Polymyxin B 10,000units/g / Bacitracin 500units/g eye ointment

Antimicrobial resistance (AMR) disseminates throughout the soil–plant continuum via complex microbial interactions. Plants shape root- and leaf-associated microbiomes that sustain plant health; however, soil-borne legacies—enriched with antibiotic-producing microbes and resistance genes—govern AMR dynamics across agroecosystems. Using 16S rRNA gene sequencing, shotgun metagenomics, and high-throughput quantitative PCR, we profiled antibiotic resistance genes (ARGs), mobile genetic elements, and virulence factor genes across bulk soil, rhizosphere, phyllosphere, and root endosphere within soil–tomato and soil–strawberry continua. Recurrent bacterial wilt amplified the resistome, particularly polypeptide resistance genes, thereby establishing the rhizosphere as a major hotspot of ARG accumulation. Multidrug-resistant Ralstonia solanacearum (R. solanacearum) strains acted as major ARG reservoirs, harboring resistance determinants on both chromosomes and megaplasmids. Collectively, these findings demonstrate that pathogen-driven restructuring of the plant microbiome accelerates ARG dissemination, establishing soil-borne diseases as critical amplifiers of AMR across agricultural ecosystems. The spread of antibiotic resistance genes (ARGs) from soils to crops, livestock, and human environments poses a critical challenge to global health within the One Health framework [1, 2]. Research and policy focus on human-centered systems such as hospitals, yet food systems—especially plant-based production—remain underexplored despite their important role in antimicrobial resistance (AMR) emergence and dissemination [3]. Soils serve as reservoirs of ARGs and human pathogens [1]. Agricultural intensification, expansion of arable land, and the increasing prevalence of “superbugs” underscore the urgency of understanding AMR dynamics across soil–plant continua [4]. ARG risk assessment requires evaluating gene types, abundance, horizontal transfer potential (HGT), and host pathogenicity [5]. The co-occurrence of ARGs with virulence factor genes (VFGs) and mobile genetic elements (MGEs) amplifies microbial risks. Plants resist phytopathogens through a “cry-for-help” strategy that recruits root microbiota to form disease-suppressive communities, also known as soil-borne legacies. Disease-suppressive soils allow plants to thrive despite phytopathogen presence [6]. Mechanisms of disease suppression include: (i) beneficial microbes occupying ecological niches and outcompeting pathogens for resources and space, thereby limiting their growth and spread; (ii) production of antimicrobial compounds (e.g., antibiotics) that inhibit proliferation, disrupt cellular integrity, and reduce virulence; and (iii) formation of symbiotic associations with plant roots, which, through signaling molecules or metabolites, induce systemic resistance. These processes activate host defenses, enabling rapid responses to pathogen invasion and limiting disease progression [7]. This study focuses on the ecological consequences of antimicrobial production (Mechanism ii). Antagonistic interactions among soil microbes frequently result from antibiotic production by specific strains in response to phytopathogens [8]. Consequently, an evolutionary “arms race” between plants and phytopathogens, together with antagonistic interactions between beneficial and pathogenic microbes, may accelerate AMR in plant-associated microbiomes, including bulk soil, rhizosphere, root endosphere, and phyllosphere [9, 10]. The extensive use of antibiotics and biocontrol agents in agriculture has further elevated resistance levels in phytopathogens [11]. Such intrinsic resistance traits allow selective isolation of Ralstonia solanacearum (R. solanacearum) in antibiotic-containing media. Moreover, its presence may indirectly enhance the AMR potential of neighboring microbial communities, including other pathogens that acquire ARGs [12]. However, the extent to which increasing resistance in R. solanacearum shapes the broader development of AMR across the soil–plant continuum remains unclear. This study investigates bacterial wilt caused by R. solanacearum, a pathogen inherently resistant to multiple antibiotics. We analyzed a tomato greenhouse with a long history of bacterial wilt outbreaks, which later spread to strawberry crops, indicating a persistent soil-borne legacy. We hypothesized that bacterial wilt caused by R. solanacearum imposes selective pressures that progressively enrich specific ARGs, with effects extending beyond the soil–tomato continuum to subsequent systems such as the soil–strawberry continuum. The objectives of this study were to: (i) monitor changes in the resistome and microbiome during R. solanacearum infection, (ii) determine whether ARGs are transferred to a subsequent soil–strawberry continuum, and (iii) assess exposure risks by identifying pathogens carrying both ARGs and MGEs (Figure 1A). Using high-throughput quantitative PCR (HT-qPCR) and shotgun metagenomics, we profiled ARGs, VFGs, and MGEs across soil–plant interfaces to clarify the ecological impact of bacterial wilt on AMR dissemination in agricultural systems. Microbial community analyses showed that invasion by R. solanacearum markedly reduced bacterial richness and diversity, causing pronounced shifts in rhizosphere, phyllosphere, and root endosphere communities (Figure S1). Dominant taxa—including Gammaproteobacteria, Alphaproteobacteria, Bacilli, and Actinobacteria—exhibited infection-dependent shifts in relative abundance (Figures S1 and S2). These findings highlight the disruptive effect of bacterial wilt on the stability of plant-associated microbial communities. Reduced diversity diminishes ecological buffering capacity, enabling pathogen-driven selection to reshape community composition. Even in asymptomatic plants, phytopathogen presence triggers subtle antagonistic interactions, recruiting beneficial microbes that suppress disease. This microbial “arms race” inadvertently enriches antibiotic-producing microbes and, consequently, ARGs (Figures S3 and S4). Thus, pathogen-driven microbiome restructuring emerges as a key ecological mechanism driving resistome amplification. Previous studies have shown that healthy plant microbiomes harbor abundant antibiotic biosynthesis genes, such as polyketide synthases and nonribosomal peptide synthetases, suggesting that microbial antibiosis plays a central role in shaping soil-borne legacies [13]. Metagenomic profiling identified 1334 ARG subtypes across 29 categories, with richness highest in healthy plants, followed by infected and dead plants (Tables S1 and S2). The resistome was primarily dominated by multidrug, bacitracin, polymyxin, and β-lactam resistance genes (Figure 1B–D). In all conditions, the rhizosphere consistently exhibited the highest abundance and diversity of ARGs, MGEs, and VFGs, confirming its role as a hotspot for resistance dissemination (Figures S5–S7). These results suggest that although beneficial microbes suppress disease and support plant health, they simultaneously impose strong antibiotic selection, enriching ARG reservoirs (Figures S8–S10). By contrast, phytopathogen infection promoted MGE mobilization and enrichment of clinically relevant ARGs, indicating that pathogen-induced stress enhances HGT (Figure S11). Within the soil–plant continuum, ARGs spread through three interconnected pathways: (i) atmospheric deposition and uptake via stomata or root wounds; (ii) dominance of antibiotic-resistant bacteria in the rhizosphere, followed by HGT to endophytes migrating through the vascular system; and (iii) transfer via soil fauna such as earthworms, which recycle ARGs through ingestion and excretion [14]. These processes establish bidirectional gene flow between soil bacteria and endophytes, enabling ARGs to enter the food chain and ultimately pose risks to human health. Collectively, these findings support the view that both resistant and diseased systems expand the resistome, albeit through distinct ecological mechanisms. Antibiotic susceptibility testing further revealed variable resistance to polymyxin B, bacitracin, chloramphenicol, penicillin, tetracycline, and actinomycin D (Figure S12). Isolation of highly pathogenic, multidrug-resistant R. solanacearum strains confirmed its role as a major reservoir of ARGs. Genomic meta-analysis revealed that both chromosomal and plasmid elements of R. solanacearum encode resistance to a wide range of antibiotic classes, including polymyxins, bacitracin, macrolides, tetracyclines, fluoroquinolones, aminocoumarins, monobactams, elfamycins, and aminoglycosides (Table S3). Combined genotypic and phenotypic resistance analyses highlight a direct pathway by which pathogen-driven selection amplifies clinically relevant traits in the soil–plant continuum, posing concrete food safety risks. Multi-model integration indicates that R. solanacearum drives ARG enrichment through both direct and indirect ecological mechanisms, with MGEs acting as key mediators of mobilization (Figure S13). This study highlights the interconnected roles of pathogen pressure, microbial interactions, and HGT in shaping resistome dynamics in agricultural ecosystems. Analysis of the soil–strawberry continuum demonstrated that bacterial wilt legacies extended beyond the tomato system (Figure 1E,F). Strawberry plants cultivated in previously infected soils exhibited significantly higher ARG abundance and diversity in fruits compared to controls (Figures S14A and S15, Table S4). Both HT-qPCR and metagenomic sequencing confirmed that soil-borne legacies of bacterial wilt increase the potential for ARG translocation into plant tissues (Figure S16). Source tracking revealed that 66%–89% of ARGs in strawberry fruits originated from healthy tomato rhizospheres, indicating direct cross-species transfer (Figure 1G and Figure S14B). This evidence confirms that soil-borne legacies act as reservoirs that facilitate ARG migration between crops, thereby expanding the ecological footprint of bacterial wilt. Notably, even asymptomatic tomato rhizospheres acted as primary ARG donors, indicating that resistance risks persist despite the absence of visible disease. These findings have direct implications for food safety, as edible tissues can accumulate ARGs derived from past phytopathogen pressures. Although plant health reflects suppression of R. solanacearum, it does not eliminate continued pathogen-driven selection. Instead, the asymptomatic phase is characterized by intense, subclinical microbial warfare [13]. During a “cry for help” response, plants recruit beneficial microbes that produce antimicrobial compounds to suppress phytopathogens [15]. However, this process exerts strong selective pressure, enriching resistance traits in both phytopathogens and beneficial microbes. Under these conditions, HGT among phytopathogens, symbionts, and commensals is likely accelerated, promoting ARG accumulation on MGEs in the rhizosphere. Death of phytopathogens further facilitates ARG dissemination across the soil–plant continuum by releasing cellular contents, reshaping microbial communities, accelerating tissue decomposition, and enabling HGT [11, 16, 17]. The soil-borne legacy, also termed inhibitory soil memory, supports healthy plant growth while simultaneously driving ARG dissemination in the soil–strawberry continuum, likely due to the high abundance of antimicrobial-producing bacteria and multiple ARGs [18]. This effect is attributed to the enrichment of antimicrobial-producing bacteria, including Actinobacteria, Bacillus, Pseudomonas, and Lysobacter, which harbor biosynthetic gene clusters and ARGs. Together with Streptomyces, these microbes promote antibiotic biosynthesis and disease suppression, while also acting as ARG reservoirs [5, 13]. Positive correlations among ARGs, MGEs, and R. solanacearum indicate that bacterial wilt serves as a vehicle for ARG dissemination across the soil–plant continuum, posing serious risks to food safety and human health and highlighting the need for enhanced monitoring (Figures S11 and S17). Metagenome-assembled genome (MAG) analyses revealed that ARGs frequently co-localize with MGEs and VFGs in both pathogens (e.g., Escherichia coli, Klebsiella pneumoniae) and beneficial taxa (e.g., Bacillus, Pseudomonas) (Figure 2A, Tables S5–S10). Their co-occurrence on the same contigs indicates strong mobilization potential, facilitating HGT across microbial guilds. At the contig level, we identified multidrug, β-lactam, and aminoglycoside resistance genes physically linked to transposases, integrases, and plasmid replication genes, providing direct evidence of mobilization potential (Figure 2B–D, Tables S11–S14). Such co-localization, especially in pathogens and commensals, suggests that agricultural soils—particularly those affected by bacterial wilt—act as reservoirs and conduits for HGT to human pathogens, thereby promoting the emergence of clinically resistant strains. These findings highlight the “double-edged sword” role of soil microbiomes: biocontrol organisms used for disease suppression may also act as ARG reservoirs, while pathogens acquire resistance traits that increase clinical significance. A critical concern is the enrichment of polypeptide resistance genes, which compromise last-resort antibiotics such as polymyxins and vancomycin. Nonribosomal antimicrobial peptides (AMPs), previously considered low-risk due to minimal toxicity and specific modes of action, are now compromised by the spread of resistance. Many pathogens and soil probiotics naturally produce AMPs to outcompete competitors, but resistance reduces their ecological and clinical efficacy [19]. Alarmingly, vancomycin resistance genes were also detected transferring from bacterial wilt-affected soils to strawberry fruits, highlighting agricultural soils as critical ecological–clinical interfaces with direct implications for food safety and public health [20]. Collectively, our findings demonstrate that R. solanacearum facilitates ARG persistence and dissemination across the soil–tomato continuum, even during asymptomatic phases. Soil-borne legacies of bacterial wilt extend these effects across crop cycles, facilitating ARG migration into subsequent crops and edible tissues. The co-occurrence of ARGs, MGEs, and VFGs in diverse microbial hosts highlights multiple transmission pathways and emphasizes the urgent need to integrate plant pathology, microbial ecology, and One Health frameworks in AMR management. This study highlights how pathogen pressure, microbial interactions, and HGT collectively shape resistome dynamics in agricultural ecosystems. Furthermore, future development of microbial fertilizers and biocontrol agents should incorporate dual criteria, simultaneously evaluating pathogen suppression efficacy and minimal ARG burden, to mitigate their unintended contribution to the public health threat of antibiotic resistance. However, several limitations should be considered. Reliance on short-read metagenomic sequencing limits the resolution of MGEs, such as plasmids, restricting accurate assignment of ARGs and MGEs to their hosts. Environmental factors—including soil pH, organic matter, and pesticide use—were not independently controlled and may have influenced ARG distributions despite standardized management practices. As a cross-sectional study, we could not capture long-term ARG persistence or microbial community dynamics. Additionally, both metagenomics and HT-qPCR are limited by host DNA contamination, complicating absolute quantification. While metagenomics provides broad ARG profiles, HT-qPCR offers higher sensitivity for rare, high-risk ARGs, and methodological differences likely explain minor inconsistencies. Future research should prioritize: (i) applying long-read sequencing or Hi-C–based binning to resolve ARG–MGE–host genomic contexts, (ii) integrating metatranscriptomics and functional assays to examine active ARG expression and microbial interactions under pathogen stress, (iii) conducting long-term monitoring and time-series analyses to track ARG dynamics across seasons and management practices, and (iv) implementing controlled experiments to disentangle the effects of environmental factors such as organic matter and pesticide residues on resistome dissemination. Zufei Xiao: Conceptualization; methodology; software; data curation; investigation; validation; formal analysis; visualization; writing—original draft; writing—review and editing. Kai Ding: Conceptualization; methodology; validation; investigation; formal analysis; funding acquisition; project administration; resources; writing—original draft; writing—review and editing. Xiaodong Guo: Investigation; validation; writing—original draft; writing—review and editing. Yi Zhao: Writing—original draft; writing—review and editing; methodology. Xinyuan Li: Writing—original draft; writing—review and editing; methodology. Daoyuan Jiang: Writing—original draft; writing—review and editing; investigation. Dong Zhu: Writing—original draft; writing—review and editing; validation; methodology. Qinglin Chen: Writing—original draft; writing—review and editing; visualization. Mui-Choo Jong: Methodology; validation; writing—original draft; writing—review and editing; data curation; supervision; software; formal analysis. David W. Graham: Writing—original draft; writing—review and editing; methodology; conceptualization. Gang Li: Conceptualization; methodology; writing—original draft; writing—review and editing; validation; investigation; supervision; project administration; resources; funding acquisition. Yong-Guan Zhu: Conceptualization; methodology; supervision; formal analysis; validation; writing—original draft; writing—review and editing; resources. All authors have read the final manuscript and approved it for publication. This study was supported by the National Natural Science Foundation of China [32361143523 (G.L.), 42090063 (G.L.)], China Postdoctoral Science Foundation [2025M771293 (Z.X.)], Fujian Provincial Natural Science Foundation of China [2025J08121 (Z.X.)], and Zhejiang Provincial Key Research and Development Program of China [2023C02004 (K.D.)]. We apologize for not being able to cite additional work owing to space limitations. The authors declare no conflicts of interest. No animals or humans were involved in this study. The raw amplicon and metagenomic data were archived in the Genome Sequence Archive at the BIG Data Center, Chinese Academy of Sciences, and assigned accession numbers CRA020401 and CRA020305, https://ngdc.cncb.ac.cn/gsa/browse/CRA020305 and https://ngdc.cncb.ac.cn/gsa/browse/CRA020401. All code and algorithms used in this study are published and cited in the Methods section. The data and scripts used are saved in GitHub https://github.com/XiaoRhywings/Soil-borne-legacy-spreads-antibiotic-resistance. Supplementary materials (methods, figures, tables, graphical abstract, slides, videos, Chinese translated version, and update materials) may be found in the online DOI or iMeta Science http://www.imeta.science/. The data that support the findings of this study are openly available in the Genome Sequence Archive at the BIG Data Center, Chinese at https://ngdc.cncb.ac.cn/gsa, reference numbers CRA020401 and CRA020305. Figure S1. Response of bacterial communities to R. solanacearum infestation in the soil–tomato continuum. Figure S2. Bacterial community responses to R. solanacearum infestation in the soil–tomato continuum. Figure S3. Relative abundance of Bacillus subtilis and Bacillus velezensis in rhizosphere soils from healthy, infected, and dead tomato plants. Figure S4. Differential metabolic pathways between healthy and infected plants in the soil–tomato continuum. Figure S5. Relative abundance of ARG types across plant health states based on metagenomic analysis. Figure S6. Distribution and composition of MGEs in the soil–tomato and soil–strawberry continua. Figure S7. Distribution and composition of VFGs in the soil–tomato and soil–strawberry continua. Figure S8. Differential ARG types between healthy and infected plants in the soil–tomato continuum. Figure S9. Response of MGEs and VFGs to R. solanacearum infestation. Figure S10. Differential ARG profiles between healthy and infected plants based on HT-qPCR. Figure S11. Linear regression analysis linking ARGs with MGEs and R. solanacearum. Figure S12. Antibiotic susceptibility test results for R. solanacearum. Figure S13. of ARG in the soil–plant continuum identified by metagenomic and HT-qPCR Figure Distribution and of ARGs revealed by metagenomic analysis. Figure the abundant ARG subtypes in the soil–strawberry continuum. Figure Distribution and composition of ARGs in the soil–strawberry continuum. Figure Linear regression analysis of the between ARG relative abundance and relative abundance in the soil–tomato and soil–strawberry continua. Figure abundance of R. solanacearum in rhizosphere soil and root endophytes of healthy, infected, and dead tomato plants. Figure of Table S1. of key ARGs by Table S2. of ARGs identified by analysis based on metagenomic sequencing across the soil–tomato continuum. Table S3. result of R. solanacearum Table S4. of MGEs identified by analysis based on metagenomic sequencing across the soil–strawberry continuum. Table S5. Distribution of ARGs identified within from the soil–tomato continuum. Table S6. Distribution of VFGs identified within from the soil–tomato continuum. Table S7. Distribution of MGEs identified within from the soil–tomato continuum. Table S8. Distribution of ARGs identified within from the soil–strawberry continuum. Table S9. Distribution of VFGs identified within from the soil–strawberry continuum. Table S10. Distribution of MGEs identified within from the soil–strawberry continuum. Table S11. carrying ARGs identified from metagenomic of the soil–tomato continuum. Table S12. carrying VFGs identified from metagenomic of the soil–tomato continuum. Table S13. carrying ARGs identified from metagenomic of the continuum. Table carrying VFGs identified from metagenomic of the continuum. Table The specific strategy for the in this study. Table used in this study. Table PCR and system for this study. Table and for shotgun metagenomic Table on R. solanacearum strains used for genomic Table of The is not for the or of by the should be to the for the

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Topical antibiotics have long been used for the prevention and treatment of superficial skin and soft tissue infections; however, increasing evidence indicates that their clinical value is undermined by rising antimicrobial resistance, high rates of allergic sensitization, inadequate activity against biofilms, and a lack of wound-healing properties. Agents such as bacitracin, neomycin, polymyxin B, mupirocin, and fusidic acid act through narrow, target-specific mechanisms that facilitate resistance selection and provide limited benefit in chronic or polymicrobial wound environments. Contemporary antimicrobial stewardship frameworks therefore discourage routine use of topical antibiotics and increasingly favor non-antibiotic antiseptics with broad-spectrum activity and low resistance risk, including silver, iodine, polyhexamethylene biguanide, octenidine, and medical-grade honey. These modalities, however, primarily serve to reduce microbial burden and do not directly address the underlying biological impairments that prevent healing. Nitric oxide-releasing gels (NORGs) represent a novel class of topical antimicrobials that combine multi-target bactericidal activity with physiologic pro-healing effects. Nitric oxide exerts potent antimicrobial and antibiofilm effects via oxidative and nitrosative stress, disruption of metabolic pathways, inhibition of DNA replication, and interference with quorum sensing. Simultaneously, nitric oxide enhances angiogenesis, modulates inflammation, improves microvascular perfusion, and promotes fibroblast and keratinocyte function. Preclinical models and early-phase clinical studies demonstrate broad-spectrum efficacy-including activity against multidrug-resistant organisms-with favorable tolerability and minimal risk of resistance development. Although the current evidence base remains preliminary, NORGs offer a promising antimicrobial platform with the potential to reduce reliance on topical antibiotics while simultaneously addressing key barriers to wound healing. Larger randomized controlled trials, direct comparisons with established advanced dressings, and robust pharmacoeconomic evaluations are needed to define their optimal role within stewardship-aligned wound-care practice.

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Laguna Lake, the largest freshwater lake in the Philippines, has been reported to harbor antibiotic-resistant bacteria, posing health risks to the millions who depend on it. However, limited knowledge of antibiotic resistance genes (ARGs) in the lake highlights the need for a comprehensive assessment of its resistome. In line with this, we characterized ARGs in the West Bay of Laguna Lake using shotgun metagenomic sequencing based on six metagenomes collected from three stations across two sampling months at a single depth. ARGs were quantified from short reads, and assembled contigs containing these genes-antibiotic-resistant contigs (ARCs)-were analyzed to assess mobility through associations with plasmids and mobile genetic elements (MGEs). β-lactam resistance genes (0.023-0.048 copies per cell) were the most prevalent, corroborating previous reports. Meanwhile, the detection of bacitracin (0.013-0.028 cpc) and polymyxin (0.009-0.011 cpc) resistance genes raises new concerns, as resistance to these antibiotic classes has not been previously reported in the lake. Furthermore, 44.8 and 30.4% of ARCs were associated with plasmids and MGEs, respectively. ARCs carrying genes for resistance to β-lactams, chloramphenicol, and tetracyclines were frequently identified as mobile, indicating a high potential for horizontal gene transfer and suggesting possible antibiotic contamination in the lake. Overall, this study provides the first metagenomic insight into the resistome of Laguna Lake using short-read sequencing and highlights its role as an environmental reservoir of mobile ARGs. The findings underscore the need for expanded ARG surveillance to improve antimicrobial resistance risk prediction.

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Helicobacter pylori uses a cluster of polar flagella for motility. H. pylori FapH forms a ring-like flagellar motor accessory associated with the outer membrane. A H. pylori ΔfapH mutant displays a motility-dependent sensitivity to bacitracin, an antibiotic that is normally excluded by the outer membrane, which suggests that FapH helps to maintain the integrity of the outer membrane during flagellar rotation. We report here that deletion of the ferric uptake regulator (fur) gene suppressed the bacitracin sensitivity of the H. pylori ΔfapH mutant. Depleting intracellular iron in the H. pylori ΔfapH mutant with the iron chelator 2,2′-dipyridyl similarly suppressed the bacitracin sensitivity of the strain. We postulate the altered expression of Fur-regulated genes as a result of deleting fur or that iron deprivation suppressed the bacitracin sensitivity of the ΔfapH mutant. We also isolated two bacitracin-resistant ΔfapH strains that had a nonsense mutation in lpxF, which encodes a lipid A 4′-phosphatase. Loss of LpxF alters the structure of the lipid A backbone in lipopolysaccharide that stabilizes the outer membrane, which we hypothesize compensated for the loss of FapH by minimizing damage to the membrane resulting from flagellar rotation.

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Introduction Information regarding the impact of topical antibiotics with or without corticosteroids on the microbiota of the horses’ eyes is limited. This study aimed to describe the bacterial ocular surface microbiota in healthy horses and evaluate the effect of topical antibiotics or antibiotic-corticosteroid medication on the ocular surface microbiota. Methods This was a prospective, randomized, longitudinal, blinded study in which one eye of 12 horses was treated 3 times daily for 7 days with neomycin, polymyxin B and bacitracin ophthalmic ointment ( n = 6) or neomycin, polymyxin B and dexamethasone ophthalmic ointment ( n = 6). The contralateral eyes operated as untreated controls. The inferior conjunctival fornix of both eyes was sampled at baseline before antibiotic administration (day 0), on days 3, 7, 9, 14, and 30. The ocular surface microbiota was characterized by amplifying the V4 region of the 16S ribosomal RNA gene. Results Alpha- (richness and diversity) and beta-diversity (weighted and unweighted UniFrac distances) measurements of the ocular surface microbiota varied similarly after treatments starting on day 1, returning to baseline measurements by day 30. At baseline, the main phyla detected in the ocular microbiota was Proteobacteria, representing 75% relative abundance, followed by Firmicutes and Bacteroidetes. After treatments, Proteobacteria declined in all groups, and Firmicutes and Bacteroidete’s relative abundance increased, returning to baseline levels on day 30. The main genera detected on the ocular surface on day 0 were Suttonella , Nicoletella, Pasteurella , and members of the family Moraxellaceae. After treatment, the relative abundance of this bacteria declined in all groups, returning to baseline levels on day 30, although some alterations were still present. Discussion Here we show that topical antibiotics administered with or without corticosteroids induce changes in the ocular surface of horses’ eyes, and the microbiota appears to return to baseline approximately three weeks after treatment discontinuation.

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Topical antibiotic ointments are widely prescribed for infection prophylaxis after surgery and trauma, yet they are an important cause of allergic contact dermatitis. Autoeczematization, or id reaction, refers to secondary eczematous eruptions that arise at sites distant from a primary localized inflammatory focus. We report a 42-year-old man who developed generalized exudative erythematous papules after application of Baramycin® (bacitracin and fradiomycin sulfate) ointment to an erosion on his right lower leg treated for cellulitis. Despite improvement of systemic inflammatory markers, well-demarcated erythema confined to the area of ointment and dressing use, accompanied by widespread papules on the trunk, face, and extremities, persisted. Delayed patch testing could have been performed after clinical improvement, but the patient was lost to follow-up, and the clinical course strongly suggested allergic contact dermatitis with secondary autoeczematization. Discontinuation of Baramycin® and initiation of topical clobetasol propionate led to the gradual resolution of the primary lesion and rapid improvement of distant eruptions. This case underscores the need to consider autoeczematization in patients presenting with diffuse eczematous eruptions following the use of topical antibiotics.

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ABSTRACT The growing threat of antimicrobial resistance necessitates the discovery of novel antibiotics with activity against drug-resistant pathogens. Members of the genus Paenibacillus are a rich source of nonribosomal peptides (NRPs), including well-known antibiotics such as polymyxins, paenibacterin, and tridecaptins. Here, we use a targeted mass spectrometry query language (MassQL)-based approach to identify the NRPs produced by a collection of 227 taxonomically diverse plant-associated Paenibacillus strains, providing detailed insights into their NRP-producing potential. Using MassQL to zoom in specifically on NRPs containing basic amino acids, we discovered a novel family of bacitracins, which we designated paenitracins. The paenitracins are the first bacitracin-type peptides reported in Paenibacillus and are distinguished from canonical bacitracins by three previously unseen amino acid substitutions. The paenitracins exhibit potent activity against gram-positive pathogens, including vancomycin-resistant Enterococcus faecium E155. Our work provides a novel metabolomics-guided and genomics-guided workflow for the discovery of bioactive NRPs as a strategy to prioritize natural product chemical space and accelerate antibiotic discovery. IMPORTANCE Members of the genus Paenibacillus play an important role in soil ecology, producing a range of important nonribosomal peptides (NRPs). A collection of plant-associated Paenibacillus spp. were analyzed for their phylogenetic and metabolic diversity. We developed a novel discovery pipeline that combines feature-based molecular networking with mass spectrometry query language queries to systematically prioritize bioactive NRPs containing basic amino acids. Thus, we provide a comprehensive genus-wide inventory of NRPs produced by Paenibacillus spp. We thereby identified the paenitracins, a new sub-family of bacitracins active against multidrug-resistant gram-positive pathogens. Our pipeline enables the discovery of novel peptidic natural products to accelerate the prioritization of chemical space for antibiotics.

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BACKGROUND: Irrigation is a key strategy in reducing bioburden, disrupting biofilms, and supporting wound healing. While saline is the standard for its safety and availability, antiseptic and antibiotic solutions are often used in clinical scenarios that require infection control. However, the rise in antibiotic stewardship and concerns regarding cytotoxicity are reshaping current practices. This review identifies recent trends, current controversies, and persistent gaps in knowledge that warrant further investigation and regulatory attention. METHODS: A literature review identified irrigation solutions commonly used in plastic surgery; labeling and concentrations were obtained from Devices@FDA, Drugs@FDA, and DailyMed, and PubMed, Cochrane Central, and Embase were searched (January 2022-July 2025) for human studies on acute wounds, chronic wounds, and implant-based breast surgery. RESULTS: In acute wounds, saline and potable tap water effectively prevent infection. In chronic wounds, such as diabetic foot ulcers and pressure injuries, antiseptic agents, including hypochlorous acid, sodium hypochlorite, polyhexanide, and citrate-based solutions, have shown promise in improving healing and reducing infection. In implant-based breast reconstruction and augmentation, data on antiseptics, such as chlorhexidine, and changes in FDA guidance for povidone-iodine and bacitracin have prompted a reevaluation of intraoperative irrigation practices. CONCLUSION: Despite widespread use, many antiseptics remain off-label, and high-quality clinical studies comparing efficacy and safety are lacking.

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