Biology subjects

Okstad, O. A.

Publications and source records attributed to Okstad, O. A..

6 recordsLinked to original sources

bioRxiv2026

Variable zinc concentrations among commercially available Mueller-Hinton Broth brands affects SIR interpretations during broth microdilution in vitro antimicrobial susceptibility testing with the novel metallo-beta-lactamase inhibitor APC148

The well-known discrepancy between the in vitro and in vivo efficacy of {beta}-lactam antibiotics in metallo-{beta}-lactamase (MBL) containing Gram-negative bacteria has during recent years been found to be at least partially explained by zinc levels at infection sites being much lower than those found in conventional cation-adjusted Mueller-Hinton Broth (caMHB) media used for in vitro susceptibility testing. Previous studies have also demonstrated that a high variability exists with respect to zinc content in caMHB from different manufacturers, potentially leading to differences in SIR interpretations for {beta}-lactam antibiotics with MBL-carrying isolates, depending on the brand of caMHB used for testing. APC148 is a zinc-chelating compound acting as an inhibitor of MBL enzymes and is currently undergoing phase one in clinical trials. In this study, ten clinical isolates of Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii harbouring MBLs (NDM, n = 6; VIM, n = 4; IMP, n = 1) were tested in a broth microdilution assay with meropenem and APC148, employing caMHB of various brands. One K. pneumoniae strain carrying only a serine-{beta}-lactamase (KPC-2) was included as control. Antimicrobial susceptibility testing (AST) by broth microdilution was performed according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MICs of meropenem alone and in combination with inhibitors were tested in four cation-adjusted Mueller Hinton II (caMHB).The four caMHBs used were analysed by ICP-MS/MS and found to have highly vaiable zinc content (in the range 0.4 to 1.9 {micro}g/mL, corresponding to 5.6 to 29.4 {micro}M). At 16{micro}g/ml APC148 lowered the MIC in nearly all strains and in caMHBs from all manufacturers. At lower concentrations of APC148 (4 or 8 {micro}g/mL), this MIC reduction could however only be retained when the zinc concentration in the broth was low, indicating that higher concentration of inhibitor is needed during in vitro Mic testing when using caMHB from certain manufacturers. The present work clearly shows that not taking the zinc concentration of the caMHB used into consideration when estimating MIC performance of compounds functioning through interactions with zinc may be a considerable source of error, and specifically when investigating potential inhibitors of metallo-{beta}-lactamase (MBL) enzymes. The present work supports the call for standardising zinc content in caMHB to be used for this purpose, to ensure that MIC results for drug combinations involving the use of zinc-chelating compounds are consistent and reproducible across laboratories.

microbiology↗

bioRxiv2025

Longitudinal analysis of the hand microbiome in response to chlorine-based antiseptic use during a military field exercise

Hand hygiene is essential for infection control, yet the impact of frequent antiseptic use on the skin microbiome, which is crucial for skin barrier function and pathogen exclusion, remains underexplored, especially in field conditions. In high-risk military settings, there is a need for safe, multipurpose antiseptics that avoid the drawbacks of alcohol-based options, including skin irritation, flammability, and unsuitability for wound application. We conducted a longitudinal study during the Norwegian-led military exercise Cold Response 2022 to assess the effects of repeated use of stabilized hypochlorous acid, a non-alcoholic antiseptic, on the hand microbiome of soldiers in a field environment. Participants used either the chlorine-based antiseptic (n = 20) or standard hygiene practices, mainly alcohol-based sanitizers (n = 19), for 10 days. Skin swabs from hands and untreated forearms were collected at baseline, post-intervention, and three weeks after discontinuation, and analyzed using 16S rRNA sequencing. Overall, our data revealed that field exposure accounted for more variation in bacterial composition than antiseptic use. When comparing alpha and beta diversity trajectories between the two antiseptic groups, there was minimal divergence during active field use, but a significant post-treatment increase in alpha diversity associated with the use of chlorine-based antiseptic. In contrast, untreated forearms showed no such group-level differences. These findings suggest that antiseptic-driven microbiome shifts are most apparent during recovery, with non-alcoholic formulations supporting faster recolonization after treatment. Stabilized hypochlorous acid represents a promising alternative to standard alcohol-based antiseptics for military personnel. IMPORTANCEEffective hand hygiene reduces pathogen transmission, but its influence on the skin microbiome has rarely been studied. Our research emphasizes the importance of longitudinal assessments by identifying greater antiseptic-driven differences occurring after cessation of treatment than during repeated use. Service members frequently use antiseptics in challenging environments, highlighting the operational need for a non-alcoholic, multipurpose product that can be safely used on both intact skin and wounds. Our findings suggest that a chlorine-based non-alcoholic antiseptic permits faster recovery of bacterial diversity after perturbation, informing product selection and hygiene policies in defense and other high-risk settings.

microbiology↗

bioRxiv2024

Skin bacterial community dynamics of hands and forearms before and after military field exercise

The human skin microbiome is crucial for skin health and immunity, especially in the context of extreme conditions faced by military personnel. Soldiers encounter unique stressors and hygienic challenges that can impact the microbial composition of their skin during field exercises and in regular occupational settings. In this study, we aimed to investigate the impact of a military field exercise on the diversity and composition of the skin bacterial microbiota using 16S rRNA sequencing. We conducted a longitudinal study during the NATO exercise Cold Response 2022, involving Norwegian soldiers (n = 19) engaged in outdoor training operations. Skin swabs were taken from soldiers hands and forearms directly before and after the 10-day winter field exercise, and following a 3-week post-exercise leave. Our results reveal hand and forearm-specific shifts in bacterial populations associated with the exercise, likely influenced by environmental exposure, reduced hygiene, and heightened social contact. Alpha diversity increased on forearms while remaining stable on hands, which appeared more resilient to perturbations. Both sites exhibited temporal changes in composition, with soil- and water-associated bacteria enriched post-exercise; most being transient on hands but more sustained on forearms. The soldiers microbiomes became more similar during the exercise, followed by divergence in the leave period. Neither skin site returned to original composition at follow-up, indicating that field exercises may have lasting effects on the microbiome. Our findings highlight the impact of outdoor exposure on microbial communities and suggest that resilience and stability differ between skin sites. ImportanceOptimizing soldier health and resilience is critical for maintaining military readiness and operational effectiveness. The skin, as the bodys first line of defense, is subjected to numerous challenges in military environments. Unique environmental and hygiene challenges can disrupt the skin microbiome and increase susceptibility to skin and soft tissue infections. This longitudinal research provides valuable insights into the effects of military service on the bacterial dynamics of the skin microbiome, but can also inform hygiene management and disease prevention in comparable situations.

microbiology↗

bioRxiv2020

Adaptation of Bacillus thuringiensis to plant colonisation affects differentiation and toxicity

Bacillus cereus group (Bacillus cereus sensu lato) has a diverse ecology, including various species that are vertebrate or invertebrate pathogens. Few isolates from the B. cereus group have however been demonstrated to benefit plant growth. Therefore, it is crucial to explore how bacterial development and toxicity evolves during plant colonization. Herein, we investigated Bacillus thuringiensis (Cry-) adaptation to the colonization of Arabidopsis thaliana roots, and monitored changes in cellular differentiation in experimentally evolved isolates. Isolates from two populations displayed improved iterative ecesis on roots and increased toxicity against insect larvae. Molecular dissection and recreation of a causative mutation revealed the importance of a non-sense mutation in the rho transcription terminator gene. Transcriptome analysis revealed how Rho impacts various B. thuringiensis genes involved in carbohydrate metabolism and virulence. Our work suggests that evolved multicellular aggregates have a fitness advantage over single cells when colonizing plants, creating a trade-off between swimming and multicellularity in evolved lineages, in addition to unrelated alterations in pathogenicity. ImportanceBiologicals-based plant protection relies on the use of safe microbial strains. During application of biologicals to the rhizosphere, microbes adapt to the niche, including genetic mutations shaping the physiology of the cells. Here, the experimental evolution of Bacillus thuringiensis lacking the insecticide crystal toxins was examined on the plant root to reveal how adaptation shapes the differentiation of this bacterium. Interestingly, evolution of certain linages led to increased emetic toxin production, hemolysis and insect larvae pathogenesis in B. thuringiensis driven by transcriptional rewiring. Further, our detailed study reveals how inactivation of the transcription termination protein Rho promotes aggregation on the plant root in addition to altered differentiation and pathogenesis in B. thuringiensis.

microbiology↗

bioRxiv2020

MogR is a ubiquitous transcriptional repressor affecting motility, biofilm formation and virulence in the Bacillus cereus group

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.

microbiology↗

bioRxiv2017

Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis)

Environmentally Transmitted Diseases Are Comparatively Poorly Understood And Managed, And Their Ecology Is Particularly Understudied. Here We Identify Challenges Of Studying Environmental Transmission And Persistence With A Six-Sided Interdisciplinary Review Of The Biology Of Anthrax (Bacillus Anthracis). Anthrax Is A Zoonotic Disease Capable Of Maintaining Infectious Spore Banks In Soil For Decades (Or Even Potentially Centuries), And The Mechanisms Of Its Environmental Persistence Have Been The Topic Of Significant Research And Controversy. Where Anthrax Is Endemic, It Plays An Important Ecological Role, Shaping The Dynamics Of Entire Herbivore Communities. The Complex Eco-Epidemiology Of Anthrax, And The Mysterious Biology Of Bacillus Anthracis During Its Environmental Stage, Have Necessitated An Interdisciplinary Approach To Pathogen Research. Here, We Illustrate Different Disciplinary Perspectives Through Key Advances Made By Researchers Working In Etosha National Park, A Long-Term Ecological Research Site In Namibia That Has Exemplified The Complexities Of AnthraxS Enzootic Process Over Decades Of Surveillance. In Etosha, The Role Of Scavengers And Alternate Routes (Waterborne Transmission And Flies) Has Proved Unimportant, Relative To The Long-Term Persistence Of Anthrax Spores In Soil And Their Infection Of Herbivore Hosts. Carcass Deposition Facilitates Green-Ups Of Vegetation To Attract Herbivores, Potentially Facilitated By Anthrax Spores Role In The Rhizosphere. The Underlying Seasonal Pattern Of Vegetation, And Herbivores Immune And Behavioral Responses To Anthrax Risk, Interact To Produce Regular \"Anthrax Seasons\" That Appear To Be A Stable Feature Of The Etosha Ecosystem. Through The Lens Of Microbiologists, Geneticists, Immunologists, Ecologists, Epidemiologists, And Clinicians, We Discuss How Anthrax Dynamics Are Shaped At The Smallest Scale By Population Genetics And Interactions Within The Bacterial Communities Up To The Broadest Scales Of Ecosystem Structure. We Illustrate The Benefits And Challenges Of This Interdisciplinary Approach To Disease Ecology, And Suggest Ways Anthrax Might Offer Insights Into The Biology Of Other Important Pathogens. Bacillus Anthracis, And The More Recently Emerged Bacillus Cereus Biovar Anthracis, Share Key Features With Other Environmentally-Transmitted Pathogens, Including Several Zoonoses And Panzootics Of Special Interest For Global Health And Conservation Efforts. Understanding The Dynamics Of Anthrax, And Developing Interdisciplinary Research Programs That Explore Environmental Persistence, Is A Critical Step Forward For Understanding These Emerging Threats.

ecology↗