Plearnpis Luxananil

Development of antibody array for simultaneous detection of foodborne pathogens.

Pathogenic bacterial contaminations present serious problems for food industry and public health. Rapid, accurate and affordable assays are needed. In this study, antibody arrays to simultaneously detect two foodborne pathogenic bacteria (Escherichia coli O157:H7 and Salmonella spp.) have been developed using chemiluminescent detecting system. Solid supports using nitrocellulose membrane and poly-l-lysine (PLL) glass slide were compared and optimized for antibody array construction. Many parameters including optimal concentrations of antibodies, blocking reagents, assay time, storage time, sensitivity and cross-reactivity were considered during optimization. This study revealed that the PLL slide was a more suitable support due to highly accurate results and the absence of non-specific background. Phosphate-buffered saline (PBS, pH 7.2) and 3% skim milk in PBS buffer were optimal spotting and blocking reagents, respectively. With the same sensitivity for bacterial detection as in a conventional ELISA (10(5)-10(6)CFU/ml for the E. coli O157:H7 and 10(6)-10(7)CFU/ml for Salmonella detections), this antibody array has advantages of a much shorter assay time of 1h and much lower required amounts of antibodies. Moreover, there was no cross-reactivity in the detection among bacteria tested in this study. Bacteria detection in food sample was feasible as demonstrated using bacteria-added milk.

Isolation of Bacterial Strains Colonizable in Mosquito Larval Guts as Novel Host Cells for Mosquito Control.

We screened for microorganisms that can be utilized as new host cells for mosquito larvicides. As long persistence in the environment is required of host cells, we examined the bacterial populations in the guts of mosquito larvae collected from natural breeding habitats. Larvae of Aedes aegypti and Culex quinquefasciatus were examined, and Bacillus species, particularly Bacillus cereus, were found to be the dominant bacterial species in their guts. To investigate the relationship between these Bacillus strains and the mosquito larvae, we re-introduced the bacteria into larvae of Aedes aegypti, C. quinquefasciatus and another common mosquito strain, Anopheles dirus. The cell numbers of Bacillus cereus strains Ae10 and Cx5 in the guts were consistent throughout a 7-d period without food supplementation, suggesting that these strains were able to colonize in the guts of the larvae. To confirm this, we introduced a plasmid containing a kanamycin resistance marker into Ae10 and Cx5 and fed these recombinant strains to C. quinquefasciatus larvae. Even when food was supplemented for 7 d, the recombinant strains, particularly Ae10, were still found in the guts. Under similar conditions, B. thuringiensis serovar israelensis c4Q2-72 was hardly detectable after 2 d, while Escherichia coli could not be detected at all. Their stable retention in mosquito larvae guts and the feasibility of genetic manipulation indicates these strains possess high potential as novel host cells for application in mosquito control.

Cloning and Characterization of a Cytolytic and Mosquito Larvicidal δ-Endotoxin from Bacillus thuringiensis subsp. darmstadiensis

The cytolytic δ-endotoxin gene from Bacillus thuringiensis subsp. darmstadiensis was amplified from genomic DNA by PCR by using primers designed from the sequence of cyt2Aa1 gene of B. thuringiensis subsp. kyushuensis. DNA sequence analysis revealed an open reading frame translating to a 259-amino acid sequence. The cloned gene was designated cyt2Aa2. This gene was highly expressed in Escherichia coli as inclusion bodies that could be solubilized in 50 mM Na2CO3, pH 10.5. Activation of the solubilized protoxin by proteinase K (1% wt/wt, proteinase K/protoxin) yielded the active fragment of about 23 kDa. Cyt2Aa2 showed high hemolytic activity against sheep erythrocytes (hemolytic end- point 0.25 μg/ml) and was toxic to Culex quinquefasciatus and Aedes aegypti larvae (LC50 0.5–1.0 μg/ml).

Bacillus siamensis sp. nov., isolated from salted crab (poo-khem) in Thailand

A Gram-positive, endospore-forming, rod-shaped bacterium, strain PD-A10(T), was isolated from salted crab (poo-khem) in Thailand and subjected to a taxonomic study. Phenotypic and chemotaxonomic characteristics, including phylogenetic analyses, showed that the novel strain was a member of the genus Bacillus. The novel strain grew in medium with 0-14 % (w/v) NaCl, at 4-55°C and at pH4.5-9. The predominant quinone was a menaquinone with seven isoprene units (MK-7). The major fatty acids were anteiso-C₁₅:₀ and anteiso-C₁₇:₀. Polar lipid analysis revealed the presence of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, lysylphosphatidylglycerol, glycolipid and unknown lipids. The DNA G+C content was 41.4 mol%. The 16S rRNA gene sequence similarities between strain PD-A10(T) and Bacillus amyloliquefaciens NBRC 15535(T), Bacillus subtilis DSM 10(T), Bacillus vallismortis DSM 11031(T) and Bacillus mojavensis IFO 15718(T) were 99.5, 99.4, 99.4 and 99.2 %, respectively. Strain PD-A10(T) showed a low degree similarity of rep-PCR fingerprints and low DNA-DNA relatedness with the above-mentioned species. On the basis of the data gathered in this study, strain PD-A10(T) should be classified as representing a novel species of the genus Bacillus, for which the name Bacillus siamensis sp. nov. is proposed. The type strain is PD-A10(T) (=BCC 22614(T)=KCTC 13613(T)).

Efficient Expression of the Mosquito Larvicidal Binary Toxin Gene from Bacillus sphaericus in Escherichia coli

The binary toxin gene encoding BinA (42 kDa) and BinB (51 kDa) from Bacillus sphaericus strain 2297 was cloned and expressed in E. coli. Low expression level was found when both proteins were expressed from a single operon. High expression was observed when the gene encoding an individual protein was placed downstream of the T7 promoter. The expression level of BinB was not different when expressed alone (non-fusion) or as a fusion form with T7 peptide (T7-BinB). Both forms of BinB were equally stable. Unlike BinB, the non-fusion form of BinA was less stable than T7-BinA. The mosquito larvicidal test showed that BinA or BinB alone was not toxic to mosquito larvae, but high toxicity was found when both BinA and BinB were applied. The results suggest that a short peptide of T7 linked to the N-terminus of either BinA or BinB does not affect their toxicity, but may make the toxin, especially BinA, more stable.

Novel and Highly Specific Monoclonal Antibody to Acidovorax citrulli and Development of ELISA-Based Detection in Cucurbit Leaves and Seed

A novel monoclonal antibody (MAb) specific to the seedborne bacterium Acidovorax citrulli was produced. MAb 11E5 reacted specifically with 19 strains of A. citrulli but not with three closely related bacteria in the family Comamonadaceae (i.e., A. facilis, Comamonas acidovorans, and C. testosteroni) and another seven phytopathogenic bacteria. Moreover, this MAb detected a strain of A. citrulli that was not detected by a commercial enzyme-linked immunosorbent assay (ELISA)-based kit and a commercial immunochromatographic strip test. In Western blot analysis, MAb 11E5 reacted with an A. citrulli protein of a molecular mass >170 kDa. MAb 11E5 was employed to develop two sandwich ELISA systems: MAb captured-sandwich ELISA (MC-sELISA) and polyclonal antibody captured-sandwich ELISA (PC-sELISA). MC-sELISA was 10 times more sensitive than PC-sELISA for detection of A. citrulli in cucurbit leaf and seed extracts. The detection limit of the MC-sELISA was 5 × 104 CFU/ml. Detection of A. citrulli in naturally infected cucurbit leaves, fruit, and seed was also feasible using MC-sELISA. The newly established MCsELISA provides another alternative for specific detection of A. citrulli in cucurbits and can be applied for routine field inspection.

Recombinant Enterobacter amnigenus highly toxic to Anopheles dirus mosquito larvae.

The mosquito-larvicidal binary toxin of Bacillus sphaericus 2297 was expressed in Enterobacter amnigenus, a Gram-negative bacterium isolated from Anopheles dirus larvae gut. The toxin was placed under the regulation of various promoters in order to improve the expression level of the toxin. Amongst the recombinants obtained, E. amnigenus harboring pBS373, a plasmid which contains the toxin genes under the control of the native B. sphaericus promoter, expressed a significant amount of protein, comparable to that found in B. sphaericus 2297. In addition, this recombinant provided approximately twenty times higher toxicity against second-instar Anopheles dirus larvae when compared to B. sphaericus 2297. The procedure of obtaining this environmentally isolated bacterium from larvae gut and introducing the system for mosquito-larvicidal toxin synthesis is noteworthy. The promising result presented here provides a substantial degree of confidence for further field studies.

A plasmid encoding a combination of mosquito-larvicidal genes from Bacillus thuringiensis subsp. israelensis and Bacillus sphaericus confers toxicity against a broad range of mosquito larvae when expressed in Gram-negative bacteria

A recombinant plasmid harboring cry4A, cry4B and cry11A from Bacillus thuringiensis subsp. israelensis and binary toxin genes from Bacillus sphaericus has been constructed. The three cry genes were placed under the control of the cry4B promoter whereas the binary toxin gene was controlled by its native promoter. The expression of toxins in Escherichia coli harboring the resulting plasmid, p4BDA-5142, was investigated. Cry4B expression was highest compared to other toxins. Although the level of toxin expression was low compared with E. coli expressing single toxins, the recombinant E. coli strain harboring p4BDA-5142 exhibited broad range mosquito-larvicidal activity against all Aedes, Culex and Anopheles larvae. This work has shown that the development of the recombinant plasmid can be used to broaden the host range spectrum of the appropriate bacterial host for mosquito control.

Development of a multiplex RT-PCR-ELISA to identify four distinct species of tospovirus

In this study, a multiplex RT-PCR-ELISA was developed to detect and differentiate four tospovirus species found in Thailand, namely Capsicum chlorosis virus (CaCV), Melon yellow spot virus (MYSV), Tomato necrotic ringspot virus (TNRV), and Watermelon silver mottle virus (WSMoV). In this system, nucleocapsid (N) gene fragments of four tospoviruses were simultaneously amplified and labeled with digoxigenin (DIG) in a single RT-PCR reaction using a pair of degenerate primers binding to the same conserved regions in all four tospovirus N genes. The DIG-labeled amplicons were distinguished into species by four parallel hybridizations to species-specific biotinylated probes in streptavidin-coated microtiter wells followed by ELISA detection using a peroxidase-conjugated anti-DIG antibody. Results indicated that the multiplex RT-PCR-ELISA assay could specifically identify each of these four tospoviruses without cross-reactivity between species or reactivity to healthy plant negative controls. Assay sensitivity was 10- to 1000-fold higher than conventional RT-PCR. When applied to naturally infected plants, all samples yielded concordant results between RT-PCR-ELISA and the reference RT-PCR. In conclusion, the multiplex RT-PCR-ELISA developed in this study has superior specificity, sensitivity, and high-throughput capacity compared to conventional RT-PCR and is an attractive alternative for the identification of different tospovirus species.

Cloning and characterization of a mosquito larvicidal toxin produced during vegetative stage of Bacillus sphaericus 2297.

The mosquitocidal toxin 1 (mtx1) gene from genomic DNA of B. sphaericus strain 2297 was cloned and expressed in E. coli. DNA sequencing analysis of the cloned gene revealed a single open reading frame encoding an 870-amino acid polypeptide. Expression level of the full-length gene in E. coli was very low even though strong promoter was used or the gene was expressed as a fusion protein. Expression level was highly improved after the putative leader sequence was deleted, and the truncated gene was expressed as a fusion protein with glutathione S-transferase (GST-tMtx1). E. coli cells expressing GST-tMtx1 was highly toxic to Culex quinquefasciatus larvae and showed lower toxicity against Anopheles dirus and Aedes aegypti larvae. Enterobacter amnigenus An11, a mosquito larval gut colonizable bacteria, transformed with the cloned gene exhibited mosquito larvicidal activity. Result suggested that there is a potential to develop this protein to be used as an alternative mosquito control agent.