{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T00:07:36Z","timestamp":1791158856394,"version":"4.1.0"},"reference-count":38,"publisher":"American Society for Microbiology","issue":"7","license":[{"start":{"date-parts":[[1999,7,1]],"date-time":"1999-07-01T00:00:00Z","timestamp":930787200000},"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":[[1999,7]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n          <jats:p>\n            Two clinical isolates of extended-spectrum \u03b2-lactamase (ESBL)-producing\n            <jats:italic>Klebsiella pneumoniae<\/jats:italic>\n            were noted to be less susceptible than expected to imipenem. Both were missing outer membrane proteins that serve as channels for antibiotic entry. The role of \u03b2-lactamase in resistance was investigated by eliminating the original ESBL and introducing plasmids encoding various ESBLs and AmpC \u03b2-lactamase types, by studying the effect of an increased inoculum, and by evaluating interactions with \u03b2-lactamase inhibitors. The contribution of porin deficiency was investigated by restoring a functional\n            <jats:italic>ompK36<\/jats:italic>\n            gene on a plasmid. Plasmids encoding AmpC-type \u03b2-lactamases provided resistance to imipenem (up to 64 \u03bcg\/ml) and meropenem (up to 16 \u03bcg\/ml) in strains deficient in porins. Carbapenem resistance showed little inoculum effect, was not affected by clavulanate but was blocked by BRL 42715, and was diminished if OmpK36 porin was restored. Plasmids encoding TEM- and SHV-type ESBLs conferred resistance to cefepime and cefpirome, as well as to earlier oxyimino-\u03b2-lactams. This resistance was magnified with an increased inoculum, was blocked by clavulanate, and was also lowered by OmpK36 porin restoration. In addition, SHV-2 \u03b2-lactamase had a small effect on carbapenem resistance (imipenem MIC, 4 \u03bcg\/ml, increasing to 16 \u03bcg\/ml with a higher inoculum) when porins were absent. In\n            <jats:italic>K. pneumoniae<\/jats:italic>\n            porin loss can thus augment resistance provided either by TEM- or SHV-type ESBLs or by plasmid-mediated AmpC enzymes to include the latest oxyimino-\u03b2-lactams and carbapenems.\n          <\/jats:p>","DOI":"10.1128\/aac.43.7.1669","type":"journal-article","created":{"date-parts":[[2018,10,9]],"date-time":"2018-10-09T00:35:16Z","timestamp":1539045316000},"page":"1669-1673","update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":213,"title":["Roles of \u03b2-Lactamases and Porins in Activities of Carbapenems and Cephalosporins against\n            <i>Klebsiella pneumoniae<\/i>"],"prefix":"10.1128","volume":"43","author":[{"given":"Luis","family":"Marti\u0301nez-Marti\u0301nez","sequence":"first","affiliation":[{"name":"<!--label omitted: 1-->Department of Microbiology, School of Medicine, University of Seville,1 and"},{"name":"<!--label omitted: 2-->Department of Microbiology University Hospital V. Macarena,2 Seville, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alvaro","family":"Pascual","sequence":"additional","affiliation":[{"name":"<!--label omitted: 1-->Department of Microbiology, School of Medicine, University of Seville,1 and"},{"name":"<!--label omitted: 2-->Department of Microbiology University Hospital V. Macarena,2 Seville, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Santiago","family":"Herna\u0301ndez-Alle\u0301s","sequence":"additional","affiliation":[{"name":"<!--label omitted: 3-->Area of Microbiology, Department of Biology and IMEDEA (CSIC-UIB), University of the Balearic Islands, Palma de Mallorca,3Spain, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dolores","family":"Alvarez-Di\u0301az","sequence":"additional","affiliation":[{"name":"<!--label omitted: 3-->Area of Microbiology, Department of Biology and IMEDEA (CSIC-UIB), University of the Balearic Islands, Palma de Mallorca,3Spain, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ana Isabel","family":"Sua\u0301rez","sequence":"additional","affiliation":[{"name":"<!--label omitted: 2-->Department of Microbiology University Hospital V. Macarena,2 Seville, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"John","family":"Tran","sequence":"additional","affiliation":[{"name":"<!--label omitted: 4-->Veterans Affairs Medical Center, Bedford and Lahey Clinic, Burlington, Massachusetts4"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vicente Javier","family":"Benedi\u0301","sequence":"additional","affiliation":[{"name":"<!--label omitted: 3-->Area of Microbiology, Department of Biology and IMEDEA (CSIC-UIB), University of the Balearic Islands, Palma de Mallorca,3Spain, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"George A.","family":"Jacoby","sequence":"additional","affiliation":[{"name":"<!--label omitted: 4-->Veterans Affairs Medical Center, Bedford and Lahey Clinic, Burlington, Massachusetts4"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"235","reference":[{"key":"e_1_3_2_2_2","doi-asserted-by":"publisher","DOI":"10.1128\/iai.63.3.903-910.1995"},{"key":"e_1_3_2_3_2","doi-asserted-by":"crossref","first-page":"257","DOI":"10.1007\/BF01644127","article-title":"Novel R-factor borne \u03b2-lactamase of Escherichia coli conferring resistance to cephalosporins.","volume":"15","author":"Bauernfeind A.","year":"1987","unstructured":"Bauernfeind A. 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J.\n              Mart\u0131\u0301nez-Mart\u0131\u0301nez\n              L.\n          Effect of OmpF\/OmpC expression in the activity of cephalosporins and carbapenems against Escherichia coli hyperproducing chromosomal beta-lactamases abstr. 12009\n          Program and abstracts of the 8th International Congress of Infectious Diseases.\n          1998\n          15\n          Excerpta Medical Communications\n          Boston Mass"},{"key":"e_1_3_2_32_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.35.6.1174"},{"key":"e_1_3_2_33_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.37.12.2760"},{"key":"e_1_3_2_34_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.34.11.2193"},{"key":"e_1_3_2_35_2","unstructured":"Sambrook\n              J.\n              Fritsch\n              E. 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