About the group
Our research
It is increasingly difficult to treat infections due to the emergence and spread of antibiotic resistant bacteria (including penicillin-resistant S. pneumoniae and methicillin-resistant S. aureus, MRSA). An understanding of the underlying mechanisms behind antibiotic resistance will lead to better treatment methods.
We study different molecular mechanisms to understand antibiotic resistance and identify novel antimicrobial target sites in pneumococci (S. pneumoniae) and staphylococci (S. aureus). These pathogens are responsible for millions of deaths worldwide every year.
News
July 2026
- Ingvild Reinseths papers on the interaction between bacteriocin enterocin EJ97s and human serum albumin is published. The bacteriocin enterocin EJ97s retains its antibacterial effect upon interaction with human serum albumin.June 2026
- Ragnhild defended her PhD - New insights into penicillin non-susceptibility in Streptococcus pneumoniae - Friday June 26th! Gratulerer! Read more about it here.
- Ingvild Linnestad, Aria Rad Saadat, Mia Hallingstad Ringstad & Andreas Grønli have all finished their master project. Congrats to all!
- Paper published by the Ingmer-lab, where we have made a contribution: Phage Intolerance Impacts Antibiotic Susceptibility and Virulence in Staphylococcus aureus
- Ragnhilds has written about basic reseach and antibiotic resistance at Forskersonen: Hvorfor dør noen bakterier når vi tar antibiotika, mens andre overlever?
May 2026:
- Rebekka's paper on pilus and natural transformation Streptococcus sanguinis published in Journal of Bacteriology: LytF contributes to pilus extrusion during natural competence in Streptococcus sanguinis SK36
- Paper published in collaboration with Vegard Eldholm at the National Institute of Public Health: Genomic epidemiology of Streptococcus pneumoniae GPSC6: post-vaccine expansion of β-lactam-susceptible serotype 24F in Europe
April 2026
- Paper published in collaboration with the Microbial Ecology and Physiology group: Distinct Denitrification Phenotypes in Closely Related Bacteria: Clues to Understanding Variations in Nitrite Accumulation Among Stutzerimonas Strains
March 2026
- Paper published in collaboration with the Microbial Ecology and Physiology group: Strain-specific challenges in applying CRISPR/Cas9-based genome editing in the novel genus Stutzerimonas
- Paper publised in collaboration with Vegard Eldholm at the National Institute of Public Health: Assessing sequencing-based pathogen surveillance of a recreational swimming area in Oslo, Norway
January 2026
- Paper published in collaboration with the Mossakowski Medical Research Institute as part of the PrevEco project: Enhancing stability and safety of chimeric peptidoglycan hydrolases by linker engineering
- Thomas' paper on garvicin KS tolerance in Listeria monocytogenes has been published: The phage shock protein response of Listeria monocytogenes influences tolerance to the multipeptide bacteriocin garvicin KS
- This month we have been teaching laboratory courses in molecular biology and molecular microbiology.
- Ragnhild has written about her work on MurM and pneumococci in Forskersonen: Hvorfor blir bakterier som gir lungesykdom motstandsdyktige mot penicillin?
- Andreas Grønli and Martine Edvardsen started their master projects in the lab. Good luck!
- Paper published in collaboration with the Aqua Medicine Unit: Streptococcus agalactiae 1a capsule (cpsE) and hemolysin (cylE) deletion mutants display attenuated virulence in Nile tilapia (Oreochromis niloticus).
Publications
Staphylococcus
Bowring J, Mikkelsen FC, Haider RM, Lehmann E, Frisch T, Kjos M, van Sorge N, Ingmer H (2026) Phage resistance impacts antibiotic susceptibility and virulence in Staphylococcus aureus. Curr Microbiol. 83:452. https://doi.org/10.1007/s00284-026-05034-6.
Barbuti MD, Skjennum EF, Mebus V, Hustad M, Morales Angeles D, Mårli MT, Frees D, Kjos M (2025) Cell splitting in Staphylococcus aureus is controlled by an adaptor protein facilitating degradation of a peptidoglycan hydrolase. PLoS Genet. doi.org/10.1371/journal.pgen.1011841.
Miah R, Johannessen M, Kjos M, Lentz C (2025) A programmable, selection-free CRISPR interference system in Staphylococcus aureus for long-term host interaction studies. iScience.113420. doi.org/10.1016/j.isci.2025.113420.
Mebus V, Busch LM, Børre M, Krogh Nielsen T, Bojer MS, Henriksen C, Barbuti MD, Morales Angeles D, Brejndahl K, Michalik S, Salazar MG, Kjos M, Völker U, Kallipolitis BH, Frees D (2025) Temperature-dependent regulation of bacterial cell division hydrolases by the coordinated action of a regulatory RNA and the ClpXP protease. The Cell Surface. https://www.sciencedirect.com/science/article/pii/S2468233025000040 bioRxiv: doi.org/10.1101/2025.04.01.646552v1
Mårli MT, Nordraak AOO, de Bakker V, Ruud-Winther A, Liu X, Veening JW, Porcellato D, Kjos M (2025) Genome-wide fitness determinants of Staphylococcus aureus during growth in milk. PLoS Pathogens. doi.org/10.1371/journal.ppat.1013080
Miah R, Johannessen M, Kjos M, Lentz CS (2024) Development of an inducer-free, virulence gene promoter controlled, and fluorescent reporter labelled CRISPR interference system in Staphylococcus aureus. Microbiol Spectr. doi.org/10.1128/spectrum.00602-24
Liu X*, de Bakker V*, Heggenhougen MV*, Frøynes Heidal A, Mårli MT, Porcellato D, Veening JW, Kjos M (2024). Genome-wide CRISPRi screens for high-throughput fitness quantification and identification of determinants for dalbavancin susceptibility in Staphylococcus aureus. mSystems. doi.org/10.1128/msystems.01289-23
Barbuti MD, Lambert E, Myrbråten IS, Ducret A, Stamsås GAH, Wilhelm L, Liu X, Salehian Z, Veening JW, Straume D, Grangeasse C, Perez C, Kjos M (2024). The function of CozE proteins is linked to lipoteichoic acid biosynthesis in Staphylococcus aureus. mBio. e01157-24. doi.org/10.1128/mbio.01157-24.
Krogh Nielsen T, Birkjær Pedersen I, Xu L, Barbuti MD, Mebus V, Justh A, Alqarzaee AA, Jacques N, Oury C, Thomas V, Kjos M, Henriksen C, Frees D (2024) The Spx stress regulator confers high-level β-lactam resistance and decreases susceptibility to last-line antibiotic in methicillin resistant Staphylococcus aureus (2024) Antimicrob Agents Chemother. e0033524. doi.org/10.1128/aac.00335-24.
Cacace E, Kim V, Knopp M, Tietgen M, Brauer-Nikonow A, Inecik K, Mateus A, Milanese A, Mårli MT, Mitosch K, Selkrig J, Brochado AR, Kuipers O, Kjos M, Zeller G, Savitski M, Göttig S, Huber W, Typas A (2023) Systematic analysis of drug combinations against Gram-positive bacteria. doi.org/10.1038/s41564-023-01486-9 Preprint: https://www.biorxiv.org/content/10.1101/2022.12.23.521747v1.
Myrbråten I, Stamsås GA, Chan H, Morales Angeles D, Knutsen TM, Salehian Z, Shapaval O, Straume D, Kjos M. (2022) SmdA is a novel cell morphology determinant in Staphylococcus aureus. mBio. doi.org/10.1128/mbio.03404-21. Commentary: doi.org/10.1128/mbio.00737-22
Fergestad M, Stamsås GA, Morales-Angeles D, Salehian Z, Wasteson Y, Kjos M (2020) PBP2A provides variable levels of protection towards different β-lactams in Staphylococcus aureus RN4220. Microbiol Open. https://doi.org/10.1002/mbo3.1057
Stamsås GA*, Myrbråten I*, Straume D, Salehian Z, Veening JW, Håvarstein LS, Kjos M (2018) CozEa and CozEb play overlapping and essential roles in controlling cell division in Staphylococcus aureus. Mol Microbiol. 109(5):615-632. Preprint available at: https://www.biorxiv.org/content/early/2018/05/23/256560. Se også: Cover
Streptococcus
Moe R, Piechowiak KW, Håvarstein LS, Kjos M, Straume D (2026) LytF contributes to pilus extrusion during natural competence in Streptococcus sanguinis SK36. J Bacteriol. https://doi.org/10.1128/jb.00118-26.
Osnes MN, Taxt AM, Gladstone RA, Bjørnstad ML, Straume D, Eldholm V (2026). Genomic epidemiology of Streptococcus pneumoniae GPSC6: post-vaccine expansion of β-lactam-susceptible serotype 24F in Europe. Microbial Genomics. 12. 001697. doi.org/10.1099/mgen.0.001697
Fyrand K, Xu C, Zegeye ED, Kjos M, Evensen Ø (2026) Streptococcus agalactiae 1a capsule (cpsE) and hemolysin (cylE) deletion mutants display attenuated virulence in Nile tilapia (Oreochromis niloticus). Fish Shellfish Immunol. 111097. doi.org/10.1016/j.fsi.2026.111097
Pongchaikul P, Hokamp K, Kjos M, Chaguza C, Audshasai T, Panagiotou S, Yahya R, Bricio-Moreno L, Hinton JCD, Kadioglu A, O’Brian M (2025) Transcriptomic analysis of the planktonic growth of Streptococcus pneumoniae serotype 1 reveals serotype-specific gene regulation. Microb Genom. 11:001582. doi.org/10.1099/mgen.0.001582.
Gjennestad R, Heggenhougen MV, Ruud Winther A, Moldstad J, Eldholm V, Kjos M, Håvarstein LS, Straume D (2025) The effect of MurM and a branched cell wall structure on penicillin resistance in Streptococcus pneumoniae. J Bacteriol. doi.org/10.1128/jb.00141-25. bioRxiv: doi.org/10.1101/2025.04.05.647355v1
Arbulu S, Oftedal T, Kjos M (2025) Transcriptomic response in planktonic and biofilm cells of S. mutans treated with sublethal concentrations of chlorhexidine. FEMS Microbiol Letters. fnaf100. doi.org/10.1093/femsle/fnaf100. Researchsquare: doi.org/10.21203/rs.3.rs-5834130/v1
Ormaasen I, Rae Simpson M, Øien T, Snipen L, Kjos M, Rudi K (2025) Tracing of streptococcal strains from infant stool across human body sites links gut-specificity to adhesins. Appl Environ Microbiol. doi.org/10.1128/aem.00196-25. bioRxiv: doi.org/10.1101/2025.01.15.633122
Glambek M, Kjos M, Mårli MT, Salehian Z, Skrede S, Sivertsen A, Kittang BR, Oppegaard O (2025) TrexAB, a novel tetracycline resistance determinant in Streptococcus dysgalactiae. Front Cell Infect Microbiol. 15. doi.org/10.3389/fcimb.2025.1583926
Mårli MT, Arntzen MØ, Teigen Schultheiss A, Allred J, Oppegård O, Kjos M*, Straume D* (2025) Self-immunity towards a competence-induced murein hydrolase in pyogenic streptococci is mediated by the Fem-transferase-like protein. Mol Microbiol. https://onlinelibrary.wiley.com/doi/10.1111/mmi.15361. bioRxiv. doi.org/10.1101/2024.09.27.615381
Eldholm V, Osnes MN, Bjørnstad ML, Straume D, Gladstone RA (2024). A genome-based survey of invasive pneumococci in Norway over four decades reveals lineage-specific responses to vaccination. Genome Medicine. 16. 123. doi.org/10.1186/s13073-024-01396-3
Miguel-Ruano V, Acebrón I, Lee M, Martín-Galiano AJ, Freton C, de Jose UP, Ramachandran B, Gago F, Kjos M, Hesek D, Grangeasse C, Håvarstein LS, Straume D, Mobashery S, Hermoso JA (2024). Characterization of VldE (Spr1875), a pneumococcal two-state L,D-endopeptidase with a four-zinc cluster in the active site. ACS Catalysis. 14. 18786-18798. doi.org/10.1021/acscatal.4c05090
Lux J, Sánchez García L, Chaparro Fernández P, Laloli L, Licheri MF, Gallay C, Hermans PWM, Croucher NJ, Veening JW, Dijkman R, Straume D, Hathaway LJ (2024). AmiA and AliA peptide ligands, found in Klebsiella pneumoniae, are imported into pneumococci and alter the transcriptome. Scientific Reports. 14. 12416. doi.org/10.1038/s41598-024-63217-2
Lux J, Portmann H, Sánchez García L, Erhardt M, Holivololona L, Laloli L, Licheri MF, Gallay C, Hoepner R, Croucher NJ, Straume D, Veening JW, Dijkman R, Heller M, Grandgirard D, Leib SL, Hathaway LJ (2024). Klebsiella pneumoniae peptide hijacks a Streptococcus pneumoniae permease to subvert pneumococcal growth and colonization. Communications Biology. 7. 425. doi.org/10.1038/s42003-024-06113-9
AlQadeeb H, Baltazar M, Cazares A, Poonpanichakul T, Kjos M, French N, Kadioglu A, O’Brien M (2024). The Streptococcus agalactiae LytSR two-component regulatory system promotes vaginal colonization and virulence. Microb Spectrum. In press. https://doi.org/10.1128/spectrum.01970-24
Ruud-Winther A, Salehian Z, Arnason Bøe C, Nesdal M, Håvarstein LS, Kjos M, Straume D (2024) Decreased susceptibility to viscosin in Streptococcus pneumoniae. Microbiol Spectr. doi.org/10.1128/spectrum.00624-24
Minhas V, Domenech A, Synefiaridou D, Straume D, Brendel M, Cebrero G, Liu X, Costa C, Baldry M, Sirard JC, Perez C, Gisch N, Hammerschmidt S, Håvarstein LS, Veening JW (2023). Competence remodels the pneumococcal cell wall exposing key surface virulence factors that mediate increased host adherence. PLoS Biology. 21. e3001990. doi.org/10.1371/journal.pbio.3001990
Audshasai T, Coles JA, Panagiotou S, Khandaker S, Scales HE, Kjos M, Baltazar M, Vignau, Brewer JM, Kadioglu A, Yang M (2022). Streptococcus pneumoniae rapidly translocates from the nasopharynx through the cribriform plate to invade and inflame the dura. mBio. 3(4):e0102422. doi.org/10.1128/mbio.01024-22
Gallay C, Sanselicio S, Anderson ME, Soh YM, Liu X, Stamsås GA, Pelliciari S, van Raaphorst R, Dénéréaz J, Kjos M, Murray H, Gruber S, Grossman AD, Veening JW (2021). CcrZ is a spatiotemporal cell cycle regulator that interacts with FtsZ and controls DNA replication by modulating the activity of DnaA. Nat Microbiol. doi.org/10.1038/s41564-021-00949-1. Commentary.
Straume D, Piechowiak KW, Kjos M, Håvarstein LS (2021) Class A PBPs: it is time to rethink traditional paradigms. Mol Microbiol. doi: https://doi.org/10.1111/mmi.14714
Ruud-Winther A, Kjos M, Herigstad ML, Håvarstein LS, Straume D (2021). EloR interacts with the lytic transglycosylase MltG at midcell in Streptococcus pneumoniae R6. J Bacteriol. doi: 10.1128/JB.00691-20. Preprint: https://www.biorxiv.org/content/10.1101/2020.12.18.423453v1.full
Kranjec C*, Morales-Angeles D*, Torrissen Mårli M, Fernandez L, Garcia P, Kjos M*, Diep DB*. (2021) Staphylococcal Biofilms: Challenges and novel therapeutic perspectives. Antibiotics. 10(2):131. https://doi.org/10.3390/antibiotics10020131
Stamsås GA*, Restelli M*, Ducret A, Freton C, Garcia PS, Håvarstein LS, Straume D, Grangeasse C and Kjos M (2020) A CozE homologue contributes to cell size homeostasis of Streptococcus pneumoniae. mBio. 11(5):e02461-20. https://doi.org/10.1128/mBio.02461-20
Alcorlo M, Straume D, Lutkenhaus J, Håvarstein LS, Hermoso JA (2020). Structural Characterization of the Essential Cell Division Protein FtsE and Its Interaction with FtsX in Streptococcus pneumoniae. mBio. 11. e01488-20. doi.org/10.1128/mBio.01488-20
Straume D, Piechowiak KW, Olsen S, Stamsås GA, Berg KH, Kjos M, Heggenhougen MV, Alcorlo M, Hermoso J and Håvarstein LS. Class A PBPs have a distinct and unique role in the construction of the pneumococcal cell wall. Proc Natl Acad Sci U S A. doi.org/10.1073/pnas.1917820117. Preprint available at: https://www.biorxiv.org/content/10.1101/665463v1.
Ruud Winther A, Kjos M, Stamsås GA, Håvarstein LS, Straume D (2019) Prevention of EloR/KhpA heterodimerization by introduction of site-specific amino acid substitutions renders the essential elongasome protein PBP2b redundant in Streptococcus pneumoniae. Sci Rep. 9:3681.
Rued BE, Alcorlo M, Edmonds KA, Martínez-Caballero S, Straume D, Fu Y, Bruce KE, Wu H, Håvarstein LS, Hermoso JA, Winkler ME, Giedroc DP (2019) Structure of the Large Extracellular Loop of FtsX and Its Interaction with the Essential Peptidoglycan Hydrolase PcsB in Streptococcus pneumoniae. mBio. 10(1). pii: e02622-18. doi: 10.1128/mBio.02622-18.
Morlot C, Straume D, Peters K, Hegnar OA, Simon N, Villard AM, Contreras-Martel C, Leisico F, Breukink E, Gravier-Pelletier C, Le Corre L, Vollmer W, Pietrancosta N, Håvarstein LS, Zapun A (2018) Structure of the essential peptidoglycan amidotransferase MurT/GatD complex from Streptococcus pneumoniae. Nat Commun. 9(1):3180. doi: 10.1038/s41467-018-05602-w.
Miller E*, Kjos M*, Abrudan M, Roberts IS, Veening JW, Rozen DE (2018) Crosstalk and eavesdropping among quorum sensing peptide signals that regulate bacteriocin production in Streptococcus pneumoniae. ISME J. 12(10):2363-2375. Preprint available at: http://biorxiv.org/content/early/2016/11/11/087247.
Moreno-Gámez S, Sorg RA, Domenech A, Kjos M, Weissing FJ, van Doorn GS, Veening JW. Quorum-sensing integrates environmental cues, cell density and cell history to control bacterial competence. Nat Comm. 8(1):854.
Stamsås GS, Straume D, Ruud Winther A, Kjos M, Frantzen CA, Håvarstein LS (2017) Identification of EloR (Spr1851) as a regulator of cell elongation in Streptococcus pneumoniae. Mol Microbiol. 10.1111/mmi.13748
Stamsås GA, Straume D, Salehian Z, Håvarstein LS (2017) Evidence that pneumococcal WalK is regulated by StkP through protein-protein interaction. Microbiology. 163(3):383-399. doi: 10.1099/mic.0.000404.
Straume D, Stamsås GA, Salehian Z, Håvarstein LS (2017) Overexpression of the fratricide immunity protein ComM leads to growth inhibition and morphological abnormalities in Streptococcus pneumoniae. Microbiology.163(1):9-21. doi: 10.1099/mic.0.000402.
Straume D, Stamsås GA, Berg KH, Salehian Z, Håvarstein LS (2017) Identification of pneumococcal proteins that are functionally linked to penicillin-binding protein 2b (PBP2b). Mol Microbiol. 103(1):99-116. doi: 10.1111/mmi.13543.
van Raaphorst R*, Kjos M*, Veening JW (2017) Chromosome segregation drives division site selection in Streptococcus pneumoniae. Proc Natl Acad Sci U S A. 114(29):E5959-E5968. *joint first authors. Se også: 1,2.
Liu X, Gallay C, Kjos M, Domenech A, Slager J, van Kessel S, Knoops K, Sorg RA, Zhang JR, Veening JW (2017) High-throughput CRISPRi phenotyping in Streptococcus pneumoniae identifies new essential genes involved in cell wall synthesis and competence development. Mol Syst Biol. 13:931.
Kjos M*, Miller E*, Slager J, Lake F, Gericke O, Roberts IS, Rozen DE, Veening JW (2016) Antibiotic-induced expression of pneumococcal bacteriocins via regulatory interplay with the competence system. PLoS Pathogens. 12(2):e1005422.
Nourikyan J*, Kjos M*, Cluzel C, Morlot C, Mercy C, Noirot-Gros MF, Lavergne JP, Guiral S, Veening JW, Grangeasse C. (2015) Autophosphorylation of the bacterial tyrosine kinase CpsD coordinates capsule synthesis and cell division of Streptococcus pneumoniae. PLoS Genetics. 11(9):e1005518
Beilharz K, van Raaphorst R, Kjos M, Veening JW (2015) Red fluorescent proteins for gene expression and protein localization studies in Streptococcus pneumoniae and efficient transformation with DNA assembled via the Gibson assembly method. Appl Environ Microbiol. 81(20):7244-52.
Attaiech L, Minnen A, Kjos M, Gruber S, Veening JW (2015) The ParB-parS chromosome segregation system modulates natural competence development in Streptococcus pneumoniae. mBio. 6(4):e00662-15.
Paixão L, Oliveira J, Verissímo A, Vinga S, Lourenço E, Ventura R, Kjos M, Veening JW, Fernandes VE, Andrew PE, Yesilkaya H and Neves AR (2015) Host glycan sugar specific pathways in Streptococcus pneumoniae: galactose as a key sugar in colonisation and infection. PLoS One. 10(3):e0121042.
Kjos M, Aprianto R, Fernandes VE, Andrew PW, van Strijp JAG, Nijland R, Veening JW (2015) Bright fluorescent Streptococcus pneumoniae for live cell imaging of host-pathogen interactions. J Bacteriol. 197:807-18.
Straume D, Stamsås GA, Håvarstein LS (2015) Natural transformation and genome evolution in Streptococcus pneumoniae. Infect Genet Evol. 33:371-80. doi: 10.1016/j.meegid.2014.10.020.
Bartual SG, Straume D, Stamsås GA, Muñoz IG, Alfonso C, Martínez-Ripoll M, Håvarstein LS, Hermoso JA (2014) Structural basis of PcsB-mediated cell separation in Streptococcus pneumoniae. Nat Commun. 2014 May 8;5:3842. doi: 10.1038/ncomms4842.
Berg KH, Straume D, Håvarstein LS (2014) The function of the transmembrane and cytoplasmic domains of pneumococcal penicillin-binding proteins 2x and 2b extends beyond that of simple anchoring devices. Microbiology. 2014 Aug;160(Pt 8):1585-98. doi: 10.1099/mic.0.078535-0.
Slager J, Kjos M, Attaiech L, Veening JW (2014) Antibiotic-induced increase of origin proximal gene copy number triggers bacterial competence. Cell. 157(2):395-406.
Kjos M, Veening JW (2014) Tracking of chromosome dynamics in live Streptococcus pneumoniae reveals that transcription promotes chromosome segregation. Mol Microbiol. 91(6):1088-1105.
Pinho MG, Kjos M, Veening JW (2013) How to get (a)round: Mechanisms controlling growth and division of coccoid bacteria. Nat Rev Microbiol. 11:601-14.
Berg KH, Stamsås GA, Straume D, Håvarstein LS (2013) Effects of low PBP2b levels on cell morphology and peptidoglycan composition in Streptococcus pneumoniae R6. J Bacteriol. 2013 Oct;195(19):4342-54. doi: 10.1128/JB.00184-13.
Berg KH, Biørnstad TJ, Straume D, Håvarstein LS (2011) Peptide-regulated gene depletion system developed for use in Streptococcus pneumoniae. J Bacteriol. 2011 Oct;193(19):5207-15. doi: 10.1128/JB.05170-11.
Eldholm V, Johnsborg O, Straume D, Ohnstad HS, Berg KH, Hermoso JA, Håvarstein LS (2010) Pneumococcal CbpD is a murein hydrolase that requires a dual cell envelope binding specificity to kill target cells during fratricide. Mol Microbiol. 2010 May;76(4):905-17. doi: 10.1111/j.1365-2958.2010.07143.x.
Bacteriocins and antimicrobial proteins
Reinseth I, Grønlien KG, Oftedal TF, Kjos M*, Carlsen H*, Tonnesen HH (2026) The bacteriocin enterocin EJ97s retains its antibacterial effect upon interaction with human serum albumin. J Appl Microbiol. lxag193. doi.org/10.1093/jambio/lxag193
Mitkowski P, Jagielska E, Korzeniowska née Wiweger M, Nowacka M, Kjos M, Kranjec C, Sabała I (2026) Enhancing stability and safety of chimeric peptidoglycan hydrolases by linker engineering. Appl Microbiol Biotechnol. doi.org/10.1007/s00253-025-13651-7
Oftedal TF, Løvdal T, Kjos M (2026) The phage shock protein response of Listeria monocytogenes influence tolerance to the multipeptide bacteriocin garvicin KS. Appl Microbiol Biotechnol. 110:11 doi.org/10.1007/s00253-025-13691-z.
Kranjec C, Oftedal TF, Ovchinnikov K, Duarte da Silva V, Hermansen S, Kaus-Drobek M, Sabała I, Porcellato D, Carlsen H, Kjos M (2025) An antibiotic-free antimicrobial combination of bacteriocins and a peptidoglycan hydrolase: in vitro and in vivo assessment of its efficacy. Appl Environ Microbiol. https://journals.asm.org/doi/10.1128/aem.02433-24 bioRxiv: doi.org/10.1101/2024.11.19.624290
Mårli MT, Arntzen MØ, Teigen Schultheiss A, Allred J, Oppegård O, Kjos M*, Straume D* (2025) Self-immunity towards a competence-induced murein hydrolase in pyogenic streptococci is mediated by the Fem-transferase-like protein. Mol Microbiol. https://onlinelibrary.wiley.com/doi/10.1111/mmi.15361. bioRxiv. doi.org/10.1101/2024.09.27.615381
Kranjec C, Ovchinnikov K, Mathew JP, Fadayomi I, Yang Y, Kjos M*, Li WW* (2024) A bacteriocin-based coating strategy to prevent vancomycin-resistant Enterococcus faecium biofilm formation on materials of interest for indwelling medical devices. Biofilm. doi.org/10.1016/j.bioflm.2024.100211
Oftedal TF, Diep DB, Kjos M. (2024) Design of novel saposin-like bacteriocins with antimicrobial activity using a hybrid approach. Probiotics Antimicrob Proteins. doi.org/10.1007/s12602-024-10264-w.
Reinseth I, Diep DB, Kjos M, Tønnesen HH, Carlsen H (2024) Exploring the feasibility of bacteriocins EntK1 and EntEJ97s in treating systemic VRE infections in mice. J Appl Microbiol. 135(3):lxae054. doi.org/10.1093/jambio/lxae054
Arbulu S, Kjos M (2024) Revisiting the role of bacteriocins in natural settings. Microbial Ecol. 87: 41. doi.org/10.1007/s00248-024-02357-4.
Hauge IH, Sandegren V, Ruud Winther A, Bøe CA, Salehian Z, Håvarstein LS, Kjos M, Straume D (2023) A novel proteinaceous molecule produced by Lysinibacillus sp. OF-1 depends on the Ami oligopeptide transporter to kill Streptococcus pneumoniae. Microbiology. 169(3):001313. https://doi.org/10.1099/mic.0.001313
Oftedal TF, Ovchinnikov K, Hestad KA, Porcellato D, Narvhus J, Kranjec C, Kjos M, Diep DB (2021) Ubericin K, a new pore-forming bacteriocin targeting mannose-PTS. Microbiol Spectrum. 9(2):e0029921. doi.org/10.1128/Spectrum.00299-21
Ovchinnikov K, Kranjec C, Telke A, Kjos M, Thorstensen T, Carlsen H, Scherer S, Diep DB (2021). A strong synergy between the thiopeptide bacteriocin micrococcin P1 and rifampicin against MRSA in a murine skin infection model . Front Immunol. 12: 676534. doi.org/10.3389/fimmu.2021.676534.
Miller E*, Kjos M*, Abrudan M, Roberts IS, Veening JW, Rozen DE (2018) Crosstalk and eavesdropping among quorum sensing peptide signals that regulate bacteriocin production in Streptococcus pneumoniae. ISME J. 12(10):2363-2375. Preprint available at: http://biorxiv.org/content/early/2016/11/11/087247.
Ovchinnikov KV, Kristiansen PE, Straume D, Jensen MS, Aleksandrzak-Piekarczyk T, Nes IF, Diep DB (2017) The Leaderless Bacteriocin Enterocin K1 Is Highly Potent against Enterococcus faecium: A Study on Structure, Target Spectrum and Receptor. Front Microbiol. 8:774. doi: 10.3389/fmicb.2017.00774.
Oppegård C, Kjos M, Veening JW, Nissen-Meyer J, Kristensen T (2016) A putative amino acid transporter determines sensitivity to the two-peptide bacteriocin plantaricin JK. MicrobiologyOpen. doi: 10.1002/mbo3.36.
Kjos M*, Miller E*, Slager J, Lake F, Gericke O, Roberts IS, Rozen DE, Veening JW (2016) Antibiotic-induced expression of pneumococcal bacteriocins via regulatory interplay with the competence system. PLoS Pathogens. 12(2):e1005422.
Kjos M*, Oppegård C*, Diep DB, Nes IF, Veening JW, Nissen-Meyer J, Kristiansen T (2014) Sensitivity to the two-peptide bacteriocin lactococcin G is dependent on an enzyme involved in cell-wall synthesis. Mol Microbiol. 92(6):1177-87
Hassan M, Kjos M, Nes IF, Diep DB, Lotfipour F (2014) Antimicrobial peptides from prokaryotes. In: Novel Antimicrobial Agents and Strategies (Phoenix DA, Harris F, Dennison SR, eds.). Wiley-VCH, Germany.
Hassan M, Kjos M, Nes IF, Diep DB, Lotfipour F (2012) Natural antimicrobial peptides from bacteria: characteristics and potential applications to fight against antibiotic resistance. J Appl Microbiol. 113(4):723-36.
Nes IF, Kjos M, Diep DB (2011) Antimicrobial components of lactic acid bacteria. In: Lactic acid bacteria: microbiological and functional aspects, fourth edition (Lahtinen S, Ouwehand AC, Salminen S, von Wright A, eds.), CRC Press Taylor & Francis, USA.
Kjos M, Borrero J, Opsata M, Birri DJ, Holo H, Cintas LM, Snipen L, Hernandez PE, Nes IF, Diep DB (2011) Target recognition, resistance, immunity and genome mining of class II bacteriocins from Gram-positive bacteria. Microbiology. 157:3256-67.
Kjos M, Nes IF, Diep DB (2011) Mechanisms of resistance to bacteriocins targeting the mannose phosphotransferase system. Appl Environ Microbiol. 77(10):3335-42.
Kjos M, Salehian Z, Nes IF, Diep DB (2010) An extracellular loop of the mannose phosphotransferase system component IIC is responsible for specific targeting by class IIa bacteriocins. J Bacteriol. 192(22):5906-13.
Kjos M, Snipen LS, Salehian Z, Nes IF, Diep DB (2010) The Abi proteins and their involvement in bacteriocin self-immunity. J Bacteriol. 192(8):2068-76.
Kjos M, Nes IF, Diep DB (2009) Class II one-peptide bacteriocins target a phylogenetically defined subgroup of mannose phosphotransferase systems on sensitive cells. Microbiology. 155(9):2949-61.
Diep DB, Straume D, Kjos M, Torres C, Nes IF (2009) An overview of the mosaic bacteriocin pln loci from Lactobacillus plantarum. Peptides 30 (8): 1562-74.
Straume D, Kjos M, Nes IF, Diep DB (2007) Quorum-sensing based bacteriocin production is down-regulated by N-terminally truncated species of gene activators. Mol Genet Gen. 278 (3): 283-93.
Straume D, Johansen RF, Bjørås M, Nes IF, Diep DB (2009) DNA binding kinetics of two response regulators, PlnC and PlnD, from the bacteriocin regulon of Lactobacillus plantarum C11. BMC Biochem. 10:17. doi: 10.1186/1471-2091-10-17.
Antibiotic resistance
Bowring J, Mikkelsen FC, Haider RM, Lehmann E, Frisch T, Kjos M, van Sorge N, Ingmer H (2026) Phage resistance impacts antibiotic susceptibility and virulence in Staphylococcus aureus. Curr Microbiol. 83:452. https://doi.org/10.1007/s00284-026-05034-6.
Gjennestad R, Heggenhougen MV, Ruud Winther A, Moldstad J, Eldholm V, Kjos M, Håvarstein LS, Straume D (2025) The effect of MurM and a branched cell wall structure on penicillin resistance in Streptococcus pneumoniae. J Bacteriol. doi.org/10.1128/jb.00141-25. bioRxiv: doi.org/10.1101/2025.04.05.647355v1
Barbuti MD, Skjennum EF, Mebus V, Hustad M, Morales Angeles D, Mårli MT, Frees D, Kjos M (2025) Cell splitting in Staphylococcus aureus is controlled by an adaptor protein facilitating degradation of a peptidoglycan hydrolase. PLoS Genet. doi.org/10.1371/journal.pgen.1011841. bioRxiv: doi.org/10.1101/2025.05.11.653310
Arbulu S, Oftedal T, Kjos M (2025) Transcriptomic response in planktonic and biofilm cells of S. mutans treated with sublethal concentrations of chlorhexidine. FEMS Microbiol Letters. fnaf100. doi.org/10.1093/femsle/fnaf100. Researchsquare: doi.org/10.21203/rs.3.rs-5834130/v1
Glambek M, Kjos M, Mårli MT, Salehian Z, Skrede S, Sivertsen A, Kittang BR, Oppegaard O (2025) TrexAB, a novel tetracycline resistance determinant in Streptococcus dysgalactiae. Front Cell Infect Microbiol. 15. doi.org/10.3389/fcimb.2025.1583926
Mårli MT, Nordraak AOO, de Bakker V, Winter AR, Liu X, Veening JW, Porcellato D, Kjos M (2025) Genome-wide fitness determinants of Staphylococcus aureus during growth in milk. PLoS Pathogens. doi.org/10.1371/journal.ppat.1013080
Ruud-Winther A, Perrin A, Nordraak AOO, Kjos M, Porcellato D (2024) An in vitro evaluation of the effect of antimicrobial treatment on bovine mammary microbiota. Sci Rep. In press. doi.org/10.1038/s41598-024-69273-y
Krogh Nielsen T, Birkjær Pedersen I, Xu L, Barbuti MD, Mebus V, Justh A, Alqarzaee AA, Jacques N, Oury C, Thomas V, Kjos M, Henriksen C, Frees D (2024) The Spx stress regulator confers high-level β-lactam resistance and decreases susceptibility to last-line antibiotic in methicillin resistant Staphylococcus aureus (2024) Antimicrob Agents Chemother. e0033524. doi.org/10.1128/aac.00335-24.
Cacace E, Kim V, Knopp M, Tietgen M, Brauer-Nikonow A, Inecik K, Mateus A, Milanese A, Mårli MT, Mitosch K, Selkrig J, Brochado AR, Kuipers O, Kjos M, Zeller G, Savitski M, Göttig S, Huber W, Typas A (2023) High-throughput profiling of drug interactions in Gram-positive bacteria. Preprint: https://www.biorxiv.org/content/10.1101/2022.12.23.521747v1.
Straume D, Piechowiak KW, Kjos M, Håvarstein LS (2021) Class A PBPs: it is time to rethink traditional paradigms. Mol Microbiol. doi: https://doi.org/10.1111/mmi.14714
Kranjec C*, Morales-Angeles D*, Mårli MT, Fernandez L, Garcia P, Kjos M*, Diep DB*. (2021) Staphylococcal Biofilms: Challenges and novel therapeutic perspectives. Antibiotics. 10(2):131. https://doi.org/10.3390/antibiotics10020131
Fergestad M, Stamsås GA, Morales-Angeles D, Salehian Z, Wasteson Y, Kjos M (2020) PBP2A provides variable levels of protection towards different β-lactams in Staphylococcus aureus RN4220. Microbiol Open. https://doi.org/10.1002/mbo3.1057
Straume D, Piechowiak KW, Olsen S, Stamsås GA, Berg KH, Kjos M, Heggenhougen MV, Alcorlo M, Hermoso J and Håvarstein LS. Class A PBPs have a distinct and unique role in the construction of the pneumococcal cell wall. Proc Natl Acad Sci U S A. doi.org/10.1073/pnas.1917820117. Preprint available at: https://www.biorxiv.org/content/10.1101/665463v1.
Genetic tools
Menestreau M, Frostegård Å, Kjos M. Strain-specific challenges in applying CRISPR/Cas9-based genome editing in the novel genus Stutzerimonas (2026) J Microbiol Methods. 107478 https://doi.org/10.1016/j.mimet.2026.107478.
Miah R, Johannessen M, Kjos M, Lentz C (2025) A programmable, selection-free CRISPR interference system in Staphylococcus aureus for long-term host interaction studies. iScience.113420. doi.org/10.1016/j.isci.2025.113420.
Miah R, Johannessen M, Kjos M, Lentz CS (2024) Development of an inducer-free, virulence gene promoter controlled, and fluorescent reporter labelled CRISPR interference system in Staphylococcus aureus. Microbiol Spectr. In press. doi.org/10.1128/spectrum.00602-24
Liu X*, de Bakker V*, Heggenhougen MV*, Frøynes Heidal A, Mårli MT, Porcellato D, Veening JW, Kjos M (2024). Genome-wide CRISPRi screens for high-throughput fitness quantification and identification of determinants for dalbavancin susceptibility in Staphylococcus aureus. mSystems. doi.org/10.1128/msystems.01289-23
van Raaphorst R, Kjos M, Veening JW (2019) BactMAP: an R package for integrating, analyzing and visualizing bacterial microscopy data. Mol Microbiol. Preprint available at: https://www.biorxiv.org/content/10.1101/728782v1
Myrbråten I, Wiull K, Straume D, Salehian Z, Håvarstein LS, Mathiesen G, Kjos M (2019) CRISPR interference for rapid knockdown of essential cell cycle genes in Lactobacillus plantarum. mSphere. 4(2):e00007-19. Editor's pick.
Kjos M. Transcriptional knockdown in pneumococci using CRISPR interference (2019) In: Streptococcus pneumoniae. Methods and Protocols (Iovino F, eds.), Methods in Molecular Biology Springer Protocols, Germany. 1968:89-98. doi: 10.1007/978-1-4939-9199-0_8.
Kjos M. Construction of fluorescent pneumococci for in vivo imaging and labelling of the chromosome (2019) In: Streptococcus pneumoniae. Methods and Protocols (Iovino F, eds.), Methods in Molecular Biology Springer Protocols, Germany. 1968:41-51. doi: 10.1007/978-1-4939-9199-0_4.
Stamsås GA*, Myrbråten I*, Straume D, Salehian Z, Veening JW, Håvarstein LS, Kjos M (2018) CozEa and CozEb play overlapping and essential roles in controlling cell division in Staphylococcus aureus. Mol Microbiol. 109(5):615-632. Preprint available at: https://www.biorxiv.org/content/early/2018/05/23/256560. Se også: Cover
Kjos M, Aprianto R, Fernandes VE, Andrew PW, van Strijp JAG, Nijland R, Veening JW (2015) Bright fluorescent Streptococcus pneumoniae for live cell imaging of host-pathogen interactions. J Bacteriol. 197:807-18.
Stamsås GA, Håvarstein LS, Straume D (2013) CHiC, a new tandem affinity tag for the protein purification toolbox. J Microbiol Methods. 2013 Jan;92(1):59-63. doi: 10.1016/j.mimet.2012.11.003.
Others
Menestreau M, Milligan DA, Sennett L, Bergaust LL, Bakken LR, Rowley G, Kjos M, Shapleigh JP, Frostegård Å (2026) Distinct denitrification phenotypes in closely related bacteria: clues to understanding variations in nitrite accumulation among Stutzerimonas strains. Environ Microbiol. doi.org/10.1111/1462-2920.70275
Wiull K, Kjos M, Eijsink VG, Mathiesen G (2025) Unveiling an inverse relationship between fitness and secretion efficiency in a Gram-positive bacterium. PNAS Nexus. pgaf131. doi.org/10.1093/pnasnexus/pgaf131
Kristensen SS, Diep DB, Mathiesen G*, Kjos M* (2023). The role of site-2-proteases in bacteria: A review of the physiology, virulence and therapeutic potential. microLife. 4: uqad025. doi.org/10.1093/femsml/uqad025.
Cacace E, Kim V, Knopp M, Tietgen M, Brauer-Nikonow A, Inecik K, Mateus A, Milanese A, Mårli MT, Mitosch K, Selkrig J, Brochado AR, Kuipers O, Kjos M, Zeller G, Savitski M, Göttig S, Huber W, Typas A (2023) High-throughput profiling of drug interactions in Gram-positive bacteria. Preprint: https://www.biorxiv.org/content/10.1101/2022.12.23.521747v1.
Gao Y, Kjos M, Arntzen MØ, Bakken LR, Frostegård Å (2023) Denitrification by bradyrhizobia under feast and famine and the role of the bc1 complex in securing electrons for N2O reduction. Appl Environ Microbiol. https://doi.org/10.1128/aem.01745-22.
Lycus P, Soriano-Laguna M, Kjos M, Richardson D, Gates A, Milligan DA, Frostegård Å, Bergaust L, Bakken LR (2018) A bet-hedging strategy of denitrifying bacteria curtails their release of N2O. Proc Natl Acad Sci U S A. 115(46):11820-11825.
Kjos M, Straume D, Nes IF, Diep DB (2009) Transposition of IS10R in Lactococcus lactis. J Appl Microbiol 106(1):288-95.
Eldholm V, Straume D, Brynildsrud OB (2026). Assessing sequencing-based pathogen surveillance of a recreational swimming area in Oslo, Norway. Access Microbiology. 8. 001062. doi.org/10.1099/acmi.0.001062.v3
Group members
Master students
Ingrid Helene Nærstad
Martine Edvardsen
Projects
- BacPress - improving high pressure processing (HPP) of sensitive high-value foods to prolong shelf life and food quality.
- Disentangling penicillin resistance and compensatory adaption in pneumococci by combining genomics and molecular microbiology
- PrevEco- OneHealth approach to sustainable prevention and treatment of infectious diseases
- BOB - The role of bacteriocins in shaping oral biofilms
- HoliCow - A holistic approach to an old problem: deciphering complex host-microbiome-pathogen relationships in bovine mastitis
- DISRUPT - nye strategiar for å motvirke biofilminfeksjonar
- Enterococcal RseP as a target for new diagnostics and antibiotics
- Identification of cell cycle proteins in Staphylococcus aureus