Antifungal compounds redirect metabolic pathways in yeasts: metabolites as indicators of modes of action

AIMS

Metabolic pathways, e.g. biosynthesis of ergosterol or carbohydrate metabolism including respiration, are well-known targets of several fungicides. With our study we wanted to prove that metabolite profiles can be used to classify fungicides according to their mode of action and that concentrations of key metabolites are changed even without detectable reduced growth rates.

METHODS AND RESULTS

We exposed the yeasts Candida albicans and Saccharomyces cerevisiae to inhibitors of the electron transport chain and to compounds known to interact with osmotic stress defence pathways. Glycerol and ethanol were chosen as key metabolites of branches of glucose catabolism. Increased glycerol concentrations were observed not only when the osmotic stress response was activated, but also as response to the inhibition of the electron transfer chain, whereas elevated ethanol levels were observed only when the respiratory pathways were blocked.

CONCLUSIONS

The treatment of the yeasts Candida albicans and Saccharomyces cerevisiae with antimycotic compounds led to a redirection of metabolic pathways, which could be followed by the quantification of both the metabolites ethanol and glycerol. Only the combination of both concentration profiles allowed the clear distinction between inhibitors of the respiratory chain and effects on the osmotic stress response pathway. IMPACT OF STUDY: The extension of the number of metabolites to a comprehensive quantitative metabolic profile of compound-treated test organisms can be an additional tool in fungicide research allowing the detection of compounds which act on fungi and, moreover, the elucidation of modes of action.

Sensitivity to bites by the bedbug, Cimex lectularius

Bedbugs are a public health problem and can cause significant economic losses, but little is known about the effects of bites on humans. We reviewed case reports and published papers on bedbug bites to assess the empirical basis of the commonly cited figure that only approximately 80% of the population are sensitive to bedbug bites. We found the sensitivity estimate to be based on only one study carried out 80 years ago. However, this study did not account for the now well-established fact that only repeated exposure to external allergens leads to skin reactions. In our sample, 18 of 19 persons showed a skin reaction after bedbug exposure, but in most cases only after repeated controlled exposure. With repeated exposure, the latency between bite and skin reactions decreased from approximately 10 days to a few seconds. Our results are relevant for the hospitality industry, where apparently increasing infestation rates are likely to lead to an increase in the number of tourists and hotel employees exposed to bedbugs. Medical and public health professionals may expect to see an increase in the prevalence of people with bedbug bite sensitivity. The significance of the delayed reaction time of skin to bites may also have implications in litigation cases where people seek compensation.

Who knows the bed bug? Knowledge of adult bed bug appearance increases with people's age in three counties of Great Britain

The current reemergence of bed bugs in the western world has a multitude of causes. One of them may be low early detection rate of emerging infestations because of a current poor knowledge among the population of what bed bugs look like. In a survey conducted in three counties of the United Kingdom, 10% of 358 individuals recognized the bed bug when presented with a live adult. Older people were more likely to correctly identify the bed bug. If an increasing knowledge of the bed bug appearance facilitates early detection of infestations, the hospitality and travel industry may benefit from educating their staff on the bed bug appearance.

Situation exploitation: higher male mating success when female resistance is reduced by feeding

Optimal male and female mating rates rarely coincide. Males often shift the rate in their favor by either increased signaling and by overcoming female resistance to copulation. The concept of sensory exploitation posits that males produce signals that mimic naturally selected benefits and so deceitfully attract females. However, males also have to overcome female resistance to actual copulation. Males may do so by copulating during situations when the female's ability to resist is decreased because of competing naturally selected demands. Males of the common bedbug, Cimex lectularius, an obligate blood feeder, mate at a rate, and in a manner that is harmful to females. Females have to feed regularly to produce eggs, and during feeding female body volume increases by 300%. Choice trials using unfed and either fed or experimentally enlarged but unfed females showed that the increased postfeeding body volume of females attracted more male mating attempts, strongly reduced female resistance to male mating attempts and resulted in a net increase in female mating rate. Our results, therefore, suggest that males have increased mating success in a situation that females cannot avoid because it is naturally selected. Such "situation exploitation" of low resistance may be a common phenomenon.