Fate of facultative pathogenic microorganisms during and after the flood of the Elbe and Mulde rivers in August 2002

Extreme precipitation in August 2002 led to the flooding of large areas of the rivers Elbe and Mulde in the eastern part of Germany. Furthermore, flooding of villages and towns impacted also the local sewage systems leading to a release of untreated water into the river where high abundances of faecal bacteria might be dangerous. After the retreat of the flood, mud enriched by an unknown degree with facultative pathogenic microorganisms remained. High bacterial cell counts were observed in the cellars of the flooded houses, the playgrounds, and the streets forming a pathogenic reservoir. This is especially important in situations where many persons try to prevent and to repair flood damages. The high cell counts were not observed in open water and in wells implying that the cellars were a special niche for the survival of bacteria. The isolates obtained from media specific for facultative pathogenic bacteria showed a high biodiversity and a surprisingly high degree of multi-resistances against antibiotics. The origin of these resistances was not the river water because isolates from the Elbe river showed much lower multi-resistances than those from the flood water. Therefore, the multi-resistant bacteria are assumed to come from flooded sewage plants or from farms. Our results demand a closer monitoring of the sources of multi-resistant bacteria during future flooding events to protect humans from infections by multi-resistant bacteria.