House Fly (Musca Domestica L.) Temporal and Spatial Immune Response to Streptococcus Pyogenes and Salmonella Typhimurium: Role of Pathogen Density in Bacterial Fate, Persistence and Transmission

House flies (Musca domestica L), feed and breed in decomposing organic waste and therefore are constantly in contact with different species of microorganisms. Because house flies live in close proximity to human and animal habitats, they pose a danger of transmitting pathogenic microorganisms from diseased sources to new environments. To elucidate pathogen vector potential of house flies, this study investigated dose-dependent survivability of GFPexpressing Streptococcus pyogenes and Salmonella typhimurium SR11 within the fly alimentary canal both spatially via epifluorescence microscopy and quantitatively via culture-recovery. Adult house flies were fed known amounts of bacteria (high or low dose), and were dissected to remove the entire alimentary canal for microscopy or were homogenized and cultured at intervals within 24 h post-ingestion. Excreta also were cultured to determine transmission potential. Also investigated was the dose-dependent local intestinal epithelial immune response of house flies to S. pyogenes and S. typhimurium, where the upregulation of three antimicrobial peptides Defensin, Cecropin and Diptericin were investigated. Both bacterial dose and species affected survivability of these pathogens in the house fly alimentary canal. High dose of both species survived throughout the 24 h period. The number of viable S. typhimurium increased in 2 numbers in both high and low dose, whereas S. pyogenes decreased in number with time progression. Viable S. typhimurium were recovered in large quantities from excreta as compared to S. pyogenes. Both bacterial species and dose also affected the temporal, spatial and class of AMP expression profiles in the gut. In S. pyogenes-fed flies, only Defensin was regionally produced in midgut tissue. In contrast, tissues from flies that were fed S. typhimurium expressed both Cecropin and Diptericin. In both species, the higher dose of bacterial challenge induced greater AMP expression than the low dose. The region of the gut showing AMP expression in both bacterial challenges was mainly the midgut, and peak expressions correlated with high numbers of bacteria as determined by culture-recovery. Dose-dependent effects or survival and transmission of bacteria from house flies has significant implications on vector potential

The role of 'filth flies' in the spread of antimicrobial resistance

'Filth flies' feed and develop in excrement and decaying matter and can transmit enteric pathogens to humans and animals, leading to colonization and infection. Considering these characteristics, 'filth flies' are potential vectors for the spread of antimicrobial resistance (AMR). This review defines the role of flies in the spread of AMR and identifies knowledge gaps. The literature search (original articles, reviews indexed for PubMed) was restricted to the English language. References of identified studies were screened for additional sources. 'Filth flies' are colonized with antimicrobial-resistant bacteria of clinical relevance. This includes extended spectrum beta-lactamase-, carbapenemase-producing and colistin-resistant (mcr-1 positive) bacteria. Resistant bacteria in flies often share the same genotypes with bacteria from humans and animals when their habitat overlap. The risk of transmission is most likely highest for enteric bacteria as they are shed in high concentration in excrements and are easily picked up by flies. 'Filth flies' can 'bio-enhance' the transmission of AMR as bacteria multiply in the digestive tract, mouthparts and regurgitation spots. To better understand the medical importance of AMR in flies, quantitative risk assessment models should be refined and fed with additional data (e.g. vectorial capacity, colonization dose). This requires targeted ecological, epidemiological and in vivo experimental studie