## 1 Introduction  
Honey is a natural substance produced by honeybees (_Apis mellifera_ L.). Honeybees collect nectar (floral honey) or secretions of living parts of plants (honeydew honey) [1, 2, 3] and transform them by adding secretions from their own salivary glands [4]. It is a complex aqueous mixture, consisting of more than 200 compounds, mainly carbohydrates. Moreover, it contains small amounts of proteins, aminoacids, phytochemicals, and plant- and bee-derived enzymes such as glucose oxidase and catalase [5, 6]. It is characterized by low water activity (aw = 0.50-0.60), low humidity (<18%), and high acidity (pH 3.4-6.1) [7, 8]. The physicochemical and biological properties of honey depend on its botanical and geographical origin [9, 10, 11].  
For centuries honey has been utilized not only as a food, but also as a medicine and food preservative [12, 13]. Recent studies confirmed its beneficial bioactivity on human health [11; 14; 15]. Antibacterial activity is the most investigated biological property of honey [16; 17] and it is attributed to different factors [2]. Honey is a hostile environment for the survival and growth of different microorganisms, due to its physicochemical properties [8; 12; 18]. Hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) is one of the major antimicrobial factors in honey. It is generated by the bee-derived enzyme glucose oxidase (GOX) or via an alternative non-enzymatic pathway comprising polyphenic compounds [6; 17; 19]. The presence of various phytochemical compounds is also important for the direct antimicrobial potential of honey [20]. Other components responsible for the antibacterial activity exerted by honey are the peptide bee defensin-1 [11; 16], methylglyoxal (MGO), which is the main antimicrobial substance of manuka honey [14; 21], and other unknown components [22].  
Despite the various antibacterial factors [17], several studies have reported the isolation of microorganisms from honeys produced in diverse geographical locations [4; 7; 12; 18]. Microorganisms in honey might be derived from primary and secondary sources. Primary sources include pollen, flowers, nectar, honeydew secretions [5; 22; 23], the environment (dust, air, soil) [7], as well as the honeybees (gut microbiota) or other insects [24; 25; 26]. Furthermore, microorganisms can be inoculated to honey during its extraction and post-harvest processing [7; 23]. They are often related to hygiene and storage conditions [3; 27]. Usually, they are yeasts, molds, and bacterial species (especially spore-forming) [18; 24; 28].  
Honey microbiome has been suggested as a potential source of antimicrobial compounds [19; 28]. Honey bacterial isolates produce antimicrobial compounds in vitro, but there is no direct evidence of such compounds present in honey [29]. Many secondary metabolites of high pharmaceutical and biotechnological interest are synthesized by nonribosomal peptide synthetases (NRPSs) and polyktetide synthases (PKSs) [30; 31]. These enzymes are large multifunctional complexes organized as modules and are implicated in the biosynthesis of nonribosomal peptides (NRPs) and polyktetides (PKs) respectively. These two large classes of natural products exert various biological properties, such as antimicrobial, anticancer, and immunosuppressive activity [32; 33].  
The aim of this study was to isolate and characterize bacteria from honeys of diverse botanical origin and locations across Greece, exhibiting antibacterial activity against five important nosocomial and foodborne pathogens. Furthermore, the presence of genes encoding PKSs and NRPSs, that might be implicated in the synthesis of antimicrobial compounds, has been investigated.