{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T13:53:25Z","timestamp":1791294805406,"version":"4.1.0"},"reference-count":40,"publisher":"Oxford University Press (OUP)","issue":"11","license":[{"start":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T00:00:00Z","timestamp":1791244800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/pages\/standard-publication-reuse-rights"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,10,6]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>This study aimed to describe penicillin G susceptibility, blaZ diversity, and genetic determinants of the cefazolin inoculum effect (CfzIE) among MSSA bloodstream isolates.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>The first three non-duplicate MSSA isolates recovered each month from blood cultures at our French university hospital between January 2010 and December 2023 were selected. Whole-genome sequencing was performed using the Illumina NextSeq platform to characterize blaZ and its genetic context. Susceptibility to penicillin G and the CfzIE were assessed using phenotypic methods.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Among 488 MSSA isolates, 373 (76.5%) carried blaZ, of which 119 (31.9%) exhibited CfzIE. Thirty BlaZ allotypes were identified overall; 26 were included in the genetic determinant analysis after exclusion of isolates with multiple or truncated blaZ. In multivariable analysis, BlaZA3 was strongly associated with CfzIE (aOR, 15.72; 95% CI, 3.33\u201374.24; P\u200a&amp;lt;\u200a0.001), as was CC7 (aOR, 5.48; 95% CI, 1.45\u201320.69; P\u200a=\u200a0.011). Among BlaZA3 isolates, CfzIE was mainly observed with complete blaR1. Among 122 isolates with a penicillin G inhibition zone \u226526\u2005mm, seven carried blaZ, including six with sharp zone edges and truncated blaZ sequences.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>CfzIE was mainly associated with a BlaZA3-related genetic background, particularly in the presence of complete blaR1, rather than with blaZ type alone. Approximately one-quarter of MSSA bloodstream isolates were susceptible to penicillin G, and rare phenotype\u2013genotype discrepancies were associated with truncated blaZ sequences.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1093\/jac\/dkag328","type":"journal-article","created":{"date-parts":[[2026,9,18]],"date-time":"2026-09-18T18:27:58Z","timestamp":1789756078000},"source":"Crossref","is-referenced-by-count":0,"title":["Genomic determinants of penicillin G susceptibility and cefazolin inoculum effect in methicillin-susceptible\n                    <i>Staphylococcus aureus<\/i>\n                    bloodstream isolates"],"prefix":"10.1093","volume":"81","author":[{"given":"Samantha","family":"Poloni","sequence":"first","affiliation":[{"name":"CHU Besan\u00e7on, Maladies infectieuses , F-25000 Besan\u00e7on 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