Abstract: Invasiveness of alien turtles results from their impact on the functioning of the local ecosystem. It is due to predation on or competing with resident species, but also transfer of new and unknown pathogenic bacteria, viruses, parasites, or fungi. Salmonella is the most often reported microorganism, both in free-living and captive turtles. Zoonotic aspect of Salmonella spp. carriage has led to the definition of RAS (Reptile Associated Salmonellosis) acquired from domestic pet reptiles. Mycobacterium spp., Leptospira spp. and aquatic bacteria are also found in turtles. Additionally, nematode transmissions from invasive turtles to the autochthonic ones have been described. Alien turtles were less affected by parasitic invasion than animals living in a native location, but the infestation of alien parasites in native turtle species was usually more severe. Reports on viral or fungal infections in turtles are scarce. The identified knowledge gaps justify the need for research which will provide basic and systematic data on microbial threats related to alien and invasive turtles present in the natural environment of Poland. It will also give more insight in the scope and the impact of the problem on epidemiology and public health.