Increased transfer of a multidrug resistance plasmid in Escherichia coli biofilms at the air-liquid interface

Antibiotic Resistance and Disinfectant Resistance Among Escherichia coli Isolated During Red Meat Production

Escherichia coli commonly found in the gastrointestinal tracts of food animals include Shiga toxin-producing E. coli (STEC, stx+, eae-), Enterohemorrhagic E. coli (EHEC, stx+, eae+), Enteropathogenic E. coli (EPEC, stx-, eae+), and "nondiarrheagenic" E. coli (NDEC, stx-, eae-). EHEC, EPEC, and STEC are associated with foodborne disease outbreaks. During meat processing, disinfectants are employed to control various bacteria, including human pathogens. Concerns exist that E. coli resistant to antibiotics are less susceptible to disinfectants used during meat processing. Since EHEC, EPEC, and STEC with reduced susceptibility to disinfectants are potential public health risks, the goal of this study was to evaluate the association of antibiotic resistant (ABR) E. coli with increased tolerance to 4% lactic acid (LA) and 150 ppm quaternary ammonium compounds (QACs). A pool of 3,367 E. coli isolated from beef cattle, veal calves, swine, and sheep at various processing stages was screened to identify ABR E. coli. Resistance to ≥1 of the six antibiotics examined was identified in 27.9%, 36.1%, 54.5%, and 28.7% among the NDEC (n = 579), EHEC (n = 693), EPEC (n = 787), and STEC (n = 1308) isolates evaluated, respectively. Disinfectant tolerance did not differ (P > 0.05) between ABR and antibiotic susceptible EHEC isolates. Comparable frequencies (P > 0.05) of biofilm formation or congo red binding were observed between ABR and antibiotic susceptible strains of E. coli. Understanding the frequencies of ABR and disinfectant tolerance among E. coli present in food-animal is a critically important component of meat safety.

Regulation of quorum sensing for the manipulation of conjugative transfer of antibiotic resistance genes in wastewater treatment system

The emergence and transmission of antibiotic resistance genes (ARGs) through plasmid-mediated conjugation has become a significant worldwide public health threat. Biofilms are widely recognized as the primary reservoirs for ARGs, providing favorable conditions for horizontal gene transfer. Quorum sensing (QS) plays a critical role in bacterial biofilm formation, which further influences the spread of bacterial resistance. In this study, we examined the effects of vanillin, a QS inhibitor (QSI), at subinhibitory concentrations (sub-MICs) ranging from 0 - 0.1 g/L, on the transfer of ARGs between Escherichia coli and Pseudomonas aeruginosa. Our findings indicated that vanillin at sub-MICs inhibited the conjugative transfer frequency of the RP4 plasmid. This inhibition was supported by the downregulation of plasmid transfer genes. The suppression of conjugation can mainly be attributed to the inhibition of biofilm formation, the synthesis of extracellular polymeric substances (EPS), and the secretion of virulence factors, all of which are regulated by the bacterial QS system. On the other hand, the levels of ROS and cell membrane permeability were not primary explanations for this phenomenon. Furthermore, vanillin also reduced the conjugative transfer frequency of ARGs in wastewater effluent, providing a potential approach to alleviate bacterial resistance in water environments. These findings underscore the regulatory role of QSI in controlling ARGs transfer and have significant implications for manipulating the dissemination of bacterial resistance in the environment.

Comprehensive insights into antibiotic resistance gene migration in microalgal-bacterial consortia: Mechanisms, factors, and perspectives

With the overuse of antibiotics, antibiotic resistance gene (ARG) prevalence is gradually increasing. ARGs are considered emerging contaminants that are broadly concentrated and dispersed in most aquatic environments. Recently, interest in microalgal-bacterial biotreatment of antibiotics has increased, as eukaryotes are not the primary target of antimicrobial drugs. Moreover, research has shown that microalgal-bacterial consortia can minimize the transmission of antibiotic resistance in the environment. Unfortunately, reviews surrounding the ARG migration mechanism in microalgal-bacterial consortia have not yet been performed. This review briefly introduces the migration of ARGs in aquatic environments. Additionally, an in-depth summary of horizontal gene transfer (HGT) between cyanobacteria and bacteria and from bacteria to eukaryotic microalgae is presented. Factors influencing gene transfer in microalgal-bacterial consortia are discussed systematically, including bacteriophage abundance, environmental conditions (temperature, pH, and nutrient availability), and other selective pressure conditions including nanomaterials, heavy metals, and pharmaceuticals and personal care products. Furthermore, considering that quorum sensing could be involved in DNA transformation by affecting secondary metabolites, current knowledge surrounding quorum sensing regulation of HGT of ARGs is summarized. In summary, this review gives valuable information to promote the development of practical and innovative techniques for ARG removal by microalgal-bacterial consortia.

Uropathogenic Escherichia coli (UPEC)-Associated Urinary Tract Infections: The Molecular Basis for Challenges to Effective Treatment

Urinary tract infections (UTIs) are among the most common bacterial infections, especially among women and older adults, leading to a significant global healthcare cost burden. Uropathogenic Escherichia coli (UPEC) are the most common cause and accounts for the majority of community-acquired UTIs. Infection by UPEC can cause discomfort, polyuria, and fever. More serious clinical consequences can result in urosepsis, kidney damage, and death. UPEC is a highly adaptive pathogen which presents significant treatment challenges rooted in a complex interplay of molecular factors that allow UPEC to evade host defences, persist within the urinary tract, and resist antibiotic therapy. This review discusses these factors, which include the key genes responsible for adhesion, toxin production, and iron acquisition. Additionally, it addresses antibiotic resistance mechanisms, including chromosomal gene mutations, antibiotic deactivating enzymes, drug efflux, and the role of mobile genetic elements in their dissemination. Furthermore, we provide a forward-looking analysis of emerging alternative therapies, such as phage therapy, nano-formulations, and interventions based on nanomaterials, as well as vaccines and strategies for immunomodulation. This review underscores the continued need for research into the molecular basis of pathogenesis and antimicrobial resistance in the treatment of UPEC, as well as the need for clinically guided treatment of UTIs, particularly in light of the rapid spread of multidrug resistance.

CRISPR-Cas-Based Antimicrobials: Design, Challenges, and Bacterial Mechanisms of Resistance

The emergence of antibiotic-resistant bacterial strains is a source of public health concern across the globe. As the discovery of new conventional antibiotics has stalled significantly over the past decade, there is an urgency to develop novel approaches to address drug resistance in infectious diseases. The use of a CRISPR-Cas-based system for the precise elimination of targeted bacterial populations holds promise as an innovative approach for new antimicrobial agent design. The CRISPR-Cas targeting system is celebrated for its high versatility and specificity, offering an excellent opportunity to fight antibiotic resistance in pathogens by selectively inactivating genes involved in antibiotic resistance, biofilm formation, pathogenicity, virulence, or bacterial viability. The CRISPR-Cas strategy can enact antimicrobial effects by two approaches: inactivation of chromosomal genes or curing of plasmids encoding antibiotic resistance. In this Review, we provide an overview of the main CRISPR-Cas systems utilized for the creation of these antimicrobials, as well as highlighting promising studies in the field. We also offer a detailed discussion about the most commonly used mechanisms for CRISPR-Cas delivery: bacteriophages, nanoparticles, and conjugative plasmids. Lastly, we address possible mechanisms of interference that should be considered during the intelligent design of these novel approaches.

An overview of plasmid transfer in the plant microbiome

Plant microbiomes are pivotal for healthy plant physiological development. Microbes live in complex co-association with plant hosts, and interactions within these microbial communities vary with plant genotype, plant compartment, phenological stage, and soil properties, among others. Plant microbiomes also harbor a substantial and diverse pool of mobile genes encoded on plasmids. Several plasmid functions attributed to plant-associated bacteria are relatively poorly understood. Additionally, the role of plasmids in disseminating genetic traits within plant compartments is not well known. Here, we present the current knowledge on the occurrence, diversity, function, and transfer of plasmids in plant microbiomes, emphasizing the factors that could modulate gene transfer in-planta. We also describe the role of the plant microbiome as a plasmid reservoir and the dissemination of its genetic material. We include a brief discussion on the current methodological limitations in studying plasmid transfer within plant microbiomes. This information could be useful to elucidate the dynamics of the bacterial gene pools, the adaptations different organisms have made, and variations in bacterial populations that might have never been described before, particularly in complex microbial communities associated with plants in natural and anthropogenic impacted environments.

Using SMART Magnetic Fluids and Gels for Prevention and Destruction of Bacterial Biofilms

Biofouling is a major problem in all natural and artificial settings where solid surfaces meet liquids in the presence of living microorganisms. Microbes attach to the surface and form a multidimensional slime that protects them from unfavorable environments. These structures, known as biofilms, are detrimental and very hard to remove. Here, we used SMART magnetic fluids [ferrofluids (FFs), magnetorheological fluids (MRFs), and ferrogels (FGs) containing iron oxide nano/microparticles] and magnetic fields to remove bacterial biofilms from culture tubes, glass slides, multiwell plates, flow cells, and catheters. We compared the ability of different SMART fluids to remove biofilms and found that commercially available, as well as homemade, FFs, MRFs, and FGs can successfully remove biofilm more efficiently than traditional mechanical methods, especially from textured surfaces. In tested conditions, SMARTFs reduced bacterial biofilms by five orders of magnitude. The ability to remove biofilm increased with the amount of magnetic particles; therefore, MRFs, FG, and homemade FFs with high amounts of iron oxide were the most efficient. We showed also that SMART fluid deposition can protect a surface from bacterial attachment and biofilm formation. Possible applications of these technologies are discussed.

Horizontal Gene Transfer of Antibiotic Resistance Genes in Biofilms

Most bacteria attach to biotic or abiotic surfaces and are embedded in a complex matrix which is known as biofilm. Biofilm formation is especially worrisome in clinical settings as it hinders the treatment of infections with antibiotics due to the facilitated acquisition of antibiotic resistance genes (ARGs). Environmental settings are now considered as pivotal for driving biofilm formation, biofilm-mediated antibiotic resistance development and dissemination. Several studies have demonstrated that environmental biofilms can be hotspots for the dissemination of ARGs. These genes can be encoded on mobile genetic elements (MGEs) such as conjugative and mobilizable plasmids or integrative and conjugative elements (ICEs). ARGs can be rapidly transferred through horizontal gene transfer (HGT) which has been shown to occur more frequently in biofilms than in planktonic cultures. Biofilm models are promising tools to mimic natural biofilms to study the dissemination of ARGs via HGT. This review summarizes the state-of-the-art of biofilm studies and the techniques that visualize the three main HGT mechanisms in biofilms: transformation, transduction, and conjugation.

Biofilms preserve the transmissibility of a multi-drug resistance plasmid

Self-transmissible multidrug resistance (MDR) plasmids are a major health concern because they can spread antibiotic resistance to pathogens. Even though most pathogens form biofilms, little is known about how MDR plasmids persist and evolve in biofilms. We hypothesize that (i) biofilms act as refugia of MDR plasmids by retaining them in the absence of antibiotics longer than well-mixed planktonic populations and that (ii) the evolutionary trajectories that account for the improvement of plasmid persistence over time differ between biofilms and planktonic populations. In this study, we evolved Acinetobacter baumannii with an MDR plasmid in biofilm and planktonic populations with and without antibiotic selection. In the absence of selection, biofilm populations were better able to maintain the MDR plasmid than planktonic populations. In planktonic populations, plasmid persistence improved rapidly but was accompanied by a loss of genes required for the horizontal transfer of plasmids. In contrast, in biofilms, most plasmids retained their transfer genes, but on average, plasmid, persistence improved less over time. Our results showed that biofilms can act as refugia of MDR plasmids and favor the horizontal mode of plasmid transfer, which has important implications for the spread of MDR.

In situ, in vivo, and in vitro approaches for studying AMR plasmid conjugation in the gut microbiome

Antimicrobial resistance (AMR) is a global threat, with evolution and spread of resistance to frontline antibiotics outpacing the development of novel treatments. The spread of AMR is perpetuated by transfer of antimicrobial resistance genes (ARGs) between bacteria, notably those encoded by conjugative plasmids. The human gut microbiome is a known 'melting pot' for plasmid conjugation, with ARG transfer in this environment widely documented. There is a need to better understand the factors affecting the incidence of these transfer events, and to investigate methods of potentially counteracting the spread of ARGs. This review describes the use and potential of three approaches to studying conjugation in the human gut: observation of in situ events in hospitalized patients, modelling of the microbiome in vivo predominantly in rodent models, and the use of in vitro models of various complexities. Each has brought unique insights to our understanding of conjugation in the gut. The use and development of these systems, and combinations thereof, will be pivotal in better understanding the significance, prevalence, and manipulability of horizontal gene transfer in the gut microbiome.

Impact of Plastic Particles on the Horizontal Transfer of Antibiotic Resistance Genes to Bacterium: Dependent on Particle Sizes and Antibiotic Resistance Gene Vector Replication Capacities

Plastic particles impact the propagation of antibiotic resistance genes (ARGs) in environmental media, and their perturbation on the horizontal gene transfer (HGT) of ARGs is recognized as a critical influencing mechanism. However, studies concerning the influence and influencing mechanisms of plastic particles on the HGT of ARGs were limited, particularly for the effect of particle sizes and ARG vector-associated mechanisms. This study explored the impact of polystyrene (PS) particles with sizes of 75, 90, 100, 1000, and 10000 nm on the HGT (via transformation) of ARGs mediated by pUC19, pSTV29, and pBR322 plasmids into Escherichia coli cells. PS particles with sizes ≤100 nm impacted the transformation of ARGs, but large particles (1000 and 10000 nm) showed no obvious effects. Effects of PS particles on the transfer of three plasmids were vastly distinct. For pUC19 with high replication capacities, the transfer was monotonously promoted. However, for pSTV29 and pBR322 with low replication capacities, suppressing effects were observed. This was attributed to two competing mechanisms. The enhancing mechanism was that the direct interaction of PS particles with membrane lipids and the indirect effect associated with bacterial oxidative stress response induced pore formation on the cell membrane and increased membrane permeability, thus enhancing plasmid entrance. The inhibiting mechanism was that PS particles interfered with plasmid replication inside E. coli, thus decreasing the bacterial tranformation. This study deepened our understanding of the environmental dissemination of ARGs in plastic contamination.

Biofilm antimicrobial susceptibility through an experimental evolutionary lens

Experimental evolution experiments in which bacterial populations are repeatedly exposed to an antimicrobial treatment, and examination of the genotype and phenotype of the resulting evolved bacteria, can help shed light on mechanisms behind reduced susceptibility. In this review we present an overview of why it is important to include biofilms in experimental evolution, which approaches are available to study experimental evolution in biofilms and what experimental evolution has taught us about tolerance and resistance in biofilms. Finally, we present an emerging consensus view on biofilm antimicrobial susceptibility supported by data obtained during experimental evolution studies.

In Situ Monitoring and Quantitative Determination of R27 Plasmid Conjugation

Horizontal gene transfer (HGT) by plasmid conjugation is a major driving force in the spread of antibiotic resistance among Enterobacteriaceae. Most of the conjugation studies are based on calculation of conjugation ratios (number of transconjugants/number of donors) after viable counting of transconjugant and donor cells. The development of robust, fast and reliable techniques for in situ monitoring and quantification of conjugation ratios might accelerate progress in understanding the impact of this cellular process in the HGT. The IncHI1 plasmids, involved in multiresistance phenotypes of relevant pathogens such as Salmonella and E. coli, are distinguished by the thermosensitivity of their conjugative transfer. Conjugation mediated by IncHI1 plasmids is more efficient at temperatures lower than 30 °C, suggesting that the transfer process takes place during the environmental transit of the bacteria. In this report, we described a methodology to monitor in situ the conjugation process during agar surface matings of the IncHI1 plasmid R27 and its derepressed derivative drR27 at different temperatures. A three-color-labeling strategy was used to visualize the spatial distribution of transconjugants within the heterogeneous environment by epifluorescence and confocal microscopy. Moreover, the fluorescent labelling was also used to quantify conjugation frequencies in liquid media by flow cytometry.

Metabolism differences of biofilm and planktonic Pseudomonas aeruginosa in viable but nonculturable state induced by chlorine stress

More than 95% of the bacteria in environment are viable but nonculturable (VBNC). However, it is difficult to elucidate directly the metabolic characteristics of these VBNC bacteria and the differences between biofilm-VBNC bacteria and planktonic-VBNC bacteria. In this study, VBNC P. aeruginosa induced by chlorine was used to clarify the metabolism characteristics and mechanism of differential metabolism between biofilm-VBNC bacteria and planktonic-VBNC bacteria. Results showed that P. aeruginosa in biofilm state was more likely to enter VBNC state. The mechanisms of differential metabolism were involved in the difference of reactive oxygen species production owing to the protection of extracellular polymers. ¹⁵N and ²H labeled single-cell Raman spectra directly proved that VBNC state bacteria still maintained low material and energy metabolism, and the metabolic activity of biofilm-VBNC P. aeruginosa was lower than that of planktonic-VBNC P. aeruginosa. GC-MS/MS analysis showed 51 metabolites with significant differences. KEGG analysis showed that the types and contents of extracellular metabolites from P. aeruginosa in VBNC states were significantly lower than those in the culturable state (p < 0.05), mainly involving in citrate cycle, glutathione metabolism, phenylalanine metabolism, tyrosine metabolism and fatty acid degradation. Also, the contents of most extracellular metabolites from P. aeruginosa in biofilm-VBNC state were lower than those in VBNC planktonic state. The significant differences (p < 0.05) were mainly involved in alanine, aspartate and glutamate metabolism, glycolysis/gluconeogenesis, D-Alanine metabolism and glycerophospholipid metabolism. The result of this research was favorable to the accurate identification of VBNC bacteria, the health risk assessment and scientific control of harmful VBNC bacteria.

Biofilm through the Looking Glass: A Microbial Food Safety Perspective

Food-processing facilities harbor a wide diversity of microorganisms that persist and interact in multispecies biofilms, which could provide an ecological niche for pathogens to better colonize and gain tolerance against sanitization. Biofilm formation by foodborne pathogens is a serious threat to food safety and public health. Biofilms are formed in an environment through synergistic interactions within the microbial community through mutual adaptive response to their long-term coexistence. Mixed-species biofilms are more tolerant to sanitizers than single-species biofilms or their planktonic equivalents. Hence, there is a need to explore how multispecies biofilms help in protecting the foodborne pathogen from common sanitizers and disseminate biofilm cells from hotspots and contaminate food products. This knowledge will help in designing microbial interventions to mitigate foodborne pathogens in the processing environment. As the global need for safe, high-quality, and nutritious food increases, it is vital to study foodborne pathogen behavior and engineer new interventions that safeguard food from contamination with pathogens. This review focuses on the potential food safety issues associated with biofilms in the food-processing environment.

Do microplastic biofilms promote the evolution and co-selection of antibiotic and metal resistance genes and their associations with bacterial communities under antibiotic and metal pressures?

Microplastic (MP) biofilms with heterogeneous bacterial compositions and structure have become a hotspot of antibiotic resistance genes (ARGs) in aquatic environments. The evolutionary features of ARGs and their related factors including class 1 integron (intI1), metal resistance genes (MRGs), and bacterial communities in MP biofilms under exogenous pressures and how they compared with natural substrates (NS) are unclear. The individual and combined pressures of sulfamethoxazole, tetracycline, and zinc were used to drive the dynamic evolution of ARGs, intI1, MRGs, and bacterial communities in the MP and NS biofilms. The exogenous pressures from the combined selection of sulfamethoxazole, tetracycline, and zinc and their increasing concentrations both significantly enhanced the abundances of ARGs on the MP compared to the NS. Meanwhile, the selective pressures resulted in obvious dissimilarities between the MP and NS bacterial communities. The core bacterial taxa and the co-occurrence patterns of ARGs and bacterial genera in the biofilms of MP and NS were obviously different, and more potential ARG host bacteria selectively colonized the MP. Metal pressure also enhanced the enrichment of ARGs in the MP biofilms by promoting the spread of intI1 via the co-selection mechanism.

Gut biofilms: Bacteroides as model symbionts to study biofilm formation by intestinal anaerobes

Bacterial biofilms are communities of adhering bacteria that express distinct properties compared to their free-living counterparts, including increased antibiotic tolerance and original metabolic capabilities. Despite the potential impact of the biofilm lifestyle on the stability and function of the dense community of micro-organisms constituting the mammalian gut microbiota, the overwhelming majority of studies performed on biofilm formation by gut bacteria focused either on minor and often aerobic members of the community or on pathogenic bacteria. In this review, we discuss the reported evidence for biofilm-like structures formed by gut bacteria, the importance of considering the anaerobic nature of gut biofilms and we present the most recent advances on biofilm formation by Bacteroides, one of the most abundant genera of the human gut microbiota. Bacteroides species can be found attached to food particles and colonizing the mucus layer and we propose that Bacteroides symbionts are relevant models to probe the physiology of gut microbiota biofilms.

A hybrid DNA sequencing approach is needed to properly link genotype to phenotype in multi-drug resistant bacteria

Antibiotic resistance genes (ARGs) are now viewed as emerging contaminants posing a potential worldwide human health risk. The degree to which ARGs are transferred to other bacteria via mobile genetic elements (MGEs), including insertion sequences (ISs), plasmids, and phages, has a strong association with their likelihood to function as resistance transfer determinants. Consequently, understanding the structure and function of MGEs is paramount to assessing future health risks associated with ARGs in an environment subjected to strong antibiotic pressure. In this study we used whole genome sequencing, done using MinION and HiSeq platforms, to examine antibiotic resistance determinants among four multidrug resistant bacteria isolated from fish farm effluent in Jeju, South Korea. The combined data was used to ascertain the association between ARGs and MGEs. Hybrid assembly using HiSeq and MinION reads revealed the presence of IncFIB(K) and pVPH2 plasmids, whose sizes were verified using pulsed field gel electrophoresis. Twenty four ARGs and 95 MGEs were identified among the 955 coding sequences annotated on these plasmids. More importantly, 22 of 24 ARGs conferring resistance to various antibiotics were found to be located near MGEs, whereas about a half of the ARGs (11 out of 21) were so in chromosomes. Our results also suggest that the total phenotypic resistance exhibited by the isolates was mainly contributed by these putatively mobilizable ARGs. The study gives genomic insights into the origins of putatively mobilizable ARGs in bacteria subjected to selection pressure.

Monitoring antibiotic resistance genes in wastewater treatment: Current strategies and future challenges

Antimicrobial resistance (AMR) is a growing threat to human and animal health. Progress in molecular biology has revealed new and significant challenges for AMR mitigation given the immense diversity of antibiotic resistance genes (ARGs), the complexity of ARG transfer, and the broad range of omnipresent factors contributing to AMR. Municipal, hospital and abattoir wastewater are collected and treated in wastewater treatment plants (WWTPs), where the presence of diverse selection pressures together with a highly concentrated consortium of pathogenic/commensal microbes create favourable conditions for the transfer of ARGs and proliferation of antibiotic resistant bacteria (ARB). The rapid emergence of antibiotic resistant pathogens of clinical and veterinary significance over the past 80 years has re-defined the role of WWTPs as a focal point in the fight against AMR. By reviewing the occurrence of ARGs in wastewater and sludge and the current technologies used to quantify ARGs and identify ARB, this paper provides a research roadmap to address existing challenges in AMR control via wastewater treatment. Wastewater treatment is a double-edged sword that can act as either a pathway for AMR spread or as a barrier to reduce the environmental release of anthropogenic AMR. State of the art ARB identification technologies, such as metagenomic sequencing and fluorescence-activated cell sorting, have enriched ARG/ARB databases, unveiled keystone species in AMR networks, and improved the resolution of AMR dissemination models. Data and information provided in this review highlight significant knowledge gaps. These include inconsistencies in ARG reporting units, lack of ARG/ARB monitoring surrogates, lack of a standardised protocol for determining ARG removal via wastewater treatments, and the inability to support appropriate risk assessment. This is due to a lack of standard monitoring targets and agreed threshold values, and paucity of information on the ARG-pathogen host relationship and risk management. These research gaps need to be addressed and research findings need to be transformed into practical guidance for WWTP operators to enable effective progress towards mitigating the evolution and spread of AMR.

Bacterial Biofilm Growth on 3D-Printed Materials

Recent advances in 3D printing have led to a rise in the use of 3D printed materials in prosthetics and external medical devices. These devices, while inexpensive, have not been adequately studied for their ability to resist biofouling and biofilm buildup. Bacterial biofilms are a major cause of biofouling in the medical field and, therefore, hospital-acquired, and medical device infections. These surface-attached bacteria are highly recalcitrant to conventional antimicrobial agents and result in chronic infections. During the COVID-19 pandemic, the U.S. Food and Drug Administration and medical officials have considered 3D printed medical devices as alternatives to conventional devices, due to manufacturing shortages. This abundant use of 3D printed devices in the medical fields warrants studies to assess the ability of different microorganisms to attach and colonize to such surfaces. In this study, we describe methods to determine bacterial biofouling and biofilm formation on 3D printed materials. We explored the biofilm-forming ability of multiple opportunistic pathogens commonly found on the human body including Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus to colonize eight commonly used polylactic acid (PLA) polymers. Biofilm quantification, surface topography, digital optical microscopy, and 3D projections were employed to better understand the bacterial attachment to 3D printed surfaces. We found that biofilm formation depends on surface structure, hydrophobicity, and that there was a wide range of antimicrobial properties among the tested polymers. We compared our tested materials with commercially available antimicrobial PLA polymers.

Properties affecting transfer and expression of degradative plasmids for the purpose of bioremediation

Plasmids, circular DNA that exist and replicate outside of the host chromosome, have been important in the spread of non-essential genes as well as the rapid evolution of prokaryotes. Recent advances in environmental engineering have aimed to utilize the mobility of plasmids carrying degradative genes to disseminate them into the environment for cost-effective and environmentally friendly remediation of harmful contaminants. Here, we review the knowledge surrounding plasmid transfer and the conditions needed for successful transfer and expression of degradative plasmids. Both abiotic and biotic factors have a great impact on the success of degradative plasmid transfer and expression of the degradative genes of interest. Properties such as ecological growth strategies of bacteria may also contribute to plasmid transfer and may be an important consideration for bioremediation applications. Finally, the methods for detection of conjugation events have greatly improved and the application of these tools can help improve our understanding of conjugation in complex communities. However, it remains clear that more methods for in situ detection of plasmid transfer are needed to help detangle the complexities of conjugation in natural environments to better promote a framework for precision bioremediation.

Oxygen concentration affects frequency and range of transconjugants for the incompatibility (Inc) P-1 and P-7 plasmids pBP136 and pCAR1

The frequency of transconjugants were compared for the incompatibility (Inc) P-1 and P-7 plasmids pBP136 and pCAR1 under aerobic and anaerobic conditions. Filter mating assays were performed with one donor strain and one recipient strain using different donors of Pseudomonas and recipient strains, including Pseudomonas, Pantoea, and Buttiauxella. Under anaerobic condition, frequencies of transconjugants for both plasmids were 101-103-fold lower than those under aerobic condition regardless of whether aerobically or anaerobically grown donors and recipients were used. To compare the transconjugant ranges under aerobic and anaerobic conditions, conjugation was performed between the donor of pBP136 and recipient bacteria extracted from environmental samples. Several transconjugants were uniquely obtained from each aerobic or anaerobic condition. Our findings indicate that a plasmid can differently spread among bacteria depending on the oxygen concentrations of the environment.

Contrasting distribution of antibiotic resistance genes and microbial communities in suspended activated sludge versus attached biofilms in an integrated fixed film activated sludge (IFAS) system

Suspended activated sludge (AS) and carrier-attached biofilms simultaneously exist in an integrated fixed film activated sludge (IFAS) system. However, the differentiation of antibiotic resistance genes (ARGs) and microbial communities in different types of biofilms is rarely reported. In this study, successions of ARGs and microbial communities of AS and two types of suspended carrier-attached biofilms over seasons were investigated in the IFAS system of one municipal wastewater treatment plant. Results showed that substantial differences were found in the distribution pattern of ARGs, bacterial communities, and predicted microbial function between AS and attached biofilms. The relative abundances of all detected ARGs in AS were significantly higher than those in attached biofilms. ARGs with higher relative abundances generally existed in K3 carrier (surface area ≥ 800 m²/m³) attached biofilms than those in K1 carrier (surface area ≥ 450 m²/m³) biofilms. The relative abundances of ARGs were negatively correlated with temperature and biochemical oxygen demand (BOD₅) and positively correlated with ammonium nitrogen contents for AS but not for attached biofilms. No significant relationship was found between the extracellular polymeric substance (EPS) content and ARG abundance for all samples. Temperature, BOD₅, and ammonium nitrogen contents were closely connected to microbial communities. The Bray-Curtis distance of bacterial communities between two adjacent sampling seasons for AS was larger than those of two attached biofilms. Network analysis indicated that the AS network had more positive links and intense connections than the attached biofilm networks, potentially facilitating the dissemination of ARGs. The differential distribution of ARGs among the three types of samples was significantly correlated with the microbial co-occurrence network topological properties. Bray-Curtis distance and network analysis suggest that microbial community is more robust in attached biofilms than in suspended AS. This work provides a more in-depth understanding of ARGs and microbial community distributions in wastewater biofilms.

Dominance Between Plasmids Determines the Extent of Biofilm Formation

Bacterial biofilms have an impact in medical and industrial environments because they often confer protection to bacteria against harmful agents, and constitute a source from which microorganisms can disperse. Conjugative plasmids can enhance bacterial ability to form biofilms because conjugative pili act as adhesion factors. However, plasmids may interact with each other, either facilitating or inhibiting plasmid transfer. Accordingly, we asked whether effects on plasmid transfer also impacts biofilm formation. We measured biofilm formation of Escherichia coli cells harboring two plasmid types, or when the two plasmids were present in the same population but carried in different cells. Using eleven natural isolated conjugative plasmids, we confirmed that some indeed promote biofilm formation and, importantly, that this ability is correlated with conjugative efficiency. Further we studied the effect of plasmid pairs on biofilm formation. We observed increased biofilm formation in approximately half of the combinations when both plasmids inhabited the same cell or when the plasmids were carried in different cells. Moreover, in approximately half of the combinations, independent of the co-inhabitation conditions, one of the plasmids alone determined the extent of biofilm formation – thus having a dominant effect over the other plasmid. The molecular mechanisms responsible for these interactions were not evaluated here and future research is required to elucidate them.

The human gut resistome: Current concepts & future prospects

The human gut is home to a myriad of organisms. While some are harmless commensals, others are transient, pathogenic flora. The gut microbiome is composed of diverse bacterial flora, and apart from playing a major role in protecting from various infectious and non-infectious diseases, it plays an important role in resistance to antimicrobials. The collection of genes or genetic material that confers antimicrobial resistance constitutes the gut resistome, and it may involve the pathogens or commensals of the intestinal tract. The diversity of this gut resistome is influenced by various environmental factors including the diet and antibiotic exposure. This review highlights the recent concepts pertaining to the human gut resistome, factors affecting it, how it impacts human health and diseases, methods to study the resistome and potential therapeutic approaches.

Growth of microorganisms in an interfacially driven space bioreactor analog

Fluid bioreactors in microgravity environments may utilize alternative methods of containment and mixing. The ring-sheared drop (RSD) is a containerless mixing device which functions in microgravity using surface tension for containment and mixes through interfacially-driven flow. To assess the feasibility of using interfacially driven flow devices, such as the RSD, as bioreactors, Escherichia coli growth and recombinant protein expression were analyzed in a ground-based analog of the RSD called the knife edge surface viscometer (KEV). Results demonstrated that the KEV can facilitate the growth of E. coli and that growth rate increases logarithmically with increasing knife edge rotation rate, similar to the standard growth method on Earth (orbital shaker). Furthermore, the KEV was shown to be viable for supporting recombinant protein expression in E. coli at levels comparable to those achieved using standard growth methods.

HIV Drugs Inhibit Transfer of Plasmids Carrying Extended-Spectrum β-Lactamase and Carbapenemase Genes

Antimicrobial-resistant (AMR) infections pose a serious risk to human and animal health. A major factor contributing to this global crisis is the sharing of resistance genes between different bacteria via plasmids. The WHO lists Enterobacteriaceae, such as Escherichia coli and Klebsiella pneumoniae, producing extended-spectrum β-lactamases (ESBL) and carbapenemases as "critical" priorities for new drug development. These resistance genes are most often shared via plasmid transfer. However, finding methods to prevent resistance gene sharing has been hampered by the lack of screening systems for medium-/high-throughput approaches. Here, we have used an ESBL-producing plasmid, pCT, and a carbapenemase-producing plasmid, pKpQIL, in two different Gram-negative bacteria, E. coli and K. pneumoniae Using these critical resistance-pathogen combinations, we developed an assay using fluorescent proteins, flow cytometry, and confocal microscopy to assess plasmid transmission inhibition within bacterial populations in a medium-throughput manner. Three compounds with some reports of antiplasmid properties were tested; chlorpromazine reduced transmission of both plasmids and linoleic acid reduced transmission of pCT. We screened the Prestwick library of over 1,200 FDA-approved drugs/compounds. From this, we found two nucleoside analogue drugs used to treat HIV, abacavir and azidothymidine (AZT), which reduced plasmid transmission (AZT, e.g., at 0.25 μg/ml reduced pCT transmission in E. coli by 83.3% and pKpQIL transmission in K. pneumoniae by 80.8% compared to untreated controls). Plasmid transmission was reduced by concentrations of the drugs which are below peak serum concentrations and are achievable in the gastrointestinal tract. These drugs could be used to decolonize humans, animals, or the environment from AMR plasmids.IMPORTANCE More and more bacterial infections are becoming resistant to antibiotics. This has made treatment of many infections very difficult. One of the reasons this is such a large problem is that bacteria are able to share their genetic material with other bacteria, and these shared genes often include resistance to a variety of antibiotics, including some of our drugs of last resort. We are addressing this problem by using a fluorescence-based system to search for drugs that will stop bacteria from sharing resistance genes. We uncovered a new role for two drugs used to treat HIV and show that they are able to prevent the sharing of two different types of resistance genes in two unique bacterial strains. This work lays the foundation for future work to reduce the prevalence of resistant infections.

Occurrence of antibiotics and antibiotic resistance genes and their correlations in lower Yangtze River, China

The overuse and misuse of antibiotics could promote the emergence of antibiotic resistance genes (ARGs) and pose a potential risk to human health and the ecological environment. In this study, fifteen antibiotics and their corresponding ARGs in water, sediment and sewage treatment plant (STP) effluent were analysed to investigate their occurrence and correlation in the Yangtze River (Jiangsu section) for the first time. The concentrations of erythromycin-H₂O (EM-H₂O) (2.08-30 ng L^-1) and ofloxacin (OFL) (290-8400 ng kg^-1) were the highest in the water and sediment, respectively, and EM-H₂O and clarithromycin (CLA) posed the highest risks to aquatic organisms. The concentrations of antibiotics in STP effluent were significantly higher (p < 0.05) than those in the water. Norfloxacin (NOR) was the most predominant antibiotic, with low removal efficiency (-38%-51%), in STPs; the concentration of NOR in the STP effluent was 4-6 orders of magnitude higher than that in the water. Moreover, the concentrations of antibiotics and their corresponding ARG abundance in downstream were higher than those in upstream, suggesting that STPs with high concentration levels might be an important source of river contamination. Additionally, the concentrations of antibiotics and the abundance of ARGs might increase after the sewage treatment process. The results also showed the prevalence of sul1 and sul2 in all the sampling sites. Significant correlations (p < 0.0001) were detected between int1 and sul1 and sul2, which resulted from the contribution of int1 to the propagation of ARGs. Overall, this study demonstrated the prevalence of antibiotics and ARGs and their inconsistent correlations in the Yangtze River (Jiangsu section) and provides support for further investigation of the occurrence and spread of antibiotics and ARGs.

Cyclic Changes in the Amide Bands Within Escherichia coli Biofilms Monitored Using Real-Time Infrared Attenuated Total Reflection Spectroscopy (IR-ATR)

Contrary to the planktonic state of bacteria, their biofilm form represents severe complications in areas such as human medicine or food industry due to the increasing resistance against harsh conditions and treatment. In the present study, infrared attenuated total reflection (IR-ATR) spectroscopy has been applied as an analytic tool studying Escherichia coli ( E. coli) biofilm formation close to real time. We report on IR spectroscopic investigations on the biofilm formation via ATR waveguides probing the biofilm in the spectral window of 1800-900 cm^-1 at dynamic flow conditions, which facilitated monitoring the growth dynamics during several days. Key IR bands are in the range 1700-1590 cm^-1 (amide I), 1580-1490 cm^-1 (amide II), and 1141-1006 cm^-1 extracellular polymeric substances (EPS), which were evaluated as a function of time. Cyclic fluctuations of the amide I and amide II bands and a continuous increase of the EPS band were related to the starvation of bottom-layered bacteria caused by the nutrient gradient. Potential death of bacteria may then result in cannibalistic behavior known for E. coli colonies. Observing this behavior via IR spectroscopy allows revealing these cyclical changes in bottom-layered bacteria within the biofilm under continuous nutrient flow, in molecular detail, and during extended periods for the first time.

Regulatory loop between the CsrA system and NhaR, a high salt/high pH regulator

In E. coli, under high pH/high salt conditions, a major Na+/H+ antiporter (NhaA) is activated to maintain an internal pH level. Its expression is induced by a specific regulator NhaR, which is also responsible for osmC and pgaA regulation. Here I report that the NhaR regulator affects the carbon storage regulatory Csr system. I found that the expression of all major components of the Csr system-CsrA regulator, CsrB and CsrC small RNAs, and the CsrB and CsrC stability were indirectly affected by nhaR mutation under stress conditions. Using a combination of experimental and in silico analyses, I concluded that the mechanism of regulation included direct and indirect activation of a two-component system (TCS) response regulator-UvrY. NhaR regulation involved interactions with the regulators H-NS and SdiA and was affected by a naturally occurring spontaneous IS5 insertion in the promoter region. A regulatory circuit was proposed and discussed.

Spatially resolved abundances of antibiotic resistance genes and intI1 in wastewater treatment biofilms

Attached growth bioprocesses that use biofilms to remove organic matter or nutrients from wastewater are known to harbor antibiotic resistance genes (ARGs). Biofilms in these processes are spatially heterogeneous, but little is known about depth stratification of ARGs in complex, mixed culture biofilms. To address this knowledge gap, we used an experimental approach combining cryosectioning and quantitative polymerase chain reaction to quantify the spatial distribution of three ARGs (sul1, ermB, and qnrS) and the class 1 integron-integrase gene intI1 in biofilms from a lab-scale rotating annular reactor fed with synthetic wastewater. We also used high throughput 16S ribosomal RNA (rRNA) gene sequencing to characterize community structure with depth in biofilms. The ARG sul1 and the integron-integrase gene intI1 were found in higher abundances in upper layers of biofilm near the fluid-biofilm interface than in lower layers and exhibited significant correlations between the distance from substratum and gene abundances. The genes ermB and qnrS were present in comparatively low relative abundances. Microbial community structure varied significantly by date of sampling and distance from the substratum. These findings highlight the genetic and taxonomic heterogeneity with distance from substratum in wastewater treatment biofilms and show that sul1 and intI1 are particularly abundant near fluid-biofilm interfaces where cells are most likely to detach and flow into downstream portions of treatment systems and can ultimately be released into the environment through effluent.

In vitro and ex vivo systems at the forefront of infection modeling and drug discovery

Bacterial infections and antibiotic resistant bacteria have become a growing problem over the past decade. As a result, the Centers for Disease Control predict more deaths resulting from microorganisms than all cancers combined by 2050. Currently, many traditional models used to study bacterial infections fail to precisely replicate the in vivo bacterial environment. These models often fail to incorporate fluid flow, bio-mechanical cues, intercellular interactions, host-bacteria interactions, and even the simple inclusion of relevant physiological proteins in culture media. As a result of these inadequate models, there is often a poor correlation between in vitro and in vivo assays, limiting therapeutic potential. Thus, the urgency to establish in vitro and ex vivo systems to investigate the mechanisms underlying bacterial infections and to discover new-age therapeutics against bacterial infections is dire. In this review, we present an update of current in vitro and ex vivo models that are comprehensively changing the landscape of traditional microbiology assays. Further, we provide a comparative analysis of previous research on various established organ-disease models. Lastly, we provide insight on future techniques that may more accurately test new formulations to meet the growing demand of antibiotic resistant bacterial infections.

Horizontal Plasmid Transfer by Transformation in Escherichia coli: Environmental Factors and Possible Mechanisms

Transformation is one mode of horizontal gene transfer (HGT) in bacteria, wherein extracellular naked DNA is taken up by cells that have developed genetic competence. Sensitivity to DNase, which degrades naked DNA, is the key to distinguishing transformation from the DNase-resistant HGT mechanisms. In general, Escherichia coli is not believed to be naturally transformable; it develops high competence only under artificial conditions, including exposure to high Ca2+ concentrations. However, E. coli can reportedly express modest competence under certain conditions that are feasible in natural environments outside laboratory. In addition, recent data suggest that environmental factors influence multiple routes of transformation. In this mini review, we (1) summarize our studies on transformation-based HGT using E. coli experimental systems and (2) discuss the possible occurrence of transformation via multiple mechanisms in the environment and its possible impact on the spread of antibiotic resistance genes.

Options and Limitations in Clinical Investigation of Bacterial Biofilms

Bacteria can form single- and multispecies biofilms exhibiting diverse features based upon the microbial composition of their community and microenvironment. The study of bacterial biofilm development has received great interest in the past 20 years and is motivated by the elegant complexity characteristic of these multicellular communities and their role in infectious diseases. Biofilms can thrive on virtually any surface and can be beneficial or detrimental based upon the community's interplay and the surface. Advances in the understanding of structural and functional variations and the roles that biofilms play in disease and host-pathogen interactions have been addressed through comprehensive literature searches. In this review article, a synopsis of the methodological landscape of biofilm analysis is provided, including an evaluation of the current trends in methodological research. We deem this worthwhile because a keyword-oriented bibliographical search reveals that less than 5% of the biofilm literature is devoted to methodology. In this report, we (i) summarize current methodologies for biofilm characterization, monitoring, and quantification; (ii) discuss advances in the discovery of effective imaging and sensing tools and modalities; (iii) provide an overview of tailored animal models that assess features of biofilm infections; and (iv) make recommendations defining the most appropriate methodological tools for clinical settings.

Reducing Bacterial Infections and Biofilm Formation Using Nanoparticles and Nanostructured Antibacterial Surfaces

With the rapid spreading of resistance among common bacterial pathogens, bacterial infections, especially antibiotic-resistant bacterial infections, have drawn much attention worldwide. In light of this, nanoparticles, including metal and metal oxide nanoparticles, liposomes, polymersomes, and solid lipid nanoparticles, have been increasingly exploited as both efficient antimicrobials themselves or as delivery platforms to enhance the effectiveness of existing antibiotics. In addition to the emergence of widespread antibiotic resistance, of equal concern are implantable device-associated infections, which result from bacterial adhesion and subsequent biofilm formation at the site of implantation. The ineffectiveness of conventional antibiotics against these biofilms often leads to revision surgery, which is both debilitating to the patient and expensive. Toward this end, micro- and nanotopographies, especially those that resemble natural surfaces, and nonfouling chemistries represent a promising combination for long-term antibacterial activity. Collectively, the use of nanoparticles and nanostructured surfaces to combat bacterial growth and infections is a promising solution to the growing problem of antibiotic resistance and biofilm-related device infections.

Molecular mechanisms of biofilm-based antibiotic resistance and tolerance in pathogenic bacteria

Biofilms are surface-attached groups of microbial cells encased in an extracellular matrix that are significantly less susceptible to antimicrobial agents than non-adherent, planktonic cells. Biofilm-based infections are, as a result, extremely difficult to cure. A wide range of molecular mechanisms contribute to the high degree of recalcitrance that is characteristic of biofilm communities. These mechanisms include, among others, interaction of antimicrobials with biofilm matrix components, reduced growth rates and the various actions of specific genetic determinants of antibiotic resistance and tolerance. Alone, each of these mechanisms only partially accounts for the increased antimicrobial recalcitrance observed in biofilms. Acting in concert, however, these defences help to ensure the survival of biofilm cells in the face of even the most aggressive antimicrobial treatment regimens. This review summarises both historical and recent scientific data in support of the known biofilm resistance and tolerance mechanisms. Additionally, suggestions for future work in the field are provided.

Biofilm: A Hotspot for Emerging Bacterial Genotypes

Bacteria have the ability to adapt to changing environments through rapid evolution mediated by modification of existing genetic information, as well as by horizontal gene transfer (HGT). This makes bacteria a highly successful life form when it comes to survival. Unfortunately, this genetic plasticity may result in emergence and dissemination of antimicrobial resistance and virulence genes, and even the creation of multiresistant "superbugs" which may pose serious threats to public health. As bacteria commonly reside in biofilms, there has been an increased interest in studying these phenomena within biofilms in recent years. This review summarizes the present knowledge within this important area of research. Studies on bacterial evolution in biofilms have shown that mature biofilms develop into diverse communities over time. There is growing evidence that the biofilm lifestyle may be more mutagenic than planktonic growth. Furthermore, all three main mechanisms for HGT have been observed in biofilms. This has been shown to occur both within and between bacterial species, and higher transfer rates in biofilms than in planktonic cultures were detected. Of special concern are the observations that mutants with increased antibiotic resistance occur at higher frequency in biofilms than in planktonic cultures even in the absence of antibiotic exposure. Likewise, efficient dissemination of antimicrobial resistance genes, as well as virulence genes, has been observed within the biofilm environment. This new knowledge emphasizes the importance of biofilm awareness and control.

Biofilm Surface Density Determines Biocide Effectiveness

High resistance of biofilms for chemical challenges is a serious industrial and medical problem. In this work a gradient of surface covered with biofilm has been produced and correlated to the effectiveness of different commercially available oxidative biocides. The results for thin Escherichia coli biofilms grown in rich media supplemented with glucose or lactose on glass or poly methyl methacrylate surfaces indicate that the effectiveness of hydrogen peroxide or chlorine dioxide and quaternary ammonium compounds is inversely proportional to the fraction of the surface covered with the biofilm. In areas where biofilm covered more than 90% of the available surface the biocide treatment was inefficient after 60 min of incubation. The combined effect of oxidant and surfactant increased the effectiveness of the biocide. On the other hand, the increased biofilm viscoelasticity reduced biocide effectiveness. The results emphasize differential biocide effectiveness depending on the fraction of the attached bacterial cells. The results suggest that biofilm biocide resistance is an acquired property that increases with biofilm maturation. The more dense sessile structures present lower log reductions compared to less dense ones.

Plasmid-Mediated Bioaugmentation for the Bioremediation of Contaminated Soils

Bioaugmentation, or the inoculation of microorganisms (e.g., bacteria harboring the required catabolic genes) into soil to enhance the rate of contaminant degradation, has great potential for the bioremediation of soils contaminated with organic compounds. Regrettably, cell bioaugmentation frequently turns into an unsuccessful initiative, owing to the rapid decrease of bacterial viability and abundance after inoculation, as well as the limited dispersal of the inoculated bacteria in the soil matrix. Genes that encode the degradation of organic compounds are often located on plasmids and, consequently, they can be spread by horizontal gene transfer into well-established, ecologically competitive, indigenous bacterial populations. Plasmid-mediated bioaugmentation aims to stimulate the spread of contaminant degradation genes among indigenous soil bacteria by the introduction of plasmids, located in donor cells, harboring such genes. But the acquisition of plasmids by recipient cells can affect the host’s fitness, a crucial aspect for the success of plasmid-mediated bioaugmentation. Besides, environmental factors (e.g., soil moisture, temperature, organic matter content) can play important roles for the transfer efficiency of catabolic plasmids, the expression of horizontally acquired genes and, finally, the contaminant degradation activity. For plasmid-mediated bioaugmentation to be reproducible, much more research is needed for a better selection of donor bacterial strains and accompanying plasmids, together with an in-depth understanding of indigenous soil bacterial populations and the environmental conditions that affect plasmid acquisition and the expression and functioning of the catabolic genes of interest.

Transfer Potential of Plasmids Conferring Extended-Spectrum-Cephalosporin Resistance in Escherichia coli from Poultry

Escherichia coli strains resistant to extended-spectrum cephalosporins (ESC) are widely distributed in Norwegian broiler production, and the majority harbor transferable IncK or IncI1 plasmids carrying bla_CMY-2. Persistent occurrence in broiler farms may occur through the survival of ESC-resistant E. coli strains in the farm environment, or by transfer and maintenance of resistance plasmids within a population of environmental bacteria with high survival abilities. The aim of this study was to determine the transferability of two successful bla_CMY-2-carrying plasmids belonging to the incompatibility groups IncK and IncI1 into E. coli and Serratia species recipients. Initially, conjugative plasmid transfer from two E. coli donors to potential recipients was tested in an agar assay. Conjugation was further investigated for selected mating pairs in surface and planktonic assays at temperatures from 12°C to 37°C. Transfer of plasmids was observed on agar, in broth, and in biofilm at temperatures down to 25°C. The IncK plasmid was able to transfer into Serratia marcescens, and transconjugants were able to act as secondary plasmid donors to different E. coli and Serratia species recipients. All transconjugants displayed an AmpC phenotype corresponding to the acquisition of bla_CMY-2. In summary, the results indicate that the IncK plasmid may transfer between E. coli and Serratia spp. under conditions relevant for broiler production.

IMPORTANCE Certain bla_CMY-2-carrying plasmids are successful and disseminated in European broiler production. Traditionally, plasmid transferability has been studied under conditions that are optimal for bacterial growth. Plasmid transfer has previously been reported between E. coli bacteria in biofilms at 37°C and in broth at temperatures ranging from 8 to 37°C. However, intergenus transfer of bla_CMY-2-carrying plasmids from E. coli to environmental bacteria in the food-processing chain has not been previously studied. We demonstrate that bla_CMY-2-carrying plasmids are capable of conjugative transfer between different poultry-associated bacterial genera under conditions relevant for broiler production. Transfer to Serratia spp. and to hosts with good biofilm-forming abilities and with the potential to act as secondary plasmid donors to new hosts might contribute to the persistence of these resistance plasmids. These results contribute to increased knowledge of factors affecting the persistence of ESC resistance in broiler production and can provide a basis for improvement of routines and preventive measures.

Conjugation in Escherichia coli Biofilms on Poly(dimethylsiloxane) Surfaces with Microtopographic Patterns

Bacterial biofilms are highly tolerant to antimicrobials and play an important role in the development and spread of antibiotic resistance based on horizontal gene transfer due to close cell-to-cell contact. As an important surface property, topography has been shown to affect bacterial adhesion and biofilm formation. Here, we demonstrate that micrometer-scale surface topographies also affect horizontal gene transfer through conjugation in bacterial biofilms. Specifically, biofilm formation and associated conjugation on poly(dimethylsiloxane) (PDMS) surfaces with 10 μm tall protruding patterns were studied using fluorescently labeled donor and recipient strains of Escherichia coli. The results demonstrate that square-shaped topographic patterns with side length of 20, 50, and 100 μm and interpattern distance equal to or larger than 10 μm promote biofilm formation and conjugation compared to the smooth control. The vertical sides of these topographic features were found to be the "hot spots" for bacterial conjugation compared to the top of patterns and grooves between topographic features. The increase in conjugation frequency on the sides of topographic patterns was attributed to the high cell density of recipient cells at these locations. A motility (motB) mutant of the recipient strain exhibited defects in biofilm formation at the "hot spots" and conjugation, which were recovered by complementing the motB gene on a plasmid. These results also provided guidance for designing surface topographies that can reduce conjugation. Specifically, 10 μm tall hexagon-shaped topographic patterns with side length of 15 μm and interpattern distance of 2 μm were prepared to reduce biofilm formation on the side of protruding patterns and interrupt cell-cell interaction in the grooves. This topography exhibited 85% and 46% reduction of biofilm formation and associated conjugation, respectively, compared to the smooth control.

Rationally designed dual functional block copolymers for bottlebrush-like coatings: In vitro and in vivo antimicrobial, antibiofilm, and antifouling properties

Numerous antimicrobial coatings have been developed for biomedical devices/implants, but few can simultaneously fulfill the requirements for antimicrobial and antifouling ability and biocompatibility. In this study, to develop an antimicrobial and antibiofilm surface coating, diblock amphiphilic molecules with antimicrobial and antifouling segments in a single chain were rationally designed and synthesized. Cationic antimicrobial polypeptides (AMP) were first synthesized by N-carboxyanhydride ring-opening polymerization (NCA-ROP). Heterofunctionalized poly(ethylene glycol) with different lengths (methacrylate-PEG_n-tosyl, n=10/45/90) was synthesized and site-specifically conjugated with polypeptides to form diblock amphiphiles. Along with increased PEG chain length, hemolytic activity was considerably improved, and broad-spectrum antimicrobial activity is retained. Three MA-PEG_n-b-AMP copolymers were further grafted onto the surface of silicone rubber (a commonly used catheter material) via plasma/UV-induced surface polymerizations to form a bottlebrush-like coating with excellent antimicrobial activity against several pathogenic bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus), and effectively prevent biofilm formation. This bottlebrush coating also greatly reduced protein adsorption and platelet adhesion, indicating its excellent antifouling ability. An in vitro cytotoxicity study also demonstrated that this coating is biocompatible with mammalian cells. After subcutaneous implantation of the materials in rats, we demonstrated that the g-PEG₄₅-b-AMP bottlebrush coating exhibits significant anti-infective activity in vivo. Thus, this facilely synthesized PEGylated AMP bottlebrush coating is a feasible method to prevent biomedical devices-associated infections.

STATEMENT OF SIGNIFICANCE

Current antimicrobial coatings are often associated with concerns such as antibiotic resistance, environmental pollution, short-time antimicrobial activity, biofouling, poor blood compatibility and cytotoxicity, etc. To overcome these drawbacks, a robust PEGylated cationic amphiphilic peptides-based bottlebrush-like surface coating is demonstrated here, which fulfil the requirements of antimicrobial and antifouling as well as biocompatibility in the meantime. Briefly, the rational designed g-PEG_n-b-AMP block copolymers (n=10/45/90) were synthesized and grafted on silicone surface. This bottlebrush-like coating efficiently kill the contacted bacteria and prevent the biofilm formation, greatly reduced protein and platelet adhesion. It also exhibits excellent blood compatibility and low cytotoxicity in vitro. In particular, g-PEG₄₅-b-AMP coating exhibits significant anti-infection effect in vivo. This coating offering an effective strategy for combating biomedical devices-associated infections.

Fate of tetracycline resistance in synthetic livestock carcass leachate for two years

To simulate the fate of antibiotic resistance in leachate from anaerobic carcass landfill site, anaerobic reactors were set-up and their antibiotic resistance activities were monitored for 2 years. Initially, Escherichia coli DH5α with tetracycline resistance pB10 plasmid was inoculated in nutrient rich anaerobic reactors. The fate of tetracycline resistant bacteria (TRB) was tracked by analysis using culture-based method, EC₅₀ (half maximal effective concentration), and quantitative polymerase chain reaction (qPCR). Based on the temporal pattern of EC₅₀ during the study period, TRB continuously increased during Phase I (0-250th day), went down in Phase II (after 250th day to 500th day), and then increased again by the end of Phase III (after 500th day to the 774th day). Interestingly, pB10 plasmid accumulated in the system as the community diversities increased over time. At the end of experiment, the tetracycline resistance microbial communities were investigated by 16s RNA gene-based pyro sequencing. The results of this study indicated that leachate with high organic strength in anaerobic conditions could be an antibiotic resistant point source in several year periods.

Plasmid transfer in biofilms: a perspective on limitations and opportunities

Biofilms dominate microbial life, and their importance for human health and the environment can no longer be dismissed. Nevertheless many of the processes governing this form of microbial growth are still poorly understood. This includes the horizontal exchange of genetic information, which is a major driver in bacterial evolution and rapid adaptation, exemplified by the alarming spread of multi-drug resistance among pathogens mediated by plasmids. Biofilms are often considered hot spot for horizontal gene transfer, yet several studies have shown that plasmid transfer is limited to the outer layers. On the basis of results from decades of research we analyse this paradox and discuss the mechanisms by which biofilm growth can promote the initial transfer of some plasmids, but also limit further plasmid invasion into the population or community. If we want to adequately promote or combat horizontal gene spread in biofilms, we need to gain better insight into the physicochemical and biological mechanisms that control this process.