Ole Andreas Løchen Økstad

• Tourasse, Nicolas Jacques; Jolley, Keith A.; Kolstø, Anne-Brit & Økstad, Ole Andreas (2023). Core genome multilocus sequence typing scheme for Bacillus cereus group bacteria. Research in Microbiology. ISSN 0923-2508. 174(6). doi: 10.1016/j.resmic.2023.104050. Full text in Research Archive
• Marienborg, Kaja; Ambur, Ole Herman; Økstad, Ole Andreas & Skaare, Dagfinn (2023). The alginate polymer OligoG alters susceptibility of biofilm-embedded non-typeable Haemophilus influenzae to ampicillin and ciprofloxacin. JAC-Antimicrobial Resistance (JAC-AMR). ISSN 2632-1823. 5(2). doi: 10.1093/jacamr/dlad046. Full text in Research Archive Show summary

  Objectives Treatment of respiratory infections with non-typeable Haemophilus influenzae (NTHi) in COPD patients is complicated by biofilm formation, protecting the bacteria against the hosts’ immune response and antibiotics. We investigated the antibiofilm and antibacterial effects of the alginate polymer OligoG, alone or combined with ampicillin or ciprofloxacin, on mature NTHi biofilms. Materials and methods Two unrelated COPD strains with PBP3-mediated β-lactam resistance, with additional TEM-1 β-lactamase (Hi-022) or quinolone resistance due to altered GyrA and ParC (Hi-072) were used. Antibiofilm and antibacterial effects were assessed macroscopically, by measurement of biofilm biomass (OD), and by viable cell counts, with determination of minimum biofilm inhibitory concentration (MBIC) and the novel parameter ‘minimum concentration for 2 log10 drop in viable cells in biofilm’ (MB2LDC). Drug interactions between OligoG and antibiotics were assessed by comparing expected and observed inhibitory effects (percent inhibition of no-treatment control) of combined treatment. Results OligoG had dose-dependent biofilm disruptive abilities and a weak inhibitory effect on viable cells. Combination with OligoG (64 g/L) significantly lowered MBIC for ampicillin (both strains) and MB2LDC for ciprofloxacin (Hi-022). For Hi-022, there was significant synergism between OligoG and both antibiotics. For Hi-072, interactions were subtle, but a tendency in direction of antagonism was significant at two concentrations of ciprofloxacin. Conclusions OligoG shows promise as a potential adjuvant to antibiotics in NTHi infections, but strain-specific factors appear to affect drug interactions and may lead to antagonism. More research is needed to clarify the mechanisms of action of OligoG and interactions with antibiotics.

• Nystedt, Helene Liepelt; Grønlien, Krister Gjestvang; Rolfsnes, Rebekka Rekkedal; Winther-Larsen, Hanne Cecilie; Økstad, Ole Andreas & Tønnesen, Hanne Hjorth (2023). Neutral natural deep eutectic solvents as anti-biofilm agents. Biofilm. 5. doi: 10.1016/j.bioflm.2023.100114. Full text in Research Archive
• Lin, Yicen; Alstrup, Monica; Pang, Janet Ka Yan; Maróti, Gergely; Er-Rafik, Mériem & Tourasse, Nicolas [Show all 8 contributors for this article] (2021). Adaptation of Bacillus thuringiensis to plant colonization affects differentiation and toxicity. mSystems. ISSN 2379-5077. 6(5). doi: 10.1128/mSystems.00864-21. Full text in Research Archive
• Smith, Veronika; Nilssen, Ida Kristine Bu; Hegna, Ida Kristin; Dalhus, Bjørn; Fagerlund, Annette & Økstad, Ole Andreas (2021). CdgL is a degenerate nucleotide cyclase domain protein affecting flagellin synthesis and motility in Bacillus thuringiensis. Research in Microbiology. ISSN 0923-2508. 172(4-5). doi: 10.1016/j.resmic.2021.103850. Full text in Research Archive
• Attieh, Zaynoun; Mouawad, Carine; Rejasse, Agnès; Jehanno, Isabelle; Perchat, Stéphane & Hegna, Ida Kristin [Show all 10 contributors for this article] (2020). The fliK Gene Is Required for the Resistance of Bacillus thuringiensis to Antimicrobial Peptides and Virulence in Drosophila melanogaster. Frontiers in Microbiology. ISSN 1664-302X. 11. doi: 10.3389/fmicb.2020.611220.
• Smith, Veronika; Josefsen, Malin; Lindbäck, Toril; Hegna, Ida Kristin; Finke, Sarah & Tourasse, Nicolas Jacques [Show all 9 contributors for this article] (2020). MogR is a ubiquitous transcriptional repressor affecting motility, biofilm formation and virulence in Bacillus thuringiensis. Frontiers in Microbiology. ISSN 1664-302X. 11. doi: 10.3389/fmicb.2020.610650. Full text in Research Archive Show summary

  Flagellar motility is considered an important virulence factor in different pathogenic bacteria. In Listeria monocytogenes the transcriptional repressor MogR regulates motility in a temperature-dependent manner, directly repressing flagellar- and chemotaxis genes. The only other bacteria known to carry a mogR homolog are members of the Bacillus cereus group, which includes motile species such as B. cereus and Bacillus thuringiensis as well as the non-motile species Bacillus anthracis, Bacillus mycoides and Bacillus pseudomycoides. Furthermore, the main motility locus in B. cereus group bacteria, carrying the genes for flagellar synthesis, appears to be more closely related to L. monocytogenes than to Bacillus subtilis, which belongs to a separate phylogenetic group of Bacilli and does not carry a mogR ortholog. Here, we show that in B. thuringiensis, MogR overexpression results in non-motile cells devoid of flagella. Global gene expression profiling showed that 110 genes were differentially regulated by MogR overexpression, including flagellar motility genes, but also genes associated with virulence, stress response and biofilm lifestyle. Accordingly, phenotypic assays showed that MogR also affects cytotoxicity and biofilm formation in B. thuringiensis. Overexpression of a MogR variant mutated in two amino acids within the putative DNA binding domain restored phenotypes to those of an empty vector control. In accordance, introduction of these mutations resulted in complete loss in MogR binding to its candidate flagellar locus target site in vitro. In contrast to L. monocytogenes, MogR appears to be regulated in a growth-phase dependent and temperature-independent manner in B. thuringiensis 407. Interestingly, mogR was found to be conserved also in non-motile B. cereus group species such as B. mycoides and B. pseudomycoides, which both carry major gene deletions in the flagellar motility locus and where in B. pseudomycoides mogR is the only gene retained. Furthermore, mogR is expressed in non-motile B. anthracis. Altogether this provides indications of an expanded set of functions for MogR in B. cereus group species, beyond motility regulation. In conclusion, MogR constitutes a novel B. thuringiensis pleiotropic transcriptional regulator, acting as a repressor of motility genes, and affecting the expression of a variety of additional genes involved in biofilm formation and virulence.

• Samuelsen, Ørjan; Åstrand, Ove Alexander Høgmoen; Frøhlich, Christopher; Heikal, Adam; Skagseth, Susann & Carlsen, Trine Josefine Olsen [Show all 17 contributors for this article] (2020). ZN148 Is a Modular Synthetic Metallo-beta-Lactamase Inhibitor That Reverses Carbapenem Resistance in Gram-Negative Pathogens In Vivo. Antimicrobial Agents and Chemotherapy. ISSN 0066-4804. 64(6). doi: 10.1128/AAC.02415-19. Full text in Research Archive
• Finke, Sarah; Fagerlund, Annette; Smith, Veronika; Krogstad, Veronica; Zhang, Mimmi Jingxi & Saragliadis, Athanasios [Show all 9 contributors for this article] (2019). Bacillus thuringiensis CbpA is a collagen binding cell surface protein under c-di-GMP control. The Cell Surface. ISSN 2468-2330. 5, p. 1–12. doi: 10.1016/j.tcsw.2019.100032. Full text in Research Archive
• Ikram, Samman; Heikal, Adam; Finke, Sarah; Hofgaard, Antje; Rehman, Yasir & Sabri, Anjum Nasim [Show all 7 contributors for this article] (2019). Bacillus cereus biofilm formation on central venous catheters of hospitalised cardiac patients. Biofouling (Print). ISSN 0892-7014. 35(2), p. 204–216. doi: 10.1080/08927014.2019.1586889. Full text in Research Archive Show summary

  Formation of bacterial biofilms is a risk with many in situ medical devices. Biofilm-forming Bacillus species are associated with potentially life-threatening catheter-related blood stream infections in immunocompromised patients. Here, bacteria were isolated from biofilm-like structures within the lumen of central venous catheters (CVCs) from two patients admitted to cardiac hospital wards. Isolates belonged to the Bacillus cereus group, exhibited strong biofilm formation propensity, and mapped phylogenetically close to the B. cereus emetic cluster. Together, whole genome sequencing and quantitative PCR confirmed that the isolates constituted the same strain and possessed a range of genes important for and up-regulated during biofilm formation. Antimicrobial susceptibility testing demonstrated resistance to trimethoprim-sulphamethoxazole, clindamycin, penicillin and ampicillin. Inspection of the genome revealed several chromosomal beta-lactamase genes and a sulphonamide resistant variant of folP. This study clearly shows that B. cereus persisting in hospital ward environments may constitute a risk factor from repeated contamination of CVCs.

• Candela, Thomas; Fagerlund, Annette; Buisson, Christophe; Gilois, Nathalie; Kolstø, Anne-Brit & Økstad, Ole Andreas [Show all 10 contributors for this article] (2019). CalY is a major virulence factor and a biofilm matrix protein. Molecular Microbiology. ISSN 0950-382X. 111(6), p. 1416–1429. doi: 10.1111/mmi.14184. Show summary

  The extracellular biofilm matrix often contains a network of amyloid fibers which, in the human opportunistic pathogen Bacillus cereus, includes the two homologous proteins TasA and CalY. We show here, in the closely related entomopathogenic species B. thuringiensis, that CalY also displays a second function. In the early stationary phase of planktonic cultures, CalY was located at the bacterial cell‐surface, as shown by immunodetection. Deletion of calY revealed that this protein plays a major role in adhesion to HeLa epithelial cells, to the insect Galleria mellonella haemocytes, and in the bacterial virulence against larvae of this insect, suggesting that CalY is a cell‐surface adhesin. In mid‐stationary phase and in biofilms, the location of CalY shifted from the cell surface to the extracellular medium, where it was found as fibers. The transcription study and the deletion of sipW suggested that CalY change of location is due to a delayed activity of the SipW signal peptidase. Using purified CalY, we found that the protein polymerization occurred only in the presence of cell‐surface components. CalY is therefore a bifunctional protein, which switches from a cell‐surface adhesin activity in early stationary phase, to the production of fibers in mid‐stationary phase and in biofilms.

• Taiaroa, George; Samuelsen, Ørjan; Kristensen, Tom; Økstad, Ole Andreas & Heikal, Adam (2018). Complete Genome Sequence of Pseudomonas aeruginosa K34-7, a Carbapenem-Resistant Isolate of the High-Risk Sequence Type 233. Microbiology Resource Announcements (MRA). ISSN 2169-8287. 7(4), p. 1–2. doi: 10.1128/MRA.00886-18. Full text in Research Archive
• Carlson, Colin; Getz, Wayne M.; Kausrud, Kyrre Linné; Cizauskas, Carrie A.; Blackburn, Jason K. & Bustos Carrillo, Fausto A [Show all 14 contributors for this article] (2018). Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis). Biological Reviews. ISSN 1464-7931. 93(4), p. 1813–1831. doi: 10.1111/brv.12420.
• Schnaars, Christian; kildahl-Andersen, Geir; Prandina, Anthony; Popal, Roya; Radix, Sylvie & Le Borgne, Marc [Show all 16 contributors for this article] (2018). Synthesis and preclinical evaluation of TPA-based zinc chelators as metallo-β-lactamase inhibitors. ACS Infectious Diseases. ISSN 2373-8227. 4(9), p. 1407–1422. doi: 10.1021/acsinfecdis.8b00137.
• Hassan, Karl A.; Fagerlund, Annette; Elbourne, Liam D.H.; Vörös, Aniko; Kroeger, Jasmin Kaori & Simm, Roger [Show all 12 contributors for this article] (2017). The putative drug efflux systems of the Bacillus cereus group. PLOS ONE. ISSN 1932-6203. 12(5), p. 1–25. doi: 10.1371/journal.pone.0176188. Full text in Research Archive Show summary

  The Bacillus cereus group of bacteria includes seven closely related species, three of which, B. anthracis, B. cereus and B. thuringiensis, are pathogens of humans, animals and/ or insects. Preliminary investigations into the transport capabilities of different bacterial lineages suggested that genes encoding putative efflux systems were unusually abundant in the B. cereus group compared to other bacteria. To explore the drug efflux potential of the B. cereus group all putative efflux systems were identified in the genomes of prototypical strains of B. cereus, B. anthracis and B. thuringiensis using our Transporter Automated Annotation Pipeline. More than 90 putative drug efflux systems were found within each of these strains, accounting for up to 2.7% of their protein coding potential. Comparative analyses demonstrated that the efflux systems are highly conserved between these species; 70± 80% of the putative efflux pumps were shared between all three strains studied. Furthermore, 82% of the putative efflux system proteins encoded by the prototypical B. cereus strain ATCC 14579 (type strain) were found to be conserved in at least 80% of 169 B. cereus group strains that have high quality genome sequences available. However, only a handful of these efflux pumps have been functionally characterized. Deletion of individual efflux pump genes from B. cereus typically had little impact to drug resistance phenotypes or the general fitness of the strains, possibly because of the large numbers of alternative efflux systems that may have overlapping substrate specificities. Therefore, to gain insight into the possible transport functions of efflux systems in B. cereus, we undertook large-scale qRTPCR analyses of efflux pump gene expression following drug shocks and other stress treatments. Clustering of gene expression changes identified several groups of similarly regulated systems that may have overlapping drug resistance functions. In this article we review current knowledge of the small molecule efflux pumps encoded by the B. cereus group and suggest the likely functions of numerous uncharacterised pumps.

• Fagerlund, Annette; Smith, Veronika; Kjendseth, Åsmund Røhr; Lindbäck, Toril; Parmer, Marthe Petrine & Andersson, K. Kristoffer [Show all 8 contributors for this article] (2016). Cyclic diguanylate regulation of Bacillus cereus group biofilm formation. Molecular Microbiology. ISSN 0950-382X. 101(3), p. 471–494. doi: 10.1111/mmi.13405. Show summary

  Biofilm formation can be considered a bacterial virulence mechanism. In a range of Gram-negatives, increased levels of the second messenger cyclic diguanylate (c-di-GMP) promotes biofilm formation and reduces motility. Other bacterial processes known to be regulated by c-di-GMP include cell division, differentiation and virulence. Among Gram-positive bacteria, where the function of c-di-GMP signaling is less well characterized, c-di-GMP was reported to regulate swarming motility in Bacillus subtilis while having very limited or no effect on biofilm formation. In contrast, we show that in the Bacillus cereus group c-di-GMP signaling is linked to biofilm formation, and to several other phenotypes important to the lifestyle of these bacteria. The Bacillus thuringiensis 407 genome encodes eleven predicted proteins containing domains (GGDEF/EAL) related to c-di-GMP synthesis or breakdown, ten of which are conserved through the majority of clades of the B. cereus group, including Bacillus anthracis. Several of the genes were shown to affect biofilm formation, motility, enterotoxin synthesis and/or sporulation. Among these, cdgF appeared to encode a master diguanylate cyclase essential for biofilm formation in an oxygenated environment. Only two cdg genes (cdgA, cdgJ) had orthologs in B. subtilis, highlighting differences in c-di-GMP signalling between B. subtilis and B. cereus group bacteria.

• Vörös, Aniko; Simm, Roger; Slamti, Leyla; McKay, Matthew J.; Hegna, Ida Kristin & Nielsen-Leroux, Christina [Show all 12 contributors for this article] (2014). SecDF as part of the sec-translocase facilitates efficient secretion of Bacillus cereus toxins and cell wall-associated proteins. PLOS ONE. ISSN 1932-6203. 9:e0103326(8). doi: 10.1371/journal.pone.0103326.
• Fagerlund, Annette; Dubois, Thomas; Økstad, Ole Andreas Løchen; Verplaetse, Emilie; Gilois, Nathalie & Bennaceur, Imene [Show all 12 contributors for this article] (2014). SinR controls enterotoxin expression in Bacillus thuringiensis biofilms. PLOS ONE. ISSN 1932-6203. 9(1). doi: 10.1371/journal.pone.0087532.
• Vik, Unni; Logares, Ramiro; Blaalid, Rakel; Halvorsen, Rune; Carlsen, Tor & Bakke, Ingrid [Show all 9 contributors for this article] (2013). Different bacterial communities in ectomycorrhizae and surrounding soil. Scientific Reports. ISSN 2045-2322. 3(347). doi: 10.1038/srep03471. Full text in Research Archive
• Bräunlich, Paula Marie; Økstad, Ole Andreas Løchen; Slimestad, Rune; Wangensteen, Helle; Malterud, Karl Egil & Barsett, Hilde (2013). Effects of Aronia melanocarpa constituents on biofilm formation of Escherichia coli and Bacillus cereus. Molecules. ISSN 1431-5157. 18(12), p. 14989–14999. doi: 10.3390/molecules181214989.
• Backe, Paul Hoff; Simm, Roger; Lærdahl, Jon Kristen; Dalhus, Bjørn; Fagerlund, Annette & Økstad, Ole Andreas Løchen [Show all 10 contributors for this article] (2013). A new family of proteins related to the HEAT-like repeat DNA glycosylases with affinity for branched DNA structures. Journal of Structural Biology. ISSN 1047-8477. 183(1), p. 66–75. doi: 10.1016/j.jsb.2013.04.007. Full text in Research Archive
• Kristoffersen, Simen Martens; Haase, Chad; Weil, M. Ryan; Passalacqua, Karla D.; Niazi, Fahim & Hutchison, Stephen [Show all 11 contributors for this article] (2012). Global mRNA decay analysis at single nucleotide resolution reveals segmental and positional degradation patterns in a Gram-positive bacterium. Genome Biology. ISSN 1465-6906. 13(4). doi: 10.1186/gb-2012-13-4-r30.
• Reiter, Lillian; Tourasse, Nicolas; Fouet, Agnes; Loll, Raphaël; Davison, Sophie & Økstad, Ole Andreas Løchen [Show all 8 contributors for this article] (2011). Evolutionary History and Functional Characterization of Three Large Genes Involved in Sporulation in Bacillus cereus Group Bacteria. Journal of Bacteriology. ISSN 0021-9193. 193(19), p. 5420–5430. doi: 10.1128/JB.05309-11.
• Papazisi, Leka; Rasko, David A.; Ratnayake, Shashikala; Bock, Geoff R.; Remortel, Brian G. & Appalla, Lakshimi [Show all 19 contributors for this article] (2011). Investigating the genome diversity of B. cereus and evolutionary aspects of B. anthracis emergence. Genomics. ISSN 0888-7543. 98(1), p. 26–39. doi: 10.1016/j.ygeno.2011.03.008.
• Kristoffersen, Simen Martens; Tourasse, Nicolas; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2011). Interspersed DNA Repeats bcr1-bcr18 of Bacillus cereus Group Bacteria Form Three Distinct Groups with Different Evolutionary and Functional Patterns. Molecular Biology and Evolution (MBE). ISSN 0737-4038. 28(2), p. 963–983. doi: 10.1093/molbev/msq269.
• Tourasse, Nicolas; Helgason, Erlendur; Klevan, Leif Are; Sylvestre, Patricia; Moya, Maryse & Haustant, Michel [Show all 10 contributors for this article] (2011). Extended and global phylogenetic view of the Bacillus cereus group population by combination of MLST, AFLP, and MLEE genotyping data. Food Microbiology. ISSN 0740-0020. 28(2), p. 236–244. doi: 10.1016/j.fm.2010.06.014.
• Tourasse, Nicolas; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2010). HyperCAT: an extension of the SuperCAT database for global multi-scheme and multi-datatype phylogenetic analysis of the Bacillus cereus group population. Database: The Journal of Biological Databases and Curation. ISSN 1758-0463.
• Kolstø, Anne-Brit; Tourasse, Nicolas & Økstad, Ole Andreas Løchen (2009). What Sets Bacillus anthracis Apart from Other Bacillus Species? Annual Review of Microbiology. ISSN 0066-4227. 63, p. 451–476. doi: 10.1146/annurev.micro.091208.073255.
• Stabell, Fredrik Bernhard; Jacobsen, Wolfgang Mathias; Risøen, Per Arne; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2009). ORF 2 from the Bacillus cereus linear plasmid pBClin15 encodes a DNA binding protein. Letters in Applied Microbiology. ISSN 0266-8254. 48(1), p. 51–57. doi: 10.1111/j.1472-765X.2008.02483.x.
• Gohar, Michel; Fægri, Karoline; Perchat, Stephane; Ravnum, Solveig; Økstad, Ole Andreas Løchen & Gominet, Myriam [Show all 8 contributors for this article] (2008). The PlcR Virulence Regulon of Bacillus cereus. PLOS ONE. ISSN 1932-6203. 3(7). doi: 10.1371/journal.pone.0002793.
• Kristoffersen, Simen Martens; Ravnum, Solveig; Tourasse, Nicolas; Økstad, Ole Andreas Løchen; Kolstø, Anne-Brit & Davies, William (2007). Low concentrations of bile salts induce stress responses and reduce motility in Bacillus cereus ATCC 14570. Journal of Bacteriology. ISSN 0021-9193. 189(14), p. 5302–5313. doi: 10.1128/JB.00239-07.
• Rasko, DA; Rosovitz, MJ; Økstad, Ole Andreas Løchen; Fouts, DE; Jiang, LX & Cer, RZ [Show all 9 contributors for this article] (2007). Complete sequence analysis of novel plasmids from emetic and periodontal Bacillus cereus isolates reveals a common evolutionary history among the B-cereus-group plasmids, including Bacillus anthracis pXO1. Journal of Bacteriology. ISSN 0021-9193. 189(1), p. 52–64. doi: 10.1128/JB.01313-06.
• Klevan, Leif Are; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2007). Exploring the evolution of the Bacillus cereus group repeat element bcr1 by comparative genome analysis of closely related strains. Microbiology (Reading). ISSN 1350-0872. 153, p. 3894–3908. doi: 10.1099/mic.0.2007/005504-0.
• Tourasse, Nicolas; Helgason, Erlendur; Økstad, Ole Andreas Løchen; Hegna, Ida Kristin & Kolstø, Anne-Brit (2006). The Bacillus cereus group: novel aspects of population structure and genome dynamics. Journal of Applied Microbiology. ISSN 1364-5072. 101, p. 579–593.
• Økstad, Ole Andreas Løchen; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Sundfær, Cathrine Kleven; Jacobsen, Wolfgang Mathias & Risøen, Per Arne [Show all 8 contributors for this article] (2004). The bcr1 DNA repeat element is specific to the Bacillus cereus group and exhibits mobile element characteristics. Journal of Bacteriology. ISSN 0021-9193. 186(22), p. 7714–7725.
• Rasko, David A; Ravel, Jacques; Økstad, Ole Andreas Løchen; Helgason, Erlendur; Cer, Regina & Jiaug, L [Show all 15 contributors for this article] (2004). The genome sequence of Bacillus cereus ATCC 10987 reveals metabolic adaptations and a large plasmid related to Bacillus anthracis pXO1. Nucleic Acids Research (NAR). ISSN 0305-1048. 32(3), p. 977–988.
• Read, Timothy D.; Peterson, Scott N.; Tourasse, Nicolas; Baillie, L. W.; Paulsen, I. W. & Nelson, K. E. [Show all 52 contributors for this article] (2003). The genome sequence of Bacillus anthracis Ames and comparison to closely related bacteria. Nature. ISSN 0028-0836. 423, p. 81–86.

View all works in Cristin

• Økstad, Ole Andreas (2023). The dynamic trio - the good, the bad and the ugly.
• Økstad, Ole Andreas (2023). Reversing carbapenem resistance in Gram-negative pathogens - Preclinical development of the modular synthetic metallo-β-lactamase inhibitor APC148.
• Ambur, Ole Herman; Skaare, Dagfinn & Økstad, Ole Andreas Løchen (2023). Alginate polymer alters susceptibility of biofilm-embedded non-typable Haemophilus influenzae .
• Glenna, S; Orr, Russell John Scott; Økstad, Ole Andreas & Voie, ØA (2023). Changes in the skin microbiome in response to antiseptic use during a NATO exercise: a metagenomic approach.
• Urtubia, Areli Moe; Winther-Larsen, Hanne Cecilie & Økstad, Ole Andreas (2023). Novel principles of drug resistance in the WHO priority 1 pathogen Acinetobacter baumannii.
• Smith, V; Hovland, R; Rongved, Pål & Økstad, Ole Andreas (2023). Preclinical development of a novel metallo-β-lactamase inhibitor APC148.
• Linke, Dirk; Økstad, Ole Andreas; Haugen, Håvard Jostein & Winther-Larsen, Hanne Cecilie (2021). The exchange program MISC - Options for internships at the University of Oslo (with descriptions of current projects).
• Liskiewicz, Krystyna Anna; Sunde, Pia Titterud; Verket, Anders; Økstad, Ole Andreas & Simm, Roger (2019). C-di-GMP signaling in Treponema denticola and its role in pathogenesis of periodontal diseases.
• Liskiewicz, Krystyna Anna; Sunde, Pia Titterud; Verket, Anders; Økstad, Ole Andreas & Simm, Roger (2019). C-di-GMP signaling in Treponema denticola and its role in pathogenesis of periodontal diseases.
• Økstad, Ole Andreas Løchen & Linke, Dirk (2018). Hvor farlig er antibiotikaresistens? Ingeniørenes Stemme. Vinter 2018, p. 37–37.
• Heggelund, Julie Elisabeth; Hausvik, Emil; Carvalho, Luiz; Økstad, Ole Andreas Løchen; Martinez, Aurora & Goldman, Adrian (2018). Targeting MFS transporters to switch off antibiotic resistance in tuberculosis.
• Heikal, Adam; Samuelsen, Ørjan; Kristensen, Tom & Økstad, Ole Andreas Løchen (2017). Complete genome sequence of a multidrug-resistant, blaNDM-1-expressing Klebsiella pneumoniae K66-45 clinical isolate from Norway. Microbiology Resource Announcements (MRA). ISSN 2169-8287. 5:e00601(27), p. 1–2. doi: 10.1128/genomeA.00601-17.
• Ho, Giang Thanh Thi; Braünlich, Marie; Økstad, Ole Andreas Løchen; Slimestad, Rune; Wangensteen, Helle & Malterud, Karl Egil [Show all 7 contributors for this article] (2015). Effects of Aronia melanocarpa on biofilm formation of Escherichia coli and Bacillus cereus.
• Ho, Giang Thanh Thi; Braünlich, Marie; Wangensteen, Helle; Malterud, Karl Egil; Økstad, Ole Andreas Løchen & Christensen, Hege Staaland [Show all 9 contributors for this article] (2014). Spennende helseeffekter av aroniabær.
• Røhr, Åsmund Kjendseth; Fagerlund, Annette; Økstad, Ole Andreas Løchen & Andersson, K. Kristoffer (2013). Characterization of a redox sensor involved in Bacillus cereus biofilm formation. NBS-nytt. ISSN 0801-3535. 1, p. 62–62. Show summary

  The facultative aerobic, opportunistic human pathogen, Bacillus cereus is known to form biofilm under certain conditions. A common mechanism for biofilm formation depends on cyclic 3’-5’-cyclic diguanylic acid (c-di-GMP) signaling. The second messenger c-di-GMP is synthesized and degraded by the protein domains GGDEF and EAL, respectively. In order to regulate the activity of such GGDEF and EAL domains, these can be coupled to various PAS domains that act as environmental sensors of e.g. redox potential or oxygen concentration. We aim to understand how sensory PAS domains regulate the enzymatic activity of GGDEF and EAL domains through inter- or intra protein mediated interactions. The protein BC0628 from B. cereus ATCC 14579 was selected as a model system because it has a PAS-GGDEF-EAL domain structure and putative sensory, diguanylate cyclase, and phosphodiesterase activities. Here we present results showing that the soluble purified enzyme appears to bind a redox active flavin cofactor in the PAS domain. Activity assays also show that both GGDEF and EAL domains are functional and that their activities are tuned by the redox state of the PAS domain flavin cofactor. Results from initial crystallization screening are positive, thus, the BC0628 appears to be good model candidate for functional PAS-GGDEF-EAL proteins and future structural studies.

• Økstad, Ole Andreas Løchen & Tourasse, Nicolas (2009). Genome dynamics in the Bacillus cereus group of bacteria: introns and repeats.
• Kolstø, Anne-Brit; Økstad, Ole Andreas Løchen; Tourasse, Nicolas; Kristoffersen, Simen Martens; Fægri, Karoline & Fagerlund, Annette (2009). Bacillus cereus group: genome plasticity for better adaptation.
• Kolstø, Anne-Brit; Tourasse, Nicolas; Økstad, Ole Andreas Løchen; Fægri, Karoline & Fagerlund, Annette (2009). Bacillus cereus gene regulation and pathogenomics.
• Økstad, Ole Andreas Løchen (2009). Differential gene expression and gene regulation during biofilm formation in Bacillus thuringiensis.
• Tourasse, Nicolas; Helgason, Erlendur; Klevan, Leif Are; Sylvestre, Patricia; Moya, Maryse & Haustant, Michel [Show all 10 contributors for this article] (2009). Global multi-datatype phylogenetic analysis of the Bacillus cereus group reveals new lineages and clusters.
• Kristoffersen, Simen Martens; Tourasse, Nicolas; Bakka, Eirik Rødseth; Read, Timothy D.; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2009). Repeated DNA elements in the Bacillus cereus group - implications for genome dynamics and stability of messenger RNA.
• Fagerlund, Annette; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2009). Differential gene expression and gene regulation during Bacillus thuringiensis biofilm formation.
• Økstad, Ole Andreas Løchen; Klevan, Leif Are; Tourasse, Nicolas; Kristoffersen, Simen Martens; Langørgen, Heidi K. & Stabell, Fredrik Bernhard [Show all 7 contributors for this article] (2008). Mobile chromosomal repeat elements in Bacillus cereus, B. thuringiensis, and B. anthracis − Comparative genomics and transcriptional analysis.
• Økstad, Ole Andreas Løchen (2008). Bacillus anthracis, B. cereus, and B. thuringiensis − pathogenic spore-forming bacteria ACTing out an identity crisis.
• Klevan, Leif Are; Tourasse, Nicolas; Kristoffersen, Simen Martens; Langørgen, Heidi K.; Stabell, Fredrik Bernhard & Kolstø, Anne-Brit [Show all 7 contributors for this article] (2008). Mobile chromosomal repeat elements in pathogenic Bacilli − comparative genomics of isolates closely related to Bacillus anthracis and co-transcription with neighbour genes.
• Kristoffersen, Simen Martens; Tourasse, Nicolas; Klevan, Leif Are; Bakka, Eirik Rødseth; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2008). The Mobile Chromosomal Repeat Element bcr1in Bacillus cereus Stabilizes Adjacent mRNAs.
• Tourasse, Nicolas; Økstad, Ole Andreas Løchen; Stabell, Fredrik Bernhard; Kristoffersen, Simen Martens & Kolstø, Anne-Brit (2008). Genome dynamics in Bacillus cereus − Bacillus anthracis − Bacillus thuringiensis.
• Kristoffersen, Simen Martens; Klevan, Leif Are; Tourasse, Nicolas; Langørgen, Heidi K.; Stabell, Fredrik Bernhard & Kolstø, Anne-Brit [Show all 7 contributors for this article] (2008). The mobile chromosomal repeat element bcr1 from the Bacillus cereus group is co−transcribed with neighboring genes and predicted to fold into a double hairpin−like structure.
• Økstad, Ole Andreas Løchen; Klevan, Leif Are; Tourasse, Nicolas; Kristoffersen, Simen Martens; Langørgen, Heidi K. & Stabell, Fredrik Bernhard [Show all 7 contributors for this article] (2008). Mobile chromosomal repeat elements in pathogenic bacilli − comparative genomics and transcriptional analysis.
• Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2007). Bacillus ACT 2007 - Oslo, 17-21 June 2007. NBS-nytt. ISSN 0801-3535. p. 28–30.
• Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2007). Mikrobiologi-konferanse i FI-regi. Norsk Farmaceutisk Tidsskrift. ISSN 0029-1935. p. 10–10.
• Økstad, Ole Andreas Løchen; Ravel, Jacques; Rasko, David A; Rosovitz, MJ; Tourasse, Nicolas & Kolstø, Anne-Brit (2007). Comprehensive whole genome sequence analysis of clinical Bacillus cereus isolates from different human infections.
• Økstad, Ole Andreas Løchen; Klevan, Are; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Kristoffersen, Simen Martens & Kolstø, Anne-Brit (2007). Mobile chromosomal repeat elements unique to the Bacillus cereus group − chromosomal organization, transcription, and secondary structure.
• Kristoffersen, Simen Martens; Ravnum, Solveig; Tourasse, Nicolas; Økstad, Ole Andreas Løchen; Kolstø, Anne-Brit & Davies, William (2007). Gene transcription responses to bile salts in Bacillus cereus ATCC 14579 – in vitro modeling of GI-tract bile exposure.
• Økstad, Ole Andreas Løchen; Tourasse, Nicolas; Hegna, Ida Kristin & Kolstø, Anne-Brit (2007). Functional and comparative genomics in pathogenic Bacillus species.
• Fægri, Karoline; Hegna, Ida Kristin; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2007). Comparative analysis of global gene expression in Bacillus cereus ATCC 14579 and a deletion mutant of a membrane transporter with similarity to tetracycline resistance genes.
• Økstad, Ole Andreas Løchen; Klevan, Are; Tourasse, Nicolas; Stabell, Fredrik Bernhard & Kolstø, Anne-Brit (2007). Mobile chromosomal repeat elements in Bacillus cereus, B. thuringiensis and B. anthracis.
• Biørnstad, Truls Johan; Jensen, Christine; Gohar, Michel; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2007). Biofilm formation in Bacillus cereus group pathogens − screening of isolates and functional dissection of candidate genes potentially involved in the process.
• Klevan, Are; Kristoffersen, Simen Martens; Langørgen, Heidi K.; Tourasse, Nicolas; Stabell, Fredrik Bernhard & Kolstø, Anne-Brit [Show all 7 contributors for this article] (2007). THE MOBILE CHROMOSOMAL REPEAT ELEMENT BCR1 IN BACILLUS CEREUS, B. THURINGIENSIS AND B. ANTHRACIS.
• Kristoffersen, Simen Martens; Ravnum, Solveig; Tourasse, Nicolas; Økstad, Ole Andreas Løchen; Kolstø, Anne-Brit & Davies, William (2007). Low concentrations of bile salts induce stress responses and reduce motility in the Bacillus cereus type strain.
• Fægri, Karoline; Ravnum, Solveig; Økstad, Ole Andreas Løchen; Tourasse, Nicolas & Kolstø, Anne-Brit (2007). Bruk av mikromatriser for å studere genregulering i Bacillus cereus.
• Økstad, Ole Andreas Løchen (2006). Infeksjonssykdommenes retur - hva kan genomforskning på patogene bakterier fortelle oss?
• Økstad, Ole Andreas Løchen; Tourasse, Nicolas; Rasko, David A; Meisal, Roger; Helgason, Erlendur & Kolstø, Anne-Brit [Show all 8 contributors for this article] (2006). Gene discovery by comparative genome hybridization (GDCGH) − investigating gene diversity in the Bacillus cereus group of bacterial pathogens.
• Fægri, Karoline; Ravnum, Solveig; Økstad, Ole Andreas Løchen; Tourasse, Nicolas & Kolstø, Anne-Brit (2006). Comparing wt Bacillus cereus with a transcriptional regulator mutant. Show summary

  PlcR is a pleiotropic transcriptional regulator found in Bacillus cereus, an opportunistic pathogen, and Bacillus thuringiensis, an insect pathogen. The PlcR regulator has been shown to positively control a wide range of virulence factors that are exported to the extracellular environment, including a multitude of degradative enzymes, hemolysins, enterotoxins, phospholipases. We have used microarrays to perform genomewide comparisons of gene expression in B. cereus ATCC 14579 (type strain) against a plcR deletion mutant to find genes that are regulated, directly or indirectly, by PlcR. In addition to confirming the results of earlier studies, we identify several new genes regulated by PlcR, including genes involved in motility, additional degradative enzymes, and prophage-related genes. Some of these genes carry an upstream regulatory PlcR-box and may thus be directly regulated. We also observe a considerable number of genes that may be subject to indirect regulation, and the mutation seems to influence central metabolic pathways involved in energy metabolism and lipid biosynthesis.

• Klevan, Leif Are; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2006). An evolutionary snapshot of the repeated element bcr1 in Bacillus cereus group strains close to the Bacillus anthracis cluster − transcription analysis, RNA folding, and traces of mobility.
• Tourasse, Nicolas; Helgason, Erlendur; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2006). Novel aspects of population and genome dynamics in the Bacillus cereus group of bacterial pathogens.
• Klevan, Are; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Helgason, Erlendur; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2006). Genome dynamics in Bacillus cereus group pathogens - in silico experiments predict mobility of the bcr1 repeat element is related to RNA secondary structure stability.
• Tourasse, Nicolas; Helgason, Erlendur; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2006). The Bacillus cereus group: novel aspects of population structure and genome dynamics.
• Fægri, Karoline; Ravnum, Solveig; Økstad, Ole Andreas Løchen; Tourasse, Nicolas & Kolstø, Anne-Brit (2006). Comparative analysis of global gene expression in Bacillus cereus ATCC 14579 and a derivative strain following gene deletion of delta-PlcR, a transcriptional regulator of extracellular virulence.
• Kristoffersen, Simen Martens; Ravnum, Solveig; Økstad, Ole Andreas Løchen; Kolstø, Anne-Brit & Davies, William (2006). Transcriptome analysis of bile salt treated Bacillus cereus ATCC 14579.
• Biørnstad, Truls Johan; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2006). Screening for biofilm formation among bacteria from the Bacillus cereus group.
• Biørnstad, Truls Johan; Jensen, Christine; Gohar, Michel; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2006). Screening for biofilm formation among bacteria from the Bacillus cereus group and dissection of candidate genes potentially involved in the process.
• Klevan, Leif Are; Tourasse, Nicolas; Helgason, Erlendur; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2005). Repeated element bcr1 from the Bacillus cereus group: Distribution, evolution and possible mobility in a set of strains closely related to B. anthracis.
• Klevan, Leif Are; Tourasse, Nicolas; Helgason, Erlendur; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2005). The repeated element bcr1: Distribution, evolution and possible mobility in the Bacillus cereus group of bacteria.
• Klevan, Leif Are; Tourasse, Nicolas; Helgason, Erlendur; Økstad, Ole Andreas Løchen & Kolstø, Anne-Brit (2005). Distribution, evolution and possible mobility of the repeated element bcr1 by examination of Bacillus cereus group strains from the B. anthracis cluster.
• Klevan, Leif Are; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Helgason, Erlendur; Kolstø, Anne-Brit & Økstad, Ole Andreas Løchen (2005). Exploring the phylogeny of Bacillus cereus strains close to the B. anthracis cluster through distribution and sequence analysis of the repeated element bcr1.
• Økstad, Ole Andreas Løchen (2004). Hva skiller en vanlig matforgiftningsbakterie fra en akutt dødelig bakterie - djevelen er i detaljene.
• Økstad, Ole Andreas Løchen; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Sundfær, Cathrine Kleven; Klevan, Are & Risøen, Per Arne [Show all 8 contributors for this article] (2004). bcr1, a novel mobile element specific to the Bacillus cereus group?
• Økstad, Ole Andreas Løchen; Tourasse, Nicolas; Stabell, Fredrik Bernhard; Sundfær, Cathrine Kleven; Klevan, Are & Risøen, Per Arne [Show all 8 contributors for this article] (2004). Comparative genome analysis of pathogenic Bacilli – the bcr1 DNA repeat is specific to the Bacillus cereus group and exhibits mobile lement characteristics.
• Økstad, Ole Andreas Løchen; Helgason, Erlendur; Tourasse, Nicolas & Kolstø, Anne-Brit (2004). Whole genome sequencing reveals unexpected similarities between a Bacillus cereus dairy isolate and highly virulent Bacillus anthracis, the cause of anthrax.
• Økstad, Ole Andreas Løchen (2003). The Bacillus cereus group of bacteria � the good, the bad, and the ugly.
• Økstad, Ole Andreas Løchen (2003). Bacillus anthracis og miltbrann.
• Stenmark, Harald Alfred; Tourasse, Nicolas; Økstad, Ole Andreas Løchen; Helgason, Erlendur & Kolstø, Anne-Brit (2003). Norsk forskningsgruppe deltar i avsløring av miltbrannbakteriens hemmeligheter. NBS-nytt. ISSN 0801-3535. p. 6–6.

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