Vector competence of Musca domestica (Diptera: Muscidae) for Yersinia pseudotuberculosis

Lack of fitness costs associated with resistance to permethrin in Musca domestica

Resistance to permethrin has been reported in Pakistani strains of Musca domestica. The present study explored the performance of biological traits and analyzed life tables to determine whether there is any detrimental effect of permethrin resistance on the fitness of permethrin-resistant strains [an isogenic resistant strain (Perm-R) and a field strain (Perm-F)] compared to a susceptible strain (Perm-S). Perm-R and Perm-F exhibited 233.93- and 6.87-fold resistance to permethrin, respectively. Life table analyses revealed that the Perm-R strain had a significantly shorter preadult duration, longer longevity, shorter preoviposition period, higher fecundity, finite rate of increase, intrinsic rate of increase, net reproductive rate and a shorter mean generation time, followed by the Perm-F strain when compared to the Perm-S strain. Data of the performance of biological traits reveled that permethrin resistance strains had a better fit than that of the Perm-S strain. The enhanced fitness of resistant strains of M. domestica may accelerate resistance development to permethrin and other pyrethroids in Pakistan. Some possible measures to manage M. domestica and permethrin resistance in situations of fitness advantage are discussed.

Bacterial Communities Associated with Houseflies (Musca domestica L.) Inhabiting Hospices in South Africa

Houseflies are alleged reservoirs as well as vectors of human and animal pathogens, including bacteria, because they frequently have contact with animal excreta and decaying organic substances. The rapid adaptation process of ingested microbes in the insect gut may involve gene transfer, including antibiotic resistance determinants among different bacterial strains. Six hundred and fifty-seven (n = 657) houseflies were collected from hospices and were identified morphologically and genetically using the 16S rRNA, CO1, and ITS2 barcoding genes. This study also characterized the bacterial communities harboured by the captured houseflies using 16S rRNA metabarcoding on the next-generation sequencing (NGS) platform and further sought to detect antibiotic resistance traits by using gene-specific PCR assays. Generated sequences for the targeted gene fragments matched with Musca domestica and all the sequences were deposited to the GenBank database. The 16S rRNA metabarcoding analysis revealed that the most abundant phyla detected with variable abundance observed among all the houseflies were Proteobacteria, followed by Firmicutes, and Bacteroidetes. Furthermore, the NGS data revealed the presence of multiple bacterial genera, including Providencia, Enterobacter, Dysgonomonas, Escherichia-Shigella, Klebsiella, Pseudomonas, and Streptococcus, which are known to harbour potentially pathogenic species of animals and humans. Antibiotic resistance genes detected from the housefly DNA in this study included ermB, tetA, blaSHV, and blaTEM. Moreover, these genes are associated with resistance to erythromycin, tetracycline, and beta-lactams antibiotics, respectively. The presence of bacterial pathogens and the detection of antibiotic resistance genes from the houseflies collected from the hospices indicates the possible health risk to patients in hospices and the surrounding community. Therefore, it is imperative to keep high standards of hygiene, food preparation, safety, and control of houseflies in hospices.

Flies as a potential vector of selected alert pathogens in a hospital environment

Multi-drug resistant pathogens are a global problem. Flies are a potential vector of multi-drug resistant pathogens, which can be particularly dangerous in the hospital environment. This study aimed to evaluate flies as vectors of alert pathogens. The research material consisted of 100 flies (Musca domestica (46.0%), Lucilia sericata (28.0%), and Calliphora vicina (26.0%)) collected at the University Hospital No. 1 dr. A. Jurasz in Bydgoszcz (Poland) in 2018-2019 (summer months). The presence of bacteria of the genera: Enterococcus, Staphylococcus, Escherichia, Leclercia, Citrobacter, Hafnia, Providencia, Proteus, Enterobacter, Klebsiella, Raoultella, Morganella, Moellerella, Bordetella, Pantoea, Serratia, Plesiomonas, Wohlfahrimonas, and Lelliottia was confirmed. The most frequently isolated species included: Enterococcus faecalis (n = 64), Escherichia coli (n = 43) and Moellerella wisconsensis (n = 24). The infection rate and antibiotic resistance of bacteria were assessed. One strain of Proteus mirabilis (isolated from Calliphora vicina) produced ESBLs (extended-spectrum beta-lactamases). The infection rate was 0.38%, 0.26%, and 0.20% for Musca domestica, Lucilia sericata, and Calliphora vicina, respectively. The flies from a hospital area were not a vector of alert pathogens. Monitoring flies as potential vectors of pathogens is an important aspect of public health, especially for hospitalized patients.

All resistance alleles are not equal: the high fitness cost of super-kdr in the absence of insecticide

BACKGROUND

Mutations in the voltage-sensitive sodium channel are an important mechanism of resistance to pyrethroid insecticides. In Musca domestica, common resistance alleles are kdr, super-kdr and kdr-his. The levels of resistance that these alleles confer is known, but the fitness of these alleles relative to each other and to susceptible alleles is unknown. We used crosses from congenic strains of M. domestica to establish populations with known allele frequencies and then examined the changes in allele and genotype frequencies over 25 generations under laboratory conditions.

RESULTS

There was a significant fitness cost for the super-kdr allele, which decreased from the starting frequency of 0.25 to 0.05 after 25 generations. The fitness of the kdr, kdr-his and susceptible alleles were similar. The greatest change in genotype frequency was seen for the super-kdr/super-kdr genotype, which was no longer detected after 25 generations.

CONCLUSION

The fitness cost associated with the super-kdr allele is consistent with previous reports and appears to be a factor in helping to restrain high levels of resistance in field populations (the super-kdr allele confers higher levels of resistance than kdr or kdr-his). It is known that the relative costs of different alleles are environmentally dependent, but our results also demonstrate that the relative fitness of given alleles depends on which alleles are present in a given population, as previous pairwise comparisons of allele fitness do not exactly match (except for super-kdr) the results obtained using this four allele study. © 2020 Society of Chemical Industry.

Prevalence of Field-Collected House Flies and Stable Flies With Bacteria Displaying Cefotaxime and Multidrug Resistance

Antibiotic use in livestock accounts for 80% of total antibiotic use in the United States and has been described as the driver for resistance evolution and spread. As clinical infections with multidrug-resistant pathogens are rapidly rising, there remains a missing link between agricultural antibiotic use and its impact on human health. In this study, two species of filth flies from a livestock operation were collected over the course of 11 mo: house flies Musca domestica (L.) (Diptera: Muscidae), representing a generalist feeder, and stable flies Stomoxys calcitrans (L.) (Diptera: Muscidae), representing a specialist (blood) feeder. The prevalence of flies carrying cefotaxime-resistant (CTX-R) bacteria in whole bodies and dissected guts were assayed by culturing on antibiotic-selective media, with distinct colonies identified by Sanger sequencing. Of the 149 flies processed, including 81 house flies and 68 stable flies, 18 isolates of 12 unique bacterial species resistant to high-level cefotaxime were recovered. These isolates also showed resistance to multiple classes of antibiotics. The CTX-R isolates were predominantly recovered from female flies, which bore at least two resistant bacterial species. The majority of resistant bacteria were isolated from the guts encompassing both enteric pathogens and commensals, sharing no overlap between the two fly species. Together, we conclude that house flies and stable flies in the field could harbor multidrug-resistant bacteria. The fly gut may serve as a reservoir for the acquisition and dissemination of resistance genes.

The Insecticide Resistance Allele kdr-his has a Fitness Cost in the Absence of Insecticide Exposure

House flies, Musca domestica L. (Diptera: Muscidae), are major pests at animal production facilities. Insecticides, particularly pyrethroids, have been used for control of house fly populations for more than 30 yr, but the evolution of resistance will likely jeopardize fly control efforts. A major mechanism of pyrethroid resistance in the house fly is target site insensitivity (due to mutations in the Voltage-sensitive sodium channel [Vssc]). Based on a survey of house fly populations in 2007 and 2008, the most common resistance allele at 2/3 of the states in the United States is kdr-his. This was unexpected given the relatively lower level of resistance this allele confers, and led to speculation that the kdr-his allele may have a minimal fitness cost in the absence of insecticide. The goal of this study was to evaluate the fitness cost of kdr-his by monitoring the changes in allele frequency over 15 generations in the absence of insecticide. In crosses with two different insecticide susceptible strains, we found that kdr-his had a significant fitness cost. The implications of these results to insecticide resistance monitoring and management are discussed.

A Robust Framework for Microbial Archaeology

Microbial archaeology is flourishing in the era of high-throughput sequencing, revealing the agents behind devastating historical plagues, identifying the cryptic movements of pathogens in prehistory, and reconstructing the ancestral microbiota of humans. Here, we introduce the fundamental concepts and theoretical framework of the discipline, then discuss applied methodologies for pathogen identification and microbiome characterization from archaeological samples. We give special attention to the process of identifying, validating, and authenticating ancient microbes using high-throughput DNA sequencing data. Finally, we outline standards and precautions to guide future research in the field.

Survival of the House Fly (Diptera: Muscidae) on Truvia and Other Sweeteners

The house fly, Musca domestica L. (Diptera: Muscidae), is a disease vector of mechanically transmitted pathogens including bacteria, viruses, and protozoans. Opportunities for pathogen transmission can increase as fly longevity increases. Dietary preferences play an important role in insect longevity; therefore, we investigated house fly preferences, sucrose availability, and caloric constraints on house fly longevity. Experimental goals were: 1) to test the effects of calorie restriction on survival of house flies by manipulating concentrations of erythritol (low caloric content) and sucrose (high caloric content), and comparing commercial sweeteners of differing calorie content, 2) to identify house fly preferences for either erythritol or sucrose, and 3) to evaluate the insecticidal activity or toxicity of erythritol on house flies. Our data show that house flies may prefer high calorie options when given a choice and that house fly longevity likely increases as calorie content increases. Additionally, no significant differences in longevity were observed between the water only control (zero calories) and erythritol treatments. This suggests that decreased survival rates and death could be the result of starvation rather than insecticidal activity. This research furthers our understanding of house fly survival and sugar-feeding behavior.

Dose-dependent fate of GFP-expressing Escherichia coli in the alimentary canal of adult house flies

The adult house fly Musca domestica (L.) (Diptera: Muscidae) can disseminate bacteria from microbe-rich substrates to areas in which humans and domesticated animals reside. Because bacterial abundance fluctuates widely across substrates, flies encounter and ingest varying amounts of bacteria. This study investigated the dose-dependent survival of bacteria in house flies. Flies were fed four different 'doses' of green fluorescent protein (GFP)-expressing Escherichia coli (GFP E. coli) (very low, low, medium, high) and survival was determined at 1, 4, 10 and 22 h post-ingestion by culture and epifluorescent microscopy. Over 22 h, the decline in GFP E. coli was significant in all treatments (P < 0.04) except the very low dose treatment (P = 0.235). Change in survival (ΔS) did not differ between flies fed low and very low doses of bacteria across all time-points, although ΔS in both treatments differed from that in flies fed high and medium doses of bacteria at several time-points. At 4, 10 and 22 h, GFP E. coli ΔS significantly differed between medium and high dose-fed flies. A threshold dose, above which bacteria are detected and destroyed by house flies, may exist and is likely to be immune-mediated. Understanding dose-dependent bacterial survival in flies can help in predicting bacteria transmission potential.

Fecal sacs attract insects to the nest and provoke an activation of the immune system of nestlings

Background

Nest sanitation is a widespread but rarely studied behavior in birds. The most common form of nest sanitation behavior, the removal of nestling feces, has focused the discussion about which selective pressures determine this behavior. The parasitism hypothesis, which states that nestling fecal sacs attract parasites that negatively affect breeding birds, was proposed 40 years ago and is frequently cited as a demonstrated fact. But, to our knowledge, there is no previous experimental test of this hypothesis.

Results

We carried out three different experiments to investigate the parasitism hypothesis. First, we used commercial McPhail traps to test for the potential attraction effect of nestling feces alone on flying insects. We found that traps with fecal sacs attracted significantly more flies (Order Diptera), but not ectoparasites, than the two control situations. Second, we used artificial blackbird (Turdus merula) nests to investigate the combined attraction effect of feces and nest materials on arthropods (not only flying insects). Flies, again, were the only group of arthropods significantly attracted by fecal sacs. We did not detect an effect on ectoparasites. Third, we used active blackbird nests to investigate the potential effect of nestling feces in ecto- and endoparasite loads in real nestlings. The presence of fecal sacs near blackbird nestlings did not increase the number of louse flies or chewing lice, and unexpectedly reduced the number of nests infested with mites. The endoparasite prevalence was also not affected. In contrast, feces provoked an activation of the immune system as the H/L ratio of nestlings living near excrements was significantly higher than those kept under the two control treatments.

Conclusions

Surprisingly, our findings do not support the parasitism hypothesis, which suggests that parasites are not the main reason for fecal sac removal. In contrast, the attraction of flies to nestling feces, the elevation of the immune response of chicks, and the recently described antimicrobial function of the mucous covering of fecal sacs suggest that microorganisms could be responsible of this important form of parental care behavior (microbial hypothesis).

Long-term persistence of Yersinia pseudotuberculosis in entomopathogenic nematodes

Entomopathogenic nematodes (EPNs) are small worms whose ecological behaviour consists to invade, kill insects and feed on their cadavers thanks to a species-specific symbiotic bacterium belonging to any of the genera Xenorhabdus or Photorhabdus hosted in the gastro-intestinal tract of EPNs. The symbiont provides a number of biological functions that are essential for its EPN host including the production of entomotoxins, of enzymes able to degrade the insect constitutive macromolecules and of antimicrobial compounds able to prevent the growth of competitors in the insect cadaver. The question addressed in this study was to investigate whether a mammalian pathogen taxonomically related to Xenorhabdus was able to substitute for or "hijack" the symbiotic relationship associating Xenorhabdus and Steinernema EPNs. To deal with this question, a laboratory experimental model was developed consisting in Galleria mellonella insect larvae, Steinernema EPNs with or without their natural Xenorhabdus symbiont and Yersinia pseudotuberculosis brought artificially either in the gut of EPNs or in the haemocoel of the insect larva prior to infection. The developed model demonstrated the capacity of EPNs to act as an efficient reservoir ensuring exponential multiplication, maintenance and dissemination of Y. pseudotuberculosis.

Temporospatial fate of bacteria and immune effector expression in house flies fed GFP-Escherichia coli O157:H7

The house fly Musca domestica L. (Diptera: Muscidae) harbours and transmits a variety of human enteropathogens including Escherichia coli (Enterobacteriales: Enterobacteriaceae) O157:H7. Interactions between ingested bacteria and the fly gut directly impact bacterial persistence, survival and ultimately fly vector competence. We assessed the temporospatial fate of green fluorescent protein (GFP)-expressing E. coli O157:H7 (GFP-ECO157) in house flies along with fly antimicrobial responses up to 12 h post-ingestion. In flies fed GFP-ECO157, culture and microscopy revealed a steady decrease in bacterial load over 12 h, which is likely to be attributable to the combined effects of immobilization within the peritrophic matrix, lysis and peristaltic excretion. However, flies can putatively transmit this pathogen in excreta because intact bacteria were observed in the crop and rectum. Quantitative reverse-transcriptase polymerase chain reaction analysis of antimicrobial peptides (AMPs) and lysozyme gene expression showed minimal upregulation in both the gut and carcass of house flies fed GFP-ECO157. However, these genes were upregulated in fly heads and salivary glands, and effector proteins were detected in the gut in some flies. Collectively, these data indicate that house flies can serve as reservoirs of E. coli O157:H7 for up to 12 h, and factors in addition to AMPs and lysozyme may contribute to bacteria destruction in the gut.

Prevalence and relative risk of Cronobacter spp., Salmonella spp., and Listeria monocytogenes associated with the body surfaces and guts of individual filth flies

Although flies are important vectors of food-borne pathogens, there is little information to accurately assess the food-related health risk of the presence of individual flies, especially in urban areas. This study quantifies the prevalence and the relative risk of food-borne pathogens associated with the body surfaces and guts of individual wild flies. One hundred flies were collected from the dumpsters of 10 randomly selected urban restaurants. Flies were identified using taxonomic keys before being individually dissected. Cronobacter spp., Salmonella spp., and Listeria monocytogenes were detected using the PCR-based BAX system Q7. Positive samples were confirmed by culture on specific media and through PCR amplification and sequencing or ribotyping. Among collected flies were the housefly, Musca domestica (47%), the blowflies, Lucilia cuprina (33%) and Lucilia sericata (14%), and others (6%). Cronobacter species were detected in 14% of flies, including C. sakazakii, C. turicensis, and C. universalis, leading to the proposal of flies as a natural reservoir of this food-borne pathogen. Six percent of flies carried Salmonella enterica, including the serovars Poona, Hadar, Schwarzengrund, Senftenberg, and Brackenridge. L. monocytogenes was detected in 3% of flies. Overall, the prevalence of food-borne pathogens was three times greater in the guts than on the body surfaces of the flies. The relative risk of flies carrying any of the three pathogens was associated with the type of pathogen, the body part of the fly, and the ambient temperature. These data enhance the ability to predict the microbiological risk associated with the presence of individual flies in food and food facilities.

Phylogenetic characterization of bacteria in the gut of house flies (Musca domestica L.)

House flies (Musca domestica L.) are cosmopolitan, ubiquitous, synanthropic insects that serve as mechanical or biological vectors for various microorganisms. To fully assess the role of house flies in the epidemiology of human diseases, it is essential to understand the diversity of microbiota harbored by natural fly populations. This study aimed to identify the diversity of house fly gut bacteria by both culture-dependent and culture-independent approaches. A total of 102 bacterial strains were isolated from the gut of 65 house flies collected from various public places including a garden, public park, garbage/dump area, public toilet, hospital, restaurant/canteen, mutton shop/market, and house/human habitation. Molecular phylogenetic analyses placed these isolates into 22 different genera. The majority of bacteria identified were known potential pathogens of the genera Klebsiella, Aeromonas, Shigella, Morganella, Providencia, and Staphylococcus. Culture-independent methods involved the construction of a 16S rRNA gene clone library, and sequence analyses supported culture recovery results. However, additional bacterial taxa not determined via culture recovery were revealed using this methodology and included members of the classes Alphaproteobacteria, Deltaproteobacteria, and the phylum Bacteroidetes. Here, we show that the house fly gut is an environmental reservoir for a vast number of bacterial species, which may have impacts on vector potential and pathogen transmission.

PhoP and OxyR transcriptional regulators contribute to Yersinia pestis virulence and survival within Galleria mellonella

The virulence of Yersinia pestis KIM6+ was compared with multiple isolates of Yersinia pseudotuberculosis and Yersinia enterocolitica toward larvae of the greater wax moth Galleria mellonella. Although Y. pestis and Y. pseudotuberculosis were able to cause lethal infection in G. mellonella, these species appeared less virulent than the majority of Y. enterocolitica strains tested. Y. pestis survived primarily within hemocytes of G. mellonella, and induced a strong antibacterial peptide response that lasted for at least 3 days in surviving larvae. Immunization with dead bacteria to induce an antibacterial response led to increased survival of the larvae following infection. Mutant strains lacking the either phoP or oxyR, which were less resistant to antibacterial peptides and hydrogen peroxide respectively, were attenuated and restoration of the wild-type genes on plasmids restored virulence. Our results indicate that the Y. pseudotuberculosis-Y. pestis lineage is not as virulent toward G. mellonella as are the majority of Y. enterocolitica isolates. Further, we have shown that G. mellonella is a useful infection model for analyzing Y. pestis host-pathogen interactions, and antibacterial peptide resistance mediated by phoP and reactive oxygen defense mediated by oxyR are important for Y. pestis infection of this insect.

Recovery of environmental human DNA by insects

We tested the hypotheses that foraging insects can acquire human DNA from the environment and that insect-delivered human DNA is of sufficient quantity and quality to permit standard forensic analyses. Houseflies, German cockroaches, and camel crickets were exposed to dusty surfaces and then assayed for human mitochondrial and nuclear loci by conventional and qPCR, and multiplex STR amplification. Over two experiments, 100% of insect groups and 94% of dust controls tested positive for human DNA. Of 177 individuals, 33-67% tested positive and 13 yielded quantifiable human DNA (mean = 0.022 ± 0.006 ng; mean dust control = 2.448 ± 0.960 ng); four had at least one positive allele call for one or more locus; eight others showed multiple peaks at some loci. Results imply that application to routine forensic casework is limited given current detection methodology yet demonstrate the potential use of insects as environmental samplers for human DNA.

Review of the carriage of zoonotic bacteria by arthropods, with special reference to Salmonella in mites, flies and litter beetles

This systematic review considers the relationship between arthropods commonly found in and around livestock premises and zoonotic bacteria. The principal focus is upon insects and arachnids on poultry units, where houses, litter and manure provide good conditions for the growth, multiplication and protection of flies, beetles and mites, and where zoonotic pathogens such as Salmonella and Campylobacter are prevalent. Other members of the Enterobacteriaceae and the taxa Clostridium, Helicobacter, Erysipelas and Chlamydiaceae are also discussed. Salmonella is widely distributed in the flies of affected livestock units and is detectable to a lesser degree in beetles and mites. Persistent carriage appears to be common and there is some field and experimental evidence to support arthropod-mediated transmission between poultry flocks, particularly carry-over from one flock to the next. Campylobacter may readily be isolated from arthropods in contact with affected poultry flocks, although carriage is short-lived. There appears to be a role for flies, at least, in the breaching of biosecurity around Campylobacter-negative flocks. The carriage of other zoonotic bacteria by arthropods has been documented, but the duration and significance of such associations remain uncertain in the context of livestock production.

The housefly, Musca domestica, as a possible mechanical vector of Newcastle disease virus in the laboratory and field

Newcastle disease (Paramyxoviridae) is a highly infectious virus shed in the faeces of infected birds. Non-biting Muscid flies characteristically visit manure and decaying organic material to feed and oviposit, and may contribute to disease transmission. The housefly, Musca domestica (Linnaeus, 1758) (Diptera: Muscidae), has been implicated as a mechanical vector of numerous pathogens. In this study 2000 aerial net-captured houseflies were examined for their ability to harbour Newcastle disease virus (NDV). In an adjacent study, laboratory-reared flies were experimentally exposed to NDV La Sota strain. The virus was detected in the dissected gastrointestinal tract of laboratory-exposed flies for up to 72 h post-exposure, whereas the untreated control flies were negative.

Horizontal transfer of the tetracycline resistance gene tetM mediated by pCF10 among Enterococcus faecalis in the house fly (Musca domestica L.) alimentary canal

The house fly (Musca domestica L.) alimentary canal was evaluated for the potential of horizontal transfer of tetM on plasmid pCF10 among Enterococcus faecalis. Two sets of experiments were conducted: (1) house flies without surface sterilization and (2) surface-sterilized flies. Both sets of flies were exposed to E. faecalis OG1RF:pCF10 as donor for 12 h and then E. faecalis OG1SSp as recipient for 1 h. Another group of flies received the recipient first for 12 h followed by exposure to the donor strain for 1 h. House flies were screened daily to determine the donor, recipient, and transconjugant bacterial load for up to 5 days. In addition, the sponge-like mouth parts used for food uptake (labellum) of surface-sterilized house flies were removed and analyzed for donors, recipients, and transconjugants, separately. In both groups of flies (n = 90 flies/group), transfer occurred within 24 h after exposure with a transconjugant/donor rate from 8.6 x 10(-5) to 4.5 x 10(1). Transconjugants were also isolated from the house fly labellum. Our data suggest that the house fly digestive tract provides a suitable environment for horizontal transfer of conjugative plasmids and antibiotic resistance genes among enterococci. Our results emphasize the importance of this insect as a potential vector of antibiotic-resistant bacterial strains.

Evaluation of metaflumizone granular fly bait for management of houseflies

The housefly, Musca domestica L. (Diptera: Muscidae), is a pest of great veterinary and public health importance. In this study, the efficacy of metaflumizone granular fly bait was assessed on first generation (F1) housefly adults raised from flies collected at a cattle feedlot in Kansas. All bioassays were conducted as choice tests, with flies having ad libitum access to water, granular sugar and bait. A commercial methomyl-based bait (Golden Malrin) was used as positive control; no bait (water and granular sugar only) was used as negative control. Fly mortality was recorded on days 2, 7 and 14. The metaflumizone bait was significantly more slow-acting than the methomyl bait (mortality rates after 2 days of exposure were 49.9% and 57.9%, respectively). However, there were no significant differences in cumulative mortality later in the bioassays. Cumulative mortality rates on days 7 and 14 were 96.1% (metaflumizone), 91.4% (methomyl) and 99.0% (metaflumizone), 97.6% (methomyl), respectively. Our results demonstrate that the metaflumizone granular fly bait may be an effective modality for incorporation into management programmes for houseflies in and around livestock production facilities as well as in residential settings.

Competence of the housefly, Musca domestica, as a vector of Microsporum canis under experimental conditions

The role of Musca domestica Linnaeus as a vector of the dermatophyte Microsporum canis was investigated under experimental laboratory conditions. About 400 4-day-old M. domestica flies were divided into two groups. Group A consisted of about 200 infected flies and group B comprised about 200 uninfected flies that were used as controls. Each trial was run three times. Flies from group A were fed for 24 h with a solution of ultra-high temperature-treated (UHT) milk containing about 10(6) colony-forming units (CFU) per mL of M. canis (infected milk inoculum [IMI]). The control group (group B) was fed with only UHT milk spiked with a teaspoon of honey. Microsporum canis was detected from faeces, vomitus, external surfaces and internal organs of 20 adult flies, eggs, first-, second- and third-stage (L1, L2, L3) larvae and pupae of each group, as well from 20 adult newly emerged flies (NEFs; from infected generations only). Samples were collected at 2, 4, 6 and 24 h post-infection (p.i.) (i.e. the times at which IMI was available) and on 2, 5, 7 and 8 days p.i. from adult flies, faeces and vomitus. Eggs, L1, L2, L3 and pupae were processed as soon as they appeared. Equivalent samples were taken from group B. All the samples were individually cultured. Microsporum canis was not isolated from the control group, from eggs, larvae, pupae or NEFs, or from faeces and vomitus, although it was detected on the body surface (26.2%) and internal organs (26.9%) of adult flies. The highest positivity for M. canis was detected on flies within the first 6 h p.i. (i.e. 57.2% on the body surface and 71.6% in the internal organs). No M. canis was isolated at 24 h p.i., but it was isolated from the body surface only at 2 and 5 days p.i. The results presented provide evidence that M. domestica transmits M. canis mechanically with its outer body surface for up to 5 days p.i., but does not do so through its vomitus and faeces or transovarially. The role played by M. domestica in the epidemiology of human and animal dermatophytoses is discussed.

Insecticidal properties of several essential oils on the house fly (Musca domestica L.)

The insecticidal activity of 34 essential oils, extracted from plants, was screened against the house fly, Musca domestica L. under laboratory conditions. Essential oils from Pogostemon cablin proved to be the most efficient at a lethal dose of 3 microg/fly after topical application. Eight oils (P. roseum, O. vulgare, O. compactum, M. pulegium, O. basilicum, O. majorana, T. vulgaris and P. graveolens) were lethal in doses ranging from 10 to 20 microg (10, 13, 13, 13, 15, 17, 18 and 19 microg/fly, respectively). The lethal doses of another 13 oils were ascertained in the range 20-50 microg/fly, nine oils had lethal doses of 50-100 microg. For two oils, the lethal dose could not be for the topical application. In the fumigant test, the most efficient proved to be Mentha pulegium oil (4.7 microg/cm(2)). For 10 oils, a lethal dose between 5 and 10 microg/cm(2) was ascertained (T. bipinata, C. aurantifolia, T. occidentalis, T. matschiana, S. officinalis, T. vulgaris, M. quinquenervia, O. compactum, C. limonum and R. officinalis, respectively). For the other 10 oils a lethal dose from 10 but to 80 microg/cm(2) was ascertained, and for 13 oils the lethal dose was higher than the highest dose in the tests.

Potential of houseflies to contaminate ready-to-eat food with antibiotic-resistant enterococci

It was shown previously that houseflies in fast-food restaurants commonly carry antibiotic-resistant and potentially virulent enterococci. In this study, the potential of field-collected houseflies to contaminate ready-to-eat (RTE) food with enterococci was assessed by laboratory bioassays. Houseflies were collected with a sweep net in a cattle feedlot and exposed in groups of 5, 10, 20, and 40 to a beef patty (from an RTE hamburger) for 0.5, 1.0, 3.0, and 24 h. The exposure of RTE food to flies resulted in 100% contamination with enterococci in all bioassays, regardless of the number of houseflies and the length of exposure time. In addition, with the increasing number of houseflies as well as with the increasing time exposure, the concentration of enterococci in RTE food increased. Even a short time exposure (0.5 h) resulted in food contamination, ranging from 3.1 x 10(3) CFU/g (5 houseflies) to 8.4 x 10(4) CFU/g (40 houseflies). The analysis of 23 randomly selected enterococcal isolates from RTE food after the fly exposure revealed a single species, Enterococcus faecalis. In contrast, four Enterococcus species, including E. faecalis (57.1%), E. gallinarum (19.1%), E. hirae (14.3%), and E. faecium (9.5%), represented 21 randomly selected and identified isolates from houseflies. Phenotypic screening showed that E. faecalis isolates from RTE food were resistant to ciprofloxacin (17.4%), tetracycline (13.0%), erythromycin (13.0%), and chloramphenicol (4.3%). This study demonstrates a great potential of houseflies from a cattle feedlot to contaminate RTE food with enterococci in a short time.

Comparative analysis of the Photorhabdus luminescens and the Yersinia enterocolitica genomes: uncovering candidate genes involved in insect pathogenicity

Background

Photorhabdus luminescens and Yersinia enterocolitica are both enteric bacteria which are associated with insects. P. luminescens lives in symbiosis with soil nematodes and is highly pathogenic towards insects but not to humans. In contrast, Y. enterocolitica is widely found in the environment and mainly known to cause gastroenteritis in men, but has only recently been shown to be also toxic for insects. It is expected that both pathogens share an overlap of genetic determinants that play a role within the insect host.

Results

A selective genome comparison was applied. Proteins belonging to the class of two-component regulatory systems, quorum sensing, universal stress proteins, and c-di-GMP signalling have been analysed. The interorganismic synopsis of selected regulatory systems uncovered common and distinct signalling mechanisms of both pathogens used for perception of signals within the insect host. Particularly, a new class of LuxR-like regulators was identified, which might be involved in detecting insect-specific molecules. In addition, the genetic overlap unravelled a two-component system that is unique for the genera Photorhabdus and Yersinia and is therefore suggested to play a major role in the pathogen-insect relationship. Our analysis also highlights factors of both pathogens that are expressed at low temperatures as encountered in insects in contrast to higher (body) temperature, providing evidence that temperature is a yet under-investigated environmental signal for bacterial adaptation to various hosts. Common degradative metabolic pathways are described that might be used to explore nutrients within the insect gut or hemolymph, thus enabling the proliferation of P. luminescens and Y. enterocolitica in their invertebrate hosts. A strikingly higher number of genes encoding insecticidal toxins and other virulence factors in P. luminescens compared to Y. enterocolitica correlates with the higher virulence of P. luminescens towards insects, and suggests a putative broader insect host spectrum of this pathogen.

Conclusion

A set of factors shared by the two pathogens was identified including those that are involved in the host infection process, in persistence within the insect, or in host exploitation. Some of them might have been selected during the association with insects and then adapted to pathogenesis in mammalian hosts.

Expression and insecticidal activity of Yersinia pseudotuberculosis and Photorhabdus luminescens toxin complex proteins

Photorhabdus luminescens toxin complex (Tc) has been characterized as a potent three-component insecticidal protein complex. Homologues of genes encoding P. luminescens Tc components have been identified in several other enterobacteria and in Gram-positive bacteria, showing these genes are widespread in bacteria. In particular, tc gene homologues have been identified in Yersinia enterocolitica, Yersinia pseudotuberculosis and Yersinia pestis and may have a role in Y. pestis evolution. Y. enterocolitica tc genes have been shown to be active against Manduca sexta larvae. Here, we demonstrate that expression optimization is essential to obtain bioactive P. luminescens Tc proteins and demonstrate that TcaAB and TcdB + TccC are stand-alone toxins against a M. sexta insect model. Moreover, we report that Y. pseudotuberculosis IP32953 Tc proteins are also toxic to M. sexta larvae but do not cross-potentiate as P. luminescens Tc components.

Plague

Bubonic plague is an often fulminant systemic zoonosis, caused by Yersinia pestis. Conventional microbiology, bacterial population genetics, and genome sequence data, all suggest that Y pestis is a recently evolved clone of the enteric pathogen Yersinia pseudotuberculosis. The genetic basis of this organism's rapid adaptation to its insect vector (the flea) with transmission between mammalian hosts by novel subcutaneous and pneumonic routes of infection is becoming clearer. This transition provides a paradigm for the way in which new pathogens could emerge. Plague in humans is controlled by suppression of rodent reservoir hosts and their fleas and by early detection and treatment of cases of disease. Detection systems for plague in non-endemic regions might now be needed because of a bioterrorism threat. Rapid diagnostic tests are available and a subunit vaccine is in clinical trials.

Ecology of antibiotic resistance genes: characterization of enterococci from houseflies collected in food settings

In this project, enterococci from the digestive tracts of 260 houseflies (Musca domestica L.) collected from five restaurants were characterized. Houseflies frequently (97% of the flies were positive) carried enterococci (mean, 3.1 x 10(3) CFU/fly). Using multiplex PCR, 205 of 355 randomly selected enterococcal isolates were identified and characterized. The majority of these isolates were Enterococcus faecalis (88.2%); in addition, 6.8% were E. faecium, and 4.9% were E. casseliflavus. E. faecalis isolates were phenotypically resistant to tetracycline (66.3%), erythromycin (23.8%), streptomycin (11.6%), ciprofloxacin (9.9%), and kanamycin (8.3%). Tetracycline resistance in E. faecalis was encoded by tet(M) (65.8%), tet(O) (1.7%), and tet(W) (0.8%). The majority (78.3%) of the erythromycin-resistant E. faecalis isolates carried erm(B). The conjugative transposon Tn916 and members of the Tn916/Tn1545 family were detected in 30.2% and 34.6% of the identified isolates, respectively. E. faecalis carried virulence genes, including a gelatinase gene (gelE; 70.7%), an aggregation substance gene (asa1; 33.2%), an enterococcus surface protein gene (esp; 8.8%), and a cytolysin gene (cylA; 8.8%). Phenotypic assays showed that 91.4% of the isolates with the gelE gene were gelatinolytic and that 46.7% of the isolates with the asa1 gene aggregated. All isolates with the cylA gene were hemolytic on human blood. This study showed that houseflies in food-handling and -serving facilities carry antibiotic-resistant and potentially virulent enterococci that have the capacity for horizontal transfer of antibiotic resistance genes to other bacteria.

[Role of Musca domestica in the transmission of multiresistant bacteria in the centres of intensive care setting in sub-Saharan Africa]

OBJECTIVE

The houseflies (Musca domestica -MD) are involved in the transmission of the diseases of the faecal danger in subsaharan Africa. What is their role in the transmission of multiresistant bacteria in an intensive care setting in Dakar?

TYPE OF STUDY

Descriptive, forward-looking.

MATERIALS AND METHODS

The study was conducted from May 1 to September 30, 2003. During this period a flytrap was put above every patient carrier of BMR (methicillin resistant Staphylococcus, extended spectrum beta-lactamases-enterobacteria, ticarcillin resistant Pseudomonas). Caught MD were carried to the microbiology laboratory and incubated in heart-brain broth at 37 degrees C for 18 hours. Then selective gelose platers were used for identification of bacteria. Comparison of antibiotic sensitivities of bacteria isolated from MD and from the patients was made.

RESULTS

Out of 441 hospitalized patients, 26 were colonised or infected by BMR. Human pathogenic microorganisms were obtained from 99 out of 120 flies. Seventeen of those flies were carried of BMR. Six among these 17 flies had BMR with sensitivity profile and phenotype of resistance identical to those of the patients under the trap with birdlime. More 3 MD carried BMR BLSE not found on our patients.

CONCLUSION

This study shows that the MD can carry BMR. Their participation in the crossed transmission, between patients, of multiresistant bacteria in intensive care setting, must be discussed. The eradication of the MD in our Africa subsaharan services must be looked for.

[Three cases of Yersinia pseudotuberculosis gastrointestinal infection having no apparent epidemiological relationship, caused by identical strains]

INTRODUCTION

Gastrointestinal infections caused by Yersinia pseudotuberculosis are uncommon in our country and the epidemiology of the infection is uncertain.

METHODS

We describe three cases of Y. pseudotuberculosis gastrointestinal infection, all detected within one month of time. A possible epidemiological relationship among these cases, as well as the microbial characteristics of the isolates, was investigated. RESULTS. No epidemiological relationships were found among the three cases. Nevertheless, all three isolates were identical according to phenotyping and molecular marker studies.

CONCLUSION

This report discusses the possible source of infection in these cases, with reference to published data from sporadic cases and outbreaks of infection by this microorganism. We suggest that future studies are needed to know the real incidence of Y. pseudotuberculosis in our country.

Resistance status of house flies (Diptera: Muscidae) from southeastern Nebraska beef cattle feedlots to selected insecticides

The status of resistance to three insecticides (permethrin, stirofos, and methoxychlor), relative to a laboratory-susceptible colony, was evaluated in field populations of house flies, Musca domestica L., collected from two beef cattle feedlots in southeastern Nebraska. Topical application and residual exposure to treated glass surfaces were suitable methods for determining the resistance status of house flies to permethrin, stirofos, or methoxychlor. However, in most cases, residual exposure was more sensitive in resistance detection (i.e., higher resistance ratios). The field populations tested were moderately resistant to permethrin (RR = 4.9-fold and RR = 7.3-fold, for topical application and residual exposure, respectively) and extremely resistant to stirofos and methoxychlor (not accurately quantifiable because of low mortality at the highest possible concentrations or doses). Probable explanations for the resistance status of these house fly populations and implications for global feedlot fly management are discussed.

Vector potential of houseflies for the bacterium Aeromonas caviae

Houseflies, Musca domestica Linnaeus (Diptera: Muscidae), have been implicated as vectors or transporters of numerous gastrointestinal pathogens encountered during feeding and ovipositing on faeces. The putative enteropathogen Aeromonas caviae (Proteobacteria: Aeromonadaceae) may be present in faeces of humans and livestock. Recently A. caviae was detected in houseflies by PCR and isolated by culture methods. In this study, we assessed the vector potential of houseflies for A. caviae relative to multiplication and persistence of the bacterium in the fly and to contamination of other flies and food materials. In experimentally fed houseflies, the number of bacteria increased up to 2 days post-ingestion (d PI) and then decreased significantly 3 d PI. A large number of bacteria was detected in the vomitus and faeces of infected flies at 2-3 d PI. The bacteria persisted in flies for up to 8 d PI, but numbers were low. Experimentally infected flies transmitted A. caviae to chicken meat, and transmissibility was directly correlated with exposure time. Flies contaminated the meat for up to 7 d PI; however, a significant decrease in contamination was observed 2-3 d PI. In the fly-to-fly transmission experiments, the transmission of A. caviae was observed and was apparently mediated by flies sharing food. These results support houseflies as potential vectors for A. caviae because the bacterium multiplied, persisted in flies for up to 8 d PI, and could be transmitted to human food items.