{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,21]],"date-time":"2025-10-21T14:38:37Z","timestamp":1761057517956,"version":"3.40.4"},"reference-count":0,"publisher":"S. Karger AG","issue":"1","license":[{"start":{"date-parts":[[2002,1,1]],"date-time":"2002-01-01T00:00:00Z","timestamp":1009843200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/www.karger.com\/Services\/SiteLicenses"},{"start":{"date-parts":[[2002,1,1]],"date-time":"2002-01-01T00:00:00Z","timestamp":1009843200000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/www.karger.com\/Services\/SiteLicenses"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Chemotherapy"],"published-print":{"date-parts":[[2002]]},"abstract":"<jats:p>&lt;i&gt;Background:&lt;\/i&gt; In a previous investigation of the genetic characterization of extended-spectrum \u03b2-lactamases (ESBLs) in &lt;i&gt;Klebsiella pneumoniae &lt;\/i&gt;from Zagreb, Croatia, 20 strains were found to produce SHV-2 \u03b2-lactamase. Those strains displayed varying degrees of \u03b2-lactam resistance and a wide range of \u03b2-lactamase activity. We concluded that more resistant isolates were hyperproducers of SHV-2 \u03b2-lactamase. &lt;i&gt;Methods:&lt;\/i&gt; In this investigation, we tried to develop hyperproducing variants from 8 low-level SHV-2 \u03b2-lactamase-producing &lt;i&gt;Klebsiella&lt;\/i&gt; strains by subculturing them in serum containing therapeutic concentrations of cefotaxime (CTX). &lt;i&gt;Results:&lt;\/i&gt; In most cases, there was a moderate increase in CTX resistance (twofold to threefold), except in one strain which displayed a 16-fold increase in the minimum inhibitory concentration (MIC) of CTX after incubation in the serum. That strain showed a marked increase in enzyme activity as well. The strains with a moderate increase in CTX MIC did not produce more enzyme after exposure to the serum, except for one strain which had a threefold rise in \u03b2-lactamase activity after exposure to serum. &lt;i&gt;Conclusions:&lt;\/i&gt; In this investigation, it was established that the mutants with high-level CTX resistance developed very quickly in the biological fluids containing therapeutic concentrations of CTX. It is reasonable to expect that a similar process occurs in patients infected with an ESBL-producing &lt;i&gt;K.\u00a0pneumoniae &lt;\/i&gt;strain during antibiotic treatment. Since most of the high-level CTX-resistant mutants did not have a marked rise in \u03b2-lactamase activity after exposure to serum, it is possible that the elevated resistance was due to some other mechanism, such as reduced penicillin-binding protein affinity, changes in outer membrane proteins or efflux by multidrug efflux pumps.<\/jats:p>","DOI":"10.1159\/000048581","type":"journal-article","created":{"date-parts":[[2003,4,15]],"date-time":"2003-04-15T13:07:10Z","timestamp":1050412030000},"page":"10-14","source":"Crossref","is-referenced-by-count":6,"title":["Selection of &lt;i&gt;Klebsiella pneumoniae &lt;\/i&gt;Mutants with High-Level Cefotaxime Resistance during Growth in Serum Containing Therapeutic Concentrations of Cefotaxime"],"prefix":"10.1159","volume":"48","author":[{"given":"Branka","family":"Bedeni\u0107","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"127","published-online":{"date-parts":[[2010,10,29]]},"container-title":["Chemotherapy"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.karger.com\/Article\/Pdf\/48581","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/www.karger.com\/Article\/Pdf\/48581","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,4,24]],"date-time":"2025-04-24T04:05:18Z","timestamp":1745467518000},"score":1,"resource":{"primary":{"URL":"https:\/\/karger.com\/article\/doi\/10.1159\/000048581"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2002]]},"references-count":0,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2002,3,1]]}},"URL":"https:\/\/doi.org\/10.1159\/000048581","archive":["Portico"],"relation":{},"ISSN":["0009-3157","1421-9794"],"issn-type":[{"type":"print","value":"0009-3157"},{"type":"electronic","value":"1421-9794"}],"subject":[],"published":{"date-parts":[[2002]]}}}