## 1 Introduction  
Recent losses of managed honeybee colonies and the need to reduce the use of veterinary medicines at the apiary level to reach sustainable beekeeping goals are leading to a growing interest in the development of new strategies for disease prevention and control, under the One Health approach [1]. American Foulbrood (AFB) and European Foulbrood (EFB) are the two major bacterial diseases affecting honeybee brood and present a considerable threat to beekeeping worldwide [2]. These diseases are classified within the OIE--World Organisation for Animal Health list, as having a socioeconomic impact in the international trade of bees and bee products [3, 4]. AFB, considered the most serious and widespread brood infection, is caused by the spore forming, Gram-positive bacterium _Paenibacillus larvae_[5, 6]. Young larvae are infected through ingestion of food contaminated by the extremely resilient endospores of the bacterium. The infection is transmitted through the resistant spores, which contaminate bees and hive equipment and remain viable for decades. AFB is highly contagious and destructive, often causing colony death if left untreated. As a result, in most countries AFB is a notifiable disease, must be reported to the relevant government authorities [6] and is included in the new EU Animal Health Law (Regulation (EU) 2016/429). EFB is caused by the bacterium _Melissococcus plutonius_, although associated with secondary invaders like _Paenibacillus alvei_, _Brevibacillus laterosporus_, _Enterococcus faecalis_ and _Achromobacter euridice_[7]. The causative agent does not form spores, and therefore the disease is considered less problematic than AFB. However, prevalence and severity of EFB are variable in different areas and appear to be influenced by environmental factors such as climatic conditions and food quality [7]. With regard to the distribution in Europe, EFB is the most widespread bacterial brood disease in Great Britain [8], and is of relevant interest in other countries, like Switzerland, where the incidence of the infection has risen consistently since the late 1990s, without a clear cause [9]. On a global scale, several antibiotics and chemotherapies are of interest in apiculture for the treatment of bacterial diseases, including: tetracyclines, streptomycin, sulfonamides, tylosin, erythromycincin, limomycin, chloramphenicol, nitrofurans, bacitracin, and penicillins [10]. Prophylactic treatment with oxytetracycline and tylosin is limited to some countries (e.g., USA, Canada, Argentina, Australia) and generally only in cases of initial stage disease [7; 10]. In the European Union, antibiotics for honey bees are not registered [6], and their use is admitted through the 'cascade' system, as described in Article 11 of Directive, 2001/82/EC, as amended by Directive 2004/28/EC and Regulation (EU) 2019/6 of the European Parliament and of the Council of 11 December 2018 on veterinary medicinal products and repealing Directive 2001/82/EC [10]. In many cases antibiotics have been used continuously and excessively or even illegally [11]. Several problems may be associated with the routine use of antibiotics: it has little impact on the epidemiology and control of bacterial diseases as they are not effective in destroying _Paenibacillus larvae_ spores or in eliminate the reservoir of _Melissococcus plutonius_ cells persisting in beehives. Moreover, their administration, especially for AFB, can only mitigate the disease by suppressing clinical signs and beekeepers may spread the infection between colonies [6; 12]. Furthermore, it has been observed that the use of antibiotics may affect the longevity of the bees and the vitality of the brood [13] as well as cause disequilibria in the normal microbiota of the beehive [14]. Another relevant issue related to the use of antibiotics is the development of resistant strains of the pathogenic bacteria. In particular OTC and sulfathiazole-resistance in _P. larvae_ has become widespread as a consequence of decade-long misuse [11; 15; 16; 17; 18].