{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,9,10]],"date-time":"2026-09-10T22:11:42Z","timestamp":1789078302775,"version":"build-2803163510"},"posted":{"date-parts":[[2026,9,7]]},"group-title":"Microbiology","reference-count":40,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,9,7]],"date-time":"2026-09-07T00:00:00Z","timestamp":1788739200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000897","name":"Cystic Fibrosis Foundation","doi-asserted-by":"crossref","award":["VANTYN21GO"],"award-info":[{"award-number":["VANTYN21GO"]}],"id":[{"id":"10.13039\/100000897","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"crossref","award":["R21AI191407"],"award-info":[{"award-number":["R21AI191407"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,9,7]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:sec>\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>\n                    <jats:italic>Pseudomonas aeruginosa<\/jats:italic>\n                    is a ubiquitous opportunistic bacterial pathogen associated with nosocomial infections and is a leading cause of infection in persons with cystic fibrosis (pwCF). The front-line treatment for multidrug-resistant\n                    <jats:italic>P. aeruginosa<\/jats:italic>\n                    infections is ceftolozane-tazobactam (C\/T). While previous research has characterized clinical\n                    <jats:italic>P. aeruginosa<\/jats:italic>\n                    isolates that evolved resistance to C\/T, the collateral effect of evolved resistance on susceptibility to bacteriophages has not been explored.\n                  <\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>\n                    We collected paired\n                    <jats:italic>P. aeruginosa<\/jats:italic>\n                    clinical isolates from 10 pwCF and 18 non-pwCF who developed treatment-emergent C\/T resistance. We compared genetic relatedness, acute and chronic virulence phenotypes, and antibiotic and phage susceptibilities between each pair of susceptible baseline and treatment-emergent C\/T-resistant isolates.\n                  <\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Treatment-emergent C\/T-resistant isolates were genetically closely related to baseline isolates in all patients. Virulence phenotypes did not differ between pre-and post-C\/T exposure isolates, but isolates from pwCF demonstrated differences in protease production, twitching motility, and amino acid auxotrophy compared to isolates from non-pwCF. Treatment-emergent C\/T resistance was associated with increased resistance to ceftazidime and ceftazidime\/avibactam, but no other trends in antibiotic or phage susceptibility were detected.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>\n                    Treatment-emergent resistance to C\/T does not cause predictable alterations in phage susceptibility across genotypically and phenotypically diverse multidrug-resistant\n                    <jats:italic>P. aeruginosa<\/jats:italic>\n                    clinical isolates.\n                  <\/jats:p>\n                <\/jats:sec>","DOI":"10.64898\/2026.09.03.749285","type":"posted-content","created":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T05:20:22Z","timestamp":1788844822000},"source":"Crossref","is-referenced-by-count":0,"title":["Variable phage susceptibility of\n                  <i>Pseudomonas aeruginosa<\/i>\n                  from patients with and without cystic fibrosis following treatment-emergent resistance to ceftolozane-tazobactam"],"prefix":"10.64898","author":[{"given":"Nathan R.","family":"Wallace","sequence":"first","affiliation":[{"name":"Division of Infectious Diseases, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Renata L.","family":"DiDonato","sequence":"additional","affiliation":[{"name":"Division of Infectious Diseases, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Blake A.","family":"Jackson","sequence":"additional","affiliation":[{"name":"Division of Infectious Diseases, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ellen 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