{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,26]],"date-time":"2026-10-26T18:38:29Z","timestamp":1793039909268,"version":"4.5.0"},"reference-count":26,"publisher":"American Society for Microbiology","issue":"11","license":[{"start":{"date-parts":[[2025,11,4]],"date-time":"2025-11-04T00:00:00Z","timestamp":1762214400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2025,11,4]],"date-time":"2025-11-04T00:00:00Z","timestamp":1762214400000},"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":["Microbiol Spectr"],"published-print":{"date-parts":[[2025,11,4]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                  <jats:sec>\n                    <jats:title\/>\n                    <jats:p>\n                      Antimicrobial resistance is a global health problem. Among various antibiotic-resistant bacteria,\n                      <jats:italic toggle=\"yes\">Staphylococcus aureus<\/jats:italic>\n                      , particularly methicillin-resistant\n                      <jats:italic toggle=\"yes\">S. aureus<\/jats:italic>\n                      (MRSA), is a clinically important pathogen responsible for serious infections because of its multidrug resistance (MDR) and association with high mortality rates. The MDR nature of MRSA, including resistance to macrolides, aminoglycosides, fluoroquinolones, and tetracyclines, limits therapeutic choices and poses significant challenges in clinical management. This study aimed to analyze the correlation between mutations in the quinolone resistance-determining region (QRDR) and the minimum inhibitory concentration (MIC) of fluoroquinolone drugs, such as ciprofloxacin and levofloxacin, in MRSA and methicillin-sensitive\n                      <jats:italic toggle=\"yes\">S. aureus<\/jats:italic>\n                      (MSSA). A total of 63\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      .\n                      <jats:italic toggle=\"yes\">aureus<\/jats:italic>\n                      clinical strains were isolated from blood samples of sepsis patients. DNA sequence analysis was performed using gDNA extracted from all\n                      <jats:italic toggle=\"yes\">S. aureus<\/jats:italic>\n                      clinical isolates to identify mutations in the QRDR of\n                      <jats:italic toggle=\"yes\">gyr<\/jats:italic>\n                      A,\n                      <jats:italic toggle=\"yes\">gyr<\/jats:italic>\n                      B,\n                      <jats:italic toggle=\"yes\">par<\/jats:italic>\n                      C, and\n                      <jats:italic toggle=\"yes\">par<\/jats:italic>\n                      E. The MICs of antimicrobials were determined by the broth microdilution method. Among these genes, only mutations in\n                      <jats:italic toggle=\"yes\">par<\/jats:italic>\n                      C showed a statistically significant positive correlation with elevated MIC levels, underscoring the primary role of\n                      <jats:italic toggle=\"yes\">par<\/jats:italic>\n                      C in mediating resistance in our clinical isolates. Notably, all isolates exhibited a substitution at serine 80 (S80) in\n                      <jats:italic toggle=\"yes\">par<\/jats:italic>\n                      C, and those harboring simultaneous substitutions at both S80 and glutamic acid 84 (E84) demonstrated markedly increased MIC values for both drugs. These findings reinforce previously reported associations between dual mutations and high-level fluoroquinolone resistance, while highlighting the distinct contribution of\n                      <jats:italic toggle=\"yes\">par<\/jats:italic>\n                      C among the QRDR genes analyzed in this study. Furthermore, we found that the most frequent mutation in the QRDR was the cytosine-to-thymine mutation.\n                    <\/jats:p>\n                    <jats:sec>\n                      <jats:title>IMPORTANCE<\/jats:title>\n                      <jats:p>\n                        Antimicrobial resistance is a growing global health crisis, making bacterial infections harder to treat.\n                        <jats:italic toggle=\"yes\">Staphylococcus aureus<\/jats:italic>\n                        , especially MRSA, is a major concern due to its resistance to multiple antibiotics, including fluoroquinolones like ciprofloxacin and levofloxacin. Our study highlights how specific genetic mutations in the quinolone resistance-determining region (QRDR) influence fluoroquinolone resistance. We found that mutations in the\n                        <jats:italic toggle=\"yes\">par<\/jats:italic>\n                        C gene, particularly substitutions at serine 80 (S80) and glutamic acid 84 (E84), significantly increase resistance. Understanding these mutations helps predict antibiotic resistance and may guide more effective treatment strategies. By identifying key genetic changes that drive fluoroquinolone resistance, our research contributes to developing improved diagnostic tools and targeted therapies to combat drug-resistant\n                        <jats:italic toggle=\"yes\">S. aureus<\/jats:italic>\n                        infections. This knowledge is crucial for clinicians and researchers working to control the spread of antibiotic-resistant bacteria and improve patient outcomes.\n                      <\/jats:p>\n                    <\/jats:sec>\n                  <\/jats:sec>","DOI":"10.1128\/spectrum.00645-25","type":"journal-article","created":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T13:03:42Z","timestamp":1760360622000},"update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":11,"title":["Correlation of QRDR mutations and MIC levels in fluoroquinolone-resistant\n                    <i>Staphylococcus aureus<\/i>\n                    clinical 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