{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,3]],"date-time":"2026-02-03T02:08:54Z","timestamp":1770084534563,"version":"3.49.0"},"reference-count":117,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,2,2]],"date-time":"2026-02-02T00:00:00Z","timestamp":1769990400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Antibiotics"],"abstract":"<jats:p>Background: Bovine mastitis (BM) remains an economically significant disease in the global dairy industry. Multidrug resistance (MDR) in Klebsiella pneumoniae and Klebsiella grimontii has increased in recent years, representing an area of concern related to BM. Methods: Bovine mastitis 1-DH1 and 2-DH2 isolates (n = 2) were investigated. Antimicrobial susceptibility testing was performed using the Neg-Urine-Combo98 panel. Antimicrobial resistance genes (ARGs), virulence factor (VF) genes and plasmid replicons were identified by whole-genome sequencing (WGS). Phylogenomic analyses were performed for a visual comparison of the genomes. Results: Phenotypically, isolates 1-DH1 and 2-DH2 were identified as K. pneumoniae-1DH1 and Klebsiella oxytoca, respectively; the latter was subsequently confirmed as K. grimontii-2DH2 by WGS. K. pneumoniae-1DH1 (20.0%, 5\/25) exhibited phenotypic resistance to amoxicillin\u2013clavulanic acid, ampicillin (AM), cefuroxime, colistin (Cl), and nitrofurantoin (Fd), whereas K. grimontii-2DH2 (8.0%, 2\/25) was resistant to AM and nalidixic acid (NA). In total, 31 and 32 ARGs and 10 and 15 VF genes were identified in K. pneumoniae-1DH1 and K. grimontii-2DH2, respectively. Two plasmid replicons were detected in K. pneumoniae-1DH1 (one harboring the blaCTX-M ARG) compared to one in K. grimontii-2DH2 (encoding both the blaCTX-M ARG and the astA VF gene) isolates, respectively. Phylogenomic analysis showed that K. pneumoniae-1DH1 clustered most closely with human-derived K. pneumoniae isolates, whereas K. grimontii-2DH2 grouped with environmental K. grimontii isolates. Conclusions: Novel phenotypic resistance profiles were observed in the BM-associated K. pneumoniae-1DH1 (MDR, Cl and Fd) and K. grimontii-2DH2 (AM and NA) isolates. Notably, K. grimontii-2DH2 harbored a plasmid replicon carrying both the blaCTX-M ARG and the astA VF gene.<\/jats:p>","DOI":"10.3390\/antibiotics15020156","type":"journal-article","created":{"date-parts":[[2026,2,2]],"date-time":"2026-02-02T12:49:44Z","timestamp":1770036584000},"page":"156","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Antimicrobial Resistance, Virulence Factors and Plasmid Replicon Patterns of Klebsiella pneumoniae and Klebsiella grimontii Isolates from Bovine Mastitic Milk in the Northwest of Portugal: Pilot Genomic Characterization"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0009-0002-2828-7202","authenticated-orcid":false,"given":"Guilherme","family":"Moreira","sequence":"first","affiliation":[{"name":"School of Medicine and Biomedical Sciences, ICBAS-UP, University of Porto, Rua de Jorge Viterbo Ferreira, nr. 228, 4050-313 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0313-7582","authenticated-orcid":false,"given":"Lu\u00eds","family":"Pinho","sequence":"additional","affiliation":[{"name":"School of Medicine and Biomedical Sciences, ICBAS-UP, University of Porto, Rua de Jorge Viterbo Ferreira, nr. 228, 4050-313 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8769-8103","authenticated-orcid":false,"given":"Jo\u00e3o R.","family":"Mesquita","sequence":"additional","affiliation":[{"name":"School of Medicine and Biomedical Sciences, ICBAS-UP, University of Porto, Rua de Jorge Viterbo Ferreira, nr. 228, 4050-313 Porto, Portugal"},{"name":"LAQV, REQUIMTE, Department of Chemistry and Biochemistry, Faculty of Sciences and Technology, University NOVA de Lisboa, 2829-516 Caparica, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9771-8769","authenticated-orcid":false,"given":"Eliane","family":"Silva","sequence":"additional","affiliation":[{"name":"School of Medicine and Biomedical Sciences, ICBAS-UP, University of Porto, Rua de Jorge Viterbo Ferreira, nr. 228, 4050-313 Porto, Portugal"},{"name":"Research Center in Biodiversity and Genetic Resources (CIBIO\/InBIO), University of Porto, Rua Padre Amando Quintas, nr. 7, 4485-661 Vair\u00e3o, Portugal"},{"name":"BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vair\u00e3o, University of Porto, 4485-661 Vair\u00e3o, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"475","DOI":"10.1051\/vetres:2003027","article-title":"Production effects related to mastitis and mastitis economics in dairy cattle herds","volume":"34","author":"Seegers","year":"2003","journal-title":"Vet. 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