Ørjan Samuelsen
Marit Hetland,
Mia Angelique Winkler,
Håkon Kaspersen,
Fredrik Håkonsholm,
Ragna-Johanne Bakksjø,
Eva Bernhoff
et al.:
A genome-wide One Health study of Klebsiella pneumoniae in Norway reveals overlapping populations but few recent transmission events across reservoirs
Genome Medicine 2025 DOI
Astri Lervik Larsen,
Torunn Annie Pedersen,
Arnfinn Sundsfjord,
Theodor Anton Ross,
Anja Dyresen Guleng,
Jon Birger Haug
et al.:
Hospital toilets and drainage systems as a reservoir for a long-term polyclonal outbreak of clinical infections with multidrug-resistant Klebsiella oxytoca species complex
Infection Prevention in Practice (IPIP) 2025 DOI
Bjørg Haldorsen,
Ørjan Samuelsen,
Jessin Janice,
Miriam Sare,
Mari Molvik,
Arnfinn Sundsfjord
et al.:
Import of global high-risk clones is the primary driver of carbapenemase-producing Pseudomonas aeruginosa in Norway
Journal of Medical Microbiology 2025 DOI
Sergio Arredondo Alonso,
Anna Kaarina Pöntinen,
João Alves Gama,
Rebecca Ashley Gladstone,
Klaus Harms,
Gerry Tonkin-Hill
et al.:
Plasmid-driven strategies for clone success in Escherichia coli
Marit Hetland,
Mia Angelique Winkler,
Håkon Kaspersen,
Fredrik Håkonsholm,
Ragna-Johanne Bakksjø,
Eva Bernhoff
et al.:
Complete genomes of 568 diverse Klebsiella pneumoniae species complex isolates from humans, animals, and marine sources in Norway from 2001 to 2020
Microbiology Resource Announcements (MRA) 2025 DOI
Anna Kaarina Pöntinen,
Rebecca Ashley Gladstone,
Henri Pesonen,
Maiju Pesonen,
Francois Pierre Alexandre Cleon,
Benjamin J Parcell
et al.:
Modulation of multidrug-resistant clone success in Escherichia coli populations: a longitudinal, multi-country, genomic and antibiotic usage cohort study
Sandra Witteveen,
Jörg B Hans,
Radosław Izdebski,
Henrik Hasman,
Ørjan Samuelsen,
Laurent Dortet
et al.:
Dissemination of extensively drug-resistant NDM-producing Providencia stuartii in Europe linked to patients transferred from Ukraine, March 2022 to March 2023
Anke Kohlenberg,
Olov Svartström,
Petra Apfalter,
Rainer Hartl,
Pierre Bogaerts,
Te-Din Huang
et al.:
Emergence of Escherichia coli ST131 carrying carbapenemase genes, European Union/European Economic Area, August 2012 to May 2024
Eurosurveillance 2024 DOI
Kara K. Tsang,
Margaret M C Lam,
Ryan R. Wick,
Kelly L. Wyres,
Michael Bachman,
Stephen Baker
et al.:
Diversity, functional classification and genotyping of SHV β-lactamases in Klebsiella pneumoniae
Tamim Khawaja,
Tommi Mäklin,
Teemu Kallonen,
Rebecca Ashley Gladstone,
Anna Kaarina Pöntinen,
Sointu Mero
et al.:
Deep sequencing of Escherichia coli exposes colonisation diversity and impact of antibiotics in Punjab, Pakistan
Aasmund Fostervold,
Niclas Peter Raffelsberger,
Marit Hetland,
Ragna-Johanne Bakksjø,
Eva Bernhoff,
Ørjan Samuelsen
et al.:
Risk of death in Klebsiella pneumoniae bloodstream infections is associated with specific phylogenetic lineages
Sergio Arredondo Alonso,
Rebecca Ashley Gladstone,
Anna Kaarina Pöntinen,
João Alves Gama,
Anita C. Schürch,
Val F. Lanza
et al.:
Mge-cluster: a reference-free approach for typing bacterial plasmids
Jessica Kate Calland,
Kaisa Haukka,
Stephen W Kpordze,
Atanyiwoen Brusah,
Marta Corbella,
Cristina Merla
et al.:
Population structure and antimicrobial resistance among Klebsiella isolates sampled from human, animal, and environmental sources in Ghana: a cross-sectional genomic One Health study
Marius Linkevicius,
Rémy A Bonnin,
Erik Alm,
Olov Svartström,
Petra Apfalter,
Rainer Hartl
et al.:
Rapid cross-border emergence of NDM-5-producing Escherichia coli in the European Union/European Economic Area, 2012 to June 2022
Niclas Peter Raffelsberger,
Dorota Julia Buczek,
Kristian Svendsen,
Lars Småbrekke,
Anna Kaarina Pöntinen,
Iren Høyland Löhr
et al.:
Community carriage of ESBL-producing Escherichia coli and Klebsiella pneumoniae: a cross-sectional study of risk factors and comparative genomics of carriage and clinical isolates
Oskar Ljungquist,
Bjørg Haldorsen,
Anna Kaarina Pöntinen,
Jessin Janice,
Ellen Haldis Josefsen,
Petter Elstrøm
et al.:
Nationwide, population-based observational study of the molecular epidemiology and temporal trend of carbapenemase-producing Enterobacterales in Norway, 2015 to 2021
Greta Petazzoni,
Greta Bellinzona,
Cristina Merla,
Marta Corbella,
Vincenzina Monzillo,
Ørjan Samuelsen
et al.:
The COVID-19 Pandemic Sparked off a Large-Scale Outbreak of Carbapenem-Resistant Acinetobacter baumannii from the Endemic Strains at an Italian Hospital
Sergio Arredondo Alonso,
George Blundell-Hunter,
Zuyi Fu,
Rebecca Ashley Gladstone,
Alfred Fillol-Salom,
Jessica Loraine
et al.:
Evolutionary and functional history of the Escherichia coli K1 capsule
Paul Christoffer Lindemann,
Torunn Pedersen,
Dorthea Hagen Oma,
Jessin Janice,
Fredrik Grøvan,
Ghantous Milad Chedid
et al.:
Intraregional hospital outbreak of OXA-244-producing Escherichia coli ST38 in Norway, 2020
Pete Kinross,
Carlo Gagliotti,
Hanna Merk,
Diamantis Plachouras,
Dominique L. Monnet,
Liselotte Diaz Högberg
et al.:
Large increase in bloodstream infections with carbapenem-resistant Acinetobacter species during the first 2 years of the COVID-19 pandemic, EU/EEA, 2020 and 2021
Eurosurveillance 2022 DOI
Tommi Mäklin,
Harry Arthur Frank Wright Thorpe,
Anna Kaarina Pöntinen,
Rebecca Ashley Gladstone,
Yan Shao,
Maiju Pesonen
et al.:
Strong pathogen competition in neonatal gut colonisation
Kenneth Lindstedt,
Dorota Julia Buczek,
Torunn Annie Pedersen,
Erik Hjerde,
Niclas Peter Raffelsberger,
Yutaka Suzuki
et al.:
Detection of Klebsiella pneumoniae human gut carriage: a comparison of culture, qPCR, and whole metagenomic sequencing methods
Aleksandra Jakovljev,
Jan Egil Afset,
Kjersti Haugum,
Harald Otto Steinum,
Torunn Gresdal Rønning,
Ørjan Samuelsen
et al.:
Phenotypic and genotypic characterisation of thymine auxotrophy in Escherichia coli isolated from a patient with recurrent bloodstream infection
Vidar Sørum,
Emma Lu Øynes,
Anna Sollied Møller,
Klaus Harms,
Ørjan Samuelsen,
Nicole L. Podnecky
et al.:
Evolutionary Instability of Collateral Susceptibility Networks in Ciprofloxacin-Resistant Clinical Escherichia coli Strains
Supathep Tansirichaiya,
Richard N. Goodman,
Xinyu Guo,
Issra Bulgasim,
Ørjan Samuelsen,
Mohammed Al-Haroni
et al.:
Intracellular Transposition and Capture of Mobile Genetic Elements following Intercellular Conjugation of Multidrug Resistance Conjugative Plasmids from Clinical Enterobacteriaceae Isolates
Jessin Janice,
Nicholas Agyepong,
Alex Owusu-Ofori,
Usha Govinden,
Sabiha Essack,
Ørjan Samuelsen
et al.:
Carbapenem resistance determinants acquired through novel chromosomal integrations in extensively drug-resistant pseudomonas aeruginosa
Rebecca Ashley Gladstone,
Alan McNally,
Anna Kaarina Pöntinen,
Gerry Tonkin-Hill,
John A. Lees,
Kusti Onni Skytén
et al.:
Emergence and dissemination of antimicrobial resistance in Escherichia coli causing bloodstream infections in Norway in 2002–17: a nationwide, longitudinal, microbial population genomic study
Niclas Peter Raffelsberger,
Marit Andrea Klokkhammer Hetland,
Kristian Svendsen,
Lars Småbrekke,
Iren Høyland Löhr,
Lotte Andreassen
et al.:
Gastrointestinal carriage of Klebsiella pneumoniae in a general adult population: a cross-sectional study of risk factors and bacterial genomic diversity
Jonina Gudmundsdottir,
Elizabeth G. Aarag Fredheim,
Catharina I.M. Koumans,
Joachim Hegstad,
Po-Cheng Tang,
Dan I. Andersson
et al.:
The chemotherapeutic drug methotrexate selects for antibiotic resistance
Tommi Mäklin,
Teemu Kallonen,
Jarno Alanko,
Ørjan Samuelsen,
Kristin Hegstad,
Veli Mäkinen
et al.:
Bacterial genomic epidemiology with mixed samples
Aasmund Fostervold,
Marit Andrea Klokkhammer Hetland,
Ragna-Johanne Bakksjø,
Eva Bernhoff,
Kathryn E. Holt,
Ørjan Samuelsen
et al.:
A nationwide genomic study of clinical Klebsiella pneumoniae in
Norway 2001–15: introduction and spread of ESBLs facilitated by
clonal groups CG15 and CG307
Christopher Frøhlich,
João Alves Gama,
Klaus Harms,
Viivi H. A. Hirvonen,
Bjarte Aarmo Lund,
Marc W. van der Kamp
et al.:
Cryptic β-Lactamase Evolution Is Driven by Low β-Lactam Concentrations
Julia Kloos,
João A Gama,
Joachim Hegstad,
Ørjan Samuelsen,
Pål J Johnsen
:
Piggybacking on Niche Adaptation Improves the Maintenance of Multidrug-Resistance Plasmids
Sergio Arredondo Alonso,
Anna Kaarina Pöntinen,
Francois Pierre Alexandre Cleon,
Rebecca Ashley Gladstone,
Anita C. Schürch,
Pål Jarle Johnsen
et al.:
A high-throughput multiplexing and selection strategy to complete bacterial genomes
Julia Maria Kloos,
Joao Pedro Alves Gama,
Pål Jarle Johnsen,
Ørjan Samuelsen
:
Host dependent maintenance of a blaNDM-1-encoding plasmid in clinical Escherichia coli isolates
Scientific Reports 2020 DOI
Torunn Annie Pedersen,
Marit Gjerde Tellevik,
Øyvind Kommedal,
Paul Christoffer Lindemann,
Sabrina John Moyo,
Jessin Janice James Peter
et al.:
Horizontal plasmid transfer among klebsiella pneumoniae isolates is the key factor for dissemination of extended-spectrum β-lactamases among children in Tanzania
Ørjan Samuelsen,
Ove Alexander Høgmoen Åstrand,
Christopher Frøhlich,
Adam Heikal,
Susann Skagseth,
Trine Josefine Olsen Carlsen
et al.:
ZN148 Is a Modular Synthetic Metallo-beta-Lactamase Inhibitor That Reverses Carbapenem Resistance in Gram-Negative Pathogens In Vivo
Hanna-Kirsti S. Leiros,
Ane Molden Thomassen,
Ørjan Samuelsen,
Carl-Fredrik Flach,
Stathis D. Kotsakis,
Joakim Larsson
:
Structural insights into the enhanced carbapenemase
efficiency of OXA-655 compared to OXA-10
Catherine Ludden,
Felix Lötsch,
Erik Alm,
Narender Kumar,
Karin Johansson,
Barbara Albiger
et al.:
Cross-border spread of blaNDM-1- and blaOXA-48-positive Klebsiella pneumoniae: a European collaborative analysis of whole genome sequencing and epidemiological data, 2014 to 2019
Ørjan Samuelsen,
Arnfinn Sundsfjord,
Miriam Sare,
Ragnhild Raastad,
Nina Handal
:
Karbapenem-resistente Enterobacterales i Norge: Epidemiologi, spredning og tiltak
Folkehelseinstituttet 2025 ARKIV
Miriam Sare,
Ørjan Samuelsen,
Niclas Peter Raffelsberger,
Arnfinn Ståle Sundsfjord,
Iren Høyland Löhr,
Aasmund Fostervold
et al.:
Risikovurdering av hypervirulente Klebsiella pneumoniae i Norge : en norsk risikovurdering av ECDC sin Rapid Risk Assessment "Emergence of hypervirulent Klebsiella pneumoniae ST23 carrying carbapenemase genes in EU/EEA countries, first update"
Folkehelseinstituttet 2024 ARKIV
Marit Hetland,
Mia Angelique Winkler,
Thomas D Stanton,
Ryan R. Wick,
Margaret MC Lam,
Aasmund Fostervold
et al.:
Klebsiella pneumoniae ecology and antimicrobial resistance in a One Health perspective
2023
Christopher Frøhlich,
Vidar Sørum,
Nobuhiko Tokuriki,
Ørjan Samuelsen
:
Evolution of ß-lactamase mediated cefiderocol resistance
2022
Pål Jarle Johnsen,
Elizabeth G Aarag Fredheim,
Ørjan Samuelsen,
Klaus Harms
:
The role of drugs used in cancer chemotherapy as drivers of antibiotic resistance evolution in Escherichia coli
2022
Julia Maria Kloos,
Lea Jänisch,
Anna Kaarina Pöntinen,
Ørjan Samuelsen,
Pål Jarle Johnsen,
Jukka Corander
et al.:
Different metabolic proficiency among dominant ExPEC lineages
2022
Rebecca Ashley Gladstone,
Alan McNally,
Pål Jarle Johnsen,
Ørjan Samuelsen,
Jukka Corander
:
Antimicrobial resistance genes and clonal success in Escherichia coli isolates causing bloodstream infection – Authors’ reply
Lancet Microbe 2021 DOI
Julia Maria Kloos,
Joao Pedro Alves Gama,
Joachim Hegstad,
Ørjan Samuelsen,
Pål Jarle Johnsen
:
E. coli Niche Adaptation Improves Plasmid Maintenance
2021
João Alves Gama,
Julia Maria Kloos,
Joachim Hegstad,
Ørjan Samuelsen,
Pål Jarle Johnsen
:
Plasmid cost alleviation as a consequence of niche-adaptation
2021
Julia Maria Kloos,
João Alves Gama,
Joachim Hegstad,
Ørjan Samuelsen,
Pål Jarle Johnsen
:
Plasmid Cost Alleviation By Hitchhiking On Niche-adaptation
2021
Bjørg Haldorsen,
Jessin Janice,
Ørjan Samuelsen
:
Evaluation of the Amplex eazyplex® SuperBug Acineto test for detection of acquired OXA and NDM carbapenemases in Acinetobacter spp.
Journal of Global Antimicrobial Resistance 2021 DOI
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Research interests
Through my positions as Professor II at the Microbial Pharmacology and Population Biology Research Group and as senior scientist at the Norwegian National Advisory Unit on Detection of Antimicrobial Resistance my research focuses broadly on the following topics molecular epidemiology, evaluation of diagnostic methods, biochemical and structural characterization of β-lactamases, development of β-lactamase inhibitors and the evolutionary aspects and transmission dynamics of resistance plasmids.