Epidemiological insight into bacterial risk associated with flooded areas of city agglomeration (Wrocław, Poland 2024)

In 2024, Poland experienced severe flooding linked to the Genoa low. Flooding can lead to the spread of waterborne diseases and other public health risks, associated with shifts in bacterial communities. This study aimed to characterize the bacterial community in the topsoil layer one week after the floodwaters receded in recreational areas of the Wrocław metropolitan region, Poland. MALDI-TOF mass spectrometry combined with bacteriological culture were used for bacteria identification. Soil samples (n = 66) were collected (September 2024) from 11 locations. At each location samples were collected in triplicates, in both flooded and non-flooded areas. A total of 46 bacterial species were identified, with greater diversity in the flooded topsoil, where 18 unique species (including more potentially pathogenic ones) were observed compared to those found only in non-flooded areas. The bacterial community structure varied across flooded areas, with decreased frequency of Bacillus cereus and Bacillus thuringiensis detection. This finding indicates that after flood disaster recreational zones may pose potential public health risks associated with pathogenic microorganisms. Such areas seem to require prolonged examination due to post-flooded changes in the natural soil composition as well as the presence of post-flooded soil organic matter that may promote growth of selected microorganisms.