Detection of Salmonella by using the colorimetric DNA/rRNA sandwich hybridization in microtiter wells

Colorimetric Approach for Nucleic Acid Salmonella spp. Detection: A Systematic Review

Water- and food-related health issues have received a lot of attention recently because food-poisoning bacteria, in particular, are becoming serious threats to human health. Currently, techniques used to detect these bacteria are time-consuming and laborious. To overcome these challenges, the colorimetric strategy is attractive because it provides simple, rapid and accurate sensing for the detection of Salmonella spp. bacteria. The aim of this study is to review the progress regarding the colorimetric method of nucleic acid for Salmonella detection. A literature search was conducted using three databases (PubMed, Scopus and ScienceDirect). Of the 88 studies identified in our search, 15 were included for further analysis. Salmonella bacteria from different species, such as S. Typhimurium, S. Enteritidis, S. Typhi and S. Paratyphi A, were identified using the colorimetric method. The limit of detection (LoD) was evaluated in two types of concentrations, which were colony-forming unit (CFU) and CFU per mL. The majority of the studies used spiked samples (53%) rather than real samples (33%) to determine the LoDs. More research is needed to assess the sensitivity and specificity of colorimetric nucleic acid in bacterial detection, as well as its potential use in routine diagnosis.

Sandwich Hybridization Assay for In Situ Real-Time Cyanobacterial Detection and Monitoring: A Review

As cyanobacterial harmful algal bloom (cHAB) events increase in scale, severity, frequency, and duration around the world, rapid and accurate monitoring and characterization tools have become critically essential for regulatory and management decision-making. The composition of cHAB-forming cyanobacteria community can change significantly over time and space and be altered by sample preservation and transportation, making in situ monitoring necessary to obtain real-time and localized information. Sandwich hybridization assay (SHA) utilizes capture oligonucleotide probes for sensitive detection of target-specific nucleic acid sequences. As an amplification-free molecular biology technology, SHA can be adapted for in-situ, real-time or near real-time detection and qualitatively or semi-quantitatively monitoring of cHAB-forming cyanobacteria, owing to its characteristics such as being rapid, portable, inexpensive, and amenable to automation, high sensitivity, specificity and robustness, and multiplexing (i.e., detecting multiple targets simultaneously). Despite its successful application in the monitoring of marine and freshwater phytoplankton, there is still room for improvement. The ability to identify a cHAB community rapidly would decrease delays in cyanotoxin analyses, reduce costs, and increase sample throughput, allowing for timely actions to improve environmental and human health and the understanding of short- and long-term bloom dynamics. Real-time detection and quantitation of HAB-forming cyanobacteria is essential for improving environmental and public health and reducing associated costs. We review and propose to apply SHA for in situ cHABs monitoring.

Salmonella in liquid eggs and other foods in fukuoka prefecture, Japan

The study aimed to evaluate the prevalence of Salmonella in retail and wholesale foods in Fukuoka Prefecture, Japan. A total of 2,021 samples collected between 1999 and 2010 were tested using a culture method. Samples consisted of liquid eggs (n = 30), meat (beef and pork) (n = 781), offal (n = 69), processed meats (n = 2), seafood (n = 232), processed seafood (dried fish) (n = 76), vegetables (n = 481), processed vegetables (n = 87), fruits (n = 167), and herbs (n = 96) from 574 outlets and wholesale agents in 15 areas (five samples were undocumented regarding outlets). Overall, liquid egg showed significantly (P < 0.001) higher frequencies of Salmonella contamination (13.3%) than beef (1/423, 0.2%) and pork (3/235, 1.3%). Salmonella enterica subsp. enterica serovar Enteritidis, the most common serovar as a human pathogen, were isolated from two liquid egg samples. No Salmonella were isolated from seafood and vegetable-related samples including seed sprouts (n = 261). In conclusion, liquid egg is a significant Salmonella vehicle, showing a need to continue the vaccination of chickens to prevent S. Enteritidis contamination in Japanese eggs. Moreover, further study is needed to evaluate Salmonella contamination in seed sprouts with more sampling from retailers there.

Prevalence of the virulence plasmid in Salmonella Typhimurium isolates from pigs

To determine the prevalence of the virulence plasmid in Salmonella Typhimurium isolates from pigs in Japan, a total of 106 porcine isolates were subjected to PCR amplification for the detection of the virulence plasmid. Out of the isolates of S. Typhimurium, 38 (35.8%) harbored the virulence plasmid. The presence of the virulence plasmid was widely observed in the isolates from systemically infected pigs (92.0%, 23/25), compared with diarrheic (18.8%, 12/64) and apparently healthy pigs (17.6%, 3/17) (P<0.01).

Improved bioluminescent enzyme immunoassay for the rapid detection of Salmonella in chicken meat samples

AIMS

To evaluate an improved bioluminescent enzyme immunoassay (BEIA) using biotinylated firefly luciferase for the rapid detection of Salmonella in naturally contaminated chicken meat samples.

METHODS AND RESULTS

Capture agents and lipopolysaccharide (LPS) extraction reagents for Salmonella were investigated to improve the sensitivity of the BEIA. Also, the use of Oxoid SPRINT (Simple Pre-enrichment and Rapid Isolation New Technology) as a pre-enrichment and selective medium for 26-h BEIA detection of Salmonella in chicken meat samples was examined. The use of polymyxin B as a capture agent on solid support and 3-[(3-Cholamidopropyl) dimethylammonio] propanesulfonic acid (CHAPS) for extraction of the LPS facilitated sensitive detection of Salmonella. Of 120 chicken meat samples, 25 samples were positive using the improved BEIA with the SPRINT and 25 samples were positive using the SPRINT followed by the standard isolation methods.

CONCLUSIONS

The improved BEIA, in which polymxin B was used as a capture agent and CHAPS was used for extraction of the antigen, had a sensitivity of 96.0% and a specificity of 98.9% for the detection of Salmonella in chicken meat.

SIGNIFICANCE AND IMPACT OF THE STUDY

The improved BEIA combined with the SPRINT medium for the detection of Salmonella in chicken meat samples produced comparable results to the culture methods in 26 h.

Sensitive genus-specific detection of Legionella by a 16S rRNA based sandwich hybridization assay

The aim of this study was to develop a sensitive, cultivation-independent analytical method for Legionella in man-made water systems which can be performed within one day in crude sample extracts. The new assay for the genus Legionella is a paramagnetic bead based fluorescence sandwich hybridization assay (SHA) for the 16S rRNA based on two oligonucleotide probes which makes the method highly specific. An advantage over RT-PCR is the exclusive detection of viable cells and, due to the high number of 16S RNA molecules, the possibility to apply the method directly in crude cell extracts without prior purification of the nucleic acids. A high sensitivity was obtained by modifying the probe chemistry and hybridization conditions. The most sensitive assay uses a 3'-end biotin-labelled capture probe and a 3'-end DIG tailed detection probe and has a detection limit of 20 amol target molecules corresponding to 1.2x10(7) molecules of 16S rRNA and approximately 1800 Legionella cells. Using this assay type the number of Legionella cells was determined in Legionella contaminated water samples. The results show that the developed SHA can be applied for estimation of the approximate number of Legionella cells based on the number of 16S rRNA molecules in a water sample.

Enrichment for isolating Salmonella Choleraesuis and other Salmonella spp. from pigs

The growth of Salmonella Choleraesuis was examined in Rappaport Vassiliadis broth (RV) and Hajna-tetrathionate broth (HTT) at 37 and 42 degrees C. As the enrichment in RV at 37 degrees C was satisfactory for isolating S. Choleraesuis, we used this enrichment for isolation from the samples collected from 15 asymptomatic pigs reared on a S. Choleraesuis contaminated farm. S. Choleraesuis was frequently isolated from six pigs (40.0%) under field conditions. The isolation of other Salmonella serovars than S. Choleraesuis was attempted by using both RV enrichment at 37 degrees C and HTT enrichment at 42 degrees C. Salmonella organisms were isolated from 156 (44.8%) of 348 fecal samples and more frequently with HTT at 42 degrees C (43.4%) than with RV at 37 degrees C (20.9%). If other serovars in addition to S. Choleraesuis are to be surveyed, HTT enrichment should be used in combination with RV enrichment.

Isolation and serological survey of Salmonella in pigs in Japan

A total of 267 fecal and serum samples collected from individual pigs reared on a Salmonella-positive farm were subjected to bacteriological and serological examinations of Salmonella. Salmonella was isolated from 47 pigs (17.6%) and prevalence of antibody to lipopolysaccharide (LPS) of S. Typhimurium, which was partly common to S. O4, 12: d: -, was observed in 90 pigs (33.7%). Salmonella was isolated from 26 (28.9%) of 90 antibody-positive pigs and 21 (11.9%) of 177 antibody-negative pigs. Twenty-one of 36 pigs (58.3%) positive for S. O4, 12: d: -, five of 10 pigs (50.0%) positive for S. Havana, and none for S. Anatum had antibodies. Thus, seropositive rates were higher than isolation-positive rates, and antibody prevalence was associated with serovars of the isolates. Then, we analyzed antibody prevalence among pigs on Japanese pig farms. The antibodies to LPS of S. Typhimurium were found in 195 of 1,498 pigs (13.0%) and in at least one serum sample on 35 of 52 farms (67.3%). Our results indicate that Salmonella does not seem to be so prevalent in pigs though it is widely prevalent among pig farms.

Isolation of Salmonella from diarrheic feces of pigs

A survey of Salmonella was carried out in fecal samples of 887 pigs with diarrhea collected from 235 pig farms between April 1996 and March 2001. Salmonella was isolated from 84 feces (9.5%) of 887 pigs and from 45 (19.1%) of 235 farms. The higher prevalence was found in weaned pigs (12.4%) and fattening pigs (17.3%) than in sows (4.2%) and suckling pigs (4.5%). Isolation rates of S. Typhimurium were higher from weaned and fattening pigs than from the others. Therefore, risk of horizontal infection of S. Typhimurium will increase, if no adequate health managements are practiced when weaned and fattening pigs have diarrhea.