Rapid separation and counting of viable microbial cells in food by nonculture method with bioplorer, a focusing-free microscopic apparatus with a novel cell separation unit

Rapid quantification of bacteria in infected root canals using fluorescence reagents and a membrane filter: a pilot study on its clinical application to the evaluation of the outcomes of endodontic treatment

Objective. The bacterial examination has been performed during the course of the root canal treatment. In the present pilot study, the new developed method, using fluorescence reagents and a membrane filter, was applied to the detection and quantification of bacteria in infected root canals, in order to evaluate the outcomes of the treatment. Methods. Six infected root canals with periapical lesions from 5 subjects were included. Informed consent was obtained from all subjects (age ranges, 23–79 years). Samples from infected root canals were collected at the beginning of the treatment (termed #25 First), the end of the first day of treatment (termed #55 First), and the next appointment day (termed #55 Second). Then, the bacterial count (CFU) was measured using fluorescence reagents (4′,6′-diamidino-2-phenylindole and propidium iodide) and the polycarbonate membrane filter by Bioplorer. Results. The mean ± SD of CFU in the sample of “#25 First” was (1.0 ± 1.4) × 10⁵. As the root canal treatment progressed, the CFU decreased as 7.9 × 10³ (#55 First) and 4.3 × 10² (#55 Second). Conclusion. In the present pilot study, rapid detection and quantification of bacteria in infected root canals were found to be successfully performed using fluorescence reagents and a membrane filter (Bioplorer analysis).

Evaluation of a novel rapid detection system for yeasts and molds

A novel system, the NISSUI rapid detection system, has been developed to rapidly detect yeasts and molds in food. This system consists of a liquid medium containing resazurin as a redox indicator, a unique original micro-well dish containing 676 micro-wells, and a fluorescence-monitoring instrument with an incubator. To evaluate this system, orange juice, milk, and physiological saline solutions artificially inoculated with yeasts or molds were used as samples. Comparison of the new system used at 28ºC for 48 h with a spread-plate method using a potato-dextrose-agar plate at 25ºC for 120 h yielded a correlation coefficient (r) of 0.95. Our data reveal that the new method considerably shortens the time required for detection of yeasts and molds in food.

Development of a density slicer for the simple collection of respective density layers after stepwise density gradient centrifugation

Density gradient centrifugation (DGC) is useful for the separation of living microbial cells from food samples that are not filterable. After DGC, however, careful operation is necessary to collect each density layer. For a simple and reproducible collection after DGC, we have developed a seamless operation system composed of a 5-needle unit, a microchannel plate, and a microflow controller, and named this a density slicer system. Two types of 5-needle units were devised and both showed nearly the same performance. Reproducible results with the automatic operation system could be demonstrated using an Escherichia coli cell suspension.

Rapid detection and identification of beer-spoilage lactic acid bacteria by microcolony method

We evaluated a microcolony method for the detection and identification of beer-spoilage lactic acid bacteria (LAB). In this approach, bacterial cells were trapped on a polycarbonate membrane filter and cultured on ABD medium, a medium that allows highly specific detection of beer-spoilage LAB strains. After short-time incubation, viable cells forming microcolonies were stained with carboxyfluorescein diacetate (CFDA) and counted with muFinder Inspection System. In our study, we first investigated the growth behavior of various beer-spoilage LAB by traditional culture method, and Lactobacillus lindneri and several L. paracollinoides strains were selected as slow growers on ABD medium. Then the detection speeds were evaluated by microcolony method, using these slowly growing strains. As a result, all of the slowly growing beer-spoilage LAB strains were detected within 3 days of incubation. The specificity of this method was found to be exceptionally high and even discriminated intra-species differences in beer-spoilage ability of LAB strains upon detection. These results indicate that our microcolony approach allows rapid and specific detection of beer-spoilage LAB strains with inexpensive CFDA staining. For further confirmation of species status of detected strains, subsequent treatment with species-specific fluorescence in situ hybridization (FISH) probes was shown as effective for identifying the CFDA-detected microcolonies to the species level. In addition, no false-positive results arising from noise signals were recognized for CFDA staining and FISH methods. Taken together, the developed microcolony method was demonstrated as a rapid and highly specific countermeasure against beer-spoilage LAB, and compared favorably with the conventional culture methods.

Separation of viable histamine-producing bacteria from yellowtail meat components by density gradient centrifugation

Quantitative separation of live cells from food samples is essential for non-culture methods to be validated. In this viewpoint, the feasibility of density gradient centrifugation (DGC) was demonstrated for the first time using samples of yellowtail meat to which Morganella morganii, a histamine producing bacterium had been added. Using a Ficoll density gradient from 50 to 10 w/v % with 10 w/v % steps, meat-free fractions of M. morganii cells were collected in 20-50 w/v % layers. The total cell collection rate ranged from 73-86 % irrespective of the cell density in the range 10(2)-10(6) cells/200 microl.

Rapid count of microbial cells in dialysate

An apparatus for the non-culture method (NCM) of microbial cell count was formerly developed and named a bioplorer. The bioplorer NCM is based on the double staining of cells with 4', 6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI) and the automatic analysis of their fluorescent microscopic images. Viable cells can be stained with DAPI, while dead cells can be stained with DAPI and PI. In this study, the bioplorer NCM has been applied to the dialysate. The viable and dead cells in dialysate could be counted within 20 min. The detection limit expressed by log(10)[cells/100 mL] was 2.0. When cell-spiked dialysate samples containing prescribed number of Bacillus subtilis cells were assayed, the numbers of cells determined by the bioplorer NCM (N(VIA)(NCM)) and a conventional culture method (CM) on R2A medium (N(VIA)(R2A-CM)) were similar in the range of 2.6-4.6 within the 95% confidence interval (NCM-CM equivalent range). When test solutions sampled from a practical facility in a hospital were assayed, N(VIA)(NCM) was greater than, but comparable to, N(VIA)(R2A-CM). The endotoxin (ET) in the test samples were assayed as well using a test kit for limulus amoebocyte lysate assay. The results of microbial cells and ET concentration indicated that the dialysate supplying line was clean and well maintained. The bioplorer NCM can determine if the microbial contamination of dialysate supplying facilities is greater than 2.6 (398 cells/100 mL).

Evaluation of cell wall binding domain of Staphylococcus aureus autolysin as affinity reagent for bacteria and its application to bacterial detection

We evaluated the cell wall binding (CWB) domain of Staphylococcus aureus autolysin as an affinity reagent for bacteria. A fusion of CWB domain and green fluorescent protein (CWB-GFP) bound to S. aureus with a dissociation constant of 15 nM. CWB-GFP bound to a wide range of gram-positive bacteria, but not to most gram-negative bacteria. We suspected that the outer membrane of gram-negative bacteria inhibits the access of CWB-GFP to peptidoglycan layer. Indeed, CWB-GFP bound to gram-negative bacteria when they were treated with benzalkonium chloride. Because CWB-GFP bound to the bacterial peptidoglycan layer, it appeared to be an effective affinity reagent for bacteria and CWB fusion with reporter proteins could be applied to detect bacteria. We also constructed a fusion of CWB and luciferase, which can be used for the rapid detection of bacteria.