Explore the vast range of titles available.

A requirement of any foodborne pathogen testing method is that it only detects live bacteria. Ethidium monoazide (EMA) and propidium monoazide (PMA) are dyes that penetrate the membranes of dead cells and form cross-linkages in the DNA, which prevents its amplification in PCR. This study investigated whether treatment with EMA or PMA would inhibit the sequencing of DNA from dead Escherichia coli. Range finding experiments with qPCR were conducted to determine the optimal concentrations of EMA and PMA needed to inhibit the amplification of DNA from dead cells while not influencing live cells. An EMA concentration that differentiated between live and dead cells could not be established. However, a PMA concentration of 25 µM effectively prevented qPCR amplification of DNA from dead E. coli while not impacting the amplification of live E. coli DNA. Sequencing experiments were conducted with PMA-treated live, untreated live, PMA-treated dead, and untreated dead E. coli. There were no significant differences in the detection of virulence genes of interest between the PMA-treated live, untreated live, and untreated dead E. coli. However, no DNA sequencing data were obtained from the PMA-treated dead E. coli. These results suggest that PMA could be incorporated into sample preparation methods prior to sequencing to selectively detect live cells of foodborne pathogens.

Background Shotgun sequencing of microbial communities provides in-depth knowledge of the microbiome by cataloging bacterial, fungal, and viral gene content within a sample, providing an advantage over amplicon sequencing approaches that assess taxonomy but not function and are taxonomically limited. However, mammalian DNA can dominate host-derived samples, obscuring changes in microbial populations because few DNA sequence reads are from the microbial component. We developed and optimized a novel method for enriching microbial DNA from human oral samples and compared its efficiency and potential taxonomic bias with commercially available kits. Results Three commercially available host depletion kits were directly compared with size filtration and a novel method involving osmotic lysis and treatment with propidium monoazide (lyPMA) in human saliva samples. We evaluated the percentage of shotgun metagenomic sequencing reads aligning to the human genome, and taxonomic biases of those not aligning, compared to untreated samples. lyPMA was the most efficient method of removing host-derived sequencing reads compared to untreated sample (8.53 ± 0.10% versus 89.29 ± 0.03%). Furthermore, lyPMA-treated samples exhibit the lowest taxonomic bias compared to untreated samples. Conclusion Osmotic lysis followed by PMA treatment is a cost-effective, rapid, and robust method for enriching microbial sequence data in shotgun metagenomics from fresh and frozen saliva samples and may be extensible to other host-derived sample types.

Bacteria in human milk contribute to the establishment of the infant gut microbiome. As such, numerous studies have characterized the human milk microbiome using DNA sequencing technologies, particularly 16S rRNA gene sequencing. However, such methods are not able to differentiate between DNA from viable and non-viable bacteria. The extent to which bacterial DNA detected in human milk represents living, biologically active cells is therefore unclear. Here, we characterized both the viable bacterial content and the total bacterial DNA content (derived from viable and non-viable cells) of fresh human milk (n = 10). In order to differentiate the living from the dead, a combination of propidium monoazide (PMA) and full-length 16S rRNA gene sequencing was used. Our results demonstrate that the majority of OTUs recovered from fresh human milk samples (67.3%) reflected DNA from non-viable organisms. PMA-treated samples differed significantly in their bacterial composition compared to untreated samples (PERMANOVA p < 0.0001). Additionally, an OTU mapping to Cutibacterium acnes had a significantly higher relative abundance in PMA-treated (viable) samples. These results demonstrate that the total bacterial DNA content of human milk is not representative of the viable human milk microbiome. Our findings raise questions about the validity of conclusions drawn from previous studies in which viability testing was not used, and have broad implications for the design of future work in this field.

Chemical biocides are commonly employed to manage problems caused by microbial processes. In the energy sector, for example, engineered systems are often treated with biocides to control microbiologically influenced corrosion (MIC), biofouling, and the biological generation of hydrogen sulfide. Standard DNA-based methods that are widely used to assess biocide effectiveness often cannot distinguish between live and dead microorganisms, potentially leading to inflated estimates of living cell populations. Incorporating propidium monoazide (PMA) viability staining technique offers a promising solution to this limitation. In this study, we explored the application of PMA within a standard DNA-based workflow to evaluate biocide performance more accurately. A model sulfate-reducing microbial consortium, derived from oilfield produced water, was exposed to widely used biocides including glutaraldehyde (Glut) and tetrakis(hydroxymethyl)phosphonium sulfate (THPS). PMA was applied prior to standard DNA extraction and subsequent qPCR and amplicon sequencing procedures. We observed PMA-derived microbial abundance at least an order of magnitude lower compared to that without PMA. The reduced PMA-derived microbial abundance correlated with the lower ability of the model microbial communities to produce hydrogen sulfide – an association that was absent based on the usual approach without PMA. Biocide-treated communities, in comparison to untreated controls, displayed significant alterations in their microbial ecological properties, such as alpha diversity, beta diversity, and taxonomic composition, as determined through 16S rRNA gene sequencing – differences that were only apparent when PMA was applied. These results confirm that incorporating PMA into standard DNA-based biocide assessment protocols is both feasible and beneficial. Since PMA implementation requires minimal additional effort, we advocate for its adoption in future biocide performance studies, in particular for engineered systems in the energy industry.

Combining membrane impermeable DNA-binding stain propidium iodide (PI) with membrane-permeable DNA-binding counterstains is a widely used approach for bacterial viability staining. In this paper we show that PI staining of adherent cells in biofilms may significantly underestimate bacterial viability due to the presence of extracellular nucleic acids (eNA). We demonstrate that gram-positive Staphylococcus epidermidis and gram-negative Escherichia coli 24-hour initial biofilms on glass consist of 76 and 96% PI-positive red cells in situ , respectively, even though 68% the cells of either species in these aggregates are metabolically active. Furthermore, 82% of E. coli and 89% S. epidermidis are cultivable after harvesting. Confocal laser scanning microscopy (CLSM) revealed that this false dead layer of red cells is due to a subpopulation of double-stained cells that have green interiors under red coating layer which hints at eNA being stained outside intact membranes. Therefore, viability staining results of adherent cells should always be validated by an alternative method for estimating viability, preferably by cultivation.

This article elaborates on possible future directions for microbial viability assessment using nucleic acid-modifying compounds in combination with DNA- (and potentially RNA-) amplification technologies. Bacteria were traditionally considered viable when they could be cultured, whereas today's viability concept is based on the presence of some form of metabolic activity, responsiveness, RNA transcripts that tend to degrade rapidly after cell death, or of an intact membrane. The latter criterion was the focus of recent approaches to limit detection to intact cells using ethidium monoazide or propidium monoazide. Membrane integrity must, however, be considered as a very conservative criterion for microbial viability. The new concept presented here aims at limiting nucleic acid-based detection to cells with an active metabolism, which might be a more appropriate viability criterion. To selectively detect only cells with metabolic and respiratory activity (while excluding inactive dead cells from detection), we suggest the use of 'activity-labile compounds'. In addition to their potential usefulness for viability assessment, these new compounds could also be beneficial for selectively amplifying nucleic acids of cells that have metabolic activities of interest. This preferential detection of microorganisms with certain metabolic capabilities is referred to as 'molecular enrichment' in distinction to 'growth enrichment'.

Traditional culture-based quantification of Bradyrhizobium diazoefficiens in inoculants presents significant limitations due to its labor-intensive and time-consuming nature. To address this limitation, we aimed to validate a propidium monoazide quantitative PCR (PMA-qPCR) assay as a rapid and reliable alternative for estimating Bradyrhizobium diazoefficiens counts in commercial inoculants. Key experiments optimized PMA concentration (50, 75 and 100 µM) to selectively inhibit DNA amplification from non-viable cells without interfering with viable cell signal. Assay´s efficiency, limit of detection and quantification, intra-assay repeatability and inter-assay reproducibility were determined. The assay demonstrated high efficiency (90–105%), a limit of detection (LOD) of 3.14 log CFU/mL, and a dynamic range from 8.74 to 3.14 log CFU/mL. Robust intra-assay repeatability (SD < 0.3) and inter-assay reproducibility (CV < 10%) were confirmed. The method successfully distinguished quarter-strength and 10-fold serial dilutions of viable bacteria, even in the presence of non-viable cells. Final validation against standard plate counting showed a strong linear correlation with an R² of 0.82. Crucially, this PMA-qPCR assay reduced processing time from 120 hours to just 5 hours, offering a significant improvement in turnaround time while maintaining strong agreement with the reference method. This study marks the first application of PMA-qPCR for Bradyrhizobium diazoefficiens quantification in inoculants, highlighting its potential as a high-throughput tool to enhance efficiency and precision for industrial batch-to-batch quality control.

Curcumin, an important constituent of turmeric, is known for various biological activities, primarily due to its antioxidant mechanism. The present study focused on the antibacterial activity of curcumin I, a significant component of commercial curcumin, against four genera of bacteria, including those that are Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa). These represent prominent human pathogens, particularly in hospital settings. Our study shows the strong antibacterial potential of curcumin I against all the tested bacteria from Gram-positive as well as Gram-negative groups. The integrity of the bacterial membrane was checked using two differential permeabilization indicating fluorescent probes, namely, propidium iodide and calcein. Both the membrane permeabilization assays confirmed membrane leakage in Gram-negative and Gram-positive bacteria on exposure to curcumin I. In addition, scanning electron microscopy and fluorescence microscopy were employed to confirm the membrane damages in bacterial cells on exposure to curcumin I. The present study confirms the broad-spectrum antibacterial nature of curcumin I, and its membrane damaging property. Findings from this study could provide impetus for further research on curcumin I regarding its antibiotic potential against rapidly emerging bacterial pathogens.

Background Viability staining with SYTO9 and propidium iodide (PI) is a frequently used tool in microbiological studies. However, data generated by such routinely used method are often not critically evaluated for their accuracy. In this study we aim to investigate the critical aspects of this staining method using Staphylococcus aureus and Pseudomonas aeruginosa as the model microorganisms for high throughput studies in microtiter plates. SYTO9 or PI was added alone or consecutively together to cells and the fluorescence intensities were measured using microplate reader and confocal laser scanning microscope. Results We found that staining of S. aureus cells with SYTO9 alone resulted in equal signal intensity for both live and dead cells, whereas staining of P. aeruginosa cells led to 18-fold stronger signal strength for dead cells than for live ones. After counterstaining with PI, the dead P. aeruginosa cells still exhibited stronger SYTO9 signal than the live cells. We also observed that SYTO9 signal showed strong bleaching effect and decreased dramatically over time. PI intensity of the culture increased linearly with the increase of dead cell numbers, however, the maximum intensities were rather weak compared to SYTO9 and background values. Thus, slight inaccuracy in measurement of PI signal could have significant effect on the outcome. Conclusions When viability staining with SYTO9 and PI is performed, several factors need to be considered such as the bleaching effect of SYTO9, different binding affinity of SYTO9 to live and dead cells and background fluorescence.

Chlorine disinfection is a commonly used disinfection process in wastewater treatment, but its effects on the indigenous bacterial community in treated wastewater have not been fully elucidated. In this study, secondary effluent samples collected in four wastewater treatment plants (WWTPs) were selected for chlorine disinfection. Shifts in the bacterial community compositions in secondary effluent samples upon chlorine disinfection, both immediately and after 24 h of storage, were investigated using Illumina MiSeq sequencing combined with propidium monoazide (PMA) treatment. The results showed that the phylum Proteobacteria was sensitive to chlorine, with the relative proportions of Proteobacteria decreased from 39.2 to 75.9 % in secondary effluent samples to 7.5 to 62.2 % immediately after chlorine disinfection. The phylogenetic analysis indicated that the most dominant genera belonging to Proteobacteria were sensitive to chlorine. In contrast, the phyla Firmicutes and Planctomycetes showed a certain resistance to chlorine, with their relative proportions increasing from 5.1 to 23.1 % and 0.8 to 9.3 % to 11.3 to 44.6 % and 1.5 to 13.3 %, respectively. Most dominant genera belonging to Firmicutes showed resistance to chlorine. A significant reduction in the richness and diversity of the bacterial community was observed after 24 h of storage of chlorinated secondary effluent. During the 24-h storage process, the relative proportions of most dominant phyla shifted in reverse from the changes induced by chlorine disinfection. Overall, chlorine disinfection not only changes the bacterial community compositions immediately after the disinfection process but also exerts further impacts over a longer period (24 h).