{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,4,21]],"date-time":"2026-04-21T18:45:05Z","timestamp":1776797105127,"version":"3.51.2"},"posted":{"date-parts":[[2025,10,14]]},"group-title":"Microbiology","reference-count":55,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2025,10,14]],"date-time":"2025-10-14T00:00:00Z","timestamp":1760400000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"name":"National Institute of Health","award":["R15AI159902"],"award-info":[{"award-number":["R15AI159902"]}]},{"name":"National Institute of Health","award":["1R35GM150871-01"],"award-info":[{"award-number":["1R35GM150871-01"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,4,18]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:p>\n                  The inoculum effect (IE) reduces antibiotic efficacy\n                  <jats:italic>in vitro<\/jats:italic>\n                  and in clinical settings, yet remains difficult to predict. IE limits antibiotic efficacy but remains unpredictable, particularly in resistant bacteria, where resistance mechanisms and bacterial physiology interact in poorly understood ways. Using\n                  <jats:italic>Escherichia coli<\/jats:italic>\n                  expressing the NDM-1 \u03b2-lactamase and clinical isolates, we quantified metabolism, growth rate, \u03b2-lactamase expression, and IE across diverse growth environments. Across enzyme classes, antibiotics, and clinical isolates, we find that IE is governed by a conserved, biphasic dependence on metabolism normalized by growth rate. Mathematical modeling shows that this behavior reflects a trade\u2370off between \u03b2\u2370lactamase\u2370mediated protection and metabolism\u2370potentiated antibiotic lethality. These findings establish a predictive, physiology-based framework for IE in resistant bacteria and explain why resistance determinants alone fail to predict treatment outcomes across environments, including the clinic.\n                <\/jats:p>\n                <jats:sec>\n                  <jats:title>Significance Statement<\/jats:title>\n                  <jats:p>Antibiotic efficacy depends on both bacterial resistance and physiology, yet these factors are rarely integrated when predicting treatment outcomes. One important consequence of their interaction is the inoculum effect (IE), in which antibiotic efficacy depends on the density of a resistant bacterial population. Here, we show that IE in \u03b2\u2370lactamase\u2013expressing bacteria is governed by a conserved physiological trade\u2370off between metabolism and growth. Across growth environments, antibiotics, inocula, and clinical isolates, IE is strongest at intermediate metabolic states, reflecting a balance between resistance\u2370mediated protection and metabolism\u2370potentiated antibiotic lethality. This framework helps explain why resistance determinants alone are insufficient to account for IE and underscores the role of bacterial physiology in shaping antibiotic responses.<\/jats:p>\n                <\/jats:sec>","DOI":"10.1101\/2025.10.14.682300","type":"posted-content","created":{"date-parts":[[2025,10,15]],"date-time":"2025-10-15T03:45:11Z","timestamp":1760499911000},"source":"Crossref","is-referenced-by-count":0,"title":["A biphasic metabolic\u2013growth trade-off governs \u03b2-lactam inoculum effects"],"prefix":"10.64898","author":[{"given":"Ariane R. Kalifa","family":"Torjeman","sequence":"first","affiliation":[{"name":"Cell Therapy Institute, Kiran Patel College of Allopathic Medicine, Nova Southeastern University, Fort Lauderdale, FL, 33314"},{"name":"Department of Biological Sciences, Halmos College of Arts and Sciences, Nova Southeastern University, Fort Lauderdale, FL, 33314"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kielan","family":"Singh","sequence":"additional","affiliation":[{"name":"Department of Biological Sciences, Halmos College of Arts and Sciences, Nova Southeastern University, Fort Lauderdale, FL, 33314"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Philopatier","family":"Ibrahim","sequence":"additional","affiliation":[{"name":"Department of Biological Sciences, Halmos College of Arts and Sciences, Nova Southeastern University, Fort Lauderdale, FL, 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