Characterization of surface antigen protein 1 (SurA1) from Acinetobacter baumannii and its role in virulence and fitness

•The surface antigen protein 1 (SurA1) gene of A. baumannii was identified, cloned and expressed.•The cytotoxic effect of recombinant SurA1 was tested on two cell lines.•SurA1 knock-out strain exhibited a lower killing activity in Galleria mellonella.•SurA1 knock-out strain showed obvious defect on fitness and growth.

Acinetobacter baumannii is a Gram-negative bacillus that causes nosocomial infections, such as bacteremia, pneumonia, and meningitis and urinary tract and wound infections. In the present study, the surface antigen protein 1 (SurA1) gene of A. baumannii strain CCGGD201101 was identified, cloned and expressed, and then its roles in fitness and virulence were investigated. Virulence was observed in the human lung cancer cell lines A549 and HEp-2 at one week after treatment with recombinant SurA1. One isogenic SurA1 knock-out strain, GR0015, which was derived from the A. baumannii strain CCGGD201101 isolated from diseased chicks in a previous study, highlighted the effect of SurA1 on fitness and growth. Its growth rate in LB broth and killing activity in human sera were significantly decreased compared with strain CCGGD201101. In the Galleria mellonella insect model, the isogenic SurA1 knock-out strain exhibited a lower survival rate and decreased dissemination. These results suggest that SurA1 plays an important role in the fitness and virulence of A. baumannii.