# Bacterial Contamination of Parcel Vending Machines in Lublin, Poland
## 4 Discussion  
In Poland, PVMs are perceived as an environmentally friendly form of last-mile delivery service, popular due to their high availability. Statistical data clearly show that since the COVID-19 pandemic, PVMs have gained a massive consumer interest that is still growing along with the number of machines located in the country [16]. According to the current data, Lublin, the city studied here, is divided into 27 districts and has approximately 310,000 inhabitants (306,951 registered residents, 52.9% aged 19-60 y.o. ), making it the eighth largest city in the country [14]. It is also often described as the most important academic, economic, and administrative center in eastern Poland, with vital international transport routes [17]. There are no official data on the numbers of PVMs in the city. According to the websites of the suppliers, there are around 1000 machines from seven companies in Lublin. The high availability of PVMs and their increasing popularity results in the presence of surfaces in public areas that are frequently touched by consumers and thus might play a role in the transmission of microorganisms between people [18]. The number and types of microorganisms present in the environment are influenced by numerous features: the number of people in the environment and their level of activity, the humidity of the environment, the presence of organic matter, the rate of removal of airborne microorganisms suspended in the air, and the type of surface and its orientation (i.e., horizontal or vertical) [19]. According to the data, most Gram-positive bacteria, such as _Enterococcus_ spp., _Staphylococcus aureus_, and _Streptococcus pyogenes_, and Gram-negative bacilli, such as _Acinetobacter_ spp., _Escherichia coli_, _Klebsiella_ spp., _Pseudomonas aeruginosa_, _Serratia marcescens_, and _Shigella_ spp., can survive on surfaces for many months, while  
Figure 6: The dendrogram was generated with the MALDI Biotyper 3.1. It demonstrates the proteomic relationships between _Bacillus_ strains isolated from parcel vending machines. bacteria such as _Bordetella pertussis_, _Haemophilus influenzae_, _Proteus vulgaris_, and _Vibrio cholerae_ have also been shown to persist on dry surfaces for only a few days [20]. In our study, a total of 140 bacterial isolates were collected from the surfaces of parcel vending machines in the urban area of the eastern Polish city--Lublin. Among 93.6% (131/140) of the isolated bacteria, most of them were opportunistic microbes, with rod-shaped _Bacillus_ spp. (74/140, 52.9%) and _Staphylococcus_ spp. (15/140, 10.7%) being the most common. These findings are consistent with those of other studies. [PERSON] et al. [6] found that endospore-forming bacilli and staphylococci were the most prevalent on both the internal (32.4% and 25.5%, respectively) and external (24.4% and 30.7%, respectively) surfaces of ATMs. Bacilli are common airborne bacteria that can settle freely on various usable surfaces in public areas thanks to sedimentation, and as environmental contaminants, they do not usually pose a threat to human health. These bacteria can also produce endospores, which allows them to survive in unfavorable conditions for long periods of time. Their spores are more resistant to disinfectants or detergents than the other groups of bacteria. _B. cereus_ and _B. thuringiensis_ are among the most studied pathogenic bacteria of the genus _Bacillus_. They are known to cause food poisoning, localized infections such as eye and ear infections, and systemic infections such as meningitis and bacteremia. For example, various food and dairy products, including the staple food rice, have been associated with _B. cereus_ strains [21]. On the other hand, the contact of many users with ATM touch panels implies the presence of a wide variety of staphylococci species derived from the human skin and respiratory microbiota [6]. The touchscreens and posterior surfaces of smartphones owned by healthcare workers were predominantly contaminated with _Bacillus_ spp.