Dynamics of the microbial community during growth of the house dust mite Dermatophagoides farinae in culture.

The variation in house dust mite microbial communities is important because various microorganisms modulate the production of allergens by their mite hosts and/or contaminate immunotherapeutic extracts. Temporal changes in mite microbiomes and the mite culture environment occurring at different stages of mite culture development are particularly understudied in this system. Here, we analyzed the dynamics of microbial communities during the culture growth of Dermatophagoides farinae. Changes in microbiomes were related to three key variables: the mite population density, microbial microcosm respiration and concentration of guanine (the mite nitrogenous waste metabolite). Mite populations exhibited the following phases: exponential growth, plateau and exponential decline. The intracellular bacterium Cardinium and the yeast Saccharomyces cerevisiae prevailed in the internal mite microbiomes, and the bacterium Lactobacillus fermentum was prevalent in the mite diet. The reduction in the mite population size during the late phases of culture development was related to the changes in their microbial profiles: the intracellular bacterium Cardinium was replaced by Staphylococcus, Oceanobacillus and Virgibacillus, and S. cerevisiae was replaced by the antagonistic fungi Aspergillus penicillioides and Candida. Increases in the guanine content were positively correlated with increases in the Staphylococcus and A. penicillioides profiles in the culture environment. Our results show that the mite microbiome exhibits strong, dynamic alterations in its profiles across different mite culture growth stages.

Function of heat shock protein 70 in the thermal stress response of Dermatophagoides farinae and establishment of an RNA interference method.

Dermatophagoides farinae are an important mite species that cause stored product deterioration and allergic diseases. They widely breed in human habitats because of their strong tolerance to extreme external temperatures. However, mechanisms underlying the stress response and tolerance of D. farinae are unclear. We hypothesized that heat shock protein 70 plays an important role in the heat stress response of D. farinae. In this study, we determined the survival rates of D. farinae at high temperatures (37 °C-45 °C) by performing temperature-gradient experiments in vitro and assessed the expression level of HSP70 by performing RT-qPCR. First, we confirmed that HSP70 regulated the heat stress response of D. farinae, with maximum heat stress regulation observed at 41 °C. Next, we confirmed the presence of a Dicer enzyme-mediated RNA interference (RNAi) pathway in D. farinae by searching the NCBI database and a Dicer site prediction website. Finally, we performed RNAi in D. farinae by using an immersion method with screened dsHSP70 fragments. Moreover, we performed concentration-gradient experiments to determine that 600 ng/µl was the minimal effective concentration of dsHSP70 for silencing HSP70. These results confirm that HSP70 regulates the heat stress response of D. farinae. The present study is the first to report the use of the non-invasive and highly sensitive immersion method for performing RNAi in D. farinae. The results of the present study provide a technical foundation for performing functional gene research and for developing molecular prevention and control strategies against medically important mites.

Reproductive biology of Euroglyphus maynei with comparisons to Dermatophagoides farinae and D. pteronyssinus.

The reproductive biology of the house dust mite, Euroglyphus maynei, is not well studied. This mite is usually less common in homes than Dermatophagoides farinae and D. pteronyssinus. When it is present, it usually co-inhabits with the Dermatophagoides spp. and is more restricted in geographical distribution. In this study, the duration of the life cycle (egg to adult) at 23 and 30 °C at 75% relative humidity (RH) and fecundity at 23 °C and 75% RH were determined for E. maynei and the data were compared to similar data for D. farinae and D. pteronyssinus. Adults hatched from eggs after 28 days at 23 °C and 20 days at 30 °C. Females produced 1.4 eggs/day during a reproductive period of 24 days at 23 °C. Euroglyphus maynei has a shorter life cycle than D. farinae and D. pteronyssinus at 23 °C but a longer life cycle at 30 °C. Euroglyphus maynei has a shorter reproductive period and produces fewer eggs than both D. farinae and D. pteronyssinus.

Diet influences growth rates and allergen and endotoxin contents of cultured Dermatophagoides farinae and Dermatophagoides pteronyssinus house dust mites.

BACKGROUND: The house dust mites Dermatophagoides farinae and Dermatophagoides pteronyssinus are cultured to obtain material for the production of allergen extracts for research, diagnostic and immunotherapeutic purposes. METHODS: We cultured mites on two different diets that supported thriving populations and determined the population growth rates, dynamics of allergen accumulation, and endotoxin concentrations in extracts made from mites harvested from the cultures. RESULTS: D. farinae populations grew faster on a diet of rodent chow/yeast than on an egg/yeast diet but a larger peak population size was achieved on the egg/yeast diet. Diet influenced the dynamics of the production of groups 1 and 2 allergens and the group 1/2 ratios for both species. To population peak, Der f 1 was produced at a faster rate on the chow/yeast diet but greater amounts of Der f 1 were produced by mites grown on the egg/yeast diet. D. pteronyssinus populations grew faster and achieved greater density on the egg/yeast diet compared to the chow/yeast diet. D. pteronyssinus produced more Der p 1 than Der p 2 when grown on chow/yeast while more Der p 2 than Der p 1 was produced on egg/yeast. Endotoxin concentrations in extracts made from whole cultures for both species at maximum population density were very different in the two diets. Washing the mites resulted in the loss of up to 88% of the allergen. CONCLUSION: Mite-culturing diet directly effects population growth, the dynamics of allergen accumulation, the group 1/2 allergen ratio and the endotoxin contents in extracts of cultured house dust mites.

Seasonal dynamics of house dust mites in dust samples collected from sleeping places in north-western Poland.

The most common families of mites found in house dust are Pyroglyphidae, Glycyphagidae and Acaridae; all are a source of many antigens responsible for allergic diseases. The aim of this study was to examine the seasonal dynamics of allergenic mite populations in dust samples collected from sleeping places in apartments in north-western Poland. The mites were isolated from the dust using a saturated saline floating method. In 132 dust samples we determined: Dermatophagoides farinae, Dermatophagoides pteronyssinus, Euroglyphus maynei, Hirstia sp., Chortoglyphus arcuatus, Lepidoglyphus destructor, Gohieria fusca and Cheyletus sp. The greatest frequency was observed for D. farinae, D. pteronyssinus, Ch. arcuatus and Cheyletus sp., in the fourth quarter and D. farinae in the third quarter. Smaller coefficients of dominance were found for D. pteronyssinus, Ch. arcuatus and Cheyletus sp., and their greatest mean concentrations were found in the first and fourth quarters. Given the division of the year into heating and non-heating seasons, mites D. farinae and D. pteronyssinus achieved the highest mean concentration in the first season, and Cheyletus sp. in the second season. The analysis of the participation of developmental stages showed that the adults of D. farinae were more prevalent than juveniles in the first, second and third quarters, and imago stages of D. pteronyssinus were more numerous in relation to juveniles in the first, third and fourth quarters. The results confirm the high incidence of house dust mites in sleeping places in north-western Poland dwellings; the best conditions for the development of these mites, mainly D. farinae and D. pteronyssinus, occur in the fourth quarter and are the least favourable in the second quarter. In many cases, these results are consistent with data from other parts of Poland collected by various authors.

Effect of insect growth regulators on protein pattern of dermatophagoides farinae and its validity on inducing human alleregens.

Two insect growth regulators, Methorprene and Hydroprene were evaluated as growth hormones on the common house dust mite; Dermatophagoides farinae. The adults and immature stages were treated with 4 concentrations of each regulator as contact and as diet. The data were recorded 30 & 90 days post-exposure. Both compounds significantly suppressed population growth, as compared to > or = 5% acetone controls. Methoprene was more effective than Hydroprene when given in diet by corporation bioassays but, slightly more effective for the 1st 30 days of the contact assays. A second set of contact and diet-incorporation assays was done using a 75% of Methoprene and Hydroprene to determine efficacy on D. farinae population dynamics, at weekly intervals for 13 weeks. The average number of the mites in the untreated control population was increased by more than 10 times than the original ones. On the other hand, the number of treated mites was not significantly increased. This was similar for both the contact and the diet-incorporation bioassays, although the average number of mites/container was significantly higher when the treatment was incorporated in the house dust mite diet than when applied directly as contact. Consequently, the insect growth regulators minimized the allergic efficacy of D. farinae in experimental exposed mice.

Present situation of house dust mites in Dakahlia Governorate, Egypt.

House dust mites are common inhalant allergens, which can precipitate atopic disease episodes. The present study revealed presence of four mites. These are Dermatophagoides farinae, D. pteronyssinus, Acheles gracilis and Ornithonyssus bacoti. Population densities of different live adult mites were investigated in different house habitats. In urban houses, pyroglyphid mites were the predominant in bedrooms and D. farinae was the most abundant. A. gracilis was more abundant in living rooms followed by D. farinae then D. pteronyssinus. A. gracilis was the most prevalent in kitchens. While in rural houses, O. bacoti was the most abundant species followed by pyroglyphid mites. Since Dermatophagoides species and A. gracilis were present in numbers high enough to allow their ecological consideration, their seasonal abundance in urban bed-rooms was investigated and revealed that both D. farinae and D. pteronyssinus have two peaks of abundance, one slightly higher in spring and the second in autumn. A. gracilis has two peaks but the higher occurred in autumn and the second in spring.