Exceptional desiccation tolerance of Acinetobacter radioresistens

The taxonomy of the genus Acinetobacter, which includes several important nosocomial pathogens, has been confused due to a lack of discriminatory phenotypic characteristics for identification. Molecular methods such as amplified ribosomal DNA restriction analysis (ARDRA) now enable the accurate identification of species. Ten clinical isolates of Acinetobacter radioresistens had genospecies confirmed by ARDRA but the APJ 20NE system, commonly used in clinical microbiology laboratories, mis-identified them as Acinetobacter lwoffii. Desiccation resistance of Acinetobacter spp. is an important attribute for their survival in the clinical environment. We investigated the ability of A. radioresistens to survive desiccation using an established glass surface model and compared the results to A. lwoffii and Acinetobacter baumannii. The 10 strains of A. radioresistens were extremely resistant to desiccation and survived for an average of 157 days at 31% relative humidity (RH). In contrast, two strains of A. lwoffii and three strains of A. baumannii survived for an average of three and 20 days respectively, at 31% RH, which was used as an approximation to climatic conditions in UK hospitals. A. radioresistens is thus well adapted for survival in the hospital environment and carriage on human skin and yet it is reported less frequently than A. lwoffii amongst clinical isolates. Cases of A. radioresistens infection may be under-reported due to mis-identification as A. lwoffii and further studies that use molecular identification methods are required to elucidate the role of A. radioresistens in human disease.