Irrigation waters and pipe-based biofilms as sources for antibiotic-resistant bacteria

Effects of Organic Soil Amendments on Antimicrobial-Resistant Bacteria in Urban Agriculture Environments

Biological soil amendments of animal origin (BSAAOs) are widely used in urban agriculture to improve soil quality. Although BSAAO use is regulated due to risks for introducing foodborne pathogens, effects on antimicrobial-resistant (AMR) bacteria are not well established. Here, we aimed to explore the impacts of BSAAOs on levels of resident AMR bacteria in leafy vegetable production environments (i.e., kale, lettuce, chard, cabbage) across urban farms and community gardens in the greater Washington D.C. area (n = 7 sites). Leaf tissue (LT), root zone soil (RZS; amended soil in crop beds), and bulk soil (BS; site perimeter) were collected and analyzed for concentrations of total heterotrophic bacteria (THB), ampicillin (Amp) or tetracycline (Tet) resistant THB, and coliforms. As expected, amended plots harbored significantly higher concentrations of THB than bulk soil (P < 0.001). The increases in total bacteria associated with reduced fractions of Tet-resistant bacteria (P = 0.008), as well as case-specific trends for reduced fractions of Amp-resistant bacteria and coliforms. Site-to-site variation in concentrations of AMR bacteria in soil and vegetable samples reflected differences in land history and crop management, while within-site variation was associated with specific amendment sources, as well as vegetable type and cultivar. Representative isolates of the AMR bacteria and coliforms were further screened for multidrug resistance (MDR) phenotypes, and a high frequency was observed for the former. In amended soils, as the soil pH (range 6.56-7.80) positively correlated with the fraction of Tet-resistant bacteria (rho = 0.529; P < 0.001), crop management strategies targeting pH may have applications to control related risks. Overall, our findings demonstrate that soil amendments promote soil bacteria concentrations and have important implications for limiting the spread of AMR bacteria, at least in the urban landscape.

In the Depths of Wash Water: Isolation of Opportunistic Bacteria from Fresh-Cut Processing Plants

The fruit and vegetable industry in post-harvest processing plants is characterized by a substantial consumption of water resources. Wash waters may serve as an environment for the periodic or permanent habitation of microorganisms, particularly if biofilm forms on the inner walls of tanks and flushing channels. Despite the implementation of integrated food safety monitoring systems in numerous countries, foodborne pathogens remain a global public health and food safety concern, particularly for minimally processed food products such as vegetables and fruits. This necessitates the importance of studies that will explore wash water quality to safeguard minimally processed food against foodborne pathogen contamination. Therefore, the current study aimed to isolate and identify bacteria contaminating the wash waters of four fresh-cut processing plants (Poland) and to evaluate the phenotypic antibiotic resistance profiles in selected species. Bacteria were isolated using membrane filtration and identified through mass spectrometry, followed by antibiotic susceptibility testing according to EUCAST guidelines. The results revealed that the level of contamination with total aerobic bacteria in the water ranged from 1.30 × 106 cfu/mL to 2.54 × 108 cfu/mL. Among the isolates, opportunistic pathogens including Enterococcus faecalis, Pseudomonas aeruginosa, Klebsiella oxytoca, Klebsiella pneumoniae, Serratia marcescens, and Proteus vulgaris strains were identified. An especially noteworthy result was the identification of cefepime-resistant K. oxytoca isolates. These findings highlight the importance of monitoring the microbial microflora in minimally processed foods and the need for appropriate sanitary control procedures to minimize the risk of pathogen contamination, ensuring that products remain safe and of high quality throughout the supply chain.

Impact of water quality on reprocessing equipment: Assessment of neurosurgical instruments cleaning and biofilm formation in hospital pipes

Background

The presence of contamination and microorganisms at any stage of processing renders a method unsafe, leading to a high risk of cross-transmission and cross-infection.

Objective

The objective of this study was to assess the cleaning quality of aspirator instruments used in neurosurgical procedures.

Methods

The experimental study was conducted at the materials and sterilization center, as well as the microbiology laboratory, of a philanthropic hospital in Brazil. A study protocol was implemented, which involved the analysis of 10 samples of Yasargil aspirators with varying dimensions. The samples were subjected to protein tests to detect the presence of organic matter and microbiological analysis. Descriptive statistics were used to analyze the data.

Results

The results indicated that 40% of the instruments tested positive for protein after manual cleaning. Furthermore, after automated cleaning, samples showed an increased microbiological load, with Escherichia coli accounting for 20% and Klebsiella aerogenes for 10% of the identified microorganisms.

Conclusion

This study provides evidence of failures in the cleaning process of healthcare products and highlights the presence of biofilm in the pipes, thereby compromising the drinking water quality standard.

Resistance to cephalosporins and quinolones in Escherichia coli isolated from irrigation water from the Rímac river in east Lima, Peru

OBJECTIVES.

To evaluate the presence and sensitivity to antimicrobials of Escherichia coli strains isolated from 24 irrigation water samples from the Rimac river of East Lima, Peru.

MATERIALS AND METHODS.

The E. coli strains were identified by PCR. Antibiotic susceptibility was processed by the disk diffusion method. Genes involved in extended spectrum beta-lactamases (BLEE), quinolones and virulence were determined by PCR.

RESULTS.

All samples exceeded the acceptable limits established in the Environmental Quality Standards for vegetable irrigation. Of the 94 isolates, 72.3% showed resistance to at least one antibiotic, 24.5% were multidrug resistant (MDR) and 2.1% were extremely resistant. The highest percentages of resistance were observed for ampicillin-sulbactam (57.1%), nalidixic acid (50%), trimethoprim-sulfamethoxazole (35.5%) and ciprofloxacin (20.4%). Among the isolates, 3.2% had a BLEE phenotype related to the bla CTX-M-15 gene. qnrB (20.4%) was the most frequent transferable mechanism of resistance to quinolones, and 2.04% had qnrS. It was estimated that 5.3% were diarrheagenic E. coli and of these, 60% were enterotoxigenic E. coli, 20% were enteropathogenic E. coli and 20% were enteroaggregative E. coli.

CONCLUSIONS.

The results show the existence of diarrheogenic pathotypes in the water used for irrigation of fresh produce and highlight the presence of BLEE- and MDR-producing E. coli, demonstrating the role played by irrigation water in the dissemination of resistance genes in Peru.

Motivation for the study. Aquatic systems, including irrigation water, have been identified as reservoirs of antimicrobial resistance, with few studies in Peru on the presence of Escherichia coli and their levels of virulence and antimicrobial resistance. Main findings. Our results show the presence of E. coli above the established standard for vegetable irrigation water, some with very high levels of antimicrobial resistance. Implications. The presence of ESBL-producing strains of extended-spectrum beta-lactamases and multidrug-resistant E. coli in irrigation water could contribute to the dissemination of resistance genes in Peru, posing a significant threat to public health.

Microbiota and Resistome Analysis of Colostrum and Milk from Dairy Cows Treated with and without Dry Cow Therapies

This study investigated the longitudinal impact of methods for the drying off of cows with and without dry cow therapy (DCT) on the microbiota and resistome profile in colostrum and milk samples from cows. Three groups of healthy dairy cows (n = 24) with different antibiotic treatments during DCT were studied. Colostrum and milk samples from Month 0 (M0), 2 (M2), 4 (M4) and 6 (M6) were analysed using whole-genome shotgun-sequencing. The microbial diversity from antibiotic-treated groups was different and higher than that of the non-antibiotic group. This difference was more evident in milk compared to colostrum, with increasing diversity seen only in antibiotic-treated groups. The microbiome of antibiotic-treated groups clustered separately from the non-antibiotic group at M2-, M4- and M6 milk samples, showing the effect of antibiotic treatment on between-group (beta) diversity. The non-antibiotic group did not show a high relative abundance of mastitis-causing pathogens during early lactation and was more associated with genera such as Psychrobacter, Serratia, Gordonibacter and Brevibacterium. A high relative abundance of antibiotic resistance genes (ARGs) was observed in the milk of antibiotic-treated groups with the Cephaguard group showing a significantly high abundance of genes conferring resistance to cephalosporin, aminoglycoside and penam classes. The data support the use of non-antibiotic alternatives for drying off in cows.

Reclaimed wastewater reuse in irrigation: Role of biofilms in the fate of antibiotics and spread of antimicrobial resistance

Reclaimed wastewater associated biofilms are made up from diverse class of microbial communities that are continuously exposed to antibiotic residues. The presence of antibiotic resistance bacteria (ARB) and their associated antibiotic resistance genes (ARGs) ensures also a continuous selection pressure on biofilms that could be seen as hotspots for antibiotic resistance dissemination but can also play a role in antibiotic degradation. In this study, the antibiotic degradation and the abundance of four ARGs (qnrS, sul1, blaTEM, ermB), and two mobile genetic elements (MGEs) including IS613 and intl1, were followed in reclaimed wastewater and biofilm samples collected at the beginning and after 2 weeks of six antibiotics exposure (10 µg L^-1). Antibiotics were partially degraded and remained above lowest minimum inhibitory concentration (MIC) for environmental samples described in the literature. The most abundant genes detected both in biofilms and reclaimed wastewater were sul1, ermB, and intl1. The relative abundance of these genes in biofilms increased during the 2 weeks of exposure but the highest values were found in control samples (without antibiotics pressure), suggesting that bacterial community composition and diversity are the driven forces for resistance selection and propagation in biofilms, rather than exposure to antibiotics. Planktonic and biofilm bacterial communities were characterized. Planktonic cells are classically defined "as free flowing bacteria in suspension" as opposed to the sessile state (the so-called biofilm): "a structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living. surface" as stated by Costerton et al. (1999). The abundance of some genera known to harbor ARG such as Streptococcus, Exiguobacterium, Acholeplasma, Methylophylaceae and Porphyromonadaceae increased in reclaimed wastewater containing antibiotics. The presence of biofilm lowered the level of these genera in wastewater but, at the opposite, could also serve as a reservoir of these bacteria to re-colonize low-diversity wastewater. It seems that maintaining a high diversity is important to limit the dissemination of antimicrobial resistance among planktonic bacteria. Antibiotics had no influence on the biofilm development monitored with optical coherence tomography (OCT). Further research is needed in order to clarify the role of inter-species communication in biofilm on antibiotic degradation and resistance development and spreading.

Formation and Microbial Composition of Biofilms in Drip Irrigation System under Three Reclaimed Water Conditions

As the second source of water for cities, reclaimed water (RW) has become an effective solution to the problem of water scarcity in modern agriculture. However, the formation of biofilm in an RW distribution system seriously affects the performance of the system and has become a technical challenge in RW utilization. In this study, we first showed that several water quality parameters, including five-day biochemical oxygen demand (BOD5), total bacteria count (TB), total nitrogen (TN), and Cl− were the main factors affecting biofilm accumulation in the drip irrigation system (DIS), with the correlation coefficient averaging above 0.85. Second, after 392 to 490 h of system operation, the total biomass and extracellular polymer (EPS) accumulation rate of biofilms increased to a maximum of 0.72 g/m2·h and 0.027g/m2·h, respectively, making this time point a critical point for controlling biofilm accumulation and clogging of the system. Third, we examined changes in biofilm microbial composition over time on Illumina’s MiSeq platform. High throughput sequencing data showed that bacterial community structure and microbial network interaction and modularity changed significantly between 392 and 490 h, resulting in maximum microbial diversity and community richness at 490 h. Spearman correlation analyses between genera revealed that Sphingomonas and Rhodococcus promote biofilm formation due to their hydrophobicity, while Bacillus, Mariniradius, and Arthronema may inhibit biofilm formation due to their antagonistic effects on other genera. In conclusion, this work has clarified the accumulation process and compositional changes of biofilms in agriculture DIS under different RW conditions, which provides a basis for improving RW utilization efficiency and reducing system maintenance costs.

Visualizing, quantifying, and controlling local hydrodynamic effects on biofilm accumulation in complex flow paths

Complex flow paths (CFPs) are commonly applied in precision equipment to accurately supply controllable fluids with designed structures. However, the presence of biofilms in CFPs causes quite a few unwanted issues, such as bio-erosion, clogging, or even health risks. To date, visualizing and quantifying the interaction between biofilm distribution and local hydrodynamics remains difficult, and the mechanism during the process is unclear. In this paper, the remodeling simulation method (3D industrial computed tomography scanning-inverse modeling-numerical simulation) and 16S rRNA high-throughput sequencing were integrated. The results indicated that local hydrodynamic characteristics significantly affected biofilm thicknesses on CFP surfaces (relative differences of 41.3-71.2%), which inversely influenced the local turbulence intensity. The average biofilm thicknesses exhibited a significant quadratic correlation with the near-wall hydraulic shear forces (r > 0.72, p < 0.05), and the biofilm reached a maximum thickness at 0.36-0.45 Pa. On the other hand, the near-wall hydraulic shear forces not only affected microbial community characteristics of biofilms, but they also influenced the number of microorganisms involved, which determined the biofilm accumulation thereafter. The PHYLUM Firmicutes and Proteobacteria were the dominant bacteria during the process. The results obtained in this paper could provide practical conceptions for the targeted control of biofilms and put forward more efficient controlling methods in commonly applied CFP systems.

Fibrous testing papers for fluorescence trace sensing and photodynamic destruction of antibiotic-resistant bacteria

The increasing prevalence of antibiotic-resistant bacteria needs rapid identification and efficient destruction routes. This study proposes testing paper derived from electrospun fibrous mats and aggregation-induced emission (AIE) probes for trace sensing and simultaneous destruction of antibiotic-resistant E. coli. Aptamers are conjugated on fibers for selective capture of E. coli, and the capture capability can be regenerated via rinsing with salt solution. Hydroxyl tetraphenylethene (TPE) is linked with two cephalosporin molecules to construct TPE-Cep probes, and the fluorescence emission is turned on specifically in the presence of β-lactamase, which is a critical marker for screening resistant bacteria. Fibrous mats are lit up only in the presence of antibiotic-resistant bacteria, and the fluorescence intensity changes could be statistically fitted into an equation for quantitative analysis. Fibrous strips display apparent color changes from blue to green for a visual readout of bacterial levels, and the limit of detection (LOD) is much lower than those of previous paper substrates. In addition, the TPE-Cep probes could produce reactive oxygen species (ROS) under room light illumination to kill the captured bacteria. Thus, the integration of aptamer-grafted electrospun fibers and functional AIE probes provides potential for selective capture, trace imaging and photodynamic destruction of antibiotic-resistant bacteria.

Mitigation of biofouling in agricultural water distribution systems with nanobubbles

Biofouling poses considerable technical challenges to agricultural irrigation systems. Controlling biofouling with strong chemical biocides is not only expensive and sometimes ineffective, but also contributes to environmental pollution. This study investigated the application of nanobubbles (NBs) on minimizing biofouling in agricultural irrigation water pipelines. Treatment performances were assessed using low concentration bubbles (LCB) and high concentration bubbles (HCB) together with a negative control (CK: no-NBs). 16 s rRNA gene sequencing and X-ray diffraction were used to characterize the microbial community and mineral compositions of biofilms in water emitters. Results demonstrated that NBs effectively mitigated biofouling through reducing fixed-biomass by 31.3-52.1%. A significantly different microbial composition was found in the biofilm community with reduced biodiversity. Molecular ecological network analysis revealed that NBs were detrimental to the mutualistic interactions among microbial species - destabilizing the network complexity and size, which was expressed as decreasing in extracellular polymers and biofilm biomass. Furthermore, NBs significantly decreased the deposition of carbonate, silicate, phosphate, and quartz on the pipe surfaces, leading to reductions of total content of minerals in biofilms. Therefore, this study demonstrated that NBs treatment could be an effective, and eco-friendly solution for biofouling control in agricultural water distribution systems.

From farm-scale to lab-scale: The characterization of engineered irrigation water distribution system biofilm models using an artificial freshwater source

Contaminants in freshwater environments, as well as the associated negative impacts on agricultural produce, have emerged as a critical theme of the water-energy-food nexus affecting food safety and irrigation management. Agricultural produce exposed to irrigation with questionable freshwater can internalize and concentrate pollutants. However, the potential risks posed by the ubiquitous presence of biofilms within irrigation water distribution systems (IWDS) remains overlooked, even though such biofilms may harbor and spread pathogenic, chemical, and other environmental pollutants. Our limited knowledge about the role and functional attributes of IWDS biofilms can be blamed mostly to experimental challenges encountered during attempted studies of these biofilms in their natural environments. Hence, a laboratory-based experimental system designed to simulate a freshwater environment was combined with a biofilm reactor capable of recreating the piping environments in water distribution systems. This experimental system was then tested to assess the robustness and repeatability of experimental early-stage biofilms with respect to physical structure and microbial community, using state-of-the-art confocal microscopy and next-generation sequencing, respectively. The results demonstrated the suitability of this laboratory-based experimental system for studying the impacts of selected pollutants on irrigation water distribution systems.

Biofilm research within irrigation water distribution systems: Trends, knowledge gaps, and future perspectives

Biofilms in irrigation water distribution systems (IWDSs) play an essential role in spreading pathogens, chemical pollutants, and environmental pollutants into downstream irrigated crops and thus should be considered a potential threat to food safety. Although the role of biofilms in drinking water distribution systems has been extensively studied in the last decade, the research on IWDS biofilms in this period has been limited. This review identifies research gaps in the field of IWDS biofilms, provides perspectives on experimental designs for investigating IWDS biofilms, and suggests potential strategies worth pursuing in IWDS management. The current state of the art of IWDS biofilms is discussed, and an analysis of the challenges in IWDS biofilm research is presented. Furthermore, this review proposes useful advanced technologies that allow a practical, in-depth fundamental understanding of IWDS biofilms. In a nutshell, this article provides future directions and insights into detailed experimental designs on a relatively under-reported research topic: "IWDS biofilms."

Creek to Table: Tracking fecal indicator bacteria, bacterial pathogens, and total bacterial communities from irrigation water to kale and radish crops

The impact of microbially contaminated irrigation water on risks to produce safety and public health is a complex issue that is not well understood. This study tracked fecal indicators, pathogenic bacteria, and total bacterial communities from a creek water irrigation source to irrigated produce to assess the impact of irrigation events on soil and produce-associated microbiota. Kale and radishes were drip-irrigated using Mid-Atlantic creek water in October 2017. Plant and soil samples were collected immediately before and after irrigation, and for 3 consecutive days thereafter. All samples (n = 134), including irrigation water, were tested for generic Escherichia coli and total coliforms (TC) using standard membrane filtration or direct plating, and for Salmonella enterica and Listeria monocytogenes by selective enrichment. DNA extracted from all samples was PCR-amplified for the V3-V4 region of the 16S rRNA gene for bacterial community profiling. In soil, TC levels were significantly higher immediately and 3 days post-irrigation compared to pre-irrigation (p < 0.01). E. coli levels in soil increased after irrigation, but the difference was not significant (p = 0.31), and die-off was not observed. No E. coli were detected on kale leaves. TC increased over the study period on radish roots (p < 0.01) but not kale leaves (p = 0.43). Although target pathogens were detected in irrigation water, S. enterica was detected from only one post-irrigation kale sample and L. monocytogenes was not detected in the field. The 16S rRNA gene sequencing data revealed differences in bacterial community structure and composition across sample types and showed that radish soil and root surface bacterial communities were more strongly influenced by irrigation compared to kale samples. This study provides insights into the impact of irrigation water on fresh produce microbiota, revealing that, although irrigation did influence crop-associated microbiota (especially below ground) in the field, bacterial pathogens were not likely transferred to the crop.

Tracing back multidrug-resistant bacteria in fresh herb production: from chive to source through the irrigation water chain

Environmental antibiotic-resistant bacteria (ARB) can be transferred to humans through foods. Fresh produce in particular is an ideal vector due to frequent raw consumption. A major contamination source of fresh produce is irrigation water. We hypothesized that water quality significantly affects loads of ARB and their diversity on fresh produce despite various other contamination sources present under agricultural practice conditions. Chive irrigated from an open-top reservoir or sterile-filtered water (control) was examined. Heterotrophic plate counts (HPC) and ARB were determined for water and chive with emphasis on Escherichia coli and Enterococcus spp. High HPC of freshly planted chive decreased over time and were significantly lower on control- vs. reservoir-irrigated chive at harvest (1.3 log (CFU/g) lower). Ciprofloxacin- and ceftazidime-resistant bacteria were significantly lower on control-irrigated chive at harvest and end of shelf life (up to 1.8 log (CFU/g) lower). Escherichia coli and Enterococcus spp. repeatedly isolated from water and chive proved resistant to up to six or four antibiotic classes (80% or 49% multidrug-resistant, respectively). Microbial source tracking identified E. coli-ST1056 along the irrigation chain and on chive. Whole-genome sequencing revealed that E. coli-ST1056 from both environments were clonal and carried the same transmissible multidrug-resistance plasmid, proving water as source of chive contamination. These findings emphasize the urgent need for guidelines concerning ARB in irrigation water and development of affordable water disinfection technologies to diminish ARB on irrigated produce.

Evaluation of Grower-Friendly, Science-Based Sampling Approaches for the Detection of Salmonella in Ponds Used for Irrigation of Fresh Produce

The recognition that irrigation water sources contribute to preharvest contamination of produce has led to new regulations on testing microbial water quality. To best identify contamination problems, growers who depend on irrigation ponds need guidance on how and where to collect water samples for testing. In this study, we evaluated several sampling strategies to identify Salmonella and Escherichia coli contamination in five ponds used for irrigation on produce farms in southern Georgia. Both Salmonella and E. coli were detected regularly in all the ponds over the 19-month study period, with overall prevalence and concentrations increasing in late summer and early fall. Of 507 water samples, 217 (42.8%) were positive for Salmonella, with a very low geometric mean (GM) concentration of 0.06 most probable number (MPN)/100 mL, and 442 (87.1%) tested positive for E. coli, with a GM of 6.40 MPN/100 mL. We found no significant differences in Salmonella or E. coli detection rates or concentrations between sampling at the bank closest to the pump intake versus sampling from the bank around the pond perimeter, when comparing with results from the pump intake, which we considered our gold standard. However, samples collected from the bank closest to the intake had a greater level of agreement with the intake (Cohen's kappa statistic = 0.53; p < 0.001) than the samples collected around the pond perimeter (kappa = 0.34; p = 0.009). E. coli concentrations were associated with increased odds of Salmonella detection (odds ratio = 1.31; 95% confidence interval = 1.10-1.56). All the ponds would have met the Produce Safety Rule standards for E. coli, although Salmonella was also detected. Results from this study provide important information to growers and regulators about pathogen detection in irrigation ponds and inform best practices for surface water sampling.

Influences of graphene oxide on biofilm formation of gram-negative and gram-positive bacteria

In this study, we evaluated the influences of graphene oxide (GO) on biofilm formation. Escherichia coli MG1655 and Bacillus subtilis 168 were used as models for Gram-negative and Gram-positive bacteria. The growth profiles and viability assays indicated that GO exhibited a high antibacterial activity, of which the negative effects on bacteria growth raised with the increasing GO concentration. The antibacterial activity of GO was mainly attributed to the membrane stress and ROS-independent oxidative stress. Moreover, it was worthy to note that the biofilm formation was enhanced in the presence of GO at low dosage whereas inhibited in the high-concentration GO environment. These results could be explained by the roles of the dead cells, which were inactivated by GO. When the concentration of GO was limited, only a part of the cells would be inactivated, which may then serve as a protection barrier as well as the necessary nutrient to the remaining living cells for the formation of biofilm. In contrast, with a sufficient presence of GO, almost all cells can be inactivated completely and thus the formation of biofilm could no longer be triggered. Overall, the present work provides significant new insights on the influence of carbon nanomaterials towards biofilm formation, which has far-reaching implications in the field of biofouling and membrane bioreactor. Graphical abstract ᅟ.

Discovery of a Novel Nitric Oxide Binding Protein and Nitric-Oxide-Responsive Signaling Pathway in Pseudomonas aeruginosa

Nitric oxide (NO) is a radical diatomic gas molecule that, at low concentrations, plays important signaling roles in both eukaryotes and bacteria. In recent years, it has become evident that bacteria respond to low levels of NO in order to modulate their group behavior. Many bacteria respond via NO ligation to a well-established NO sensor called H-NOX (heme-nitric oxide/oxygen binding domain). Many others, such as Pseudomonas aeruginosa, lack an annotated hnoX gene in their genome yet are able to respond to low levels of NO to disperse their biofilms. This suggests the existence of a previously uncharacterized NO sensor. In this study, we describe the discovery of a novel nitric oxide binding protein (NosP; NO-sensing protein), which is much more widely conserved in bacteria than H-NOX, as well as a novel NO-responsive pathway in P. aeruginosa. We demonstrate that biofilms of a P. aeruginosa mutant lacking components of the NosP pathway lose the ability to disperse in response to NO. Upon cloning, expressing, and purifying NosP, we find it binds heme and ligates to NO with a dissociation rate constant that is comparable to that of other well-established NO-sensing proteins. Moreover, we show that NO-bound NosP is able to regulate the phosphorelay activity of a hybrid histidine kinase that is involved in biofilm regulation in P. aeruginosa. Thus, here, we present evidence of a novel NO-responsive pathway that regulates biofilm in P. aeruginosa.

Prevalence of bacterial resistance within an eco-agricultural system in Hangzhou, China

The wide use of antibiotics in the animal husbandry and the relevant sustainable industries may promote the emergence of antibiotic-resistant bacteria (ARB), which constitutes a growing threat to human health. The objective of this study was to determine the abundance and diversity of sulfonamide- and tetracycline-resistant bacteria within an eco-agricultural system (EAS) in Hangzhou, China. We investigated samples at every link in the EAS, from livestock manure, to biogas residues and biogas slurry, to vegetable and ryegrass fields, to a fish pond. A combination of culture-based and 16S rRNA gene-based sequencing method was used in this study. Within the studied system, the average rate of bacterial resistance to sulfonamide (46.19 %) was much higher than that of tetracycline (8.51 %) (p < 0.01). There were 224 isolates that were enumerated and sequenced, 108 of which were identified to species level. The genera comprising the sulfamethoxazole-resistant (SMX^r) bacteria were generally different from those of tetracycline-resistant (TC^r) bacteria. Staphylococcus and Acinetobacter were the most dominant genera of SMX^r bacteria (19.30 % of the total resistant bacteria) and TC^r bacteria (14.04 % of the total resistant bacteria), respectively. Several strains of resistant opportunistic pathogens (e.g., Pantoea agglomerans) were detected in edible vegetable samples, which may exert a potential threat to both pig production and human health. In general, this study indicates that the EAS is an important reservoir of antibiotic-resistant bacteria, some of which may be pathogenic.