Henry Youn, Canal-Domènech Berta, González Jaime, La Mendola Christine, Kawecki Tadeusz J
Department of Ecology and Evolution, UNIL - University of Lausanne, Lausanne, Switzerland.
Microbiol Spectr. 2025 Sep 2;13(9):e0306524. doi: 10.1128/spectrum.03065-24. Epub 2025 Aug 12.
In the last 20 years, (Pe) has emerged as a model to explore insect immunity to bacterial intestinal pathogens. Laboratory studies have characterized multiple detrimental effects of Pe on . However, these effects require that the bacteria are ingested in extremely high concentrations of 10-10 CFU per mL (OD 20-200), questioning the relevance of this pathogen in nature. Here, we tested whether the need for such high doses may be due to protective effects of the antifungal agent methylparaben (Nipagin), a standard ingredient of laboratory diets. While significant mortality of flies fed diet containing methylparaben required pathogen concentrations of >10 CFU per mL, we could induce mortality with 500,000-fold lower dose when methylparaben was absent. Here, even this small infection dose (10 CFU per mL) led to high bacterial loads (10 CFU per fly) after several days, indicating the ability of Pe to grow and overcome the flies' defenses in the absence of methylparaben. Consistent with these results, we show strong bactericidal properties of methylparaben on Pe . We also demonstrate that, in the absence of methylparaben, infected flies can easily transmit the pathogen to other adults and to offspring, resulting in high mortality and thus highlighting the potential of Pe as a pathogen of in nature. For those reasons, careful consideration should be given to food additives used in standard diets in laboratory research on host-pathogen interactions.IMPORTANCEAccurate characterization of pathogen infections requires appropriate experimental methodologies. Infections of insects with Pe are frequently studied using fruit flies as a model organism, with laboratory cultures typically maintained on artificial media containing various food preservatives. In this study, we show that one commonly used preservative, methylparaben, significantly influences the outcome of oral infections with Pe. We found that minimal infection doses, far below the standards of the field, could still be lethal to flies raised on media without methylparaben. This increased virulence was also associated with increased transmission of the pathogen, both from infected adult flies to their offspring and to uninfected adults. Our findings show how subtle variations in experimental conditions can profoundly affect how we perceive pathogenic threats.
在过去20年里，奇异变形杆菌（Pe）已成为探索昆虫对肠道细菌病原体免疫的模型。实验室研究已明确了Pe对……的多种有害影响。然而，这些影响要求细菌以每毫升10¹⁰ - 10¹²CFU（OD 20 - 200）的极高浓度摄入，这使人质疑这种病原体在自然环境中的相关性。在此，我们测试了对如此高剂量的需求是否可能归因于抗真菌剂对羟基苯甲酸甲酯（尼泊金）的保护作用，它是实验室果蝇饲料的标准成分。虽然喂食含对羟基苯甲酸甲酯饲料的果蝇出现显著死亡率时所需的病原体浓度>每毫升10⁴CFU，但在没有对羟基苯甲酸甲酯的情况下，我们能用低500,000倍的剂量诱导死亡率。在此，即使这个小感染剂量（每毫升10³CFU）在几天后也导致了高细菌载量（每只果蝇10⁷CFU），这表明在没有对羟基苯甲酸甲酯的情况下Pe有生长并克服果蝇防御的能力。与这些结果一致，我们展示了对羟基苯甲酸甲酯对Pe的强大杀菌特性。我们还证明，在没有对羟基苯甲酸甲酯的情况下，受感染的果蝇能轻易地将病原体传播给其他成虫和后代，导致高死亡率，从而凸显了Pe在自然环境中作为果蝇病原体的潜力。基于这些原因，在宿主 - 病原体相互作用的实验室研究中，应仔细考虑标准饲料中使用的食品添加剂。
重要性
病原体感染的准确表征需要适当的实验方法。用Pe感染昆虫经常以果蝇作为模式生物进行研究，实验室培养物通常维持在含有各种食品防腐剂的人工培养基上。在本研究中，我们表明一种常用的防腐剂对羟基苯甲酸甲酯会显著影响Pe口服感染的结果。我们发现，远低于野外标准的最小感染剂量，对在没有对羟基苯甲酸甲酯的培养基上饲养的果蝇仍可能是致命的。这种增加的毒力还与病原体传播增加有关，既从受感染的成年果蝇传播到其后代，也传播到未受感染的成虫。我们的研究结果表明实验条件的细微变化会如何深刻地影响我们对致病威胁的认知。
