{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,22]],"date-time":"2025-10-22T10:29:52Z","timestamp":1761128992944},"reference-count":0,"publisher":"American Society for Microbiology","issue":"8","license":[{"start":{"date-parts":[[1990,8,1]],"date-time":"1990-08-01T00:00:00Z","timestamp":649468800000},"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":[[1990,8]]},"abstract":"<jats:p>The incidence of tolerance and paradoxical response to bactericidal activity of penicillin was investigated in 50 clinical isolates of Enterococcus faecalis. Of the isolates tested, 86% exhibited the paradoxical phenomenon whereby there were more survivors at high than at low concentrations above the MIC. Low penicillin concentrations caused decreases equal to or higher than 99.9% in 11 strains, from 99.9 to 99.5% in 23 strains, and lower than 99.5% in 9 strains. Of the total strains, 14% were killed to the same extent by all concentrations above the MIC. The bactericidal activities of other beta-lactams (ampicillin and piperacillin) and other cell wall inhibitors (vancomycin and daptomycin) were also tested against some of these strains. In general, beta-lactams exhibited the best bactericidal activity at 2 x MIC. Piperacillin was the most active, as at 2 x MIC it reduced the original inoculum by 99.9% or more in most of the strains. No concentration of vancomycin above the MIC caused 99.9% killing of the strains, whereas daptomycin was bactericidal at 8 x MIC in most cases. Paradoxical response to bactericidal activity of beta-lactams was abolished by incubation of the inoculum with 2 x MIC before exposure to higher antibiotic concentrations. These findings suggest that enterococci are not always tolerant to cell wall-active antibiotics and that accurate in vitro bactericidal tests may be useful for the choice of appropriate therapy for infections caused by these microorganisms.<\/jats:p>","DOI":"10.1128\/aac.34.8.1518","type":"journal-article","created":{"date-parts":[[2012,6,28]],"date-time":"2012-06-28T00:05:50Z","timestamp":1340841950000},"page":"1518-1522","update-policy":"http:\/\/dx.doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":25,"title":["In vitro response to bactericidal activity of cell wall-active antibiotics does not support the general opinion that enterococci are naturally tolerant to these antibiotics"],"prefix":"10.1128","volume":"34","author":[{"given":"R","family":"Fontana","sequence":"first","affiliation":[{"name":"Institute of Microbiology, University of Verona, Italy."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"A","family":"Grossato","sequence":"additional","affiliation":[{"name":"Institute of Microbiology, University of Verona, Italy."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"M","family":"Ligozzi","sequence":"additional","affiliation":[{"name":"Institute of Microbiology, University of Verona, Italy."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"E A","family":"Tonin","sequence":"additional","affiliation":[{"name":"Institute of Microbiology, University of Verona, Italy."}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"235","container-title":["Antimicrobial Agents and Chemotherapy"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/journals.asm.org\/doi\/pdf\/10.1128\/AAC.34.8.1518","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/journals.asm.org\/doi\/pdf\/10.1128\/AAC.34.8.1518","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2022,2,21]],"date-time":"2022-02-21T15:13:30Z","timestamp":1645456410000},"score":1,"resource":{"primary":{"URL":"https:\/\/journals.asm.org\/doi\/10.1128\/AAC.34.8.1518"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1990,8]]},"references-count":0,"journal-issue":{"issue":"8","published-print":{"date-parts":[[1990,8]]}},"alternative-id":["10.1128\/AAC.34.8.1518"],"URL":"https:\/\/doi.org\/10.1128\/aac.34.8.1518","relation":{},"ISSN":["0066-4804","1098-6596"],"issn-type":[{"value":"0066-4804","type":"print"},{"value":"1098-6596","type":"electronic"}],"subject":[],"published":{"date-parts":[[1990,8]]},"assertion":[{"value":"1990-08-01","order":2,"name":"published","label":"Published","group":{"name":"publication_history","label":"Publication History"}}]}}