Sublethal antibiotic treatment leads to multidrug resistance via radical-induced mutagenesis

Ciprofloxacin-resistant Salmonella Typhimurium demonstrates cross-tolerance to heat treatments in liquid food matrices

The alarming occurrence of antimicrobial resistance (AMR) in human bacterial isolates indicates that prevention and control protocols are not adequately managing this global threat. The agri-food chain plays a noteworthy role in the dissemination of AMR via the handling and consumption of contaminated food products. However, it remains unclear whether acquisition of AMR in bacteria might indirectly enhance bacterial tolerance to food preservation methods (i.e., cross-tolerance), resulting in defective pathogen reduction. In this study, five ciprofloxacin (CIP) resistant variants (RVs) were generated after exposing Salmonella Typhimurium LT2 (SeT) to an upward CIP gradient. We thereupon observed up to 125-fold increases in the minimum inhibitory concentration to CIP in all five RVs. Moreover, two RVs showed reduced sensitivity to heat in laboratory media compared to SeT. The most tolerant strain displayed mutations in genes previously implicated in AMR, coding for RNA polymerase subunits (rpoD), regulatory protein RamR (ramR) and enzyme adenylate cyclase (cyaA). Validation in liquid food matrices revealed enhanced thermotolerance of the RV to treatments performed at 50 °C in orange juice (×986.7 survival risk after 15 min of treatment), and 54 °C in milk (more than ×10,000 survival risk after 30 min) and liquid-whole egg (×976.7 survival risk after 40 min). Furthermore, virulence assays in nematode Caenorhabditis elegans showed mutations conferring AMR and cross-tolerance did not result in a substantial loss of pathogenicity. Hence, exposures to CIP might lead to the selection of S. Typhimurium variants that pose limits to heat treatment efficacy, thereby increasing their survival risk and ultimately allowing them to reach the end consumer - thus also limiting the scope of antibiotic action during eventual infection.

Stresses in the food chain and their impact on antibiotic resistance of foodborne pathogens: A review

Antibiotic resistance in foodborne pathogens represents a major public health concern. The farm-to-fork continuum is recognized as a critical pathway for the development and spread of this resistance. Throughout the food chain, foodborne pathogens are exposed to diverse environmental stresses, including temperature extremes, osmotic pressure, food additives, and disinfectants, and others. These stress factors can influence antibiotic resistance, with effects varying based on the type and intensity of stress, the pathogen species and strain, and the specific antibiotic involved. Stress conditions can trigger bacterial adaptive responses, such as general stress response systems, the SOS response, and genetic mutations, which can confer cross-protection and enhance antibiotic resistance. Conversely, stress-induced injury or metabolic suppression may increase bacterial susceptibility to certain antibiotics. Understanding these complex interactions is crucial, as suboptimal food processing can inadvertently select for resistant strains. Investigating the molecular mechanisms underlying stress adaptation is essential for developing effective strategies to mitigate antibiotic resistance. Optimizing food processing protocols and implementing robust monitoring systems throughout the food chain are essential steps to reduce these risks. A comprehensive understanding of stress-induced antibiotic resistance will provide a scientific basis for improving food safety and safeguarding global public health.

Disinfectants and one health review: The role of reactive oxygen species in the bactericidal activity of chlorine against Salmonella

Salmonella are among the most common foodborne pathogens in humans, and they are associated with mild to severe diseases commonly referred to as salmonellosis. The genus resides in various animals' intestinal tracts, including humans. It is one of the most diverse genera of bacteria, including over 2500 serovars. Consumption of poultry products contaminated with Salmonella is a significant source of disease transmission in humans. Because of this food safety concern, the poultry industry and governments spend billions of dollars on Salmonella containment methods. However, a completely effective strategy is yet to be established. Chlorine has been commonly used as a disinfectant in the poultry industry. In humans, antibiotic therapy is the primary means for managing Salmonella infection. However, widespread use of both compounds at sub-inhibitory concentrations has allowed resistant strains to emerge and rapidly spread globally. Both antimicrobial compounds involve generating reactive oxygen species (ROS) as a bactericidal mechanism of action. However, ROS generation and its association with bacterial survival and growth inhibition have not been widely explored. Thus, a better understanding of ROS generation during antimicrobial treatments may help devise better Salmonella containment strategies.

Metabolic byproduct utilization and the evolution of mutually beneficial cooperation in Escherichia coli

Understanding how cooperation evolves in microbial populations, particularly under environmental stress such as antibiotic exposure, remains a key topic in evolutionary biology. Here, we investigate cooperative interactions between antibiotic-resistant and antibiotic-sensitive strains of Escherichia coli. Under antibiotic stress, a small number of antibiotic-sensitive strains rapidly evolve into antibiotic-resistant strains. Resistant E. coli produce indole, which induces a protective response in sensitive cells, enabling them to survive in antibiotic stress conditions. In turn, antibiotic-sensitive E. coli could help reduce toxic accumulation of indole, indirectly benefiting the resistant strain. Indole is harmful to the growth of the antibiotic-resistant strain but benefits the antibiotic-sensitive strain by helping turn-on the multi-drug exporter to neutralize the antibiotic. This mutual exchange leads to increased fitness for both strains in cocultures, demonstrating a mechanism by which mutually beneficial cooperation can evolve in bacterial communities. Our findings provide insight into how mutualism can emerge under antibiotic pressure through metabolic byproduct exchange, revealing new dynamics in the evolution of bacterial cooperation.

Enhanced methanogenesis and efficient ciprofloxacin degradation via nZVI@LDH in an electricity-driven anaerobic bioreactor: A biotic-abiotic hybrid system for ROS regulation and ARGs mitigation

The escalating presence of antibiotic contaminants in wastewater presents substantial environmental and public health challenges, primarily due to their role in the proliferation of antibiotic resistance genes (ARGs). This study examines the effectiveness of a hybrid system integrating nano zerovalent iron (nZVI) and layered double hydroxides (LDH) in treating wastewater contaminated with ciprofloxacin (CIP). Reactor experiments revealed that incorporating nZVI@LDH mitigated the shock caused by CIP while sustaining a methane production rate that was 116 % higher than that of the control group. Furthermore, there was a 50 % increase in CIP removal efficiency. Notably, there was a significant enrichment of hydrogenotrophic methanogens, such as Methanobacterium and Methanolinea, in the nZVI@LDH-enhanced reactors. Additionally, the levels of reactive oxygen species decreased by 50 %, from 11,813 ± 1230 to 4525 ± 1030 counts/s, and the abundance of ARGs declined by 75-88 % compared to the control reactors. An external electric field further promoted electron transfer, boosting the relative abundance of electrochemically active bacteria, with Proteobacteria comprising up to 40 % of the microbial community in the 1 V + nZVI@LDH reactor. This hybrid system demonstrates significant efficacy in degrading CIP and decreasing ARGs generation, underscoring its potential as a sustainable strategy for managing antibiotic-laden wastewater.

Biocides as drivers of antibiotic resistance: A critical review of environmental implications and public health risks

The widespread and indiscriminate use of biocides poses significant threats to global health, socioeconomic development, and environmental sustainability by accelerating antibiotic resistance. Bacterial resistance development is highly complex and influenced significantly by environmental factors. Increased biocide usage in households, agriculture, livestock farming, industrial settings, and hospitals produces persistent chemical residues that pollute soil and aquatic environments. Such contaminants contribute to the selection and proliferation of resistant bacteria and antimicrobial resistance genes (ARGs), facilitating their dissemination among humans, animals, and ecosystems. In this review, we conduct a critical assessment of four significant issues pertaining to this topic. Specifically, (i) the role of biocides in exerting selective pressure within the environmental resistome, thereby promoting the proliferation of resistant microbial populations and contributing to the global spread of antimicrobial resistance genes (ARGs); (ii) the role of biocides in triggering transient phenotypic adaptations in bacteria, including efflux pump overexpression, membrane alterations, and reduced porin expression, which often result in cross-resistance to multiple antibiotics; (iii) the capacity of biocides to disrupt bacteria and make the genetic content accessible, releasing DNA into the environment that remains intact under certain conditions, facilitating horizontal gene transfer and the spread of resistance determinants; (iv) the capacity of biocides to disrupt bacterial cells, releasing intact DNA into the environment and enhancing horizontal gene transfer of resistance determinants; and (iv) the selective interactions between biocides and bacterial biofilms in the environment, strengthening biofilm cohesion, inducing resistance mechanisms, and creating reservoirs for resistant microorganisms and ARG dissemination. Collectively, this review highlights the critical environmental and public health implications of biocide use, emphasizing an urgent need for strategic interventions to mitigate their role in antibiotic resistance proliferation.

Synergistic effects of quaternary ammonium compounds and antibiotics on the evolution of antibiotic resistance

The usage of quaternary ammonium compounds (QACs) as disinfectants has surged dramatically during the COVID-19 pandemic and thereafter. QACs can promote antimicrobial resistance, but the combined effects of QACs and antibiotics in driving resistance evolution were yet revealed. This study aimed to evaluate antibiotic resistance of wastewater microorganisms under coexposure to typical antibiotics and the most widely used QAC, dodecyl dimethyl benzyl ammonium chloride (DDBAC). DDBAC exhibited synergistic effects with multiple antibiotics (ampicillin, azithromycin, ciprofloxacin, kanamycin, polymyxin B) in enhancing activated sludge resistance by 1.53-6.67 folds, compared with antibiotics exposure alone. DDBAC-ampicillin coexposure enriched multidrug and aminoglycoside ARGs with relatively high horizontal gene transfer potential. The synergistic mechanism was further explored using sludge-isolated pathogenic E. coli. DDBAC at 1-10 mg/L alone did not induce notable resistance, but synergized with ampicillin on enhancing resistance by 6.56-22.90 folds. Based on mutation analysis and transcriptomics, DDBAC-enhanced resistance evolution was attributable to efflux pump upregulation, target modification, and inhibition of ATP synthesis (a less reported mechanism). Five DDBAC-induced, resistance-conferring mutant genes were highly enriched in globally collected E. coli strains from wastewater outflow (n = 537) than soil/sediments (n = 714, p < 0.05). Considering the strong adsorption and persistence of QACs, their coexistence with antibiotics poses elevated antimicrobial resistance risks, particularly in wastewater treatment systems with long solid retention time and sewage sludge applied farmland.

Basic Nitrogenous Heterocyclic Rings at the 7-Position of Fluoroquinolones Foster Their Induction of Antibiotic Resistance in Escherichia coli

The extensive prescription of fluoroquinolone antibiotics has resulted in their ubiquitous presence in the environment, fueling the ongoing development of antibiotic resistance. Besides antibiotics, fluoroquinolone production intermediates, an overlooked category of pollutants that oftentimes possess the intact fluoroquinolone core structure, may also contribute to this public health crisis. To assess their relative potency and collectively examine the structural effects of fluoroquinolones on resistance development, wild-type Escherichia coli K12 was exposed to ten fluoroquinolone antibiotics and five intermediates at their environmentally relevant concentrations for 30 days. Phenotypic resistance alterations revealed that the absence of the C7 ring system in fluoroquinolones significantly impaired their capacity to induce resistance in E. coli, potentially due to diminished oxidative DNA damage and gyrase-mediated dsDNA breaks. Genetic and transcriptional analyses indicated that a uniform resistance mechanism emerged under both antibiotic and intermediate stress. Quantitative structure-activity relationship (QSAR) analysis further emphasized the positive impact of both basic nitrogenous heterocyclic rings at C7 (particularly the hydrogen-bond-donor pharmacophores) and aromatic rings at N1 in promoting resistance development, while highlighting the adverse effects of hydrophobic and hydrogen-bond-donor groups at N1. A robust QSAR model was developed and applied to assess the relative risks of other 105 fluoroquinolones. This study underscored the direct role of fluoroquinolone production intermediates in promoting environmental antibiotic resistance and illustrated how different structural features of fluoroquinolone pollutants will influence this process, offering theoretical insights for future antibiotic design and environmental regulation efforts.

Role of organophosphorus pesticides in facilitating plasmid-mediated conjugative transfer: Efficiency and mechanisms

Non-antibiotic conditions, including organophosphorus pesticides (OPPs), have been implicated in the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) to varying degrees. While most studies focus on the toxicity of OPPs to humans and animals, their roles in ARG dissemination remain largely unexplored. In this study, we investigate the effects and involved molecular mechanisms of environmentally relevant concentrations of malathion and dimethoate, two representative OPPs, on plasmid-mediated conjugal transfer. By detecting reactive oxygen species (ROS) production and cell membrane permeability, we gained insights into the underlying processes. Furthermore, we substantiated the role of ROS and cell membrane permeability in plasmid-mediated conjugative transfer through the analysis of relevant antioxidant enzyme activities, cell membrane-related indices, and RNA sequences. Additionally, our examination of proton motive force and adenosine triphosphate content provided evidence that OPPs create conditions conducive to plasmid-mediated conjugative transfer from an energetic perspective. The findings of the present study highlight the potential risk of OPPs in promoting ARG spread, which could ultimately provide new theoretical support and direction for future research on the impacts of pesticides on ARG propagation.

Effect of subinhibitory concentrations on the spreading of the ampicillin resistance gene blaCMY-2 in an activated sludge microcosm

As the problem of multi-resistant bacteria grows a better understanding of the spread of antibiotic resistance genes is of utmost importance for society. Wastewater treatment plants contain subinhibitory concentrations of antibiotics and are thought to be hotspots for antibiotic resistance gene propagation. Here we evaluate the influence of sub-minimum inhibitory concentrations of antibiotics on the spread of resistance genes within the bacterial community in activated sludge laboratory-scale sequencing batch reactors. The mixed communities were fed two different ampicillin concentrations (500 and 5000 µg/L) and the reactors were run and monitored for 30 days. During the experiment the β-lactamase resistance gene blaCMY-2 was monitored via qPCR and DNA samples were taken to monitor the effect of ampicillin on the microbial community. The relative copy number of blaCMY-2 in the reactor fed with the sub-minimum inhibitory concentration of 500 µg/L ampicillin was spread out over a wider range of values than the control and 5000 µg/L ampicillin reactors indicating more variability of gene number in the 500 µg/L reactor. This result emphasises the problem of sub-minimum inhibitory concentrations of antibiotics in wastewater. High-throughput sequencing showed that continuous exposure to ampicillin caused a shift from a Bacteroidetes to Proteobacteria in the bacterial community. The combined use of qPCR and high-throughput sequencing showed that ampicillin stimulates the spread of resistance genes and leads to the propagation of microbial populations which are resistant to it.

Moonlighting antibiotics: the extra job of modulating biofilm formation

The widespread use of antibiotics to treat bacterial infections has led to the common perception that their only function is to inhibit growth or kill bacteria. However, it has become clear that when antibiotics reach susceptible bacteria at non-lethal concentrations, they perform additional functions that significantly impact bacterial physiology, shaping both individual and collective behaviors. A key bacterial behavior influenced by sub-lethal antibiotic doses is biofilm formation, a multicellular, surface-associated mode of growth. This review explores different contexts in which natural and clinical antibiotics act as modulators of bacterial biofilm formation. We discuss cases that provide mechanistic insights into antibiotic modes of action, highlighting emerging common patterns and novel findings that pave the way for future research.

Vitamin B6 resensitizes mcr-carrying Gram-negative bacteria to colistin

Antimicrobial resistance poses a severe threat to human health, with colistin serving as a critical medication in clinical trials against multidrug-resistant Gram-negative bacteria. However, the efficacy of colistin is increasingly compromised due to the rise of MCR-positive bacteria worldwide. Here, we reveal a notable metabolic disparity between mcr-positive and -negative bacteria through transcriptome and metabolomics analysis. Specifically, pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, was significantly diminished in mcr-positive bacteria. Conversely, supplementing with PLP could reverse the metabolic profile of drug-resistant bacteria and effectively restore colistin's bactericidal properties. Mechanistically, PLP was found to augment bacterial proton motive force by inhibiting the Kdp transport system, a bacterial K+ transport ATPase, thereby facilitating the binding of the positively charged colistin to the negatively charged bacterial membrane components. Furthermore, PLP supplementation triggers ferroptosis-like death by accumulating ferrous ions and inducing lipid peroxidation. These two modes of action collectively resensitize mcr-harboring Gram-negative bacteria to colistin therapy. Altogether, our study provides a novel metabolic-driven antibiotic sensitization strategy to tackle antibiotic resistance and identifies a potentially safe antibiotic synergist.

Trophic transfer of sulfonamide antibiotics in aquatic food chains: A comprehensive review with a focus on environmental health risks

Antibiotics, which have been identified as emerged pollutants, are creating an increase in environmental concerns, with sulfonamide antibiotics (SAs) being among the most commonly discovered antibiotics. Due to their widespread usage and inadequate sewage treatment, SAs are frequently released into the aquatic environment. The introduction of SAs into aquatic environments can kill or inhibit the growth or metabolic activity of microorganisms, thereby affecting biological communities and ecological functions and disrupting the equilibrium of aquatic ecosystems. The transmission of SAs to human beings can occur through trophic transfer of food chains, particularly when humans consume aquatic food. This study examines the trophic transfer of SAs along the aquatic food chain, provides a summarize of the spatial distribution of SAs in aquatic environments, and evaluates the environmental risks associated with it. The prevalence of SAs was predominantly noted in the aqueous phase, with relatively lower concentrations detected in sediments, solidifying their status as one of the most widespread antibiotics among aquatic organisms. SAs, characterized by their high biomagnification capacity and strong bioaccumulative properties in invertebrates, emerge as the antibiotic type with the greatest ecological risks. The ecological risk posed by sulfonamide antibiotics to aquatic organisms is more pronounced than the health risk to humans, suggesting that the adverse effects on aquatic life warrant greater attention. Additionally, this study offers practical recommendations to address the limitations of previous research, emphasizing the importance of regulating exposure and establishing a robust health risk prediction system as effective measures for antibiotic control.

Antimicrobial Prescription Practices and Stewardship in Washington State Small and Mixed Animal Veterinary Medicine

INTRODUCTION

Judicious antimicrobial use is essential for the continued treatment of infections in small and mixed animal veterinary medicine. To better support Washington (WA) State veterinarians in antimicrobial stewardship, we surveyed licensed small and mixed animal veterinarians and led group conversations regarding antimicrobial prescription practices.

METHODS

Survey questions included demographic information, factors influencing prescription practices and clinical cases. Responses were summarised and logistic regressions were performed to identify factors associated with antibiotic treatment choices. Group conversations, led by a licensed veterinarian, focused on resource gaps for veterinarians, management of clinical scenarios and interpretation of minimum inhibitory concentrations (MICs) and breakpoints. A systematic qualitative analysis of conversation transcripts identified key themes such as common barriers to stewardship.

RESULTS

Among 53 responses to clinical scenarios, veterinarians selected the most appropriate treatment choice, according to a veterinary microbiologist, 62% of the time. Variability was observed in culture and susceptibility practices and antibiotic choices. Survey respondents reported an influence of the client ability to medicate (92%), considerations of resistance (91%), client finances (75%) and availability of antimicrobials (75%) on their prescription decisions. There were no significant associations between opinions about contributing factors to antimicrobial resistance (AMR) or guidelines used and treatment choices in clinical scenarios. Among 15 veterinarians interviewed in group conversations, a systematic qualitative analysis of conversation transcripts revealed key themes, including reliance on human medicine as a resource and a lack of support for veterinarians in interpreting MICs and breakpoints.

CONCLUSIONS

The variability in veterinary antibiotic treatment decisions in this study suggests a need for further dissemination of standardised antimicrobial stewardship resources for veterinarians. Client-related challenges and the cost of culture and susceptibility are major barriers to stewardship. To address these barriers, it is necessary to provide standardised, easy-to-access guidance for veterinarians in interpreting MICs and breakpoints, as well as develop antimicrobial use resources for clients.

Insights into the mobility and bacterial hosts of antibiotic resistance genes under dinotefuran selection pressure in aerobic granular sludge based on metagenomic binning and functional modules

Dinotefuran (DIN) is toxic to non-target organisms and accelerates the evolution of antibiotic resistance, which poses a problem for the stable operation of the activated sludge process in wastewater treatment plants (WWTPs). However, the emergence and the transfer mechanism of antibiotic resistance genes (ARGs) in activated sludge systems under DIN stress remains unclear. Thus, in the study, the potential impact of DIN on ARGs and virulence factor genes (VFGs) in aerobic granular sludge (AGS) was investigated in depth using metagenomic binning and functional modules. It was found that DIN stress increased the total abundance of ARGs, mobile genetic elements (MGEs), and VFGs in the AGS system, with the highest abundance of fabG (4.6%), tnpA (55.6%) and LPS (39.0%), respectively. The proliferation of the enteric pathogens Salmonella enterica and Escherichia coli in the system indicates that DIN induces exposure of harmless bacteria to the infected environment. The genera Nitrospira (1169 ARG subtypes) and Dechloromonas (663 ARG subtypes) were identified as the potentially antibiotic-resistant bacteria carrying the most ARGs and MGEs in the metagenome-assembled genomes. Co-localization patterns of some ARGs, MGEs, and the SOS response-related gene lexA were observed on metagenome-assembled contigs under high levels of DIN exposure, suggesting DIN stimulated ROS production (101.8% increase over control), altered cell membrane permeability, and increased the potential for horizontal gene transfer (HGT). Furthermore, the DNA damage caused by DIN in AGS led to the activation of the antioxidant system and the SOS repair response, which in turn promoted the expression of the type IV secretion system and HGT through the flagellar channel. This study extends the previously unappreciated DIN understanding of the spread and associated risks of ARGs and VFGs in the AGS system of WWTPs. It elucidates how DIN facilitates HGT, offering a scientific basis for controlling emerging contaminant-induced resistance.

The role of bacterial metabolism in antimicrobial resistance

The relationship between bacterial metabolism and antibiotic treatment is complex. On the one hand, antibiotics leverage cell metabolism to function. On the other hand, increasing research has highlighted that the metabolic state of the cell also impacts all aspects of antibiotic biology, from drug efficacy to the evolution of antimicrobial resistance (AMR). Given that AMR is a growing threat to the current global antibiotic arsenal and ability to treat infectious diseases, understanding these relationships is key to improving both public and human health. However, quantifying the contribution of metabolism to antibiotic activity and subsequent bacterial evolution has often proven challenging. In this Review, we discuss the complex and often bidirectional relationships between metabolism and the various facets of antibiotic treatment and response. We first summarize how antibiotics leverage metabolism for their function. We then focus on the converse of this relationship by specifically delineating the unique contribution of metabolism to three distinct but related arms of antibiotic biology: antibiotic efficacy, AMR evolution and AMR mechanisms. Finally, we note the relevance of metabolism in clinical contexts and explore the future of metabolic-based strategies for personalized antimicrobial therapies. A deeper understanding of these connections is crucial for the broader scientific community to address the growing crisis of AMR and develop future effective therapeutics.

Genetic adaptation to amoxicillin in Escherichia coli: The limited role of dinB and katE

Bacteria can quickly adapt to sub-lethal concentrations of antibiotics. Several stress and DNA repair genes contribute to this adaptation process. However, the pathways leading to adaptation by acquisition of de novo mutations remain poorly understood. This study explored the roles of DNA polymerase IV (dinB) and catalase HP2 (katE) in E. coli's adaptation to amoxicillin. These genes are thought to play essential roles in beta-lactam resistance-dinB in increasing mutation rates and katE in managing oxidative stress. By comparing the adaptation rates, transcriptomic profiles, and genetic changes of wild-type and knockout strains, we aimed to clarify the contributions of these genes to beta-lactam resistance. While all strains exhibited similar adaptation rates and mutations in the frdD gene and ampC operon, several unique mutations were acquired in the ΔkatE and ΔdinB strains. Overall, this study distinguishes the contributions of general stress-related genes on the one hand, and dinB, and katE on the other hand, in development of beta-lactam resistance.

Effect of non-antibiotic factors on conjugative transfer of antibiotic resistance genes in aquaculture water

Aquaculture water with antibiotic resistance genes (ARGs) is escalating due to the horizontal gene transfer. Non-antibiotic stressors specifically found, including those from fishery feed and disinfectants, are potential co-selectors. However, the mechanisms underlying this process remains unclear. Intragenus and intergenus conjugative transfer systems of the antibiotic-resistant plasmid RP4 were established to examine conjugative transfer frequency under exposure to five widely used non-antibiotic factors in aquaculture water: iodine, oxolinic acid, NO2-N, NO3-N and H2O2 and four different recipient bacteria: E. coli HB101, Citrobacter portucalensis SG1, Vibrio harveyi and Vibrio alginolyticus. The study found that low concentrations of non-antibiotic factors significantly promoted conjugative transfer, whereas high concentrations inhibited it. Moreover, the conjugation transfer efficiencies were significantly different with different bacterial species within (E. coli HB101 ∼ 10-3 %) or cross genera (C. portucalensis SG1 ∼10-5 %, V. harveyi ∼1 %). Besides, excessive exposure concentrations inhibited the expression of related genes and the generation of reactive oxygen species (ROS). Regulation of multiple related genes and ROS-induced SOS responses are common primary mechanisms. However, the mechanisms of non-antibiotic factors differ from those of standard antibiotics, with direct changes in cell membrane permeability potentially playing a dominant role. Additionally, variations among non-antibiotic factors and the specific characteristics of bacterial species contribute to differences in conjugation mechanisms. Notably, this study found that non-antibiotic factors could increase the frequency of intergeneric conjugation beyond that of intrageneric conjugation. Furthermore, non-antibiotic factors influenced by multiple transport systems may raise the risk of unintended cross-resistance, significantly amplifying the potential for resistance gene spread. This study underscores the significance of non-antibiotic factors in the propagation of ARGs, highlighting their role in advancing aquaculture development and protecting human health.

Antibiotic resistance evolution driven synergistically by antibiotics and typical organic pollutants in antibiotic production wastewater

A major concern regarding the risk of antibiotic production wastewater (APW) for the transmission of antibiotic resistance (AR) stems from the residual antibiotics. However, APW also contains high concentrations of organic pollutants, many of which have severe biological toxicity and joint toxicity with antibiotics. The contribution of these organic pollutants to the development of AR in the APW treatment system is unknown. In this study, a wild-type Escherichia coli strain was exposed to six typical organic pollutants in APW individually and synergistically with the antibiotic ampicillin (AMP). Independent exposure to organic compounds had negligible effects on the evolution of AR, whereas they synergistically induced AR mutations and increased antibiotic persistence with AMP, especially the raw material d-p-hydroxyphenylglycine (DHPG), at relevant concentrations in APW. Combined exposure to 1-500 mg/L DHPG and 1 mg/L AMP synergistically increased the mutation frequencies against multiple antibiotics by up to 2928.9-fold in a dose-time pattern, and the combination index reached 445.7. Phenotypic and genotypic analyses revealed that the synergism between DHPG and AMP was associated with increased antibacterial activity, enhanced oxidative stress, and stimulation of efflux pump expression. Overall, our results highlight the elevated risk of AR induction caused by antibiotics and organic pollutants in APW.

Insights into antibiotic resistance promoted by quinolone exposure

Quinolone-induced antibiotic resistance (QIAR) refers to the phenomenon by which bacteria exposed to sublethal levels of quinolones acquire resistance to non-quinolone antibiotics. We have explored this in Escherichia coli MG1655 using a variety of compounds and bacteria carrying a quinolone-resistance mutation in gyrase, mutations affecting the SOS response, and mutations in error-prone polymerases. The nature of the antibiotic-resistance mutations was determined by whole-genome sequencing. Exposure to low levels of most quinolones tested led to mutations conferring resistance to chloramphenicol, ampicillin, kanamycin, and tetracycline. The mutations included point mutations and deletions and could mostly be correlated with the resistance phenotype. QIAR depended upon DNA gyrase and involved the SOS response but was not dependent on error-prone polymerases. Only moxifloxacin, among the quinolones tested, did not display a significant QIAR effect. We speculate that the lack of QIAR with moxifloxacin may be attributable to it acting via a different mechanism. In addition to the concerns about antimicrobial resistance to quinolones and other compounds, QIAR presents an additional challenge in relation to the usage of quinolone antibacterials.

The impact of antioxidant-ciprofloxacin combinations on the evolution of antibiotic resistance in Pseudomonas aeruginosa biofilms

The evolution of antimicrobial resistance (AMR) in biofilms, driven by mechanisms like oxidative stress, is a major challenge. This study investigates whether antioxidants (AOs) such as N-acetyl-cysteine (NAC) and Edaravone (ED) can reduce AMR in Pseudomonas aeruginosa biofilms exposed to sub-inhibitory concentrations of ciprofloxacin (CIP). In vitro experimental evolution studies were conducted using flow cells and glass beads biofilm models. Results showed that combining CIP with antioxidants (CIP-AOs) effectively reduced the development of CIP resistance. Isolates from biofilms treated with CIP-AO had significantly lower minimum inhibitory concentrations (MICs) of CIP compared to those treated with CIP alone. Whole-genome sequencing (WGS) revealed mutations in the negative regulators of efflux pumps, nfxB, and nalC, in CIP-only treated biofilm populations. The occurrence of nfxB mutations was significantly lower in flow cell biofilms treated with CIP-AO compared to CIP alone. These findings suggest that antioxidants could play a role in mitigating AMR development in biofilms.

The SOS Response Activation and the Risk of Antibiotic Resistance Enhancement in Proteus spp. Strains Exposed to Subinhibitory Concentrations of Ciprofloxacin

The widespread and inappropriate use of antibiotics, for therapeutic and prophylactic purposes, has contributed to a global crisis of rapidly increasing antimicrobial resistance of microorganisms. This resistance is often associated with elevated mutagenesis induced by the presence of antibiotics. Additionally, subinhibitory concentrations of antibiotics can trigger stress responses in bacteria, further exacerbating this problem. In the present study, we investigated the effect of low doses of ciprofloxacin on the induction of the SOS response and the subsequent development of antibiotic resistance in Proteus spp. strains. Our findings revealed an increase in mutation frequencies within the studied strains, accompanied by a significant upregulation of recA expression. These observations were consistent across experiments involving two subinhibitory concentrations of ciprofloxacin. To establish mutation frequencies and assess gene expression changes, we utilized the RifS-to-RifR forward mutagenesis assay and RT-qPCR analysis, respectively. Furthermore, employing the microdilution method, we demonstrated that these changes could promote cross-resistance to multiple classes of antibiotics in Proteus spp. clinical strains. This, combined with the recurrent nature of Proteus-associated infections, poses a substantial risk of therapeutic failure. In conclusion, exposure to low doses of ciprofloxacin can significantly impact the susceptibility of Proteus bacilli, not only reducing their sensitivity to ciprofloxacin itself but also fostering resistance to other antibiotic classes. These findings underscore the importance of cautious antibiotic use and highlight the potential consequences of subinhibitory antibiotic exposure in clinical and environmental settings.

Increased risk of antibiotic resistance in surface water due to global warming

As the pace of global warming accelerates, so do the threats to human health, urgent priority among them being antibiotic-resistant infections. In the context of global warming, this review summarises the direct and indirect effects of rising surface water temperatures on the development of bacterial antibiotic resistance. First, the resistance of typical pathogens such as E. coli increased with average temperature. This is not only related to increased bacterial growth rate and horizontal gene transfer frequency at high temperatures but also heat shock responses and cumulative effects. Secondly, the acceleration of bacterial growth indirectly promotes antibiotic residues in surface water, which is conducive to the growth and spread of resistant bacteria. Furthermore, the cascading effects of global warming, including the release of nutrients into the water and the resulting increase of bacteria and algae, indirectly promote the improvement of resistance. Water treatment processes exposed to high temperatures also increase the risk of resistance in surface water. The fitness costs of antibiotic resistance under these dynamic conditions are also discussed, concluding the relationship between various factors and resistance persistence. It was expected to provide a comprehensive basis for mitigating antibiotic resistance in the face of global warming.

Biochar and theaflavins mitigate the antibiotic resistome and antibiotic-resistant pathogens in a soil-lettuce continuum

Antibiotic resistance can be transferred into the food chain, leading to increased risks to human health from ready-to-eat vegetables. Mitigating the transmission of antibiotic resistance from soil to vegetables by green materials is of great significance. Here, we deciphered the roles of biochar and theaflavins in mitigating antibiotic resistance genes (ARGs) and antibiotic-resistant pathogens (ARPs) in a soil-lettuce continuum. Metagenomic results showed that biochar led to a significant decrease in the abundance of ARGs in lettuce leaves, while theaflavins contributed to a significant reduction in the diversity and abundance of ARGs in soil, particularly targeting dominant ARG types such as sulfonamide and aminoglycoside resistance genes. Meanwhile, biochar and theaflavins alleviated the potential mobility of ARGs, in lettuce leaves and soil, respectively, including the spread of ARGs to human pathogens. In addition, the diversity of ARG hosts was reduced in the soil-lettuce continuum and ARPs were not detected in lettuce leaves after the application of biochar or theaflavins. Overall, this study provides a novel perspective on green materials for mitigating the antibiotic resistome and ARPs in the soil-lettuce continuum, contributing to food security and human health.

Pathogen-encoded Rum DNA polymerase drives rapid bacterial drug resistance

The acquisition of multidrug resistance by pathogenic bacteria is a potentially incipient pandemic. Horizontal transfer of DNA from mobile integrative conjugative elements (ICEs) provides an important way to introduce genes that confer antibiotic (Ab)-resistance in recipient cells. Sizable numbers of SXT/R391 ICEs encode a hypermutagenic Rum DNA polymerase (Rum pol), which has significant homology with Escherichia coli pol V. Here, we show that even under tight transcriptional and post-transcriptional regulation imposed by host bacteria and the R391 ICE itself, Rum pol rapidly accelerates development of multidrug resistance (CIPR, RifR, AmpR) in E. coli in response to SOS-inducing Ab and non-Ab external stressors bleomycin (BLM), ciprofloxacin (CIP) and UV radiation. The impact of Rum pol on the rate of acquisition of drug resistance appears to surpass potential contributions from other cellular processes. We have shown that RecA protein plays a central role in controlling the ability of Rum pol to accelerate antibiotic resistance. A single amino acid substitution in RecA, M197D, acts as a 'Master Regulator' that effectively eliminates the Rum pol-induced Ab resistance. We suggest that Rum pol should be considered as one of the major factors driving development of de novo Ab resistance in pathogens carrying SXT/R391 ICEs.

Genetic stability of Mycobacterium smegmatis under the stress of first-line antitubercular agents

The sustained success of Mycobacterium tuberculosis as a pathogen arises from its ability to persist within macrophages for extended periods and its limited responsiveness to antibiotics. Furthermore, the high incidence of resistance to the few available antituberculosis drugs is a significant concern, especially since the driving forces of the emergence of drug resistance are not clear. Drug-resistant strains of Mycobacterium tuberculosis can emerge through de novo mutations, however, mycobacterial mutation rates are low. To unravel the effects of antibiotic pressure on genome stability, we determined the genetic variability, phenotypic tolerance, DNA repair system activation, and dNTP pool upon treatment with current antibiotics using Mycobacterium smegmatis. Whole-genome sequencing revealed no significant increase in mutation rates after prolonged exposure to first-line antibiotics. However, the phenotypic fluctuation assay indicated rapid adaptation to antibiotics mediated by non-genetic factors. The upregulation of DNA repair genes, measured using qPCR, suggests that genomic integrity may be maintained through the activation of specific DNA repair pathways. Our results, indicating that antibiotic exposure does not result in de novo adaptive mutagenesis under laboratory conditions, do not lend support to the model suggesting antibiotic resistance development through drug pressure-induced microevolution.

Antibiotic intermediates and antibiotics synergistically promote the development of multiple antibiotic resistance in antibiotic production wastewater

Antibiotic resistance (AR) is a major public health concern. Antibiotic intermediates (AIs) used in the production of semisynthetic antibiotics have the same bioactive structure as parent antibiotics and synthetic antibiotic production wastewater usually contains high concentrations of residual AIs; however, the effects of AIs and their interactive effects with antibiotics on the emergence of AR are unknown. In this study, antibiotic-sensitive E. coli K12 was exposed to five types of β-lactam AIs and their parent antibiotic ampicillin to analyze their impact on the evolution of multiple AR. The results indicated that AI 6-APA inhibits bacterial growth and stimulates the production of reactive oxygen species, as well as induces AR and antibiotic persistence like the parent antibiotic AMP. Combined exposure to 6-APA and AMP synergistically stimulated the induction of multiple AR and antibiotic persistence. The resistance mutation frequency increased up to 6.1 × 106-fold under combined exposure and the combination index reached 1326.5, indicating a strong synergy of 6-APA and AMP. Phenotypic and genotypic analyses revealed that these effects were associated with the overproduction of reactive oxygen species, enhanced stress response signatures, and activation of efflux pumps. These findings provide evidence and mechanistic insights into AR induction by AIs in antibiotic production wastewater.

Ketoprofen promotes the conjugative transfer of antibiotic resistance among antibiotic resistant bacteria in natural aqueous environments

The emergence and spread of antibiotic resistance in the environment pose a serious threat to global public health. It is acknowledged that non-antibiotic stresses, including disinfectants, pharmaceuticals and organic pollutants, play a crucial role in horizontal transmission of antibiotic resistance genes (ARGs). Despite the widespread presence of non-steroidal anti-inflammatory drugs (NSAIDs), notably in surface water, their contributions to the transfer of ARGs have not been systematically explored. Furthermore, previous studies have primarily concentrated on model strains to investigate whether contaminants promote the conjugative transfer of ARGs, leaving the mechanisms of ARG transmission among antibiotic resistant bacteria in natural aqueous environments under the selective pressures of non-antibiotic contaminants remains unclear. In this study, the Escherichia coli (E. coli) K12 carrying RP4 plasmid was used as the donor strain, indigenous strain Aeromonas veronii containing rifampicin resistance genes in Taihu Lake, and E. coli HB101 were used as receptor strains to establish inter-genus and intra-genus conjugative transfer systems, examining the conjugative transfer frequency under the stress of ketoprofen. The results indicated that ketoprofen accelerated the environmental spread of ARGs through several mechanisms. Ketoprofen promoted cell-to-cell contact by increasing cell surface hydrophobicity and reducing cell surface charge, thereby mitigating cell-to-cell repulsion. Furthermore, ketoprofen induced increased levels of reactive oxygen species (ROS) production, activated the DNA damage-induced response (SOS), and enhanced cell membrane permeability, facilitating ARG transmission in intra-genus and inter-genus systems. The upregulation of outer membrane proteins, oxidative stress, SOS response, mating pair formation (Mpf) system, and DNA transfer and replication (Dtr) system related genes, as well as the inhibition of global regulatory genes, all contributed to higher transfer efficiency under ketoprofen treatment. These findings served as an early warning for a comprehensive assessment of the roles of NSAIDs in the spread of antibiotic resistance in natural aqueous environments.

High salt condition alters LPS synthesis and induces the emergence of drug resistance mutations in Helicobacter pylori

The burgeoning emergence of drug-resistant Helicobacter pylori strains poses a significant challenge to the clinical success of eradication therapies and is primarily attributed to mutations within drug-targeting genes that lead to antibiotic resistance. This study investigated the effect of high salt conditions on the occurrence of drug-resistance mutations in H. pylori. We found that high salt condition significantly amplifies the frequency of drug resistance mutations in H. pylori. This can be chiefly attributed to our discovery indicating that high salt concentration results in elevated reactive oxygen species (ROS) levels, initiating DNA damage within H. pylori. Mechanistically, high salt condition suppresses lipopolysaccharide (LPS) synthesis gene expression, inducing alterations in the LPS structure and escalating outer membrane permeability. This disruption of LPS synthesis attenuates the expression and activity of SodB, facilitates increased ROS levels, and consequently increases the drug resistance mutation frequency. Impairing LPS synthesis engenders a reduction in intracellular iron levels, leading to diminished holo-Fur activity and increased apo-Fur activity, which represses the expression of SodB directly. Our findings suggest a correlation between high salt intake and the emergence of drug resistance in the human pathogen H. pylori, implying that dietary choices affect the risk of emergence of antimicrobial resistance.IMPORTANCEDrug resistance mutations mainly contribute to the emergence of clinical antibiotic-resistant Helicobacter pylori, a bacterium linked to stomach ulcers and cancer. In this study, we explored how elevated salt conditions influence the emergence of drug resistance in H. pylori. We demonstrate that H. pylori exhibits an increased antibiotic resistance mutation frequency when exposed to a high salt environment. We observed an increase in reactive oxygen species (ROS) under high salt conditions, which can cause DNA damage and potentially lead to mutations. Moreover, our results showed that high salt condition alters the bacterium's lipopolysaccharide (LPS) synthesis, leading to a reduced expression of SodB in a Fur-dependent manner. This reduction, in turn, elevates ROS levels, culminating in a higher frequency of drug-resistance mutations. Our research underscores the critical need to consider environmental influences, such as diet and lifestyle, in managing bacterial infections and combating the growing challenge of antibiotic resistance.

Clinicopathological Profile in Patients with Tubercular Cervical Lymphadenitis and Its Treatment Outcome

Tuberculosis is a common occurrence in developing countries. Drug resistance, co-morbidities, and limited availability of new rapid tests such as the GeneXpert/MTB Rif assay make diagnosis and treatment of extrapulmonary tuberculosis burdensome. A cross-sectional study was carried out at Employees' State Insurance Corporation Medical College and Hospital, Faridabad, Haryana of patients treated for tubercular cervical lymphadenopathy from December 2021 to March 2023 in the department of ENT. This study included 58 patients. The clinicopathological profile of patients and the outcome of treatment with antitubercular therapy were noted. The majority of patients had level V (39.6%) involvement. Incidental diagnosis of diabetes mellitus was seen in 2 cases (3.4%). Fever was the commonest constitutional symptom observed in 27.5% of cases. FNAC was suggestive of tubercular abscess in 48.2% and the GeneXpert MTB/RIF assay detected Mycobacterial tuberculosis in all the cases with rifampicin resistance in only one case. 56 cases (96.5%) had complete resolution after completion of antitubercular therapy including patients with rifampicin resistance and patients with diabetes mellitus. In the remaining two cases, treatment was prolonged for a few months before the resolution of the disease was observed. Timely diagnosis, patient compliance to antitubercular therapy, and adequate management of comorbidities lead to successful treatment outcomes in tubercular cervical lymphadenitis. Delayed response to treatment in a few cases needs further research into factors like immune status, nutrition, living conditions, and quality of drugs available to the public.

Bisphenol S Promotes the Transfer of Antibiotic Resistance Genes via Transformation

The antibiotic resistance crisis has seriously jeopardized public health and human safety. As one of the ways of horizontal transfer, transformation enables bacteria to acquire exogenous genes naturally. Bisphenol compounds are now widely used in plastics, food, and beverage packaging, and have become a new environmental pollutant. However, their potential relationship with the spread of antibiotic resistance genes (ARGs) in the environment remains largely unexplored. In this study, we aimed to assess whether the ubiquitous bisphenol S (BPS) could promote the transformation of plasmid-borne ARGs. Using plasmid pUC19 carrying the ampicillin resistance gene as an extracellular ARG and model microorganism E. coli DH5α as the recipient, we established a transformation system. Transformation assays revealed that environmentally relevant concentrations of BPS (0.1-10 μg/mL) markedly enhanced the transformation frequency of plasmid-borne ARGs into E. coli DH5α up to 2.02-fold. Fluorescent probes and transcript-level analyses suggest that BPS stimulated increased reactive oxygen species (ROS) production, activated the SOS response, induced membrane damage, and increased membrane fluidity, which weakened the barrier for plasmid transfer, allowing foreign DNA to be more easily absorbed. Moreover, BPS stimulates ATP supply by activating the tricarboxylic acid (TCA) cycle, which promotes flagellar motility and expands the search for foreign DNA. Overall, these findings provide important insight into the role of bisphenol compounds in facilitating the horizontal spread of ARGs and emphasize the need to monitor the residues of these environmental contaminants.

Multi-component liquid-infused systems: a new approach to functional coatings

Antifouling liquid-infused surfaces have generated interest in multiple fields due to their diverse applications in industry and medicine. In nearly all reports to date, the liquid component consists of only one chemical species. However, unlike traditional solid surfaces, the unique nature of liquid surfaces holds the potential for synergistic and even adaptive functionality simply by including additional elements in the liquid coating. In this work, we explore the concept of multi-component liquid-infused systems, in which the coating liquid consists of a primary liquid and a secondary component or components that provide additional functionality. For ease of understanding, we categorize recently reported multi-component liquid-infused surfaces according to the size of the secondary components: molecular scale, in which the secondary components are molecules; nanoscale, in which they are nanoparticles or their equivalent; and microscale, in which the additional components are micrometer size or above. We present examples at each scale, showing how introducing a secondary element into the liquid can result in synergistic effects, such as maintaining a pristine surface while actively modifying the surrounding environment, which are difficult to achieve in other surface treatments. The review highlights the diversity of fabrication methods and provides perspectives on future research directions. Introducing secondary components into the liquid matrix of liquid-infused surfaces is a promising strategy with significant potential to create a new class of multifunctional materials. Keywords: Active surfaces; Antimicrobial; Antifouling; Interfaces; Sensing surfaces.

Machine learning-assisted SERS approach enables the biochemical discrimination in Bcl-2 and Mcl-1 expressing yeast cells treated with ketoconazole and fluconazole antifungals

Antifungal medications are important due to their potential application in cancer treatment either on their own or with traditional treatments. The mechanisms that prevent the effects of these medications and restrict their usage in cancer treatment are not completely understood. The evaluation and discrimination of the possible protective effects of the anti-apoptotic members of the Bcl-2 family of proteins, critical regulators of mitochondrial apoptosis, against antifungal drug-induced cell death has still scientific uncertainties that must be considered. Novel, simple, and reliable strategies are highly demanded to identify the biochemical signature of this phenomenon. However, the complex nature of cells poses challenges for the analysis of cellular biochemical changes or classification. In this study, for the first time, we investigated the probable protective activities of Bcl-2 and Mcl-1 proteins against cell damage induced by ketoconazole (KET) and fluconazole (FLU) antifungal drugs in a yeast model through surface-enhanced Raman spectroscopy (SERS) approach. The proposed SERS platform created robust Raman spectra with a high signal-to-noise ratio. The analysis of SERS spectral data via advanced unsupervised and supervised machine learning methods enabled unquestionable differentiation (100 %) in samples and biomolecular identification. Various SERS bands related to lipids and proteins observed in the analyses suggest that the expression of these anti-apoptotic proteins reduces oxidative biomolecule damage induced by the antifungals. Also, cell viability assay, Annexin V-FITC/PI double staining, and total oxidant and antioxidant status analyses were performed to support Raman measurements. We strongly believe that the proposed approach paves the way for the evaluation of various biochemical structures/changes in various cells.

An inclusive study to elucidation the heavy metals-derived ecological risk nexus with antibiotic resistome functional shape of niche microbial community and their carbon substrate utilization ability in serpentine soil

Heavy metals (HMs) contained terrestrial ecosystems are often significantly display the antibiotic resistome in the pristine area due to increasing pressure from anthropogenic activity, is complex and emerging research interest. This study investigated that impact of chromium (Cr), nickel (Ni), cobalt (Co) concentrations in serpentine soil on the induction of antibiotic resistance genes and antimicrobial resistance within the native bacterial community as well as demonstrated their metabolic fingerprint. The full-length 16S-rRNA amplicon sequencing observed an increased abundance of Firmicutes, Actinobacteriota, and Acidobacteriota in serpentine soil. The microbial community in serpentine soil displayed varying preferences for different carbon sources, with some, such as carbohydrates and carboxylic acids, being consistently favored. Notably, 27 potential antibiotic resistance opportunistic bacterial genera have been identified in different serpentine soils. Among these, Lapillicoccus, Rubrobacter, Lacibacter, Chloroplast, Nitrospira, Rokubacteriales, Acinetobacter, Pseudomonas were significantly enriched in high and medium HMs concentrated serpentine soil samples. Functional profiling results illustrated that vancomycin resistance pathways were prevalent across all groups. Additionally, beta-lactamase, aminoglycoside, tetracycline, and vancomycin resistance involving specific bio-maker genes (ampC, penP, OXA, aacA, strB, hyg, aph, tet(A/B), otr(C), tet(M/O/Q), van(A/B/D), and vanJ) were the most abundant and enriched in the HMs-contaminated serpentine soil. Overall, this study highlighted that heavy-metal enriched serpentine soil is potential to support the proliferation of bacterial antibiotic resistance in native microbiome, and might able to spread antibiotic resistance to surrounding environment.

Antibiotic Resistance of Bacteria Isolated from Clinical Samples and Organs of Rescued Loggerhead Sea Turtles (Caretta caretta) in Southern Italy

Antimicrobial resistance affects all environments, endangering the health of numerous species, including wildlife. Increasing anthropic pressure promotes the acquisition and dissemination of antibiotic resistance by wild animals. Sea turtles, being particularly exposed, are considered sentinels and carriers of potential zoonotic pathogens and resistant strains. Therefore, this study examined the antibiotic resistance profiles of bacteria isolated from loggerhead sea turtles hospitalised in a rescue centre of Southern Italy over a 9-year period. Resistance to ceftazidime, doxycycline, enrofloxacin, flumequine, gentamicin, oxytetracycline and sulfamethoxazole-trimethoprim was evaluated for 138 strains isolated from the clinical samples or organs of 60 animals. Gram-negative families were the most isolated: Vibrionaceae were predominant, followed by Shewanellaceae, Pseudomonadaceae, Enterobacteriaceae and Morganellaceae. These last three families exhibited the highest proportion of resistance and multidrug-resistant strains. Among the three Gram-positive families isolated, Enterococcaceae were the most represented and resistant. The opportunistic behaviour of all the isolated species is particularly concerning for diseased sea turtles, especially considering their resistance to commonly utilised antibiotics. Actually, the multiple antibiotic resistance was higher when the sea turtles were previously treated. Taken together, these findings highlight the need to improve antimicrobial stewardship and monitor antibiotic resistance in wildlife, to preserve the health of endangered species, along with public and environmental health.

Bioenergetic stress potentiates antimicrobial resistance and persistence

Antimicrobial resistance (AMR) is a global health crisis and there is an urgent need to better understand AMR mechanisms. Antibiotic treatment alters several aspects of bacterial physiology, including increased ATP utilization, carbon metabolism, and reactive oxygen species (ROS) formation. However, how the "bioenergetic stress" induced by increased ATP utilization affects treatment outcomes is unknown. Here we utilized a synthetic biology approach to study the direct effects of bioenergetic stress on antibiotic efficacy. We engineered a genetic system that constitutively hydrolyzes ATP or NADH in Escherichia coli. We found that bioenergetic stress potentiates AMR evolution via enhanced ROS production, mutagenic break repair, and transcription-coupled repair. We also find that bioenergetic stress potentiates antimicrobial persistence via potentiated stringent response activation. We propose a unifying model that antibiotic-induced antimicrobial resistance and persistence is caused by antibiotic-induced. This has important implications for preventing or curbing the spread of AMR infections.

The DNA damage response of Escherichia coli, revisited: Differential gene expression after replication inhibition

In 1967, in this journal, Evelyn Witkin proposed the existence of a coordinated DNA damage response in Escherichia coli, which later came to be called the "SOS response." We revisited this response using the replication inhibitor azidothymidine (AZT) and RNA-Seq analysis and identified several features. We confirm the induction of classic Save our ship (SOS) loci and identify several genes, including many of the pyrimidine pathway, that have not been previously demonstrated to be DNA damage-inducible. Despite a strong dependence on LexA, these genes lack LexA boxes and their regulation by LexA is likely to be indirect via unknown factors. We show that the transcription factor "stringent starvation protein" SspA is as important as LexA in the regulation of AZT-induced genes and that the genes activated by SspA change dramatically after AZT exposure. Our experiments identify additional LexA-independent DNA damage inducible genes, including 22 small RNA genes, some of which appear to activated by SspA. Motility and chemotaxis genes are strongly down-regulated by AZT, possibly as a result of one of more of the small RNAs or other transcription factors such as AppY and GadE, whose expression is elevated by AZT. Genes controlling the iron siderophore, enterobactin, and iron homeostasis are also strongly induced, independent of LexA. We confirm that IraD antiadaptor protein is induced independent of LexA and that a second antiadaptor, IraM is likewise strongly AZT-inducible, independent of LexA, suggesting that RpoS stabilization via these antiadaptor proteins is an integral part of replication stress tolerance.

Exploring the links between SOS response, mutagenesis, and resistance during the recovery period

Although the mechanistic connections between SOS-induced mutagenesis and antibiotic resistance are well established, our current understanding of the impact of SOS response levels, recovery durations, and transcription/translation activities on mutagenesis remains relatively limited. In this study, when bacterial cells were exposed to mutagens like ultraviolet light for defined time intervals, a compelling connection between the rate of mutagenesis and the RecA-mediated SOS response levels became evident. Our observations also indicate that mutagenesis primarily occurs during the subsequent recovery phase following the removal of the mutagenic agent. When transcription/translation was inhibited or energy molecules were depleted at the onset of treatment or during the early recovery phase, there was a noticeable decrease in SOS response activation and mutagenesis. However, targeting these processes later in the recovery phase does not have the same effect in reducing mutagenesis, suggesting that the timing of inhibiting transcription/translation or depleting energy molecules is crucial for their efficacy in reducing mutagenesis. Active transcription, translation, and energy availability within the framework of SOS response and DNA repair mechanisms appear to be conserved attributes, supported by their consistent manifestation across diverse conditions, including the use of distinct mutagens such as fluoroquinolones and various bacterial strains.

Estimating mutation rates under heterogeneous stress responses

Exposure to environmental stressors, including certain antibiotics, induces stress responses in bacteria. Some of these responses increase mutagenesis and thus potentially accelerate resistance evolution. Many studies report increased mutation rates under stress, often using the standard experimental approach of fluctuation assays. However, single-cell studies have revealed that many stress responses are heterogeneously expressed in bacterial populations, which existing estimation methods have not yet addressed. We develop a population dynamic model that considers heterogeneous stress responses (subpopulations of cells with the response off or on) that impact both mutation rate and cell division rate, inspired by the DNA-damage response in Escherichia coli (SOS response). We derive the mutant count distribution arising in fluctuation assays under this model and then implement maximum likelihood estimation of the mutation-rate increase specifically associated with the expression of the stress response. Using simulated mutant count data, we show that our inference method allows for accurate and precise estimation of the mutation-rate increase, provided that this increase is sufficiently large and the induction of the response also reduces the division rate. Moreover, we find that in many cases, either heterogeneity in stress responses or mutant fitness costs could explain similar patterns in fluctuation assay data, suggesting that separate experiments would be required to identify the true underlying process. In cases where stress responses and mutation rates are heterogeneous, current methods still correctly infer the effective increase in population mean mutation rate, but we provide a novel method to infer distinct stress-induced mutation rates, which could be important for parameterising evolutionary models.

Role of RelA-synthesized (p)ppGpp and ROS-induced mutagenesis in de novo acquisition of antibiotic resistance in E. coli

The stringent response of bacteria to starvation and stress also fulfills a role in addressing the threat of antibiotics. Within this stringent response, (p)ppGpp, synthesized by RelA or SpoT, functions as a global alarmone. However, the effect of this (p)ppGpp on resistance development is poorly understood. Here, we show that knockout of relA or rpoS curtails resistance development against bactericidal antibiotics. The emergence of mutated genes associated with starvation and (p)ppGpp, among others, indicates the activation of stringent responses. The growth rate is decreased in ΔrelA-resistant strains due to the reduced ability to synthesize (p)ppGpp and the persistence of deacylated tRNA impeding protein synthesis. Sluggish cellular activity causes decreased production of reactive oxygen species (ROS), thereby reducing oxidative damage, leading to weakened DNA mismatch repair, potentially reducing the generation of mutations. These findings offer new targets for mitigating antibiotic resistance development, potentially achieved through inhibiting (p)ppGpp or ROS synthesis.

Antibacterial insights into alternariol and its derivative alternariol monomethyl ether produced by a marine fungus

Alternaria alternata FB1 is a marine fungus identified as a candidate for plastic degradation in our previous study. This fungus has been recently shown to produce secondary metabolites with significant antimicrobial activity against various pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and the notorious aquaculture pathogen Vibrio anguillarum. The antibacterial compounds were purified and identified as alternariol (AOH) and its derivative, alternariol monomethyl ether (AME). We found that AOH and AME primarily inhibited pathogenic bacteria (MRSA or V. anguillarum) by disordering cell division and some other key physiological and biochemical processes. We further demonstrated that AOH could effectively inhibit the unwinding activity of MRSA topoisomerases, which are closely related to cell division and are the potential action target of AOH. The antibacterial activities of AOH and AME were verified by using zebrafish as the in vivo model. Notably, AOH and AME did not significantly affect the viability of normal human liver cells at concentrations that effectively inhibited MRSA or V. anguillarum. Finally, we developed the genetic operation system of A. alternata FB1 and blocked the biosynthesis of AME by knocking out omtI (encoding an O-methyl transferase), which facilitated A. alternata FB1 to only produce AOH. The development of this system in the marine fungus will accelerate the discovery of novel natural products and further bioactivity study.IMPORTANCEMore and more scientific reports indicate that alternariol (AOH) and its derivative alternariol monomethyl ether (AME) exhibit antibacterial activities. However, limited exploration of their detailed antibacterial mechanisms has been performed. In the present study, the antibacterial mechanisms of AOH and AME produced by the marine fungus Alternaria alternata FB1 were disclosed in vitro and in vivo. Given their low toxicity on the normal human liver cell line under the concentrations exhibiting significant antibacterial activity against different pathogens, AOH and AME are proposed to be good candidates for developing promising antibiotics against methicillin-resistant Staphylococcus aureus and Vibrio anguillarum. We also succeeded in blocking the biosynthesis of AME, which facilitated us to easily obtain pure AOH. Moreover, based on our previous results, A. alternata FB1 was shown to enable polyethylene degradation.

Discovery of indolylacryloyl-derived oxacins as novel potential broad-spectrum antibacterial candidates

The emergence of serious bacterial resistance towards clinical oxacins poses a considerable threat to global public health, necessitating the development of novel structural antibacterial agents. Seven types of novel indolylacryloyl-derived oxacins (IDOs) were designed and synthesized for the first time from commercial 3,4-difluoroaniline via an eight-step procedure. The synthesized compounds were characterized by modern spectroscopic techniques. All target molecules were evaluated for antimicrobial activities. Most of the prepared IDOs showed a broad antibacterial spectrum and strong activities against the tested strains, especially ethoxycarbonyl IDO 10d (0.25-0.5 μg/mL) and hydroxyethyl IDO 10e (0.25-1 μg/mL) exhibited much superior antibacterial efficacies to reference drug norfloxacin. These highly active IDOs also displayed low hemolysis, cytotoxicity and resistance, as well as rapid bactericidal capacity. Further investigations indicated that ethoxycarbonyl IDO 10d and hydroxyethyl IDO 10e could effectively reduce the exopolysaccharide content and eradicate the formed biofilm, which might delay the development of drug resistance. Preliminary exploration of the antibacterial mechanism revealed that active IDOs could not only destroy membrane integrity, resulting in changes in membrane permeability, but also promote the accumulation of reactive oxygen species, leading to the production of malondialdehyde and decreased bacterial metabolism. Moreover, they exhibited the capability to bind with DNA and DNA gyrase, forming supramolecular complexes through various noncovalent interactions, thereby inhibiting DNA replication and causing bacterial death. All the above results suggested that the newly developed indolylacryloyl-derived oxacins should hold great promise as potential multitargeting broad-spectrum antibacterial candidates to overcome drug resistance.

A role for the stringent response in ciprofloxacin resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major cause of nosocomial infections and the leading cause of chronic lung infections in cystic fibrosis and chronic obstructive pulmonary disease patients. Antibiotic treatment remains challenging because P. aeruginosa is resistant to high concentrations of antibiotics and has a remarkable ability to acquire mutations conferring resistance to multiple groups of antimicrobial agents. Here we report that when P. aeruginosa is plated on ciprofloxacin (cipro) plates, the majority of cipro-resistant (ciproR) colonies observed at and after 48 h of incubation carry mutations in genes related to the Stringent Response (SR). Mutations in one of the major SR components, spoT, were present in approximately 40% of the ciproR isolates. Compared to the wild-type strain, most of these isolates had decreased growth rate, longer lag phase and altered intracellular ppGpp content. Also, 75% of all sequenced mutations were insertions and deletions, with short deletions being the most frequently occurring mutation type. We present evidence that most of the observed mutations are induced on the selective plates in a subpopulation of cells that are not instantly killed by cipro. Our results suggests that the SR may be an important contributor to antibiotic resistance acquisition in P. aeruginosa.

Can plastic pollution drive the emergence and dissemination of novel zoonotic diseases?

As the volume of plastic in the environment increases, so too does human interactions with plastic pollution. Similarly, domestic, feral, and wild animals are increasingly interacting with plastic pollution, highlighting the potential for contamination of plastic wastes with animal faeces, urine, saliva, and blood. Substantial evidence indicates that once in the environment, plastics rapidly become colonised by microbial biofilm (the so-called 'plastisphere), which often includes potentially harmful microbial pathogens (including pathogens that are zoonotic in nature). Climate change, increased urbanisation, and the intensification of agriculture, mean that the three-way interactions between humans, animals, and plastic pollution are becoming more frequent, which is significant as almost 60% of emerging human infectious diseases during the last century have been zoonotic. Here, we critically review the potential for contaminated environmental plastics to facilitate the evolution of novel pathogenic strains of microorganisms, and the subsequent role of plastic pollution in the cyclical dissemination of zoonotic pathogens. As the interactions between humans, animals, and plastic pollution continues to grow, and the volume of plastics entering the environment increases, there is clearly an urgent need to better understand the role of plastic waste in facilitating zoonotic pathogen evolution and dissemination, and the effect this can have on environmental and human health.

Inappropriate prescription of intravenous antibiotics at a tertiary children's hospital in China

BACKGROUND

Antibiotics are one of the most frequently prescribed medication classes worldwide. Inappropriate prescription of antibiotics has increased the risk of drug-resistant infections and associated mortality. The aim of this study was to examine the patterns of intravenous antibiotics prescribing in emergency and outpatient departments of a tertiary children's hospital in China.

METHODS

Data on intravenous prescriptions dispensed by the emergency and outpatient department from January 1, 2015 to May 31, 2016 were extracted from the information system of the Children's Hospital of Fudan University. Prevalence of intravenous antibiotics use and the suitability of intravenous antibiotic prescription were evaluated on the basis of a completed microbiological examination, antibiotics susceptibility testing, and dose prescribed for patients diagnosed with pneumonia, acute bronchitis, fever, and acute upper respiratory infection (AURI) patients. The prescription rate was expressed as the number of intravenous antibiotic prescriptions per total number of prescriptions.

RESULTS

Overall, 94.2% of pediatric patients and 78.5% of issued intravenous prescriptions were for antibiotics. beta-lactam antibacterial (90.5%) and macrolides (18.5%) were the most commonly used categories of antibiotics, while cefuroxime (28.8%) was the most used antibiotic. Besides, pneumonia (31.3%), acute bronchitis (14.1%), fever (6.5%), and AURI (5.5%) were the most commonly recorded infections. However, in these four diseases, the rate of conducting microbiological examination was 0.3%, 0.2%, 2.1%, and 2.8%, respectively. Approximately, 52.1%, 40.0%, 40.4%, and 30.5% of intravenous antibiotic prescriptions were inappropriately used in pneumonia, acute bronchitis, fever, and AURI, respectively. Doses higher and lower than the recommended were often for each of these four diseases.

CONCLUSIONS

The frequency of intravenous antibiotic prescription was high in pediatric emergency and outpatient departments. Inappropriate use of intravenous antibiotics commonly occurred in pneumonia, acute bronchitis, fever, and AURI. Appropriate interventions and prevention strategies need to be developed to curtail inappropriate prescribing of antibiotics.

A combined evaluation of the characteristics and antibiotic resistance induction potential of antibiotic wastewater during the treatment process

Antibiotic wastewater contains a variety of pollutant stressors that can induce and promote antibiotic resistance (AR) when released into the environment. Although these substances are mostly in concentrations lower than those known to induce AR individually, it is possible that antibiotic wastewater discharge might still promote the AR transmission risk via additive or synergistic effects. However, the comprehensive effect of antibiotic wastewater on AR development has rarely been evaluated, and its treatment efficiency remains unknown. Here, samples were collected from different stages of a cephalosporin production wastewater treatment plant, and the potential AR induction effect of their chemical mixtures was explored through the exposure of the antibiotic-sensitive Escherichia coli K12 strain. Incubation with raw cephalosporin production wastewater significantly promoted mutation rates (3.6 × 103-9.3 × 103-fold) and minimum inhibition concentrations (6.0-6.7-fold) of E. coli against ampicillin and chloramphenicol. This may be attributed to the inhibition effect and oxidative stress of cephalosporin wastewater on E. coli. The AR induction effect of cephalosporin wastewater decreased after the coagulation sedimentation treatment and was completely removed after the full treatment process. A Pearson correlation analysis revealed that the reduction in the AR induction effect had a strong positive correlation with the removal of organics and biological toxicity. This indicates that the antibiotic wastewater treatment had a collaborative processing effect of conventional pollutants, toxicity, and the AR induction effect. This study illustrates the potential AR transmission risk of antibiotic wastewater and highlights the need for its adequate treatment.

Deterministic effect of oxygen level variation on shaping antibiotic resistome

An increase in acquisition of antibiotic resistance genes (ARGs) by pathogens under antibiotic selective pressure poses public health threats. Sub-inhibitory antibiotics induce bacteria to generate reactive oxygen species (ROS) dependent on dissolved oxygen (DO) levels, while molecular connection between ROS-mediated ARG emergence through DNA damage and metabolic changes remains elusive. Thus, the study investigates antibiotic resistome dynamics, microbiome shift, and pathogen distribution in hyperoxic (5-7 mg L-1), normoxic (2-4 mg L-1), and hypoxic (0.5-1 mg L-1) conditions using lab-scale bioreactor. Composite inoculums in the reactor were designed to represent comprehensive microbial community and AR profile from selected activated sludge. RT-qPCR and metagenomic analysis showed an increase in ARG count (100.98 ppm) with enrichment of multidrug efflux pumps (acrAB, mexAB) in hyperoxic condition. Conversely, total ARGs decreased (0.11 ppm) under hypoxic condition marked by a major decline in int1 abundance. Prevalence of global priority pathogens increased in hyperoxic (22.5%), compared to hypoxic (0.9%) wherein major decrease were observed in Pseudomonas, Shigella, and Borrelia. The study observed an increase in superoxide dismutase (sodA, sodB), DNA repair genes (nfo, polA, recA, recB), and ROS (10.4 µmol L-1) in adapted biomass with spiked antibiotics. This suggests oxidative damage that facilitates stress-induced mutagenesis providing evidence for observed hyperoxic enrichment of ARGs. Moreover, predominance of catalase (katE, katG) likely limit oxidative damage that deplete ARG breeding in hypoxic condition. The study proposes a link between oxygen levels and AR development that offers insights into mitigation and intervention of AR by controlling oxygen-related stress and strategic selection of bacterial communities.

Increased expression of Mycobacterium tuberculosis Rv3737 gene associated with low-level amikacin resistance

INTRODUCTION

As an infectious disease, tuberculosis (TB) poses a serious threat to public health. Although amikacin (AMK) is an important antibiotic for the treatment of drug-resistant TB, its resistance mechanisms are not fully understood.

METHODS

To investigate the role of Rv3737 gene on AMK drug susceptibility, a Mycobacterium tuberculosis (M.tb) Rv3737 knockout strain (H37Rv△Rv3737) and a Mycobacterium smegmatis (M.sm) Rv3737 overexpressing strain (Msm/pMV261-Rv3737) were used to detect their minimal inhibitory concentrations (MICs) in this study.

RESULTS

The AMK MICs of Rv3737 knockout and overexpressing strains were 4-fold lower and 2-fold higher than those of the wild-type and empty plasmid strains, respectively. The results of clinical isolates showed that no Rv3737 gene mutation was found to be associated with AMK susceptibility, while the rrs A1401G mutation remained the main mechanism of high level of AMK resistance (MIC>32 μg/ml). There was a positive correlation between Rv3737 mRNA expression level and AMK MIC. In the isolates with low-level AMK resistance (MIC = 4 μg/ml) without rrs A1401G mutation, the expression level of Rv3737 gene was significantly higher than those of susceptible isolates.

CONCLUSIONS

In this study, the Rv3737 gene was reported for the first time for its effect on AMK susceptibility in M.tb. Although the rrs A1401G mutation remains the main reason of high-level AMK resistance, high expression of the Rv3737 gene was associated with low-level AMK resistance in clinical isolates.

Vancomycin and nisin-modified magnetic Fe3O4@SiO2 nanostructures coated with chitosan to enhance antibacterial efficiency against methicillin resistant Staphylococcus aureus (MRSA) infection in a murine superficial wound model

BACKGROUND

The objective of this research was to prepare some Fe3O4@SiO2@Chitosan (CS) magnetic nanocomposites coupled with nisin, and vancomycin to evaluate their antibacterial efficacy under both in vitro and in vivo against the methicillin-resistant Staphylococcus. aureus (MRSA).

METHODS

In this survey, the Fe3O4@SiO2 magnetic nanoparticles (MNPs) were constructed as a core and covered the surface of MNPs via crosslinking CS by glutaraldehyde as a shell, then functionalized with vancomycin and nisin to enhance the inhibitory effects of nanoparticles (NPs). X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), and dynamic light scattering (DLS) techniques were then used to describe the nanostructures.

RESULTS

Based on the XRD, and FE-SEM findings, the average size of the modified magnetic nanomaterials were estimated to be around 22-35 nm, and 34-47 nm, respectively. The vancomycin was conjugated in three polymer-drug ratios; 1:1, 2:1 and 3:1, with the percentages of 45.52%, 35.68%, and 24.4%, respectively. The polymer/drug ratio of 1:1 exhibited the slowest release rate of vancomycin from the Fe3O4@SiO2@CS-VANCO nanocomposites during 24 h, which was selected to examine their antimicrobial effects under in vivo conditions. The nisin was grafted onto the nanocomposites at around 73.2-87.2%. All the compounds resulted in a marked reduction in the bacterial burden (P-value < 0.05).

CONCLUSION

The vancomycin-functionalized nanocomposites exhibited to be more efficient in eradicating the bacterial cells both in vitro and in vivo. These findings introduce a novel bacteriocin-metallic nanocomposite that can suppress the normal bacterial function on demand for the treatment of MRSA skin infections.