High throughput, real-time detection of Naegleria lovaniensis in natural river water using LED-illuminated Fountain FlowTMCytometry

An Optimized Most Probable Number (MPN) Method to Assess the Number of Thermophilic Free-Living Amoebae (FLA) in Water Samples

Detection and quantification of pathogenic free-living amoebae (FLA) in water samples is critical for assessing water quality and for disease management issues. The most probable number (MPN) is commonly used to account for FLA in water. Nevertheless, this requires a high number of water replicates and working volumes, and a consequent number of non-nutrient agar (NNA)-plates seeded with Escherichia coli. Herein, we aimed at optimizing this difficult method, taking also into account key factors such as (i) the counting method, (ii) the delay between sample collection and sample processing, and (iii) the temperature during water sample transportation. To simplify the MPN method, we filtrated 1 × 1000 and 1 × 100 mL water samples, and cellulose acetate filters were cut in 10 parts and inverted on NNA-plates overlaid with E. coli. The comparison between the classical and our optimized MPN method showed that the final counts were similar, therefore validating the use of the optimized method. Our results also showed that for thermophilic FLA (such as Naegleria fowleri), water samples can be kept at around +30°C and processed within 24 h. This improved MPN method is now routinely used in our laboratory to control Naegleria sp. in the water samples in Guadeloupe.

Rapid, sensitive detection of bacteria in platelet samples with Fountain Flow Cytometry

BACKGROUND

There is a current need to develop a technique for bacterial screening of platelet donations that is more rapid, sensitive, and economical than alternatives. The objective of this research was to perform a pilot test of the viability of Fountain Flow Cytometry (FFC), for the rapid and sensitive detection of bacteria in platelet donations.

METHODS

Platelet samples were inoculated with serial dilutions of five selected bacterial strains. Samples were then centrifuged, reconstituted in buffer, and stained with a live/dead bacterial stain cocktail. The resulting aqueous sample was measured by FFC, in which the sample passed as a stream in front of an LED, which excited the fluorescent labels. Fluorescence was detected with a digital camera as the sample flowed toward it.

RESULTS

Fountain Flow Cytometry enumeration yielded results that were linear with bacterial concentration, having an R2 of ≥0.98 with a detection efficiency of 92%±3%. Measurements of uninoculated samples showed a false-positive detection rate at ~400 colony forming units (CFU)/mL. Detection of bacterial concentrations in platelets above this threshold can be made in ~15 minutes, including sample preparation time.

CONCLUSION

This pilot study supports the efficacy of FFC for the rapid and sensitive screening of platelet donations for bacteria.

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Fishing on chips: up-and-coming technological advances in analysis of zebrafish and Xenopus embryos

Biotests performed on small vertebrate model organisms provide significant investigative advantages as compared with bioassays that employ cell lines, isolated primary cells, or tissue samples. The main advantage offered by whole-organism approaches is that the effects under study occur in the context of intact physiological milieu, with all its intercellular and multisystem interactions. The gap between the high-throughput cell-based in vitro assays and low-throughput, disproportionally expensive and ethically controversial mammal in vivo tests can be closed by small model organisms such as zebrafish or Xenopus. The optical transparency of their tissues, the ease of genetic manipulation and straightforward husbandry, explain the growing popularity of these model organisms. Nevertheless, despite the potential for miniaturization, automation and subsequent increase in throughput of experimental setups, the manipulation, dispensing and analysis of living fish and frog embryos remain labor-intensive. Recently, a new generation of miniaturized chip-based devices have been developed for zebrafish and Xenopus embryo on-chip culture and experimentation. In this work, we review the critical developments in the field of Lab-on-a-Chip devices designed to alleviate the limits of traditional platforms for studies on zebrafish and clawed frog embryo and larvae. © 2014 International Society for Advancement of Cytometry.

Quantitative detection and identification of Naegleria spp. in various environmental water samples using real-time quantitative PCR assay

Naegleria spp. is a free-living amoeba that can be found in various aquatic environments. There are some Naegleria spp. that can cause fatal infections in animals and humans, and the most important source of infection is through direct water contact. In this study, a real-time quantitative PCR was developed to detect and quantify the Naegleria spp. in various environmental water samples. The water samples were taken from rivershed, water treatment plants, and thermal spring recreation areas. The total detection rate was 4.0% (7/176) for Naegleria spp. The percentages of samples containing Naegleria spp. from river water, raw drinking water, and thermal spring water were 0% (0/100), 10.7% (3/28) and 8.3% (4/48), respectively. The concentration of Naegleria spp. in detected positive raw drinking water and thermal spring water samples was in the range of 3.9-12.6 and 1.1-24.2 cells/L, respectively. The identified species included Naegleria australiensis, Naegleria lovaniensis, and Naegleria spitzbergeniensis. The presence of Naegleria spp. in various aquatic environments is considered a potential public health threat.

Fountain flow cytometry

Fountain Flow Cytometry (FFC) is a simple and inexpensive technology that is adaptable to situations requiring detection and enumeration of cells/organisms at low concentrations, but is limited to particles of relatively high fluorescence intensity. This work presents the basic physics behind the novel scheme Fountain Flow Cytometry employs for the detection of target particles, a hybrid of conventional flow cytometry and video epifluorescence microscopy. The method is based on LED-induced fluorescence of labeled particles and requires no filtration step. Unlike conventional flow cytometry, the resulting fluorescence is measured with a digital camera as the measured sample flows toward the camera along the optical axis. An automated target particle recognition and enumeration computer program, Biocount, is used to count particles. FFC allows for detection of target particles in transparent and translucent fluids, such as environmental water, blood, and beverages. In addition, FFC can be used for detection of target particles in the presence of high photometric background, including unbound fluorescent dye. This facilitates use of the technique in situations where cells are unwashed. Current applications extend, but are not limited to, particles from µm-size bacteria to multi-millimeter-sized multicellular organisms.

Wormometry-on-a-chip: Innovative technologies for in situ analysis of small multicellular organisms

Small multicellular organisms such as nematodes, fruit flies, clawed frogs, and zebrafish are emerging models for an increasing number of biomedical and environmental studies. They offer substantial advantages over cell lines and isolated tissues, providing analysis under normal physiological milieu of the whole organism. Many bioassays performed on these alternative animal models mirror with a high level of accuracy those performed on inherently low-throughput, costly, and ethically controversial mammalian models of human disease. Analysis of small model organisms in a high-throughput and high-content manner is, however, still a challenging task not easily susceptible to laboratory automation. In this context, recent advances in photonics, electronics, as well as material sciences have facilitated the emergence of miniaturized bioanalytical systems collectively known as Lab-on-a-Chip (LOC). These technologies combine micro- and nanoscale sciences, allowing the application of laminar fluid flow at ultralow volumes in spatially confined chip-based circuitry. LOC technologies are particularly advantageous for the development of a wide array of automated functionalities. The present work outlines the development of innovative miniaturized chip-based devices for the in situ analysis of small model organisms. We also introduce a new term "wormometry" to collectively distinguish these up-and-coming chip-based technologies that go far beyond the conventional meaning of the term "cytometry."

An innovative continuous flow system for monitoring heavy metal pollution in water using transgenic Xenopus laevis tadpoles

While numerous detection methods exist for environmental heavy metal monitoring, easy-to-use technologies combining rapidity with in vivo measurements are lacking. Multiwell systems exploiting transgenic tadpoles are ideal but require time-consuming placement of individuals in wells. We developed a real-time flow-through system, based on Fountain Flow cytometry, which measures in situ contaminant-induced fluorescence in transgenic amphibian larvae immersed in water samples. The system maintains the advantages of transgenic amphibians, but requires minimal human intervention. Portable and self-contained, it allows on-site measurements. Optimization exploited a transgenic Xenopus laevis bearing a chimeric gene with metal responsive elements fused to eGFP. The transgene was selectively induced by 1 microM Zn(2+). Using this tadpole we show the continuous flow method to be as rapid and sensitive as image analysis. Flow-through readings thus accelerate the overall process of data acquisition and render fluorescent monitoring of tadpoles suitable for on-site tracking of heavy metal pollution.