/non-commercial-tdm-license"}],"content-domain":{"domain":["journals.asm.org"],"crossmark-restriction":true},"short-container-title":["Antimicrob Agents Chemother"],"published-print":{"date-parts":[[2002,12]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n          <jats:p>\n            The relationships between porin deficiency, active efflux of fluoroquinolones, and extended-spectrum \u03b2-lactamase (ESBL) production were determined for 53 clinical isolates of\n            <jats:italic>Klebsiella pneumoniae<\/jats:italic>\n            . Thirty-two ESBL-positive strains (including 22 strains expressing porins and 10 strains lacking porins) and 21 ESBL-negative strains were evaluated. Active efflux of norfloxacin was defined as a \u226550% increase in the accumulation of norfloxacin in the presence of carbonyl cyanide\n            <jats:italic>m<\/jats:italic>\n            -chlorophenylhydrazone (CCCP) in comparison with the corresponding basal value in the absence of CCCP. The quinolone resistance-determining regions of both\n            <jats:italic>gyrA<\/jats:italic>\n            and\n            <jats:italic>parC<\/jats:italic>\n            from 13 strains, representing all isolates with different porin profiles and with or without active efflux, were determined. Porin loss was significantly more common among ESBL-positive strains (10 of 32 [31.2%]) than among ESBL-negative strains (0 of 2 [0%]) (\n            <jats:italic>P<\/jats:italic>\n            &lt; 0.01). Active efflux was observed in 7 of 10 (70%) strains lacking porins and in 4 of 43 (9.3%) strains producing porins (\n            <jats:italic>P<\/jats:italic>\n            &lt; 0.001). The 11 strains showing active efflux corresponded to 3 of 21 (14.3%) ESBL-negative strains and 8 of 32 (25.5%) ESBL-positive strains (\n            <jats:italic>P<\/jats:italic>\n            &gt; 0.05). Basal values of norfloxacin accumulation were higher in strains lacking active efflux than in those that had this mechanism (\n            <jats:italic>P<\/jats:italic>\n            &lt; 0.05). In the absence of topoisomerase changes, the contribution of either porin loss or active efflux to fluoroquinolone resistance in\n            <jats:italic>K. pneumoniae<\/jats:italic>\n            was negligible. It is concluded that among\n            <jats:italic>K. pneumoniae<\/jats:italic>\n            strains of clinical origin, porin loss was observed only in those producing ESBL, and that a significant number of porin-deficient strains also expressed active efflux of norfloxacin. In terms of fluoroquinolone resistance, both mechanisms are significant only in the presence of topoisomerase modifications.\n          <\/jats:p>","DOI":"10.1128\/aac.46.12.3926-3932.2002","type":"journal-article","created":{"date-parts":[[2002,11,15]],"date-time":"2002-11-15T20:02:26Z","timestamp":1037390546000},"page":"3926-3932","update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":54,"title":["Energy-Dependent Accumulation of Norfloxacin and Porin Expression in Clinical Isolates of\n            <i>Klebsiella pneumoniae<\/i>\n            and Relationship to Extended-Spectrum \u03b2-Lactamase Production"],"prefix":"10.1128","volume":"46","author":[{"given":"Luis","family":"Marti\u0301nez-Marti\u0301nez","sequence":"first","affiliation":[{"name":"Department of Microbiology, School of Medicine, University of Seville"},{"name":"University Hospital V. Macarena, Seville"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alvaro","family":"Pascual","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Medicine, University of Seville"},{"name":"University Hospital V. Macarena, Seville"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mari\u0301a del Carmen","family":"Conejo","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Medicine, University of Seville"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Isabel","family":"Garci\u0301a","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Medicine, University of Seville"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Providencia","family":"Joyanes","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Medicine, University of Seville"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Antonio","family":"Dome\u0301nech-Sa\u0301nchez","sequence":"additional","affiliation":[{"name":"Laboratory of Microbiology, IMEDEA (CSIC-UIB), Universitat de les Illes Balears, Palma de Mallorca, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vicente Javier","family":"Benedi\u0301","sequence":"additional","affiliation":[{"name":"Laboratory of Microbiology, IMEDEA (CSIC-UIB), Universitat de les Illes Balears, Palma de Mallorca, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"235","reference":[{"key":"e_1_3_2_2_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.42.7.1636"},{"key":"e_1_3_2_3_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.41.3.563"},{"key":"e_1_3_2_4_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.33.8.1318"},{"key":"e_1_3_2_5_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.41.3.699"},{"key":"e_1_3_2_6_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.41.7.1609"},{"key":"e_1_3_2_7_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.41.11.2544"},{"key":"e_1_3_2_8_2","doi-asserted-by":"crossref","first-page":"151","DOI":"10.1093\/nar\/18.1.151","volume":"18","year":"1990","unstructured":"Dimri, G. 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