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Antibiotic resistance in bacteria is a global public health threat. To understand how the evolution of antibiotic susceptibility is affected by environmental conditions and prior evolutionary history, we worked with populations from the Long-Term Evolution Experiment (LTEE) with Escherichia coli. These populations previously evolved independently for 50,000 generations in an environment without antibiotics, making them an ideal system for studying the effect of evolutionary history on adaptation to new selective pressures. We further evolved five of the LTEE populations, as well as their shared ancestor, under either carbon- or nitrogen-limited conditions and then tested intrinsic resistance to four antibiotics. Evolution under elemental limitation did not have a significant impact on resistance to any of the tested antibiotics. However, some LTEE populations did have higher resistance than other populations. Susceptibility also varied within one population, which had the lowest level of resistance to all four antibiotics. We hypothesized that resistance levels might differ between two clades of bacteria that have coexisted within this population for more than 40,000 generations. Interestingly, although antibiotic susceptibility varied within the population, there was no consistent difference between clades. Instead, one particular clone isolated from the population exhibited higher resistance than the other clones sampled. These findings indicate that antibiotic resistance can vary both within and between experimentally evolved populations, even in the absence of direct selection on resistance. Our results also show that measured levels of susceptibility may depend on stochastic sampling effects during isolation of clones.IMPORTANCEAntibiotic resistance is one of the most pressing health challenges worldwide, and understanding how bacteria evolve resistance, even when not directly exposed to antibiotics, is critical for managing and predicting emerging threats. Our study leverages the unique Long-Term Evolution Experiment with Escherichia coli to show that both the evolutionary history of bacterial populations and random variation among individual clones can significantly influence intrinsic antibiotic susceptibility. Our results also suggest that elemental limitation, while a critical environmental variable, may not be an important driver of intrinsic antibiotic susceptibility, at least over short time frames.

In February and March 2025, the American Society for Microbiology (ASM)'s Council on Microbial Sciences (COMS) hosted a series of virtual retreats to integrate the communities of Clinical Infections and Vaccines (CIV) and Clinical and Public Health Microbiology (CPHM) under the umbrella of the new scientific unit ASM Health. Representatives from these two communities invited experts and ASM members to reflect on the current state of the science, identify challenges hindering scientific advancements, and propose recommendations for overcoming these challenges. Sessions focused on progress in (i) vaccines, therapeutics, diagnostics, and global pathogen surveillance; (ii) improving data integration and cross-agency sharing; (iii) supporting the microbial health workforce; and (iv) gaining public support and confidence in microbiology. Four major recommendations emerged for ASM Health. First, increased support for microbiological science is crucial to ensure the advancement of vaccines, therapeutics, diagnostics, and global pathogen surveillance to mitigate infectious disease threats. Second, enhancement of data integration and sharing in real-time via information systems will facilitate a deeper understanding of disease epidemiology. Third, modern approaches to recruitment, career path, and profession awareness, and dynamic training programs are necessary to achieve microbial workforce balance. Fourth, microbiologists will benefit from outreach training and resources designed to restore public trust in an environment that questions science and evidence-based approaches. ASM is uniquely positioned to take a pivotal leadership role to develop these concepts into specific programs, as well as to enhance partnerships across the spectrum to innovate in funding, both for scientific research and public health.

Utilizing treatment strategies based on collateral sensitivity (CS) represents a promising approach to suppressing antibiotic resistance. Although the mechanism of CS between numerous drugs has been researched, the mechanism of CS between tigecycline and colistin remains unclear. Therefore, the purpose of our research is to investigate the possible mechanism by which tigecycline affects colistin CS in the Enterobacter cloacae complex. Tigecycline induction significantly reduced the minimum inhibitory concentration of carbapenem-resistant Enterobacter cloacae complex (CRECC) to colistin, and sequencing revealed a single-base deletion at the RamR binding site. Complementation experiments demonstrated that deletion of the RamR binding site increased the resistance of CRECC417 to colistin and tigecycline by 2-fold and 4-fold, respectively. Transcriptomic comparison analysis of strains before and after CRECC417 induction revealed a total of 1,977 genes with significant differences in expression. Genes associated with carbohydrate, amino acid, and inorganic ion metabolism were the most highly enriched. Furthermore, the observed increase in colistin susceptibility in CRECC417R can be attributed to the inhibition of quorum sensing and biofilm formation pathways, as well as increased expression levels of genes associated with lipopolysaccharide biosynthesis and modification.IMPORTANCEDue to the overuse of antibiotics, antimicrobial resistance (AMR) has become a serious threat to global public health. Dosage regimens based on bacterial CS can reduce antibiotic use without reducing efficacy, thereby reducing antibiotic-related toxicity risks, expanding the scope of antibiotic application, and limiting the development of antibiotic resistance. In this study, we analyzed the drug resistance mutations and global transcriptional changes in CRECC after tigecycline induction through genomics and transcriptomics. Our study showed that tigecycline exposure significantly inhibited quorum sensing pathways and biofilm formation. There were significant changes in the transcriptional levels of genes related to cell membrane lipopolysaccharide synthesis and modification, but no mutations were found in genes related to colistin resistance. These findings provide valuable insights for further investigation into the CS between tigecycline and colistin.

Invasive infections caused by Streptococcus pyogenes (iGAS) have increased in Europe over the past decade, with a marked upsurge after the COVID-19 pandemic. Here, we examined whether the increase in iGAS infections in Norway was associated with the spread of variants that had acquired new virulence factors. A collection of 1,163 iGAS isolates submitted to the National Reference Laboratory between January 2017 and April 2023, representing 87% of all cases recorded by the Norwegian Surveillance System for Infectious Diseases, was analyzed by whole genome sequencing. Resistance to one or more antibiotics was found in 15.6% of the isolates: 14.1% were resistant to tetracycline, 6.4% to erythromycin, and 4.0% to clindamycin. Resistance to other antibiotics was < 1%. The dominating emm types were emm1 (30.9%), emm12 (13.8%), emm89 (9.3%), emm28 (8.3%), emm4 (6.0%), and emm87 (4.5%), with the remaining isolates belonging to 55 other emm types; 62.3% of emm1 belonged to the hypervirulent lineage M1_UK. Genetic characterization of the virulence factors of the dominant six emm types demonstrated extensive competition between related phages, leading to phage switching and interplay between integration and excision of temperate phages carrying virulence factors. Bacteriophages carrying virulence factors speC and spd1 displayed a particularly high turnover rate, with several pairs of otherwise genomically identical isolates exhibiting different phage-carrying status. We identified and characterized four new speC and spd1-carrying phages. The rapid turnover pattern of these, as well as other phages carrying superantigens and DNAses suggests an important role in pathogenesis.IMPORTANCEThis analysis of 1,163 iGAS isolates collected between January 2017 and April 2023 aimed to map virulence factor content to understand the observed increased incidence of iGAS in Norway. Our findings indicate that 15.6% of the isolates were resistant to at least one antibiotic, with tetracycline resistance being the most common. The dominant emm types were emm1, emm4, emm12, emm28, emm87, and emm89, which together accounted for 72.7% of the isolates. The study highlights the dynamic nature of virulence factor-carrying temperate phages, particularly the ones carrying speC and spd1, which frequently integrate and excise within emm types. Four previously unseen phages carrying speC and spd1 were identified and characterized. This research underscores the complexity of iGAS epidemiology and the need for continuous surveillance to understand the evolving landscape of bacterial virulence factors, antibiotic resistance, and circulating emm types.

Nicholas A. Wood works in the field of biophysics with an emphasis on in situ protein structures in microbiological systems. In this mSphere of Influence article, he reflects on the power and limitations of AlphaFold, open questions in structural biology, and the cross-disciplinary potential of microbiological training.

Laura Veschetti works in the field of microbial genomics and adaptation. In this mSphere of Influence article, she reflects on how the work of Marvig et al. on within-host evolution of Pseudomonas aeruginosa, together with long-term evolution experiments by Lenski and colleagues, reshaped her understanding of microbial identity by framing variability as a defining biological feature rather than an exception. Drawing on concepts from population genomics, pangenomics, and regulatory heterogeneity, she discusses how focusing on evolutionary processes rather than static reference genomes has influenced her approach to studying bacterial adaptation.

The annual fall meeting for the Theobald Smith Society (TSS), the New Jersey Branch of the American Society for Microbiology (ASM), took place in November 2025 at Cooper Medical School of Rowan University in Camden, New Jersey. A total of 72 branch members from across New Jersey participated, including undergraduate and graduate students, postdoctoral trainees, faculty, and professionals from government and industry. This report highlights the scope and diversity of research carried out by TSS members and celebrates their impactful discoveries.

Forest soils harbor a diverse array of bacteria that play a crucial role in nutrient cycling. However, the differential effects of coniferous versus mixed conifer-broadleaf forests on the distribution of both abundant and rare bacterial taxa remain poorly understood. In this study, we integrated 16S rRNA gene amplicon sequencing with metagenomic shotgun sequencing to conduct a comparative analysis of soil bacterial communities in a conifer plantation and an adjacent mixed conifer-broadleaf forest, specifically examining their community structure, assembly mechanisms, co-occurrence networks, and functional potential. Both abundant and rare taxa showed significant differences in community composition between the two forest types. Soil pH and organic matter content significantly influenced the total and abundant bacterial communities, while available phosphorus and potassium were key determinants of rare community composition. Co-occurrence network analysis revealed that abundant communities formed highly clustered, simplified networks, contrasting with more fragmented and keystone-rich networks in rare communities. Null model analyses indicated that community assembly was largely driven by stochastic processes, with ecological drift accounting for about 80% of the variation in total and rare communities, and dispersal limitation explaining nearly 72% of the variation in abundant communities. Functional predictions indicated that bacterial communities in mixed forests were enriched in pathways linked to glycosylation, carbohydrate degradation, and nitrogen fixation, while coniferous forests favored pathways related to autophagy, signaling, and stress responses. This study highlights the complementary roles of abundant and rare bacterial taxa in forest soil ecosystems and underscores the importance of preserving mixed forests to sustain microbial functional diversity.IMPORTANCEForest soils host a complex web of common and rare bacteria that quietly regulate nutrient cycles. By comparing pure conifer stands with mixed conifer-broadleaf forests, we found that abundant species underpin essential functions while rarer microbes fill specialized niches. Acidity and nutrients strongly influence which bacteria thrive; mixed stands favored microbes that break down carbohydrates and fix nitrogen, whereas conifer soils supported organisms adapted to stress and nutrient-poor conditions. These findings emphasize the importance of preserving diverse forest ecosystems for soil health, carbon storage, and effective forest management strategies in climate change adaptation.

Rift Valley fever virus (RVFV) is a zoonotic arbovirus that infects and causes disease in both humans and livestock. In humans, RVFV infection mostly results in febrile illness but has the potential to cause severe complications such as hepatitis and encephalitis. There are currently no licensed vaccines for human use; however, several candidates have been shown to be safe and immunogenic in pre-clinical studies. However, there remain gaps in our knowledge, including the duration of immunity and efficacy of protection from divergent disease manifestations over time. This pilot study investigated the duration of immunity following low-dose vaccination with live-attenuated RVFV ΔNSsΔNSm in two murine models with divergent RVF disease manifestations. Following percutaneous infection with wild-type (WT) RVFV, C57BL/6 mice readily succumb to fulminant hepatitis 3 to 5 days post-infection (dpi). In contrast, CC057/Unc mice from the Collaborative Cross Resource experience self-limiting liver disease and develop late-onset encephalitis. Following ΔNSsΔNSm vaccination, both humoral and cellular immunity decreased over time but were comparable between the two mouse strains at 1 and 3 months. Vaccinated mice were challenged with WT RVFV (ZH501) 6 months later, and 83% of C57BL/6 mice and 100% of CC057/Unc mice survived. Taken together, this study highlights the potential of ΔNSsΔNSm to provide durable protection against lethal RVF hepatitis and encephalitis.IMPORTANCERift Valley fever virus (RVFV) causes both morbidity and mortality in endemic areas of Africa and the Middle East; however, no vaccines are available for humans. Pre-clinical studies have investigated the safety and immunogenicity of ΔNSsΔNSm vaccine (a live-attenuated version of RVFV that has two virulence factors deleted), but the duration of immunity and protection in the context of divergent RVF disease manifestations was unknown. This pilot study demonstrated that a single, low dose of ΔNSsΔNSm provided substantial protection to mice from RVF hepatitis and encephalitis 6 months post-vaccination. These pre-clinical data could support further development of a live-attenuated vaccine based on this platform for human use.