Assessment of the genetic diversity of lymnaeid (Gastropoda: Pulmonata) snails and their infection status with trematode cercariae in different regions of Thailand

Lymnaeid snails are some of the most widespread snails and are the first intermediate host of trematode parasites that affect human and livestock health. A full understanding of the genetic relationship of hosts and parasites is of paramount importance for effective parasite management. The present study assessed the prevalence of trematode larvae in lymnaeid snails and examined the genetic diversity of these snails collected across Thailand. We collected 672 lymnaeid snails from 39 locations in 22 provinces of six regions in Thailand. Subsequently, cercarial infection in the snails was observed by using the shedding method. Lymnaeid snails released 5 types of trematode cercariae, namely, xiphidiocercariae, echinostome cercariae I, echinostome cercariae II, furcocercous cercariae, and strigea cercariae. The phylogenetic analysis based on ITS2 and 28S rDNA sequences revealed 5 cercaria types assigned to four trematode families, of which two belong to the group of human intestinal flukes. Combination of shell morphology and sequence analysis of the mitochondrial COI and 16S rDNA genes, the lymnaeid snails were classified into two species, Radix rubiginosa and Orientogalba viridis. Moreover, the combined dataset of mtDNA genes (COI + 16S rDNA) from R. rubiginosa and O. viridis revealed 32 and 15 different haplotypes, respectively, of which only a few haplotypes were infected with cercariae. The genetic diversity and genetic structure revealed that R. rubiginosa and O. viridis experienced a bottleneck phenomenon, and showed limited gene flow between populations. Population demographic history analyses revealed that R. rubiginosa and O. viridis experienced population reductions followed by recent population expansion. These findings may improve our understanding of parasite-lymnaeid evolutionary relationships, as well as the underlying molecular genetic basis, which is information that can be used for further effective control of the spread of trematode disease.

Population genetic structure of Indoplanorbis exustus (Gastropoda: Planorbidae) in Thailand and its infection with trematode cercariae

Indoplanorbis exustus is a freshwater gastropod belonging to the family Planorbidae. This snail is widely distributed across the tropics and plays an important role as the intermediate host for trematodes. However, relatively little is understood regarding the genetic relationship between I. exustus and trematodes. The goals of this study were to investigate the current transmission status of trematode cercariae in I. exustus in Thailand and to examine the genetic diversity, genetic structure, and demographic history of I. exustus. We collected 575 I. exustus from 21 provinces across six regions of Thailand and investigated cercarial infections by using the shedding method. I. exustus from two provinces were infected with cercarial trematodes, and two types of cercarial stages were molecularly identified as furcocercous cercaria and xiphidiocercariae. Phylogenetic tree analysis based on 28S rDNA and ITS2 sequences demonstrated that furcocercous cercaria and xiphidiocercariae were closely clustered with a clade of Euclinostomum sp. and Xiphidiocercariae sp., respectively. Phylogenetic and network analyses of I. exustus haplotypes based on the COI, 16S rDNA, and ITS1 genes demonstrated four main clades. Only snails in clade A were distributed in all regions of Thailand and harbored trematode cercariae. The level of genetic diversity of I. exustus was relatively high, but most populations were not genetically different, thus suggesting the appearance of gene flow within the I. exustus populations. Overall, the haplotype network was star-shaped, thus suggesting the recent demographic expansion of populations. This result was also supported by the unimodal mode of the mismatch distribution graph and the large negative values of the neutrality tests. Therefore, the I. exustus snail was likely another freshwater snail of the invasive species in Thailand. This information will aid in monitoring the spread of the parasitic trematodes carried by I. exustus from different populations.

Genetic variation of the freshwater snail Indoplanorbis exustus (Gastropoda: Planorbidae) in Thailand, inferred from 18S and 28S rDNA sequences

Indoplanorbis exustus, a freshwater pulmonate snail, is widely distributed in tropical and subtropical zones and plays a significant role as an intermediate host for trematode parasites. Various genetic markers have been used for species identification and phylogenetic studies of this snail. However, there are limited studies about their molecular genetics based on nuclear ribosomal DNA (rDNA) genes. A genetic analysis of I. exustus in Thailand was conducted based on the nuclear 18S rDNA (339 bp) and 28S rDNA (1036 bp) genes. Indoplanorbis snails were collected from 29 localities in 21 provinces covering six regions of Thailand. Nucleotide sequences from 44 snails together with sequences from the GenBank database were examined for phylogenetic relationships and genetic diversity. All sequences of the selected nucleotide regions exhibited a high level of similarity (99%) to the sequences of I. exustus in the GenBank database. The maximum likelihood tree based on the 18S and 28S rDNA fragment sequences of I. exustus in Thailand revealed only one group with clear separation from another genus in the family Planorbidae. The I. exustus 28S rDNA sequences showed intraspecific genetic divergence ranging from 0 to 0.78% and were classified into 8 different haplotypes. Conversely, the 18S rDNA data showed lower variation than the 28S rDNA data and revealed a single haplotype and intraspecific distances of zero among all sampled individuals. The haplotype network of 28S rDNA sequences of I. exustus in Thailand revealed six unique haplotypes and two haplotypes shared by at least two regions. Overall, both markers were successful in the identification of I. exustus. However, these markers, particularly the 18S rDNA, may not be suitable for genetic analysis within the species, particularly for population genetic studies, due to their limited variation as seen in this study. In summary, this study not only enhances understanding of genetic variation in I. exustus but is also useful for the selection of molecular markers in future genetic research.

Genome mining reveals novel biosynthetic gene clusters in entomopathogenic bacteria

The discovery of novel bioactive compounds produced by microorganisms holds significant potential for the development of therapeutics and agrochemicals. In this study, we conducted genome mining to explore the biosynthetic potential of entomopathogenic bacteria belonging to the genera Xenorhabdus and Photorhabdus. By utilizing next-generation sequencing and bioinformatics tools, we identified novel biosynthetic gene clusters (BGCs) in the genomes of the bacteria, specifically plu00736 and plu00747. These clusters were identified as unidentified non-ribosomal peptide synthetase (NRPS) and unidentified type I polyketide synthase (T1PKS) clusters. These BGCs exhibited unique genetic architecture and encoded several putative enzymes and regulatory elements, suggesting its involvement in the synthesis of bioactive secondary metabolites. Furthermore, comparative genome analysis revealed that these BGCs were distinct from previously characterized gene clusters, indicating the potential for the production of novel compounds. Our findings highlighted the importance of genome mining as a powerful approach for the discovery of biosynthetic gene clusters and the identification of novel bioactive compounds. Further investigations involving expression studies and functional characterization of the identified BGCs will provide valuable insights into the biosynthesis and potential applications of these bioactive compounds.

Identification and genetic characterization of Angiostrongylus cantonensis isolated from the human eye

Angiostrongylus cantonensis, or the rat lungworm, is the causative agent of human angiostrongyliasis associated with eosinophilic meningitis or meningoencephalitis. Additionally, this nematode can cause ocular angiostrongyliasis, though this is rare. The worm can cause permanent damage to the affected eye and sometimes even blindness. Genetic characterization of the worm from clinical samples is limited. In the present study, we investigated the genetics of A. cantonensis recovered from a patient's eye in Thailand. We sequenced two mitochondrial genes (cytochrome c oxidase subunit I, or COI, and cytochrome b, or cytb) and nuclear gene regions (66-kDa protein and internal transcribed spacer 2, or ITS2) from a fifth-stage larva of Angiostrongylus sample that was surgically removed from the human eye. All sequences of the selected nucleotide regions were highly similar (98-100%) to the sequences of A. cantonensis in the GenBank database. The maximum likelihood and neighbor-joining trees of the COI gene indicated that A. cantonensis was closely related to the AC4 haplotype, whereas the cytb and 66-kDa protein genes were closely clustered with the AC6 and Ac66-1 haplotypes, respectively. In addition, the phylogeny of the concatenated nucleotide datasets of the COI and cytb revealed that the worm was closely related to the Thai strain and strains from other countries. This study confirms the identification and genetic variation of the fifth-stage larvae of A. cantonensis recovered from a patient's eye in Thailand. Our findings are important for future research on the genetic variation of A. cantonensis that causes human angiostrongyliasis.

Antibacterial activity of vB_AbaM_PhT2 phage hydrophobic amino acid fusion endolysin, combined with colistin against Acinetobacter baumannii

Phage lytic enzymes are promising antimicrobial agents. In this study, an endolysin derived from vB_AbaM_PhT2 (vPhT2), was identified. This endolysin represented the conserved lysozyme domain. Recombinant endolysin (lysAB- vT2) and hydrophobic fusion endolysin (lysAB-vT2-fusion) were expressed and purified. Both endolysins showed lytic activity against bacterial crude cell wall of Gram-negative bacteria. The MIC of lysAB-vT2-fusion was 2 mg/ml corresponding to 100 µM, while the MIC of lysAB-vT2 was more than 10 mg/ml (400 µM). Combination of lysAB-vT2-fusion with colistin, polymyxin B or copper was synergistic against A. baumannii (FICI value as 0.25). Antibacterial activity of lysAB-vT2-fusion plus colistin at the fractional inhibitory concentrations (FICs) revealed that it can inhibit Escherichia coli, Klebsiella pneumoniae and various strains of extremely drug-resistant A. baumannii (XDRAB) and phage resistant A. baumannii. The lysAB- vT2-fusion still retained its antibacterial activity after incubating the enzyme at 4, 20, 40 and 60 °C for 30 min. The lysAB-vT2-fusion could inhibit the mature biofilm, and incubation of lysAB-vT2-fusion with T24 human cells infected with A. baumannii led to a partial reduction of LDH release from T24 cells. In summary, our study highlights the antimicrobial ability of engineered lysAB-vT2-fusion endolysin, which can be applied for the control of A. baumannii infection.

Entomopathogenic nematodes isolated from agricultural areas of Thailand and their activity against the larvae of Aedes aegypti, Aedes albopictus and Culex quinquefasciatus (Diptera: Culicidae)

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis have been considered to be effective biological control agents for several insects. In this study, we isolated and identified EPNs from soil samples in agricultural areas of northern Thailand and evaluated their efficacy for controlling larvae of three mosquito vector species, Aedes aegypti, Ae. albopictus and Culex quinquefasciatus. A total of 51 of 1,000 soil samples were positive (5.1% prevalence) for EPNs, which were identified through sequencing of the rDNA and ITS to 37 Steinernema isolates (3.7%) and 14 Heterorhabditis isolates (1.4%). For the bioassay, the larvae of mosquitoes were exposed to Steinernema surkhetense (eALN6.3_TH), Steinernema lamjungense (eALN11.5_TH), Heterorhabditis indica (eACM14.2_TH) and Heterorhabditis bacteriophora (eALN18.2_TH). Heterorhabditis bacteriophora showed the highest efficacy against Ae. aegypti and Cx. quinquefasciatus. At 96 h after exposure, the mortality rates were 60.0 and 91.7%, respectively. The EPNs were observed in the dead mosquito larvae, which were mostly found in the thorax followed by the head and abdomen. Some EPNs were dead with melanization, and some were able to survive in the cavity of mosquito larvae. Our results show the low prevalence of EPN in agricultural areas of Thailand. Moreover, H. bacteriophora may be considered an alternative biocontrol agent for managing and controlling these vector mosquitoes.

Entomopathogenic Nematodes and Their Symbiotic Bacteria from the National Parks of Thailand and Larvicidal Property of Symbiotic Bacteria against Aedes aegypti and Culex quinquefasciatus

Simple Summary

Entomopathogenic nematodes (EPNs) are insect-parasitizing nematodes of the genera Heterorhabditis and Steinernema that are symbiotically associated with the symbiotic bacteria Photorhabdus and Xenorhabdus, respectively. Heterorhabditis indica, H. baujardi, Heterorhabditis SGmg3, Steinernema guangdongense, S. surkhetense, S. minutum, and S. longicaudum were isolated from soil samples in the national parks of Thailand. For symbiotic bacterial isolates, P. luminescens subsp. akhurstii, P. luminescens subsp. hainanensis, P. luminescens subsp. australis, Xenorhabdus stockiae, X. indica, X. griffiniae, X. japonica, and X. hominickii were isolated from those EPNs. In mosquito larvicidal bioassays, Photorhabdus isolates were effective against both Aedes aegypti and Culex quinquefasciatus. In conclusion, a wide diversity of entomopathogenic nematodes and symbiotic bacteria was found in the national parks of Thailand. Moreover, isolated Photorhabdus bacteria were shown to have potential as biocontrol agents to control culicine mosquitoes.

Abstract

Entomopathogenic nematodes (EPNs) are insect parasitic nematodes of the genera Het-erorhabditis and Steinernema. These nematodes are symbiotically associated with the bacteria, Photorhabdus and Xenorhabdus, respectively. National parks in Thailand are a potentially rich resource for recovering native EPNs and their symbiotic bacteria. The objectives of this study are to isolate and identify EPNs and their bacterial flora from soil samples in four national parks in Thailand and to evaluate their efficacy for controlling mosquito larvae. Using a baiting method with a Galleria mellonella moth larvae and a White trap technique, 80 out of 840 soil samples (9.5%) from 168 field sites were positive for EPNs. Sequencing of an internal transcribed spacer resulted in the molecular identification of Heterorhabditis nematode isolates as H. indica, H. baujardi and Heterorhabditis SGmg3, while using 28S rDNA sequencing, Steinernema nematode species were identified as S. guang-dongense, S. surkhetense, S. minutum, S. longicaudum and one closely related to S. yirgalemense. For the symbiotic bacterial isolates, based on recA sequencing, the Photorhabdus spp. were identified as P. luminescens subsp. akhurstii, P. luminescens subsp. hainanensis and P. luminescens subsp. australis. Xenorhabdus isolates were identified as X. stockiae, X. indica, X. griffiniae, X. japonica and X. hominickii. Results of bioassays demonstrate that Photorhabdus isolates were effective on both Aedes aegypti and Culex quinquefasciatus. Therefore, we conclude that soil from Thailand’s national parks contain a high diversity of entomopathogenic nematodes and their symbiotic bacteria. Photorhabdus bacteria are larvicidal against culicine mosquitoes and may serve as effective biocontrol agents.

Genetic analysis of a 66-kDa protein-encoding gene of Angiostrongylus cantonensis and Angiostrongylus malaysiensis

The rat lungworm Angiostrongylus cantonensis is globally known to be the cause of oeosinophilic meningitis in humans. Another congener, Angiostrongylus malaysiensis, is closely related to A. cantonensis and has been described as a potential human pathogenic parasite. These 2 worms are similar in terms of life cycle, host range and morphological and genetic information. However, there are limited studies about their genetic diversity based on the 66-kDa protein-encoding gene. The objective of this study was to explore the 66-kDa protein sequence variation of A. cantonensis and A. malaysiensis collected from Thailand. Two adult and 53 third-stage larval specimens of Angiostrongylus from 4 geographic locations in Thailand were molecularly identified using the 66-kDa protein gene. The phylogenetic trees (Bayesian inference tree and maximum-likelihood tree) showed that Angiostrongylus formed a monophyletic clade with a clear separation between A. cantonensis and A. malaysiensis. The genetic distance between A. cantonensis and A. malaysiensis varies from 0.82 to 2.86%, with a total of 16 variable sites. The analysis of genetic diversity revealed 1 and 5 new haplotypes of A. cantonensis and A. malaysiensis, respectively, and showed genetic differences between the populations of A. cantonensis and A. malaysiensis. The haplotype networks of A. cantonensis and A. malaysiensis populations in Thailand are similar to those of populations in some countries, indicating the range expansion of genomic origin between populations in different areas. In conclusion, the 66-kDa protein gene was a good genetic marker for studying genetic diversity and discriminating between A. cantonensis and A. malaysiensis.

Genome analysis of secondary metabolite‑biosynthetic gene clusters of Photorhabdus akhurstii subsp. akhurstii and its antibacterial activity against antibiotic-resistant bacteria

Xenorhabdus and Photorhabdus can produce a variety of secondary metabolites with broad spectrum bioactivity against microorganisms. We investigated the antibacterial activity of Xenorhabdus and Photorhabdus against 15 antibiotic-resistant bacteria strains. Photorhabdus extracts had strong inhibitory the growth of Methicillin-resistant Staphylococcus aureus (MRSA) by disk diffusion. The P. akhurstii s subsp. akhurstii (bNN168.5_TH) extract showed lower minimum inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC). The interaction between either P. akhurstii subsp. akhurstii (bNN141.3_TH) or P. akhurstii subsp. akhurstii (bNN168.5_TH) or P. hainanensis (bNN163.3_TH) extract in combination with oxacillin determined by checkerboard assay exhibited partially synergistic interaction with fractional inhibitory concentration index (FICI) of 0.53. Time-killing assay for P. akhurstii subsp. akhurstii (bNN168.5_TH) extract against S. aureus strain PB36 significantly decreased cell viability from 10⁵ CFU/ml to 10³ CFU/ml within 30 min (P < 0.001, t-test). Transmission electron microscopic investigation elucidated that the bNN168.5_TH extract caused treated S. aureus strain PB36 (MRSA) cell membrane damage. The biosynthetic gene clusters of the bNN168.5_TH contained non-ribosomal peptide synthetase cluster (NRPS), hybrid NRPS-type l polyketide synthase (PKS) and siderophore, which identified potentially interesting bioactive products: xenematide, luminmide, xenortide A-D, luminmycin A, putrebactin/avaroferrin and rhizomide A-C. This study demonstrates that bNN168.5_TH showed antibacterial activity by disrupting bacterial cytoplasmic membrane and the draft genome provided insights into the classes of bioactive products. This also provides a potential approach in developing a novel antibacterial agent.

Insights into mobile genetic elements and the role of conjugative plasmid in transferring aminoglycoside resistance in extensively drug-resistant Acinetobacter baumannii AB329

Acinetobacter baumannii is a major cause of nosocomial infection, and the incidence of extensively drug-resistant A. baumannii (XDRAB) infections has dramatically increased worldwide. In this study, we aimed to explore the complete genome sequence of XDRAB 329, ST1166/98 (Oxford/Pasteur), which is an outbreak clone from a hospital in Thailand. Whole-genome sequencing (WGS) was performed using short-read Illumina and long-read PacBio sequencing, and a conjugation assay of its plasmid was performed. The complete genome sequence of A. baumannii AB329 revealed a circular chromosome 3,948,038 bp in length with 39% GC content. Antibiotic resistance genes (ARGs), including beta-lactam resistance (bla _OXA-51, bla _ADC-25, bla _OXA-23, bla _TEM-1D), aminoglycoside resistance (aph(3')-Ia, aph(3″)-Ib, aph(6)-Id, armA), tetracycline resistance (tet(B), tet (R)), macrolide resistance (mph(E), msr(E)), and efflux pumps, were found. Mobile genetic elements (MGEs) analysis of A. baumannii AB329 revealed two plasmids (pAB329a and pAB329b), three prophages, 19 genomic islands (GIs), and 33 insertion sequences (ISs). pAB329a is a small circular plasmid of 8,731 bp, and pAB329b is a megaplasmid of 82,120 bp. aph(3')-VIa was detected in pAB329b, and a major facilitator superfamily (MFS) transporter was detected in the prophage. Acinetobacter baumannii resistance island 4 (AbaR4) harboring tetracycline and aminoglycoside resistance was detected in the genome of A. baumannii AB329. pAB329b, which belongs to Rep-type GR6 (plasmid lineage LN_1), is a conjugative plasmid with the ability to transfer an aminoglycoside resistance gene to sodium azide-resistant A. baumannii. This study provides insights into the features of the MGEs of XDRAB, which are the main reservoir and source of dissemination of ARGs.

Preliminary Survey of Larval Trematodes in Freshwater Snails of Phitsanulok Province in Lower Northern Thailand

Background:

Freshwater snails serve as intermediate hosts for a variety of trematodes that cause illness in the human and animal populations. Several species of freshwater snails in Thailand have been found to have larval trematode infections. We aimed to investigate a freshwater snail in Phitsanulok Province and report on its current status of larval trematode infection.

Methods:

Freshwater snails were collected from six localities (rice field and irrigation canal) by handpicking and using a count per unit of time sampling approach. The snails were identified by their external shell morphology. The shedding method was applied to observe the cercariae, which were photographed under a light microscope to determine their morphological types.

Results:

A total of 211 snails were classified into seven genera. The most abundant snail species was Lymnaea sp., representing 31.3% of the sample, followed by Physella sp., Bithynia sp., Pomacea canaliculata, Filopaludina martensi, Indoplanorbis exustus, and Melanoides tuberculata, in that order. From the sample, 21 snails (9.95%), including Bithynia sp., Lymnaea sp., I. exustus, and M. tuberculata, were infected with cercarial trematodes, which could be categorized into four types, namely amphistome, parapleurolophocercous, echinostome, and xiphidiocercaria. Amphistome emerged from Bithynia sp., and I. exustus was the most common cercaria to be recovered, representing 80.9% of all infected snails.

Conclusion:

This study presents the current prevalence of cercariae in infected snails within the studied area. It is important to manage intermediate host snails in order to restrict trematode life cycle completion.

Molecular identification and phylogeny of Steinernema and Heterorhabditis nematodes and their efficacy in controlling the larvae of Aedes aegypti, a major vector of the dengue virus

Aedes aegypti is the mosquito vector of several arboviruses, especially the dengue virus. Aedes aegypti strain resistant to chemical insecticides have been reported worldwide. To tackle this, an entomopathogenic nematode (EPN) may be an alternative bio-control agent. To this end, this study aims to isolate, identify, and analyze the phylogeny of EPNs in Thailand and evaluate their efficacy for controlling the Ae. aegypti larvae. From 12 provinces in Thailand, soil samples were randomly collected, with 118 out of 1,100 them being positive for EPNs (10.73% prevalence) in genera Steinernema (4.46%) and Heterorhabditis (6.27%). Then, molecular discrimination of these two genus was performed based on the sequencing and phylogenetic analysis of the 28S rDNA and internal transcribed spacer regions. The most abundant species of EPN were Heterorhabditis indica, with minor species of Heterorhabditis sp. SGmg3, H. baujardi, S. surkhetense, S. kushidai, S. siamkayai, Steinernema sp. YNd80, Steinernema sp. YNc215, S. guangdongense, and S. huense. The larvicidal activity of five selected EPN isolates were tested against Ae. aegypti. Ten larvae of Ae. aegypti were incubated with different concentration (80, 160, 320, and 640 IJs/larva) of the infective juveniles of EPN in a 24-well and 6-well plates for 4 days. The mortality rates of the larvae were observed daily. Steinernema surkhetense (ePYO8.5_TH) showed the potential to kill mosquito larvae, with the highest mortality rate of 92 ± 9.37% and 89 ± 9.91% after it was treated with 640 IJs/larva in a 24-well plate and 1600 IJs/larva in a 6-well plate, respectively. There is an abundant distribution of EPNs across the country, and S. surkhetense ePYO8.5_TH may be used as a biocontrol agent against Ae. aegypti larvae.

Identification of entomopathogenic nematodes and their symbiotic bacteria in national parks of Thailand, and mosquitocidal activity of Xenorhabdus griffiniae against Aedes aegypti larvae

Entomopathogenic nematodes (EPN) Steinernema and Heterorhabditis with symbionts with Xenorhabdus and Photorhabdus bacteria, respectively, are reported as biocontrol agents for insect control. The objectives of this study were to identify EPN and their symbiotic bacteria in national parks of Phitsanulok Province, Thailand, and to test how Xenorhabdus isolates attack Aedes aegypti larvae. We collected 810 soil samples from four national parks. The juvenile stage of EPN was isolated from soil samples using a baiting technique with Galleria mellonella followed by a White trap. Partial regions of 28S rDNA and internal transcript spacer were sequenced to identify EPN, and recA sequencing was used to discriminate between Xenorhabdus and Photorhabdus. We found that 74 of the 810 soil samples (9.1%) were positive for the EPN. The EPN were molecularly identified as S. surkhetense, S. longicaudum, H. indica and Heterorhabditis sp. SGmg3, and their symbiotic bacteria were identified as X. stockiae, X. griffiniae, X. indica, X. vietnamensis, P. luminescens subsp. akhurstii, and P. temperata subsp. temperata. Xenorhabdus griffiniae showed potential larvicidal activity against A. aegypti (91% mortality at 72 and 96 h after exposure). This study demonstrates the diversity of EPN and symbiotic bacteria in national parks of Thailand and the potential to use X. griffiniae as a biocontrol agent to kill A. aegypti larvae.

A study on Xenorhabdus and Photorhabdus isolates from Northeastern Thailand: Identification, antibacterial activity, and association with entomopathogenic nematode hosts

Xenorhabdus and Photorhabdus are gram negative bacteria that can produce several secondary metabolites, including antimicrobial compounds. They have a symbiotic association with entomopathogenic nematodes (EPNs). The aim of this study was to isolate and identify Xenorhabdus and Photorhabdus species and their associated nematode symbionts from Northeastern region of Thailand. We also evaluated the antibacterial activity of these symbiotic bacteria. The recovery rate of EPNs was 7.82% (113/1445). A total of 62 Xenorhabdus and 51 Photorhabdus strains were isolated from the EPNs. Based on recA sequencing and phylogeny, Xenorhabdus isolates were identified as X. stockiae (n = 60), X. indica (n = 1) and X. eapokensis (n = 1). Photorhabdus isolates were identified as P. luminescens subsp. akhurstii (n = 29), P. luminescens subsp. hainanensis (n = 18), P. luminescens subsp. laumondii (n = 2), and P. asymbiotica subsp. australis (n = 2). The EPNs based on 28S rDNA and internal transcribed spacer (ITS) analysis were identified as Steinernema surkhetense (n = 35), S. sangi (n = 1), unidentified Steinernema (n = 1), Heterorhabditis indica (n = 39), H. baujardi (n = 1), and Heterorhabditis sp. SGmg3 (n = 3). Antibacterial activity showed that X. stockiae (bMSK7.5_TH) extract inhibited several antibiotic-resistant bacterial strains. To the best of our knowledge, this is the first report on mutualistic association between P. luminescens subsp. laumondii and Heterorhabditis sp. SGmg3. This study could act as a platform for future studies focusing on the discovery of novel antimicrobial compounds from these bacterial isolates.

Population Genetics Analysis of a Pomacea Snail (Gastropoda: Ampullariidae) in Thailand and its Low Infection by Angiostrongylus cantonensis

Pomacea is a freshwater snail in family Ampullariidae that is native to South and Central America. This snail is among the more important intermediate hosts for Angiostrongylus cantonensis and agricultural pests. Herein, we investigated the prevalence of A. cantonensis larvae and the genetic diversity of Pomacea samples collected across Thailand based on mitochondrial cytochrome c oxidase subunit I (COI) gene sequences. The larval-infection rate was 1.7% in Pomacea canaliculata specimens collected from the Uttaradit Province of northern Thailand. We randomly selected specimens of P. canaliculata and P. maculata for genetic analysis. We analyzed 244 COI sequences, including 49 sequences from samples collected from Thailand and a publicly accessible database of snails in their native and non-native ranges. A maximum-likelihood tree of P. canaliculata and P. maculata revealed two main clades. The genetic diversity analysis identified seven P. canaliculata haplotypes and six P. maculata haplotypes, and showed genetic differences between the populations of P. canaliculata and P. maculata. The haplotype networks of P. canaliculata and P. maculata populations in Thailand are similar to those of populations in multiple countries, indicating that this species spread widely to many parts of the world.

Low genetic diversity and the phylogeny of Achatina fulica, an intermediate host of Angiostrongylus cantonensis in Thailand, inferred from 16S mitochondrial sequences

The giant African land snail, Achatina fulica, is a pulmonate land snail of the Achatinidae family. The snail is native of East Africa and has spread to tropical and subtropical areas in different parts of the world. Achatina fulica is an important agricultural pests and the intermediate host for Angiostrongylus spp., especially Angiostrongylus cantonensis, which causes eosinophilic meningoencephalitis in humans. However, information on the genetic diversity and phylogenetic relationships among A. fulica populations in Thailand is limited. The goal of this study was to evaluate the genetic diversity and analyze haplotype network relationships between A. fulica populations in Thailand and other areas of the world. We collected A. fulica from 22 provinces in 6 regions of Thailand and analyzed a phylogenetic tree and haplotype network based on a fragment of 239 base pairs of the 16S rRNA sequence. The maximum likelihood, neighbor joining, and Bayesian inference trees for the 133 A. fulica 16S rRNA sequences revealed only one group, closely related only to A. fulica haplotype C, in all regions of Thailand. The haplotype network analysis showed that haplotype C is associated with F, P, E, Q, H and D. The genetic distance between the haplotype and A. fulica isolates in Thailand varies from 0 and 0.024, with a total of 21 variable sites. Haplotype C is predominant in Thailand and associated with other haplotypes from several areas. As inferred from 16S rDNA sequences, this study demonstrated low genetic diversity in A. fulica in Thailand. Low genetic diversity in the population can increase susceptibility to A. cantonensis infection, which may be associated with the current distribution of A. cantonensis.

Photorhabdus heterorhabditis subsp. aluminescens subsp. nov., Photorhabdus heterorhabditis subsp. heterorhabditis subsp. nov., Photorhabdus australis subsp. thailandensis subsp. nov., Photorhabdus australis subsp. australis subsp. nov., and Photorhabdus aegyptia sp. nov. isolated from Heterorhabditis entomopathogenic nematodes

Three Gram-stain-negative, rod-shaped, non-spore-forming bacteria, BA1^T, Q614^T and PB68.1^T, isolated from the digestive system of Heterorhabditis entomopathogenic nematodes, were biochemically and molecularly characterized to clarify their taxonomic affiliations. The 16S rRNA gene sequences of these strains suggest that they belong to the Gammaproteobacteria, to the family Morganellacea, and to the genus Photorhabdus. Deeper analyses using whole genome-based phylogenetic reconstructions suggest that BA1^T is closely related to Photorhabdus akhursti, that Q614^T is closely related to Photorhabdus heterorhabditis, and that PB68.1^T is closely related to Photorhabdus australis. In silico genomic comparisons confirm these observations: BA1^T and P. akhursti 15138^T share 68.8 % digital DNA-DNA hybridization (dDDH), Q614^T and P. heterorhabditis SF41^T share 75.4 % dDDH, and PB68.1^T and P. australis DSM 17609^T share 76.6  % dDDH. Physiological and biochemical characterizations reveal that these three strains also differ from all validly described Photorhabdus species and from their more closely related taxa, contrary to what was previously suggested. We therefore propose to classify BA1^T as a new species within the genus Photorhabdus, Q614^T as a new subspecies within P. heterorhabditis, and PB68.1^T as a new subspecies within P. australis. Hence, the following names are proposed for these strains: Photorhabdus aegyptia sp. nov. with the type strain BA1^T(=DSM 111180^T=CCOS 1943^T=LMG 31957^T), Photorhabdus heterorhabditis subsp. aluminescens subsp. nov. with the type strain Q614^T (=DSM 111144^T=CCOS 1944^T=LMG 31959^T) and Photorhabdus australis subsp. thailandensis subsp. nov. with the type strain PB68.1^T (=DSM 111145^T=CCOS 1942^T). These propositions automatically create Photorhabdus heterorhabditis subsp. heterorhabditis subsp. nov. with SF41^T as the type strain (currently classified as P. heterorhabditis) and Photorhabdus australis subsp. australis subsp. nov. with DSM17609^T as the type strain (currently classified as P. australis).

Genetic analysis of Cryptozona siamensis (Stylommatophora, Ariophantidae) populations in Thailand using the mitochondrial 16S rRNA and COI sequences

Cryptozona siamensis, one of the most widespread land snails, is native to Thailand, and plays a key role as an agricultural pest and intermediate host for Angiostrongylus spp. However, its genetic diversity and population structure has not yet been investigated, and are poorly understood. Therefore, a genetic analysis of the C. siamensis population in Thailand was conducted, based mitochondrial 16S rRNA (402 bp) and COI (602 bp) gene fragment sequences. Cryptozona siamensis randomly collected from 17 locations in four populations across Thailand, between May 2017 and July 2018. Fifty-eight snails were used to examine the phylogeny, genetic diversity, and genetic structure. The maximum likelihood tree based on the 16S rRNA and COI fragment sequences revealed two main clades. A total of 14 haplotypes with 44 nucleotide variable sites were found in the 16S rRNA sequences, while 14 haplotypes with 57 nucleotide variable sites were found in the COI sequences. The genetic diversity of C. siamensis in term of the number of haplotypes and haplotype diversity, was found to be high but the nucleotide diversity showed low levels of genetic differentiation for the COI sequence as also noted with the 16S rRNA sequence. The population genetic structure of C. siamensis revealed genetic difference in most populations in Thailand. However, low genetic difference in some populations may be due to high gene flow. This study provides novel insights into the basic molecular genetics of C. siamensis.

Insight into Molecular Epidemiology, Antimicrobial Resistance, and Virulence Genes of Extensively Drug-Resistant Acinetobacter baumannii in Thailand

Extensively drug-resistant Acinetobacter baumannii (XDR-AB) is a major threat to public health worldwide. A retrospective study for 27 XDR-AB isolates from four tertiary hospitals in Thailand was conducted. Beta-lactamase and virulence genes were characterized by PCR. The bla_ADC, bla_OXA-51, and bla_OXA-23 were detected in all isolates, whereas bla_PER-1 and bla_NDM-1 genes were present in 7.4% and 3.7% of isolates. All isolates had virulence genes, including genes in iron acquisition system, biofilm formation and secretion systems. The plasmids in XDR-AB belonged to GR2 (100%), GR6 (40.7%), and GR1 (7.4%). Multilocus sequence typing sequence types (STs) were further investigated. The data demonstrated that XDR-AB isolates had nine STs: ST195 (n = 4), ST208 (n = 4), ST368 (n = 1), ST451 (n = 5), ST457 (n = 2), ST1947 (n = 1), ST1166 (n = 7), including two novel STs namely ST1682 (n = 2) and ST1684 (n = 1). We observed that the majority ST1166 (25.9%) was associated with the prevalence of GR2 and GR6 plasmids and traU virulence gene. Genome-based single nucleotide polymorphism phylogenetic analysis of the isolates with two novel ST types indicated that the two isolates belonged to the international clone II (IC2) within the same cluster. In conclusion, our data showed the dissemination of XDR-AB isolates harbored virulence genes and antibiotic resistance genes among four hospitals in Thailand. The results highlighted the difficulty posed for the empirical treatment of the patients with the A. baumannii infection.

Essential Gene Clusters Involved in Copper Tolerance Identified in Acinetobacter baumannii Clinical and Environmental Isolates

Copper is widely used as antimicrobial in agriculture and medicine. Copper tolerance mechanisms of pathogenic bacteria have been proven to be required for both copper tolerance and survival during bacterial infections. Here, we determined both copper-tolerant phenotype and genotype in A. baumannii originated from clinical and environmental samples. Using copper susceptibility testing, copper-tolerant A. baumannii could be found in both clinical and environmental isolates. Genotypic study revealed that representative copper-related genes of the cluster A (cueR), B (pcoAB), and D (oprC) were detected in all isolates, while copRS of cluster C was detected in only copper-tolerant A. baumannii isolates. Moreover, we found that copper-tolerant phenotype was associated with amikacin resistance, while the presence of copRS was statistically associated with bla_NDM-1. We chose the A. baumannii strain AB003 as a representative of copper-tolerant isolate to characterize the effect of copper treatment on external morphology as well as on genes responsible for copper tolerance. The morphological features and survival of A. baumannii AB003 were affected by its exposure to copper, while whole-genome sequencing and analysis showed that it carried fourteen copper-related genes located on four clusters, and cluster C of AB003 was found to be embedded on genomic island G08. Transcriptional analysis of fourteen copper-related genes identified in AB003 revealed that copper treatment induced the expressions of genes of clusters A, B, and D at the micromolar level, while genes of cluster C were over-expressed at the millimolar levels of copper. This study showed that both clinical and environmental A. baumannii isolates have the ability to tolerate copper and carried numerous copper tolerance determinants including intrinsic copper tolerance (clusters A, B, and D) and acquired copper tolerance (cluster C) that could respond to copper toxicity. Our evidence suggests that we need to reconsider the use of copper in hospitals and other medical environments to prevent the selection and spread of copper-tolerant organisms.

Genetic characterization of Angiostrongylus larvae and their intermediate host, Achatina fulica, in Thailand

Angiostrongyliasis is a parasitic disease caused by nematodes of the genus Angiostrongylus. Distribution of this worm corresponds to the dispersal of its main intermediate host, the giant African land snail Achatina fulica. Genetic characterization can help identify parasitic pathogens and control the spreading of disease. The present study describes infection of A. fulica by Angiostrongylus, and provides a genetic outlook based on sequencing of specific regions. We collected 343 land snails from 22 provinces across six regions of Thailand between May 2017 and July 2018. Artificial digestion and Baermann’s technique were employed to isolate Angiostrongylus larvae. The worm and its intermediate host were identified by sequencing with specific nucleotide regions. Phylogenetic tree was constructed to evaluate the relationship with other isolates. A. fulica from Chaiyaphum province was infected with A. cantonensis, whereas snails collected from Phrae and Chiang Rai provinces were infected with A. malaysiensis. The maximum likelihood tree based on 74 A. fulica COI sequences revealed monophyletic groups and identified two haplotypes: AF1 and AF2. Only AF1, which is distributed in all regions of Thailand, harbored the larvae of A. cantonensis and A. malaysiensis. Two mitochondrial genes (COI and cytb) and two nuclear regions (ITS2 and SSU rRNA) were sequenced in 41 Angiostrongylus specimens. The COI gene indicated that A. cantonensis was closely related to the AC10 haplotype; whereas the cytb gene revealed two new haplotypes: AC19 and AC20. SSU rRNA was useful for the identification of A. cantonensis; whereas ITS2 was a good genetic marker for differentiating between A. cantonensis and A. malaysiensis. This study provides genetic information about the parasite Angiostrongylus and its snail intermediate host. The data in this work may be useful for further study on the identification of Angiostrongylus spp., the genetic relationship between intermediate host and parasite, and control of parasites.

Cyclo(tetrahydroxybutyrate) production is sufficient to distinguish between Xenorhabdus and Photorhabdus isolates in Thailand

Bacteria of the genera Photorhabdus and Xenorhabdus produce a plethora of natural products to support their similar symbiotic life cycles. For many of these compounds, the specific bioactivities are unknown. One common challenge in natural product research when trying to prioritize research efforts is the rediscovery of identical (or highly similar) compounds from different strains. Linking genome sequence to metabolite production can help in overcoming this problem. However, sequences are typically not available for entire collections of organisms. Here, we perform a comprehensive metabolic screening using HPLC-MS data associated with a 114-strain collection (58 Photorhabdus and 56 Xenorhabdus) across Thailand and explore the metabolic variation among the strains, matched with several abiotic factors. We utilize machine learning in order to rank the importance of individual metabolites in determining all given metadata. With this approach, we were able to prioritize metabolites in the context of natural product investigations, leading to the identification of previously unknown compounds. The top three highest ranking features were associated with Xenorhabdus and attributed to the same chemical entity, cyclo(tetrahydroxybutyrate). This work also addresses the need for prioritization in high-throughput metabolomic studies and demonstrates the viability of such an approach in future research.

Identification of entomopathogenic nematodes and symbiotic bacteria from Nam Nao National Park in Thailand and larvicidal activity of symbiotic bacteria against Aedes aegypti and Aedes albopictus

Entomopathogenic nematodes (EPNs) that are symbiotically associated with Xenorhabdus and Photorhabdus bacteria can kill target insects via direct infection and toxin action. There are limited reports identifying such organisms in the National Park of Thailand. Therefore, the objectives of this study were to identify EPNs and symbiotic bacteria from Nam Nao National Park, Phetchabun Province, Thailand and to evaluate the larvicidal activity of bacteria against Aedes aegypti and Ae. albopictus. A total of 12 EPN isolates belonging to Steinernema and Heterorhabditis were obtained form 940 soil samples between February 2014 and July 2016. EPNs were molecularly identified as S. websteri (10 isolates) and H. baujardi (2 isolates). Symbiotic bacteria were isolated from EPNs and molecularly identified as P. luminescens subsp. akhurstii (13 isolates), X. stockiae (11 isolates), X. vietnamensis (2 isolates) and X. japonica (1 isolate). For the bioassay, bacterial suspensions were evaluated for toxicity against third to early fourth instar larvae of Aedes spp. The larvae of both Aedes species were orally susceptible to symbiotic bacteria. The highest larval mortality of Ae. aegypti was 99% after exposure to X. stockiae (bNN112.3_TH) at 96 h, and the highest mortality of Ae. albopictus was 98% after exposure to P. luminescens subsp. akhurstii (bNN121.4_TH) at 96 h. In contrast to the control groups (Escherichia coli and distilled water), the mortality rate of both mosquito larvae ranged between 0 and 7% at 72 h. Here, we report the first observation of X. vietnamensis in Thailand. Additionally, we report the first observation of P. luminescens subsp. akhurstii associated with H. baujardi in Thailand. X. stockiae has potential to be a biocontrol agent for mosquitoes. This investigation provides a survey of the basic diversity of EPNs and symbiotic bacteria in the National Park of Thailand, and it is a bacterial resource for further studies of bioactive compounds.

Isolation and identification of Xenorhabdus and Photorhabdus bacteria associated with entomopathogenic nematodes and their larvicidal activity against Aedes aegypti

BACKGROUND

Aedes aegypti is a potential vector of West Nile, Japanese encephalitis, chikungunya, dengue and Zika viruses. Alternative control measurements of the vector are needed to overcome the problems of environmental contamination and chemical resistance. Xenorhabdus and Photorhabdus are symbionts in the intestine of entomopathogenic nematodes (EPNs) Steinernema spp. and Heterorhabditis spp. These bacteria are able to produce a broad range of bioactive compounds including antimicrobial, antiparasitic, cytotoxic and insecticidal compounds. The objectives of this study were to identify Xenorhabdus and Photorhabdus isolated from EPNs in upper northern Thailand and to study their larvicidal activity against Ae. aegypti larvae.

RESULTS

A total of 60 isolates of symbiotic bacteria isolated from EPNs consisted of Xenorhabdus (32 isolates) and Photorhabdus (28 isolates). Based on recA gene sequencing, BLASTN and phylogenetic analysis, 27 isolates of Xenorhabdus were identical and closely related to X. stockiae, 4 isolates were identical to X. miraniensis, and one isolate was identical to X. ehlersii. Twenty-seven isolates of Photorhabdus were closely related to P. luminescens akhurstii and P. luminescens hainanensis, and only one isolate was identical and closely related to P. luminescens laumondii. Xenorhabdus and Photorhabdus were lethal to Ae aegypti larvae. Xenorhabdus ehlersii bMH9.2_TH showed 100% efficiency for killing larvae of both fed and unfed conditions, the highest for control of Ae. aegypti larvae and X. stockiae (bLPA18.4_TH) was likely to be effective in killing Ae. aegypti larvae given the mortality rates above 60% at 72 h and 96 h.

CONCLUSIONS

The common species in the study area are X. stockiae, P. luminescens akhurstii, and P. luminescens hainanensis. Three symbiotic associations identified included P. luminescens akhurstii-H. gerrardi, P. luminescens hainanensis-H. gerrardi and X. ehlersii-S. Scarabaei which are new observations of importance to our knowledge of the biodiversity of, and relationships between, EPNs and their symbiotic bacteria. Based on the biological assay, X. ehlersii bMH9.2_TH begins to kill Ae. aegypti larvae within 48 h and has the most potential as a pathogen to the larvae. These data indicate that X. ehlersii may be an alternative biological control agent for Ae. aegypti and other mosquitoes.

Screening of the Antimicrobial Activity against Drug Resistant Bacteria of Photorhabdus and Xenorhabdus Associated with Entomopathogenic Nematodes from Mae Wong National Park, Thailand

Photorhabdus and Xenorhabdus are symbiotic with entomopathogenic nematodes (EPNs) of the genera Heterorhabditis and Steinernema, respectively. These bacteria produce several secondary metabolites including antimicrobial compounds. The objectives of this study were to isolate and identify EPNs and their symbiotic bacteria from Mae Wong National Park, Thailand and to evaluate the antibacterial activities of symbiont extracts against drug resistant bacteria. A total of 550 soil samples from 110 sites were collected between August 2014 and July 2015. A total of EPN isolates were obtained through baiting and White trap methods, which yielded 21 Heterorhabditis and 3 Steinernema isolates. Based on molecular identification and phylogenetic analysis, the most common species found in the present study was P. luminescens subsp. akhurstii associated with H. indica. Notably, two species of EPNs, H. zealandica and S. kushidai, and two species of symbiotic bacteria, X. japonica and P. temperata subsp. temperata represented new recorded organisms in Thailand. Furthermore, the association between P. temperata subsp. temperata and H. zealandica has not previously been reported worldwide. Disk diffusion, minimal inhibitory concentration, and minimal bactericidal concentration analyses demonstrated that the crude compound extracted by ethyl acetate from P. temperata subsp. temperata could inhibit the growth of up to 10 strains of drug resistant bacteria. Based on HPLC-MS analysis, compound classes in bacterial extracts were identified as GameXPeptide, xenoamicin, xenocoumacin, mevalagmapeptide phurealipids derivatives, and isopropylstilbene. Together, the results of this study provide evidence for the diversity of EPNs and their symbiotic bacteria in Mae Wong National Park, Thailand and demonstrate their novel associations. These findings also provide an important foundation for further research regarding the antimicrobial activity of Photorhabdus bacteria.

Photorhabdusluminescens subsp. namnaonensis subsp. nov., isolated from Heterorhabditisbaujardi nematodes

A lightly yellowish-pigmented, oxidase-negative bacterial strain (PB45.5T) isolated from the Nam Nao district of Phetchabun in central Thailand was investigated to determine its taxonomic position. Cells of the isolate showed a rod shaped appearance. The strain stained Gram-negative. Strain PB45.5T shared highest 16S rRNA gene sequence similarity with the type strains of Photorhabdus luminescens subsp. akhurstii (99.2 %) and Photorhabdus luminescens subsp. hainanensis (99.1 %) and lower similarities to all other Photorhabdus luminescens subspecies (<98.0 %). Multilocus sequence analysis (MLSA) based on concatenated partial recA, dnaN, gltX, gyrB and infB gene sequences confirmed the affiliation obtained by 16S rRNA gene sequence analysis but showed a clear distinction of PB45.5T from the closest related type strains. Strain PB45.5T shared only 96.9 % sequence similarity (concatenated nucleotide sequences) with P. luminescens subsp. akhurstii FRG04T and 96.8 % with P. luminescens subsp. hainanensis C8404T. The fatty acid profile of the strain consisted of the major fatty acids C14 : 0, C16 : 0, C17 : 0 cyclo, C16 : 1ω7c and/or iso-C15 : 0 2-OH, and C18 : 1ω7c. The MLSA results and the differential biochemical and chemotaxonomic properties showed that strain PB45.5T represents a novel P. luminescens subspecies, for which the name Photorhabdus luminescens subsp. namnaonensis subsp. nov. (type strain PB45.5T=LMG 29915T=CCM 8729T) is proposed.

PRELIMINARY SURVEY OF ENTOMOPATHOGENIC NEMATODES IN UPPER NORTHERN THAILAND

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis are used as biocontrol agents for insect pests. Survey of indigenous EPNs provides not only the diversity aspects but also the contribution in pest management in local areas. The objective of this study was to survey EPNs in upper northern Thailand. Nine hundred seventy soil samples were obtained from 194 sites in upper northern region of Thailand; of these 60 (6.2%) had EPNs in 2 genera: Steinernema (32 isolates) and Heterorhabditis (28 isolates). Most EPNs were isolated from loam with a soil temperature of 24-38°C, a pH of 1.5-7.0 and a soil moisture content of 0.5-6.8%. Molecular identification based on sequencing of a partial region of an internal transcribed spacer was performed for Heterorhabditis and the 28S rDNA for Steinernema. A BLASTN search of known sequence EPNs revealed 24 isolates of S. websteri and one isolate of S. scarabaei were identified; closely related to S. websteri (accession no. JF503100) and S. scarabaei (accession no. AY172023). The Heterorhabditis species identified were: H. indica (11 isolates), H. gerrardi (2 isolates) and Heterorhabditis sp (8 isolates). Phylogenetic analysis revealed 11 isolates of Heterorhabditis were related to H. indica; 2 isolates were related to Heterorhabditis gerrardi and 8 isolates were closely related to Heterorhabditis sp SGmg3. The study results show the genetic diversity of EPNs and describe a new observation of S. scarabaei and H. gerrardi in Thailand. This finding is new and provides important information for further study on using native EPNs in biological control.

A reproducible method for extraction of Plasmodium falciparum DNA by microwave irradiation and its potential for rapid molecular diagnosis

Malaria remains one of the most important communicable diseases. A rapid, simple and accurate method is a crucial part of malaria diagnosis. The aim of this study was to reevaluate the microwave irradiation method to extract DNA from Plasmodium falciparum and compare with six other existing DNA extraction methods such as QIAamp DNA mini kit (Qiagen), FTA elute card, phenol-chloroform, Chelex, Chelex without proteinase-K and Rapid boiling. Two different P. falciparum isolates were used: (i) Laboratory strains with 0.3% parasitemia and (ii) clinical isolate with 0.6% parasitemia. Each DNA extraction method was validated for the presence of P. falciparum by a routine nested and real time PCR. In order to evaluate the sensitivity of the DNA extraction by microwave, double serial dilution of P. falciparum from in vitro culture at parasitemia that ranged from 0.0001 to 0.17% were used to extract the DNA by microwave and the P. falciparum DNA was then detected by nested and real-time PCR. The nested and real-time PCR were able to detect. P. falciparum DNA at the parasitemia level as low as 0.0003% and 0.0001%, respectively. Our results can reproduce the results from earlier studies and reveal microwave as a rapid and simple tool to extract P. falciparum DNA and subsequent molecular diagnosis of malaria.

Towards monitoring the sandflies (Diptera: Psychodidae) of Thailand: DNA barcoding the sandflies of Wihan Cave, Uttaradit

Sandflies vary in their distributions and role in pathogen transmission. Attempts to record distributions of sandflies in Thailand have faced difficulties due to their high abundance and diversity. We aim to provide an insight into the diversity of sandflies in Thailand by (i) conducting a literature review, and (ii) DNA barcoding sandflies collected from Wihan Cave where eight morphologically characterized species were recorded. DNA barcodes generated for 193 sandflies fell into 13 distinct species clusters under four genera (Chinius, Idiophlebotomus, Phlebotomus and Sergentomyia). Five of these species could be assigned Linnaean species names unambiguously and two others corresponded to characterized morphospecies. Two species represented a complex under the name Sergentomyia barraudi while the remaining four had not been recognized before in any form. The resulting species checklist and DNA barcode library contribute to a growing set of records for sandflies which is useful for monitoring and vector control.

DISTRIBUTION OF ENTOMOPATHOGENIC NEMATODES IN LOWER NORTHERN THAILAND

Entomopathogenic nematodes (EPNs) are used successfully for biological control of subterranean larval pests leading to reduced environmental contamination if chemical control measures are employed. Their diversity and distribution in Thailand are unclear, so the present study sought to obtain a better understanding these EPN populations in the lower northern region of Thailand. We collected 930 soil samples from 186 sites of Kamphaeng Phet, Nakhon Sawan, Phetchabun, Phichit, Phitsanulok, Sukhothai, Tak, Uthai Thani, and Uttaradit Provinces, Thailand from December 2011 to November 2012. Galleria mellonella was used as host for isolating and propagating EPNs. Seventy soil samples (7.5%) yielded EPNs of two genera, Steinernema (3.0%) and Heterorhabditis (4.5%). The majority of the isolated EPNs were found in loam at 26°C-33°C and pH values of 5.0-7.0. Molecular identification from partial 28S rDNA sequences revealed S. websteri, isolated from soil samples from Nakhon Sawan and Uthai Thani. Phylogenetic analysis of these EPNs showed they are closely related to S. websteri JC1032. The identification that S. websteri was the predominant EPN should enable its application for biological control in the local prevailing soil conditions.

A Photorhabdus natural product inhibits insect juvenile hormone epoxide hydrolase

Simple urea compounds ("phurealipids") have been identified from the entomopathogenic bacterium Photorhabdus luminescens, and their biosynthesis was elucidated. Very similar analogues of these compounds have been previously developed as inhibitors of juvenile hormone epoxide hydrolase (JHEH), a key enzyme in insect development and growth. Phurealipids also inhibit JHEH, and therefore phurealipids might contribute to bacterial virulence.

High prevalence of multi-drug resistant Streptococcus pneumoniae among healthy children in Thailand

Antibiotic resistance in Streptococcus pneumoniae is an emerging health problem worldwide. The incidence of antimicrobial-resistant S. pneumoniae is increasing, and nasal colonization of S. pneumoniae in children increases the risk of pneumococcal infection. In this study, the prevalence of S. pneumoniae nasal colonization was studied in Thai children from three different districts. S. pneumoniae nasal colonization was found in 38 of 237 subjects (16.0%). The carriage rate indicated higher rates in two rural districts (18.2% and 29.8%) than in the urban district (2.8%). The antibiotic susceptibility pattern was determined using the disk diffusion method. Prevalence of multi-drug resistance S. pneumoniae (MDR-SP) was 31.6%. Resistance to commonly prescribed antibiotics was found for ampicillin (5.3%), azithromycin (26.3%), cefepime (2.6%), chloramphenicol (18.4%), clindamycin (18.4%), erythromycin (21.1%), oxacillin (44.7%), trimethoprim/sulfamethoxazole (78.9%) and tetracycline (15.8%). All isolates were sensitive to ceftriaxone. The pulsed-field gel electrophoresis pattern was used to compare genetic diversity of the S. pneumoniae isolates. PFGE demonstrated the variation in genotypes of S. pneumoniae from different areas. High prevalence of multi-drug resistance S. pneumoniae nasal colonization in healthy Thai children was indicated. Effective strategies for appropriate use of antibiotics are therefore needed in the community.

Characterization and Detection of Endolysin Gene from Three Acinetobacter baumannii Bacteriophages Isolated from Sewage Water

Acinetobacter baumannii is an opportunistic pathogen that exists in hospital environments. The emergence of multidrug resistant A. baumannii (MDRAB) has been reported worldwide. It is necessary to find a novel and effective treatment for MDRAB infection. In this study, three bacteriophages, designated as ØABP-01, ØABP-02 and ØABP-04 were selected for analysis. Transmission electron microscopy showed that bacteriophage ØABP-01 belonged to the Podoviridae family and bacteriophage ØABP-02 and ØABP-04 are classified into the family Myoviridae. ØABP-01 had the widest host range. ØABP-01, ØABP-02 and ØABP-04 exhibited a latent period of 15, 20 and 20 min. The burst sizes of the three bacteriophages were 110, 120 and 150 PFU/cell. DNA restriction analysis using EcoRI, HindIII, PstI, SphI, BamHI and SmaI showed different DNA fragment patterns between the three bacteriophages. ØABP-01 and ØABP-04 was positive for the endolysin gene as determined by PCR. In conclusion, bacteriophage ØABP-01 showed broad host-specificity, good lytic activity and a short latency period, making it an appropriate candidate for studying the control and diagnosis associated with MDRAB infections.

Antiparasitic chaiyaphumines from entomopathogenic Xenorhabdus sp. PB61.4

A new class of four depsipentapeptides called chaiyaphumines A-D (1-4) was isolated from Xenorhabdus sp. PB61.4. Their structures were elucidated by detailed 1D and 2D NMR experiments and by a Marfey's analysis following flash hydrolysis of the peptide. Verification of the structure was achieved by three-dimensional modeling using NOE-derived distance constraints, molecular dynamics, and energy minimization. Chaiyaphumine A (1) showed good activity against Plasmodium falciparum (IC50 of 0.61 μM), the causative agent of malaria, and was active against other protozoal tropical disease causing agents.

Diversity of Xenorhabdus and Photorhabdus spp. and their symbiotic entomopathogenic nematodes from Thailand

Xenorhabdus and Photorhabdus spp. are bacterial symbionts of entomopathogenic nematodes (EPNs). In this study, we isolated and characterized Xenorhabdus and Photorhabdus spp. from across Thailand together with their associated nematode symbionts, and characterized their phylogenetic diversity. EPNs were isolated from soil samples using a Galleria-baiting technique. Bacteria from EPNs were cultured and genotyped based on recA sequence. The nematodes were identified based on sequences of 28S rDNA and internal transcribed spacer regions. A total of 795 soil samples were collected from 159 sites in 13 provinces across Thailand. A total of 126 EPNs isolated from samples taken from 10 provinces were positive for Xenorhabdus (n = 69) or Photorhabdus spp. (n = 57). Phylogenetic analysis separated the 69 Xenorhabdus isolates into 4 groups. Groups 1, 2 and 3 consisting of 52, 13 and 1 isolates related to X. stockiae, and group 4 consisting of 3 isolates related to X. miraniensis. The EPN host for isolates related to X. stockiae was S. websteri, and for X. miraniensis was S. khoisanae. The Photorhabdus species were identified as P. luminescens (n = 56) and P. asymbiotica (n = 1). Phylogenenic analysis divided P. luminescens into five groups. Groups 1 and 2 consisted of 45 and 8 isolates defined as subspecies hainanensis and akhurstii, respectively. One isolate was related to hainanensis and akhurstii, two isolates were related to laumondii, and one isolate was the pathogenic species P. asymbiotica subsp. australis. H. indica was the major EPN host for Photorhabdus. This study reveals the genetic diversity of Xenorhabdus and Photorhabdus spp. and describes new associations between EPNs and their bacterial symbionts in Thailand.

Identification and isolation of insecticidal oxazoles from Pseudomonas spp

Two new and five known oxazoles were identified from two different Pseudomonas strains in addition to the known pyrones pseudopyronine A and B. Labeling experiments confirmed their structures and gave initial evidence for a novel biosynthesis pathway of these natural oxazoles. In order to confirm their structure, they were synthesized, which also allowed tests of their bioactivity. Additionally, the bioactivities of the synthesis intermediates were also investigated revealing interesting biological activities for several compounds despite their overall simple structures.

Enzyme-linked immunosorbent assay for the diagnosis of melioidosis: better than we thought

We used Bayesian latent-class models to generate receiver operating characteristic curves and to revise the cutoff values for an enzyme-linked immunosorbent assay that has been developed previously for melioidosis. The new cutoff was unbiased towards misclassification caused by an imperfect gold standard and resulted in an increase in both sensitivity (from 66.4% to 80.2%) and specificity (82.1% and 95.0%).

Effect of colony morphology variation of Burkholderia pseudomallei on intracellular survival and resistance to antimicrobial environments in human macrophages in vitro

Background

Primary diagnostic cultures from patients with melioidosis demonstrate variation in colony morphology of the causative organism, Burkholderia pseudomallei. Variable morphology is associated with changes in the expression of a range of putative virulence factors. This study investigated the effect of B. pseudomallei colony variation on survival in the human macrophage cell line U937 and under laboratory conditions simulating conditions within the macrophage milieu. Isogenic colony morphology types II and III were generated from 5 parental type I B. pseudomallei isolates using nutritional limitation. Survival of types II and III were compared with type I for all assays.

Results

Morphotype was associated with survival in the presence of H₂O₂ and antimicrobial peptide LL-37, but not with susceptibility to acid, acidified sodium nitrite, or resistance to lysozyme, lactoferrin, human neutrophil peptide-1 or human beta defensin-2. Incubation under anaerobic conditions was a strong driver for switching of type III to an alternative morphotype. Differences were noted in the survival and replication of the three types following uptake by human macrophages, but marked strain-to strain-variability was observed. Uptake of type III alone was associated with colony morphology switching.

Conclusions

Morphotype is associated with phenotypes that alter the ability of B. pseudomallei to survive in adverse environmental conditions.

Factors predicting and reducing mortality in patients with invasive Staphylococcus aureus disease in a developing country

Background

Invasive Staphylococcus aureus infection is increasingly recognised as an important cause of serious sepsis across the developing world, with mortality rates higher than those in the developed world. The factors determining mortality in developing countries have not been identified.

Methods

A prospective, observational study of invasive S. aureus disease was conducted at a provincial hospital in northeast Thailand over a 1-year period. All-cause and S. aureus-attributable mortality rates were determined, and the relationship was assessed between death and patient characteristics, clinical presentations, antibiotic therapy and resistance, drainage of pus and carriage of genes encoding Panton-Valentine Leukocidin (PVL).

Principal Findings

A total of 270 patients with invasive S. aureus infection were recruited. The range of clinical manifestations was broad and comparable to that described in developed countries. All-cause and S. aureus-attributable mortality rates were 26% and 20%, respectively. Early antibiotic therapy and drainage of pus were associated with a survival advantage (both p<0.001) on univariate analysis. Patients infected by a PVL gene-positive isolate (122/248 tested, 49%) had a strong survival advantage compared with patients infected by a PVL gene-negative isolate (all-cause mortality 11% versus 39% respectively, p<0.001). Multiple logistic regression analysis using all variables significant on univariate analysis revealed that age, underlying cardiac disease and respiratory infection were risk factors for all-cause and S. aureus-attributable mortality, while one or more abscesses as the presenting clinical feature and procedures for infectious source control were associated with survival.

Conclusions

Drainage of pus and timely antibiotic therapy are key to the successful management of S. aureus infection in the developing world. Defining the presence of genes encoding PVL provides no practical bedside information and draws attention away from identifying verified clinical risk factors and those interventions that save lives.

Genetic diversity and microevolution of Burkholderia pseudomallei in the environment

Background

The soil dwelling Gram-negative pathogen Burkholderia pseudomallei is the cause of melioidosis. The diversity and population structure of this organism in the environment is poorly defined.

Methods and Findings

We undertook a study of B. pseudomallei in soil sampled from 100 equally spaced points within 237.5 m² of disused land in northeast Thailand. B. pseudomallei was present on direct culture of 77/100 sampling points. Genotyping of 200 primary plate colonies from three independent sampling points was performed using a combination of pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Twelve PFGE types and nine sequence types (STs) were identified, the majority of which were present at only a single sampling point. Two sampling points contained four STs and the third point contained three STs. Although the distance between the three sampling points was low (7.6, 7.9, and 13.3 meters, respectively), only two STs were present in more than one sampling point. Each of the three samples was characterized by the localized expansion of a single B. pseudomallei clone (corresponding to STs 185, 163, and 93). Comparison of PFGE and MLST results demonstrated that two STs contained strains with variable PFGE banding pattern types, indicating geographic structuring even within a single MLST-defined clone.

Conclusions

We discuss the implications of this extreme structuring of genotype and genotypic frequency in terms of micro-evolutionary dynamics and ecology, and how our results may inform future sampling strategies.

The soil dwelling Gram-negative bacterium Burkholderia pseudomallei is the cause of melioidosis, a serious human infection that occurs in Southeast Asia and northern Australia. The purpose of this study was to evaluate the population genetic structure of B. pseudomallei in the environment. To achieve this, we undertook soil sampling and culture for the presence of B. pseudomallei in 100 equally spaced points within an area of disused land in northeast Thailand, and undertook detailed genotyping of primary plate colonies isolated from three independent sampling points. Our results demonstrated that multiple B. pseudomallei genotypes were present within a single soil sample, and that different genotypes were present at independent but nearby sampling points. The B. pseudomallei genetic population was unevenly distributed within a given sample, with a predominant genotype co-existing with several genotypes present as a minority population. We discuss the implications of this structuring of genotypic frequency in terms of micro-evolutionary dynamics and ecology, and how our results may inform future sampling strategies.

Prospective clinical evaluation of the accuracy of 16S rRNA real-time PCR assay for the diagnosis of melioidosis

The accuracy of a Burkholderia pseudomallei 16s rRNA real-time PCR assay was evaluated against culture for the diagnosis of melioidosis in Thailand. A total of 846 samples were obtained from 383 patients with suspected melioidosis. One or more specimens were PCR positive for 47 of 77 patients with culture-proven melioidosis (sensitivity 61.0%, 95% CI: 49.2-72.0%). PCR was negative for all 306 patients who were culture negative for B. pseudomallei (specificity 100%, 95% CI: 98.8-100%). Diagnostic sensitivity of PCR was 22.7% for patients who were culture positive for blood only, compared with 79.4% for patients who were culture positive for samples other than blood. The median (interquartile range) B. pseudomallei colony count in blood for 44 of 77 patients with positive blood cultures was 2.4 CFU/ml (0.2-13.5 CFU/ml); this may explain the low sensitivity of PCR for this specimen. The PCR assay described here is not sufficiently sensitive to replace culture in our clinical setting.

Simultaneous infection with more than one strain of Burkholderia pseudomallei is uncommon in human melioidosis

A prospective study was performed to determine the rate at which patients with melioidosis are infected with more than one strain of Burkholderia pseudomallei. Genotyping of 2,058 bacterial colonies isolated from 215 samples taken from 133 patients demonstrated that mixed infection is uncommon (2/133 cases [1.5%; 95% confidence interval, 0.2 to 5.3%]).

Molecular phylogeny of black flies (Diptera: Simuliidae) from Thailand, using ITS2 rDNA

The sequences of the second internal transcribed spacer (ITS2) of ribosomal DNA (rDNA) were determined for 40 black fly species from Thailand, belonging to 4 subgenera of the genus Simulium, namely Gomphostilbia (12 species), Nevermannia (5 species), Montisimulium (1 species), Simulium sensu stricto (21 species), and an unknown subgenus with one species (Simulium baimaii). The length of the ITS2 ranged from 247 to 308 bp. All black fly species had high AT content, ranging from 71 to 83.8%. Intraindividual variation (clonal variation) occurred in 13 species, ranging from 0.3 to 1.1%. Large intrapopulation and interpopulation heterogeneities exist in S. feuerboni from the same and different locations in Doi Inthanon National Park, northern Thailand. Phylogenetic relationships among 40 black fly species were examined using PAUP (version 4.0b10) and MrBAYS (version 3.0B4). The topology of the trees revealed two major monophyletic clades. The subgenus Simulium and Simulium baimaii were placed in the first monophyletic clade, whereas the subgenera Nevermannia + Montisimulium were placed as the sister group to the subgenus Gomphostilbia in the second monophyletic clade. Our results suggest that S. baimaii belongs to the malyschevi-group or variegatum-group in the subgenus Simulium. The molecular phylogeny generally agrees with existing morphology-based phylogenies.

Accuracy of enzyme-linked immunosorbent assay using crude and purified antigens for serodiagnosis of melioidosis

Five enzyme-linked immunosorbent assays developed to detect antibodies to different Burkholderia pseudomallei antigen preparations were evaluated as diagnostic tests for melioidosis in northeast Thailand. The highest diagnostic indices were observed for an affinity-purified antigen (sensitivity, 82%; specificity, 72%) and crude B. pseudomallei antigen (sensitivity, 81%; specificity, 70%), an improvement over the indirect hemagglutination assay (sensitivity, 73%; specificity, 64%).