Highlights d The wAlbB strain of Wolbachia bacteria was established in Aedes aegypti populations d Wolbachia frequencies remained high and stable at some sites d Dengue incidence decreased at release sites

BackgroundAntimicrobial resistance is currently a major global issue. As the rate of emergence of antimicrobial resistance has superseded the rate of discovery and introduction of new effective drugs, the medical arsenal now is experiencing shortage of effective drugs to combat diseases, particularly against diseases caused by the dreadful multidrug-resistant strains, such as the methicillin-resistant Staphylococcus aureus (MRSA). The ability of fly larvae to thrive in septic habitats has prompted us to determine the antibacterial activity and minimum inhibitory concentrations (MICs) of larval extract of flies, namely Lucilia cuprina, Sarcophaga peregrina and Musca domestica against 4 pathogenic bacteria [Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa and Escherichia coli] via a simple and sensitive antibacterial assay, resazurin-based turbidometric (TB) assay as well as to demonstrate the preliminary chemical profile of larval extracts using gas chromatography-mass spectrophotometry (GC-MS).ResultsThe resazurin-based TB assay demonstrated that the L. cuprina larval extract was inhibitory against all tested bacteria, whilst the larval extract of S. peregrina and M. domestica were only inhibitory against the MRSA, with a MIC of 100 mg ml-1. Subsequent sub-culture of aliquots revealed that the larval extract of L. cuprina was bactericidal against MRSA whilst the larval extracts of S. peregrina and M. domestica were bacteriostatic against MRSA. The GC-MS analysis had quantitatively identified 20 organic compounds (fatty acids or their derivatives, aromatic acid esters, glycosides and phenol) from the larval extract of L. cuprina; and 5 fatty acid derivatives with known antimicrobial activities from S. peregrina and M. domestica.ConclusionThe resazurin-based turbidometric assay is a simple, reliable and feasible screening assay which evidently demonstrated the antibacterial activity of all fly larval extracts, primarily against the MRSA. The larval extract of L. cuprina exerted a broad spectrum antibacterial activity against all tested bacteria. The present study revealed probable development and use of novel and effective natural disinfectant(s) and antibacterial agent(s) from flies and efforts to screen more fly species for antibacterial activity using resazurin-based TB assay should be undertaken for initial screening for subsequent discovery and isolation of potential novel antimicrobial substances, particularly against the multi-drug resistant strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-017-0936-3) contains supplementary material, which is available to authorized users.

Aedes aegypti mosquitoes carrying the w AlbB Wolbachia strain show a reduced capacity to transmit dengue virus. w AlbB has been introduced into wild Ae. aegypti populations in several field sites in Kuala Lumpur, Malaysia, where it has persisted at high frequency for more than 2 years and significantly reduced dengue incidence. Although these encouraging results indicate that w AlbB releases can be an effective dengue control strategy, the long-term success depends on w AlbB maintaining high population frequencies and virus transmission inhibition, and both could be compromised by Wolbachia– host coevolution in the field. Here, w AlbB-carrying Ae. aegypti collected from the field 20 months after the cessation of releases showed no reduction in Wolbachia density or tissue distribution changes compared to a w AlbB laboratory colony. The w AlbB strain continued to induce complete unidirectional cytoplasmic incompatibility, showed perfect maternal transmission under laboratory conditions, and retained its capacity to inhibit dengue. Additionally, a field-collected w AlbB line was challenged with Malaysian dengue patient blood, and showed significant blocking of virus dissemination to the salivary glands. These results indicate that w AlbB continues to inhibit currently circulating strains of dengue in field populations of Ae. aegypti , and provides additional support for the continued scale-up of Wolbachia wAlbB releases for dengue control. This article is part of the theme issue ‘Novel control strategies for mosquito-borne diseases’.