flow cytometric data acquisition of microbial aggregates

Kvantitativ analyse af mikrobiel autoaggregering ved hjælp af billeddannelsesflowcytometri

Bacterial autoaggregation is considered a primary step in biofilm formation. In this process (sometimes also called autoagglutination or flocculation), bacteria of the same type form multicellular clumps that eventually settle at the bottom of culture tubes or attach to their target tissue or surface1.
Autoaggregation is a widely observed phenomenon and has been shown so far in Gram-negative pathogens such as the opportunistic pathogen Acinetobacter baumannii2, the dental pathogen Aggregobacter actinomycetemcomitans3, and the emerging pathogen Burkholderia pseudomallei4. Autoaggregation has also been described in several probiotic Gram-positive strains5,6,7,8. In Lactobacillus (L.) acidophilus, autoaggregation was partially mediated by S-layer proteins and correlated with an adhesion to xylan7. Similarly, we found a correlation between glucose-dependent autoaggregation and induction of the adhesive properties (as judged by adhesion to mucin) of the probiotic species Lacticaseibacillus rhamnosus GG, Lacticaseibacillus casei, L. acidophilus, Lacticaseibacillus paracasei, and Lactiplantibacillus plantarum5. The increased autoaggregation most likely reflected changes in the expression of cellular adhesins in response to glucose and its catabolites9. While the molecular mechanisms of autoaggregation remain to be determined, it has been shown that this process alters the phenotype of the aggregated bacteria and grants them enhanced tolerance to environmental stressors1, as well as increased sensitivity to quorum sensing molecules10.
Several approaches have been used to measure autoaggregation; one experimental approach is to let cultures stand statically in narrow culture tubes for a given time. Control cultures remain turbid, whereas autoaggregation cultures will settle at the bottom of the tube. A more quantitative approach measures autoaggregation by sedimentation or settling assay11.
Flow cytometry has also been increasingly employed in recent years to investigate bacterial autoaggregation. This method is appropriate for analyzing particles between approximately 0.5 and 1000 &#181;m in size. The single bacterium or formed aggregates are suspended in fluid, fed into a stream, and can be detected one by one11. Recording forward scattered light allows measuring the relative size of the cell or aggregate. It is relatively fast and straightforward but cannot detect several parameters, such as aggregate size or the average number of cells in aggregates. Therefore, this approach can be complemented microscopically, allowing more parameters to be checked12. However, traditional microscopy is time-consuming and thereby limits the number of tested samples and the statistical power of the analysis. In general, imaging flow cytometry provides several features compared to traditional flow cytometry, such as simultaneous analysis of cell morphology and phenotype, conducting image-based analysis, detecting rare events, and validating flow cytometry data13. These advantages enhance the capabilities of flow cytometry and facilitate a more detailed examination of cell populations.
This study provides a valuable protocol for imaging flow cytometry to monitor autoaggregation in lactic acid bacteria (LAB). These Gram-positive rods are facultative anaerobes and belong to the LAB group. These efficient glucose fermenters generate lactic acid as their main end-product of carbohydrate metabolism14. These bacteria are beneficial core members of the microbiome and are naturally found in the gastrointestinal tract (GIT) of humans and animals, as well as in the urogenital tract of females15. Therefore, the exact characterization of their autoaggregation properties is of high biotechnological and clinical interest.
Our previous findings indicated that the basal level of autoaggregation differs between different probiotic strains. This heterogeneity is affected by the different carbohydrates used as a carbon source5. To overcome this fundamental property of probiotic bacteria, the effects of carbohydrates from the diet were monitored on autoaggregation on the single-cell level using IFC. This IFC-based approach combines the power and speed of traditional flow cytometers with the microscope&#39;s resolution. Therefore, it allows high-rate complex morphometric measurements in a phenotypically defined way16,17. This approach can be extended to other probiotic and pathogenic bacteria, combined with fluorescent reporters to monitor gene expression, and fluorescently labeled strains to monitor the presence and abundance of specific bacterial species in heterogeneous aggregates.

Forfatter Spotlight: Fremme af forskning i mikrobiel autoaggregering ved hjælp af billeddannelsesflowcytometri

Imaging Flow Cytometry til at studere mikrobiel autoaggregering

This study utilized Lactobacillus species as a model to demonstrate the effectiveness of imaging flow cytometry analysis in studying microbial autoaggregation. The focus is on analyzing the response of autoaggregation of Lactobacillus species to simple carbohydrates from the diet. The most used methods for measuring autoaggregation are spectral photometry, which measures microbial suspensions, turbidity, or optical density, and traditional microscopy techniques, such as bright field, phase contrast, and fluorescent microscopy.When talking about hight-throughput imaging, one major experimental challenge is single event segmentation. In this protocol, it is a single aggregate. Imaging flow cytometry addresses this challenge elegantly and give researchers a powerful tool for studying autoaggregation.

Flowcytometrisk dataindsamling af mikrobielle aggregater

For at begynde den flowcytometriske analyse skal du først indstille 785-nanometer laseren til en effekt på fem milliwatt til mørkefeltmålinger. Brug et 60X-objektiv med en numerisk blænde på 0,9. Vælg derefter indstillingen for høj følsomhed, og indstil hastigheden til lav.For at sikre kalibreringsperlens stabilitet skal du trykke på Play-knappen i fluidics-boksen og undersøge perlebillederne, som skal fremstå skarpe og klare. Opret et nyt punktdiagram i arbejdsområdet ved at vælge Nyt punktdiagram. Vælg derefter det område i Brightfield-kanalen, der svarer til SSC-kanalintensiteten, og ekskluder de kalibreringsperler, der kører samtidigt i prøven.Tryk derefter på knappen Indlæs og placer et rør indeholdende Lactobacilli sample i holderen. I feltet Indstillinger for anskaffelse skal du angive eksempelnavnet og angive placeringen for datalagring. Angiv antallet af hændelser, der skal indsamles, typisk inden for intervallet 10.000 til 20.000 hændelser.Begynd nu anskaffelsesprocessen ved at klikke på Optage knappen placeret i Erhvervelse boks. Processen stopper, når den angivne mængde hændelser er nået. Tryk på knappen Retur for at tømme røret og fjerne det fra holderen som bedt om i pop op-vinduet.Når du har gentaget processen for alle prøver, skal du gemme skabelonen for at opretholde ensartetheden i dataindsamlingen. For dataanalyse, for at indlæse råfilen i analysesoftwaren, skal du klikke på Filer og åbne rif-filen. I det åbnede vindue skal du vælge Brug anskaffelsesanalyse og derefter klikke på OK. Klik derefter på knappen Nyt histogram for at oprette et histogram af gradientrodens middelkvadrat og vælg populationen fra erhvervelsen, der skal analyseres.Under funktionen X-akse skal du vælge Gradient RMS for Brightfield-kanalen. Placer derefter en port for at udelade ikke-fokuserede hændelser ved at klikke på knappen Opret linjeområde i analyseområdet. Opret et punktdiagram af området i forhold til højde-bredde-forholdet ved at klikke på knappen Nyt punktplot i analyseområdet.Vælg den fokuserede population i vinduet Nyt punktdiagram. Vælg derefter området for Brightfield-kanalen for X-Axis-funktionen. Vælg billedformatet for Y-akse-funktionen.Tegn en port på punktdiagrammet ved hjælp af knappen Opret rektangel baseret på arealværdien for den samlede hændelsespopulation. På samme måde skal du tegne en anden port for singler og små aggregater. Gem dataanalysen som en skabelon ved at klikke på fanen Filer, vælge Gem som skabelon og derefter åbne den næste eksempelfil under den samme skabelon for at oprette dataanalysefilen.For at måle den aggregerede størrelsesfordeling skal du starte med at plotte et histogram af arealet af populationen af aggregeringshændelser. Gem dataanalysen ved at klikke på filen og vælge indstillingen Gem som skabelon. Når du har gemt, skal du åbne den næste eksempelfil under den samme skabelon til dataanalysefilen.Enkeltceller, små aggregater, store aggregater og kæder blev observeret i LGG og L.paracasei, men det var ikke muligt at skelne mellem kæder og større aggregater. Signifikante variationer i aggregeringsegenskaberne for forskellige LAB-stammer blev observeret som reaktion på fermenterbare eller ikke-fermenterbare sukkerarter.

Research

JoVE Journal

Biology

Flow Cytometric Data Acquisition of Microbial Aggregates

Imaging Flow Cytometry to Study Microbial Autoaggregation

Beneficial and probiotic bacteria play essential roles in their hosts, providing various health benefits, including immunity to infectious diseases. The ...

Lactobacillaceae Sample Preparation for Flow Cytometric Analysis

Lactobacillaceae Prøveforberedelse til flowcytometrisk analyse