Larvicidal activity of Xenorhabdus and Photorhabdus bacteria against Aedes aegypti and Aedes albopictus

Objective:To evaluate the efficacy of symbiotic bacteria,Xenorhabdus indica,Xenorhabdus stockiae,Photorhabdus luminescens subsp,akhurstii and Photorhabdus luminescens subsp.hainanensis as a larvicide against Aedes aegypti and Aedes albopictus.Methods:Larvae (L3-L4) of Aedes aegyptiand Aedes albopictus were given 2 mL of a suspension 107-108 CFU/mL of each symbiotic bacterium.Distilled water and Escherichia coli ATCC· 25922 were used as the control.The morality rate of the larval mosquitoes was observed at 24,48,72 and 96 h.The experiment was performed in triplicates.Results:The larvae of both Aedes species started to die at 24 h exposure.Aedes aegypti showed the highest mortality rate (87％-99％),96 h after exposure to Xenorhabdus stockiae (bNBP22.2_TH).The mortality rate of Aedes albopictus was between 82％ and 96％ at 96 h after exposure to Xenorhabdus indica (bKK26.2_TH).Low effectiveness of distilled water and Escherichia coliATCC· 25922 were observed in both Aedes larvae,with a mortality rate of 2％ to 12％.Conclusions:The study confirms the oral toxicity of Xenorhabdus and Photorhabdus bacteria against Aedes spp.Xenorhabdus stockiae and Xenorhabdusindica may be an alternative agent for control Aedes spp.This is basic information for further study on the mechanism of action on Aedes larvae or application to control mosquito larvae in the community.

Comparison of LAMP and PCR for molecular mass screening of sand flies for Leishmania martiniquensis infection

BACKGROUND Leishmaniasis caused by Leishmania martiniquensis infection has been reported in human and domestic animals of Martinique Island, Germany, Switzerland, USA, Myanmar and Thailand. The peculiar clinical features of disseminated cutaneous and visceral forms co-existence render the urgent need of specific diagnostic tool to identify the natural sand fly vectors for effective prevention and control strategies. Loop-mediated isothermal amplification (LAMP) of 18S rRNA gene as well as polymerase chain reaction (PCR) of minicircle kinetoplast DNA gene (PCR-mkDNA) have never been applied to detect L. martiniquensis and L. siamensis in sand fly vectors. OBJECTIVE The present study was aimed to validate malachite green-LAMP (MG-LAMP) and PCR-mkDNA techniques to detect L. martiniquensis in sand fly vectors, compared with the conventional PCR of internal transcribed spacer 1 (PCR-ITS1). METHODS We compared the validity of LAMP of 18S rRNA gene and PCR-mkDNA, to PCR-ITS1 in simulation model of L. martiniquensis infection in Sergentomyia gemmea sand flies. Attributable to the sensitivity and specificity, PCR-mkDNA was consecutively applied to detect L. martiniquensis in 380 female sand fly individuals captured in the newly identified affected region of Lamphun Province, Thailand. FINDINGS AND MAIN CONCLUSIONS Results showed that PCR-mkDNA could detect at least one promastigote per sand fly, which was 10-time superior to LAMP and PCR-ITS1. In addition, PCR-mkDNA was more specific, able to differentiate L. martiniquensis from other viscerotropic Leishmania species, such as L. siamensis, L. (L.) donovani, and L. (L.) infantum. Consecutively, mass screening of L. martiniquensis in 380 female sand fly individuals by PCR-mkDNA was implemented in a new affected area of Thailand where a patient with leishmaniasis/HIV co-infection resides; however Leishmania DNA was undetected. In conclusion, PCR-mkDNA is a promising tool for molecular mass screening of L. martiniquensis infection in outbreak areas where several species of Leishmania and sand flies co-exist.