Flow cytometry, a powerful novel tool to rapidly assess bacterial viability in metal working fluids: Proof-of-principle

Direct and indirect technical guide for the early detection and management of fungal plant diseases

Fungal plant diseases are a major threat to plants and vegetation worldwide. Recent technological advancements in biotechnological tools and techniques have made it possible to identify and manage fungal plant diseases at an early stage. These techniques include direct methods, such as ELISA, immunofluorescence, PCR, flow cytometry, and in-situ hybridization, as well as indirect methods, such as fluorescence imaging, hyperspectral techniques, thermography, biosensors, nanotechnology, and nano-enthused biosensors. Early detection of fungal plant diseases can help to prevent major losses to plantations. This is because early detection allows for the implementation of control measures, such as the use of fungicides or resistant varieties. Early detection can also help to minimize the spread of the disease to other plants. The techniques discussed in this review provide a valuable resource for researchers and farmers who are working to prevent and manage fungal plant diseases. These techniques can help to ensure food security and protect our valuable plant resources.

A Label-Free Optical Flow Cytometry Based-Method for Rapid Assay of Disinfectants' Bactericidal Activity

Selecting the appropriate disinfectant to control and prevent healthcare-associated infections (HAIs) is a challenging task for environmental health experts due to the large number of available disinfectant products. This study aimed to develop a label-free flow cytometry (FCM) method for the rapid evaluation of bactericidal activity and to compare its efficacy with that of standard qualitative/quantitative suspension tests. The bactericidal efficiency of eight commercial disinfectants containing quaternary ammonium compounds (QACs) was evaluated against four strains recommended by EN 13727 (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus hirae) and four multidrug-resistant pathogens. The proposed FCM protocol measures changes in scattered light and counts following disinfectant exposure, neutralization, and culture steps. Unlike other available FCM-based methods, this approach does not rely on autofluorescence measurements, impedance cytometry, or fluorescent dyes. The FCM scattered light signals revealed both decreased count rates and morphological changes after treatment with minimum inhibitory concentrations (MICs) and higher concentrations for all tested bacteria. The results from the FCM measurements showed excellent correlation with those from standard assays, providing a rapid tool for monitoring the susceptibility profile of clinical, multidrug-resistant pathogens to chemical disinfectants, which could support infection prevention and control procedures for healthcare environments. This label-free FCM protocol offers a novel and rapid tool for environmental health experts, aiding in the optimization of disinfectant selection for the prevention and control of HAIs.

Enhancing microbiologically influenced corrosion protection of carbon steels with silanized epoxy-biocide hybrid coatings

Microbial biofilms and microbiologically influenced corrosion (MIC) pose serious problems in pipelines transporting freshwater from the reservoir to service water systems and fire water systems of power reactors. The present work aims to design a silane-based epoxy-biocide hybrid coating along with antibacterial compounds on carbon steels (CS) for controlling the MIC of pipeline materials. The optimal inhibitory concentrations of biocides are identified and a robust protocol has been developed to prepare epoxy-based coatings impregnated with three biocides (25 ppm each of benzalkonium chloride, bronopol, and isothiazoline). Microbiological and accelerated corrosion studies were carried out by exposing the coated CS specimens to the enriched freshwater bacterial culture (FWC). As compared to the impedance value of 102 Ohms for the polished CS, the values were 106 and 105 Ohms, respectively, for epoxy-coated specimens (CSE) and epoxy-coated specimens impregnated with biocides (CSEB). The corrosion protection efficiency of CSE and CSEB coated specimens exposed to FWC was 99.9% and 98.1%, respectively. Confocal microscopic analysis showed the average biomass thickness was 51.3 ± 0.6 µm and 24.4 ± 0.5 µm, respectively, for CSE and CSEB specimens in comparison to 94.1 ± 0.2 µm on CS specimens. The improved anticorrosion and antifouling behaviors observed in the CSEB specimens suggest that the new coating strategy has the potential for the development of multifunctional hybrid epoxy coatings for pipeline materials to mitigate MIC-related issues in water-transporting pipeline systems.

Microbial Community Establishment, Succession, and Temporal Dynamics in an Industrial Semi-Synthetic Metalworking Fluid Operation: A 50-Week Real-Time Tracking

Microorganisms colonizing modern water-based metalworking fluids (MWFs) have been implicated in various occupational respiratory health hazards to machinists. An understanding of the exposure risks from specific microbial groups/genera/species (pathogenic or allergenic) and their endotoxins and the need for strategies for effective, timely fluid management warrant real-time extended tracking of the establishment of microbial diversity and the prevailing fluid-related factors. In the current study, the microbial community composition, succession, and dynamics of a freshly recharged industrial semi-synthetic MWF operation was tracked in real-time over a period of 50 weeks, using a combination of microbiological and molecular approaches. Substantial initial bacterial count (both viable and non-viable) even in the freshly recharged MWF pointed to the inefficiency of the dumping, cleaning, and recharge (DCR) process. Subsequent temporal analysis using optimized targeted genus/group-specific qPCR confirmed the presence of Pseudomonads, Enterics, Legionellae, Mycobacteria (M. immunogenum), Actinomycetes, and Fungi. In contrast, selective culturing using commercial culture media yielded non-specific isolates and collectively revealed Gram-negative (13 genera representing 19 isolates) and Gram-positive (2 genera representing 6 isolates) bacteria and fungi but not mycobacteria. Citrobacter sp. and Bacillus cereus represented the most frequent Gram-negative and Gram-positive isolates, respectively, across different media and Nectria haematococca isolation as the first evidence of this fungal pathogen colonizing semi-synthetic MWF. Unbiased PCR-DGGE analysis revealed a more diverse whole community composition revealing 22 bacterial phylotypes and their succession. Surges in the endotoxin level coincided with the spikes in Gram-negative bacterial population and biocide additions. Taken together, the results showed that semi-synthetic MWF is conducive for the growth of a highly diverse microbial community including potential bacterial and fungal pathogens, the current DCR practices are inefficient in combating microbial reestablishment, and the practice of periodic biocide additions facilitates the build-up of endotoxins and non-viable bacterial population.

The MprF homolog LysX synthesizes lysyl-diacylglycerol contributing to antibiotic resistance and virulence

Lysyl-diacylglycerol (Lys-DAG) was identified three decades ago in Mycobacterium phlei, but the biosynthetic pathway and function of this aminoacylated lipid have since remained uncharacterized. Combining genetic methods, mass spectrometry, and biochemical approaches, we show that the multiple peptide resistance factor (MprF) homolog LysX from Corynebacterium pseudotuberculosis and two mycobacterial species is responsible for Lys-DAG synthesis. LysX is conserved in most Actinobacteria and was previously implicated in the synthesis of another modified lipid, lysyl-phosphatidylglycerol (Lys-PG), in Mycobacterium tuberculosis. Although we detected low levels of Lys-PG in the membrane of C. pseudotuberculosis, our data suggest that Lys-PG is not directly synthesized by LysX and may require an additional downstream pathway, which is as yet undefined. Our results show that LysX in C. pseudotuberculosis is a major factor of resistance against a variety of positively charged antibacterial agents, including cationic antimicrobial peptides (e.g., human peptide LL-37 and polymyxin B) and aminoglycosides (e.g., gentamycin and apramycin). Deletion of lysX caused an increase in cellular membrane permeability without dissipation of the membrane potential, suggesting that loss of the protein does not result in mechanical damage to the cell membrane. Furthermore, lysX-deficient cells exhibited an attenuated virulence phenotype in a Galleria mellonella infection model, supporting a role for LysX during infection. Altogether, Lys-DAG represents a novel molecular determinant for antimicrobial resistance and virulence that may be widespread in Actinobacteria and points to a richer landscape than previously realized of lipid components contributing to overall membrane physiology in this important bacterial phylum. IMPORTANCE In the past two decades, tRNA-dependent modification of membrane phosphatidylglycerol has been implicated in altering the biochemical properties of the cell surface, thereby enhancing the antimicrobial resistance and virulence of various bacterial pathogens. Here, we show that in several Actinobacteria, the multifunctional protein LysX attaches lysine to diacylglycerol instead of phosphatidylglycerol. We found that lysyl-diacylglycerol (Lys-DAG) confers high levels of resistance against various cationic antimicrobial peptides and aminoglycosides and also enhances virulence. Our data show that Lys-DAG is a lipid commonly found in important actinobacterial pathogens, including Mycobacterium and Corynebacterium species.

Survival characteristics and transcriptome profiling reveal the adaptive response of the Brucella melitensis 16M biofilm to osmotic stress

Brucella can inhabit hostile environments, including osmotic stress. How Brucella responds collectively to osmotic stress is largely unexplored, particularly in spatially structured communities such as a biofilm. To gain insight into this growth mode, we set out to characterize the Brucella melitensis 16M biofilm, describe its phenotype, and carry out a comparative transcriptomic analysis between biofilms under osmotic stress and control conditions. We determined that the bacteria challenged with 1.5 M NaCl had a reduced ability to aggregate and form clumps and develop a biofilm; however, the salt stress promoted the release of the outer membrane vesicles from the biofilm. Together with the genotypical response to osmotic stress, we identified 279 differentially expressed genes in B. melitensis 16M grown under osmotic conditions compared with control conditions; 69 genes were upregulated and 210 downregulated. Under osmotic stress, the main changed genes of biofilm were predicted to be involved in flagellar assembly, cell envelope, translation, small RNA regulation, transport and binding proteins, and energy metabolism. In addition, the ABC transporter was enriched in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. We highlight 12 essential ABC transporter genes associated with a bacterial response to osmotic stress at the biofilm stage, including one specific locus, BME_RS12880, mediating betaine accumulation in biofilms to eliminate osmotic stress. The current study results can help researchers gain insights into B. melitensis 16M biofilm adaptation to osmotic stress and provide information for developing intervention strategies to control Brucella.

Differentiation of DNA or membrane damage of the cells in disinfection by flow cytometry

Recently, the viabilities changes of fungal spores in the water supply system during different disinfection processes have been revealed. SYBR Green I (SG), a nucleic acid stain, its fluorescence intensity is correlated with the amount of double-stranded DNA. This study established a new method through successive SG-SG-PI staining (PI: Propidium Iodide) with flow cytometry (FCM). It could successfully distinguish DNA damage and membrane damage of fungal spores, clearly elucidating the intrinsic disinfection mechanism during the chemical disinfection. This method was briefly described as follows: firstly, (1) the fungal spores were stained with SG and washed by centrifugation; and then, (2) the washed spores were treated with disinfectants and terminated; after that, (3) the disinfected spores were re-stained with SG and analyzed by FCM; finally, (4) the SG re-stained spores were stained with PI and analyzed by FCM. The percentages of spores with DNA damage and membrane damage were determined by the fluorescence intensity obtained from steps (3) and (4), respectively. The repeatability and applicability of this developed method were confirmed. It was further applied to explore the inactivation mechanism during chlorine-based disinfection, and results demonstrated that chloramine attacked the DNA more seriously than the membrane, while chlorine and chlorine dioxide worked in a reverse way.

Enhanced biogas production in anaerobic digestion of sludge medicated by biochar prepared from excess sludge: Role of persistent free radicals and electron mediators

The addition of biochars to promote the efficiency of anaerobic digestion (AD) has widely received concerns. However, the role of persistent free radicals (PFRs) and the electron transfer ability of biochar in AD has not yet been noticed. In this study, biochars were prepared from excess sludge under 400 °C (B400) or 600 °C (B600) and different ratios of sludge to biochar (5:1, 10:1, 20:1) were applied in the AD of sludge. The results verified that PFRs in biochar participated in the sterilization of microorganisms in sludge, resulting in the release of organic matters. Similar to electron mediators, biochars possessed electron exchangeability and the addition of biochars boosted the biogas production by maximum of 54.5%. The enhancing effect of B400 surpassed that of B600 as high temperature destroyed functional groups and reduced the defect degree of biochar. This study achieved in-situ resource utilization and provided references for the improvement of anaerobic digestion.

Assessment of mechanisms of infectious pneumonia based on expression of fibrinogen, procalcitonin, high-sensitivity C-reactive protein expression, T helper 17 cells, regulatory T cells interleukin-10, and interleukin-17

BACKGROUND

Infectious pneumonia is one of the important causes of neonatal death that can lead to the imbalance of T helper 17 cells (Th17) and T regulatory T cells (Treg) cells. The correlation between plasma fibrinogen (FIB), procalcitonin (PCT), C-reactive protein (CRP) and Th17/Treg-IL-10/IL-17 axis balance and their specific role in the occurrence and development of infectious pneumonia are not completely clear.

METHODS

Thirty specific-pathogen free Sprague Dawley (SD) rats were randomly divided into a control group for comparison and IPN model group. After the establishment of infectious pneumonia model, levels of FIB, PCT, hs-CRP, IL-10, and IL-17 in the serum of the two groups were measured using enzyme linked immunosorbent assay (ELISA), the pathological changes of lung tissue were observed using hematoxylin and eosin (HE) staining, the number of Treg and Th17 cells and the ratio of Th17/Treg in serum were detected using flow cytometry, and the levels of retinoic acid-related orphan receptor γt and forkhead box P3 (FOXP3) in lung tissue were detected using reverse transcription polymerase chain reaction (RT-PCR) and western blot.

RESULTS

The results showed that the serum levels of FIB, PCT, hs-CRP, Th17 cell number, Th17/Treg ratio, left lung dry and wet weight, lung tissue wet/dry ratio, lung pathology score and IL-17 level in the model group were significantly higher than those in the control group, while the number of Treg cells and the level of IL-10 in the model group were significantly lower than those in the control group. In addition, the expression of Foxp3mRNA and protein in lung tissue of model group decreased significantly, while the expression level of ROR- γ t mRNA and protein increased.

CONCLUSIONS

In infectious pneumonia, the expression levels of FIB, PCT and hs-CRP are up-regulated, and Th17 cells are activated, Treg cells are inhibited, proinflammatory cytokine IL-17 expression is up-regulated, anti-inflammatory cytokine IL-10 expression is down-regulated, resulting in increased inflammatory response, thus promoting the occurrence and development of infectious pneumonia.

Recent progress in cytometric technologies and their applications in ecotoxicology and environmental risk assessment

Environmental toxicology focuses on identifying and predicting impact of potentially toxic anthropogenic chemicals on biosphere at various levels of biological organization. Presently there is a significant drive to gain deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity. Most notable is increased focus on elucidation of cellular-response networks, interactomes, and greater implementation of cell-based biotests using high-throughput procedures, while at the same time decreasing the reliance on standard animal models used in ecotoxicity testing. This is aimed at discovery and interpretation of molecular pathways of ecotoxicity at large scale. In this regard, the applications of cytometry are perhaps one of the most fundamental prospective analytical tools for the next generation and high-throughput ecotoxicology research. The diversity of this modern technology spans flow, laser-scanning, imaging, and more recently, Raman as well as mass cytometry. The cornerstone advantages of cytometry include the possibility of multi-parameter measurements, gating and rapid analysis. Cytometry overcomes, thus, limitations of traditional bulk techniques such as spectrophotometry or gel-based techniques that average the results from pooled cell populations or small model organisms. Novel technologies such as cell imaging in flow, laser scanning cytometry, as well as mass cytometry provide innovative and tremendously powerful capabilities to analyze cells, tissues as well as to perform in situ analysis of small model organisms. In this review, we outline cytometry as a tremendously diverse field that is still vastly underutilized and often largely unknown in environmental sciences. The main motivation of this work is to highlight the potential and wide-reaching applications of cytometry in ecotoxicology, guide environmental scientists in the technological aspects as well as popularize its broader adoption in environmental risk assessment.

Estimation of Microbial Viability Using Flow Cytometry

For microorganisms in particular, viability is a term that is difficult to define and a state consequently difficult to measure. The traditional (and gold standard) usage equates viability and culturability (i.e., the ability to multiply) but the process of determining culturability is often too slow. Flow cytometry provides the opportunity to make rapid and quantitative measurements of dye uptake in large numbers of cells and we can therefore exploit the flow cytometric approach to evaluate so-called viability stains and to develop protocols for more routine assessments of microbial viability. This article provides a commentary and several protocols have been included to ensure that users have a firm basis for attempting these reasonably difficult assays on traditional flow cytometer instruments. What is clear is that each assay must be carefully validated with the particular microorganism of interest before being applied in any research, clinical, or service form. © 2020 The Authors.

Green Synthesis of Ciprofloxacin-Loaded Cerium Oxide/Chitosan Nanocarrier and its Activity Against MRSA-Induced Mastitis

Methicillin-resistant Staphylococcus aureus (MRSA)-induced mastitis is one of the biggest animal welfare issues and economic burdens worldwide. As a possible effective treatment, ciprofloxacin (CIP)-loaded cerium oxide (CeO₂)/chitosan (CS) nanocomposite was synthesized using an eco-friendly approach, characterized, and evaluated. From 350 mastitis-positive milk samples, 35 mecA-positive MRSA strains were confirmed by antibiotic sensitivity testing and PCR. CeO₂ nanoparticles (NPs) were synthetized using the seeds' extract of Amomum subulatum (aka black cardamom/BC) as a reducing and capping agent, which was conjugated with CS by ionic gelation before CIP was nanoencapsulated. The resulting NPs were characterized physically (by using FESEM, TEM, EDS, XRD, FTIR, ZP, and UV-Vis spectrophotometry), biologically and pharmacologically (through in-vitro/ex-vivo antibacterial, cytotoxic, and drug release behavior assays). The CIP-nanocomposite was represented by pure, stable, small, pseudospherical NPs of crystalline nature. FTIR confirmed the surface linkage of CS and CIP in CeO₂ NPs. CIP-CeO₂/CS nanocarrier exerted enhanced antibacterial activity at lower MIC (8 μg/mL) compared to that of free CIP drug alone. Also, they were hemocompatible and not hepatotoxic. CIP release from the nanocarrier was better sustained in physiological-like conditions. Taken together, the phytogenic CIP-CeO₂/CS nanocarrier could be considered as a potent and safe therapeutic solution for MRSA-induced mastitis.

Breast Cancer Inhibition by Biosynthesized Titanium Dioxide Nanoparticles Is Comparable to Free Doxorubicin but Appeared Safer in BALB/c Mice

Cancer remains a global health burden prompting affordable, target-oriented, and safe chemotherapeutic agents to reduce its incidence rate worldwide. In this study, a rapid, cost-effective, and green synthesis of titanium dioxide (TiO₂) nanoparticles (NPs) has been carried out; Ex vivo and in vivoevaluation of their safety and anti-tumor efficacy compared to doxorubicin (DOX), a highly efficient breast anti-cancer agent but limited by severe cardiotoxicity in many patients.Thereby,TiO₂ NPs were eco-friendly synthetized using aqueous leaf extract of the tropical medicinal shrub Zanthoxylum armatum as a reducing agent. Butanol was used as a unique template. TiO₂ NPs were physically characterized by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscope (SEM), X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) as routine state-of-the art techniques. The synthesized TiO₂ NPs were then evaluated for their cytotoxicity (by MTT, FACS, and oxidative stress assays) in 4T1 breast tumor cells, and their hemocompatibility (by hemolysis assay). In vivo anti-tumor efficacy and safety of the TiO₂ NPs were further assessed using subcutaneous 4T1 breast BALB/c mouse tumor model.The greenly prepared TiO₂ NPs were small, spherical, and crystalline in nature. Interestingly, they were hemocompatible and elicited a strong DOX-like concentration-dependent cytotoxicity-induced apoptosis both ex vivo and in vivo (with a noticeable tumor volume reduction). The underlying molecular mechanism was, at least partially, mediated through reactive oxygen species (ROS) generation (lipid peroxidation). Unlike DOX (P < 0.05), it is important to mention that no cardiotoxicity or altered body weight were observed in both the TiO₂ NPs-treated tumor-bearing mouse group and the PBS-treated mouse group (P > 0.05). Taken together, Z. armatum-derived TiO₂ NPs are cost-effective, more efficient, and safer than DOX. The present findings shall prompt clinical trials using green TiO₂ NPs, at least as a possible alternative modality to DOX for effective breast cancer therapy.

Effect of subinhibitory exposure to quaternary ammonium compounds on the ciprofloxacin susceptibility of Escherichia coli strains in animal husbandry

BACKGROUND

Quaternary ammonium compound based disinfectants are commonly used in pig and poultry husbandry to maintain farm hygiene. However, studies have shown that subinhibitory concentrations of these disinfectants may increase antibiotic resistance. Investigation of antibiotic susceptibility is usually assessed via the microbroth dilution method, although this conventional culture-based technique only provides information on the bacteriostatic activity of an antimicrobial agent. Therefore, experiments were performed to investigate the effect of prior benzalkonium chloride (BKC) exposure on the viability of subsequent ciprofloxacin (CIP) treated Escherichia coli.

RESULTS

Following CIP treatment, bacterial cell counts were significantly higher after exposure to a subinhibitory BKC concentration than without BKC exposure. The flow cytometric results suggested a BKC-dependent onset of membrane damage and loss of membrane potential.

CONCLUSION

Our results indicate a lower bactericidal effect of CIP treatment on BKC-exposed E. coli isolates compared to unexposed E. coli isolates.