Development of the immunomagnetic enrichment method selective for Vibrio parahaemolyticus serotype K and its application to food poisoning study

Anti-Interference Detection of Vibrio parahaemolyticus from Aquatic Food Based on Target-Cyclized RCA with Dynamic Adapter Followed by LAMP

Vibrio parahaemolyticus (V. parahaemolyticus) is considered the most concerning pathogen for seafood. Like other pathogens in food samples, its gene detection suffers from a problem of background interference when isothermal detection methods are used. The sensitivity and specificity greatly decrease due to large amounts of background genome. Here we describe a novel isothermal detection technology based on target-cyclized rolling circle amplification combined with loop-mediated isothermal amplification (tRCA-lamp). By avoiding unexpected ligation, a short dynamic adapter is employed to increase the sensitivity of target cyclization in the presence of the background genome. At the amplification step, highly specific detection is obtained by linear RCA and simplified LAMP (only two primers are used). Furthermore, visual detection is easily realized with hydroxynaphthol blue (HNB). In the oyster samples, the tRCA-lamp approach can detect V. parahaemolyticus with a detection limit of 22 cfu/g with none necessary to enrich the bacteria and remove the host DNA. This method gets rid of the complicated primer design process and can be extended to the detection of other pathogens in food samples.

Development of a magnetic separation method to capture sepsis associated bacteria in blood

Bloodstream infections are important public health problems, associated with high mortality due to the inability to detect the pathogen quickly in the early stages of infection. Such inability has led to a growing interest in the development of a rapid, sensitive, and specific assay to detect these pathogens. In an effort to improve diagnostic efficiency, we present here a magnetic separation method for bacteria that is based on mutated lysozyme (LysE35A) to capture S. aureus from whole blood. LysE35A-coated beads were able to bind different MSSA and MRSA isolates in the blood and also other six Gram-positive and two Gram-negative species in whole blood. This system was capable to bind bacteria at low concentrations (10CFU/ml) in spiked blood. Samples captured with the mutated lysozyme showed more responsive amplification of the 16S gene than whole blood at concentrations of 10(3)-10(5)CFU. These data demonstrate detection of S. aureus directly in blood samples, without in vitro cultivation. Our results show that capture with LysE35A-coated beads can be useful to develop a point of care diagnostic system for rapid and sensitive detection of pathogens in clinical settings.

Characteristics of a sharp decrease in Vibrio parahaemolyticus infections and seafood contamination in Japan

Vibrio parahaemolyticus has been one of the most important foodborne pathogens in Japan since the 1960s, and a large epidemic was caused by the pandemic serotype O3:K6 from 1997 to 2001. V. parahaemolyticus infections, however, have sharply declined since that time. Data on serotypes isolated from 977 outbreaks were collected and analysed. Total and pathogenic, thermostable direct hemolysin (TDH) gene-positive V. parahaemolyticus were qualitatively and quantitatively detected in 842 seafood samples from wholesale markets in 2007-2009. Strains isolated from patients and seafood were analysed by serotyping, tdh-PCR, group-specific PCR for pandemic strains, and pulsed-field gel electrophoresis (PFGE). The sharp decrease in the infections from 1999 onwards was noted not only for O3:K6 infections but also for other serotypes. The change in the seafood contamination situation from 2001 to 2007-2009 was characterised by a decrease to three-fourths in the frequency of tdh-positive samples, although that decrease was small compared to the 18-fold decrease in the cases of V. parahaemolyticus outbreaks. PFGE detected the pandemic O3:K6 serotype in the same profile in seafood and patients from 1998 to the present. Because of no large decrease in seafood contamination by V. parahaemolyticus from the production to distribution stages and the presence of pandemic O3:K6 serotype in seafood to the present, it was suggested that the change of seafood contamination was unrelated to the sharp decrease in V. parahaemolyticus infections. V. parahaemolyticus infections might be prevented at the stages after the distribution stage.

Bacterial capture by peptide-mimetic oligoacyllysine surfaces

Most procedures for detecting pathogens in liquid media require an initial concentration step. However, poor recovery efficiencies of conventional methods, such as filtration, often lead to low sensitivity. Here, we describe a strategy for concentrating bacteria using their binding affinity for an oligoacyllysine (OAK), a novel peptide-mimetic antimicrobial compound. We show that the resin-linked OAK (ROAK) efficiently captures a variety of pathogens in different media, upon brief incubation with ROAK beads or after continuous flow through a ROAK-packed column. Using Escherichia coli expressing green fluorescent protein, we show that binding occurs rapidly during incubation and persists after filtration as visualized by confocal microscopy. The high binding affinity of bacteria was confirmed by surface plasmon resonance technology using an OAK-linked chip. ROAK-bound bacteria remained viable and were readily identifiable by real-time PCR after ethanol elution. A single ROAK bead is estimated to capture about 3,000 bacterial cells in culture medium, in contaminated saline or tap water. ROAK beads can be regenerated for multiple uses after brief ethanol treatment. Collectively, the data support the notion that OAK-based coating of polymeric surfaces might represent a useful means for medium filtration as well as for concentration of bacteria.

Bacterial Separation and Concentration from Complex Sample Matrices: A Review

The use of many rapid detection technologies could be expanded if the bacteria were separated, concentrated, and purified from the sample matrix before detection. Specific advantages of bacterial concentration might include facilitating the detection of multiple bacterial strains; removal of matrix-associated assay inhibitors; and provision of adequate sample size reduction to allow for the use of representative food sample sizes and/or small media volumes. Furthermore, bacterial concentration could aid in improving sampling techniques needed to detect low levels of pathogens or sporadic contamination, which may perhaps reduce or even eliminate the need for cultural enrichment prior to detection. Although bacterial concentration methods such as centrifugation, filtration, and immunomagnetic separation have been reported for food systems, none of these is ideal and in many cases a technique optimized for one food system or microorganism is not readily adaptable to others. Indeed, the separation and subsequent concentration of bacterial cells from a food sample during sample preparation continues to be a stumbling block in the advancement of molecular methods for the detection of foodborne pathogens. The purpose of this review is to provide a detailed understanding of the science, possibilities, and limitations of separating and concentrating bacterial cells from the food matrix in an effort to further improve our ability to harness molecular methods for the rapid detection of foodborne pathogens.

Global dissemination of Vibrio parahaemolyticus serotype O3:K6 and its serovariants

Vibrio parahaemolyticus is recognized as a cause of food-borne gastroenteritis, particularly in the Far East, where raw seafood consumption is high. An unusual increase in admissions of V. parahaemolyticus cases was observed at the Infectious Diseases Hospital in Calcutta, a city in the northeastern part of India, beginning February 1996. Analysis of the strains revealed that a unique serotype, O3:K6, not previously isolated during the surveillance in Calcutta accounted for 50 to 80% of the infections in the following months. After this report, O3:K6 isolates identical to those isolated in Calcutta were reported from food-borne outbreaks and from sporadic cases in Bangladesh, Chile, France, Japan, Korea, Laos, Mozambique, Peru, Russia, Spain, Taiwan, Thailand, and the United States. Other serotypes, such as O4:K68, O1:K25, and O1:KUT (untypeable), that had molecular characteristics identical to that of the O3:K6 serotype were subsequently documented. These serotypes appeared to have diverged from the O3:K6 serotype by alteration of the O:K antigens and were defined as "serovariants" of the O3:K6 isolate. O3:K6 and its serovariants have now spread into Asia, America, Africa, and Europe. This review traces the genesis, virulence features, molecular characteristics, serotype variants, environmental occurrence, and global spread of this unique clone of V. parahaemolyticus.

Automated methods for multiplexed pathogen detection

Detection of pathogenic microorganisms in environmental samples is a difficult process. Concentration of the organisms of interest also co-concentrates inhibitors of many end-point detection methods, notably, nucleic acid methods. In addition, sensitive, highly multiplexed pathogen detection continues to be problematic. The primary function of the BEADS (Biodetection Enabling Analyte Delivery System) platform is the automated concentration and purification of target analytes from interfering substances, often present in these samples, via a renewable surface column. In one version of BEADS, automated immunomagnetic separation (IMS) is used to separate cells from their samples. Captured cells are transferred to a flow-through thermal cycler where PCR, using labeled primers, is performed. PCR products are then detected by hybridization to a DNA suspension array. In another version of BEADS, cell lysis is performed, and community RNA is purified and directly labeled. Multiplexed detection is accomplished by direct hybridization of the RNA to a planar microarray. The integrated IMS/PCR version of BEADS can successfully purify and amplify 10 E. coli O157:H7 cells from river water samples. Multiplexed PCR assays for the simultaneous detection of E. coli O157:H7, Salmonella, and Shigella on bead suspension arrays was demonstrated for the detection of as few as 100 cells for each organism. Results for the RNA version of BEADS are also showing promising results. Automation yields highly purified RNA, suitable for multiplexed detection on microarrays, with microarray detection specificity equivalent to PCR. Both versions of the BEADS platform show great promise for automated pathogen detection from environmental samples. Highly multiplexed pathogen detection using PCR continues to be problematic, but may be required for trace detection in large volume samples. The RNA approach solves the issues of highly multiplexed PCR and provides "live vs. dead" capabilities. However, sensitivity of the method will need to be improved for RNA analysis to replace PCR.

Prevalence of pandemic thermostable direct hemolysin-producing Vibrio parahaemolyticus O3:K6 in seafood and the coastal environment in Japan

Although thermostable direct hemolysin (TDH)-producing Vibrio parahaemolyticus has caused many infections in Asian countries, the United States, and other countries, it has been difficult to detect the same pathogen in seafoods and other environmental samples. In this study, we detected and enumerated tdh gene-positive V. parahaemolyticus in Japanese seafoods with a tdh-specific PCR method, a chromogenic agar medium, and a most-probable-number method. The tdh gene was detected in 33 of 329 seafood samples (10.0%). The number of tdh-positive V. parahaemolyticus ranged from <3 to 93/10 g. The incidence of tdh-positive V. parahaemolyticus tended to be high in samples contaminated with relatively high levels of total V. parahaemolyticus. TDH-producing strains of V. parahaemolyticus were isolated from 11 of 33 tdh-positive samples (short-necked clam, hen clam, and rock oyster). TDH-producing strains of V. parahaemolyticus were also isolated from the sediments of rivers near the coast in Japan. Representative strains of the seafood and sediment isolates were examined for the O:K serovar and by the PCR method specific to the pandemic clone and arbitrarily primed PCR and pulsed-field gel electrophoresis techniques. The results indicated that most O3:K6 tdh-positive strains belonged to the pandemic O3:K6 clone and suggested that serovariation took place in the Japanese environment.

Isolation of a pandemic O3:K6 clone of a Vibrio parahaemolyticus strain from environmental and clinical sources in Thailand

Application of an immunomagnetic enrichment method selective for Vibrio parahaemolyticus serovar K6 allowed isolation of a strain belonging to the pandemic O3:K6 clone of V. parahaemolyticus from fresh shellfish not implicated in a clinical case in southern Thailand. Arbitrarily primed PCR profiles of this strain, clinical O3:K6 strains isolated from sporadic diarrhea cases in the same area, and a standard pandemic O3:K6 strain were indistinguishable.

Improvement of the immunomagnetic separation method selective for Escherichia coli O157 strains

Immunomagnetic separation is a useful enrichment method selective for Escherichia coli O157 cells against non-O157 E. coli cells from a preenrichment culture. However, E. coli cells are adsorbed onto a solid surface nonspecifically. With the conventional immunomagnetic separation method, this nonspecific adsorption interfered with immunomagnetic separation. It was found that this interference could be reduced with a low-ionic-strength solution. When immunomagnetic separation was carried out with this solution, the proportion of E. coli O157 cells to non-O157 E. coli cells increased from 9.6 to 31.4 times compared to the proportion obtained by the conventional immunomagnetic separation method. The effectiveness of this solution was successfully evaluated by the use of E. coli O157-spiked samples.

Detection of Bacteroides forsythus by immunomagnetic capture and a polymerase chain reaction-DNA probe assay

The aim of this study was to combine immunomagnetic capture and a polymerase chain reaction (PCR) followed by hybridization with a DNA probe for the detection of Bacteroides forsythus. Magnetic beads were coated with the immunoglobulin G fraction of an antiserum specific for B. forsynthus. Aliquots were incubated with various concentrations of a suspension of B. forsythus or with a suspension containing 16 bacterial species, at a concentration of 10(10) cells/ml, spiked with dilutions of B. forsythus. Beads with bound bacteria were boiled, and the target DNA in the supernatant was amplified to generate a 392-bp PCR fragment specific for B. forsythus. The amplified product was detected by dot-blot hybridization with a digoxigenin-labeled 392-bp probe. The detection limit was determined to be 10 cells/ml using immunocapture on a suspension of B. forsythus and 100 on spiked bacterial suspensions. Subgingival plaque samples were obtained from 39 Bolivian individuals with poor oral hygiene. Each sample was analyzed by the above procedure and by immunofluorescence. The overall prevalence of individuals harboring B. forsythus was 62% by immunofluorescence and 82% by PCR-DNA probe assay. The immunocapture, PCR. DNA-probe procedure should be useful for the detection of B. forsythus, particularly in false-negative samples obtained by less sensitive techniques.

Detection of Coxiella burnetii in cow's milk by PCR-enzyme-linked immunosorbent assay combined with a novel sample preparation method

The use of an adequate concentration of Triton X-100 enhanced immunomagnetic separation of Coxiella burnetii from milk. PCR-enzyme-linked immunosorbent assay (PCR-ELISA) could detect coxiellas more sensitively than could conventional PCR. PCR-ELISA is therefore thought to be suitable for the simultaneous assay of a large number of samples. However, the number of cows from which raw milk tested positive for coxiellas by PCR-ELISA was inconsistent with that found with the antibody to coxiella by indirect immunofluorescence assay. The inconsistency is thought to be associated with the differences in the infectious route, infectious dose, or the timing of yielding the antibody and the period of duration of the antibody.

Improved method for preparation of samples for the polymerase chain reaction for detection of Coxiella burnetii in milk using immunomagnetic separation

Immunomagnetic separation (IMS) improved the detection of Coxiella burnetii in cow's milk by the polymerase chain reaction (PCR). IMS represents a novel approach to the isolation of microorganism from milk. The combination of IMS and PCR analysis has an adequate sensitivity for detection of C. burnetii.

Magnetic separation techniques in diagnostic microbiology

The principles of magnetic separation aided by antibodies or other specific binding molecules have been used for isolation of specific viable whole organisms, antigens, or nucleic acids. Whereas growth on selective media may be helpful in isolation of a certain bacterial species, immunomagnetic separation (IMS) technology can isolate strains possessing specific and characteristic surface antigens. Further separation, cultivation, and identification of the isolate can be performed by traditional biochemical, immunologic, or molecular methods. PCR can be used for amplification and identification of genes of diagnostic importance for a target organism. The combination of IMS and PCR reduces the assay time to several hours while increasing both specificity and sensitivity. Use of streptavidin-coated magnetic beads for separation of amplified DNA fragments, containing both biotin and a signal molecule, has allowed for the conversion of the traditional PCR into an easy-to-read microtiter plate format. The bead-bound PCR amplicons can also easily be sequenced in an automated DNA sequencer. The latter technique makes it possible to obtain sequence data of 300 to 600 bases from 20 to 30 strains, starting with clinical samples, within 12 to 24 h. Sequence data can be used for both diagnostic and epidemiologic purposes. IMS has been demonstrated to be a useful method in diagnostic microbiology. Most recent publications describe IMS as a method for enhancing the specificity and sensitivity of other detection systems, such as PCR, and providing considerable savings in time compared with traditional diagnostic systems. The relevance to clinical diagnosis has, however, not yet been fully established for all of these new test principles. In the case of PCR, for example, the presence of specific DNA in a food sample does not demonstrate the presence of a live organism capable of inducing a disease. However, all tests offering increased sensitivity and specificity of detection, combined with reduced time of analysis, have to be seriously evaluated.