Analysis of the virulence and genetic differences among endemic Acinetobacter baumannii clones

Objective ST191, ST195, and ST208 of the Acinetobacter baumannii strains are prevalent carbapenem resistance clones found in China and abroad. This study aimed to compare the virulence levels of ST191, ST195, and ST208 and then investigate the differences in virulence factors among these prevalent clones.Methods A total of 233 Acinetobacter baumannii strains typed as ST191, ST195, and ST208 were collected from the Fifth Medical Center of the Chinese People’s Liberation Army (PLA) General Hospital (North Campus). The virulence levels of ST191, ST195, and ST208 were evaluated using the Galleria mellonella infection survival test and then compared whether there were any differences in their virulence factors using the Virulence Factor Database (VFDB).Results A total of 38 ST191, 104 ST195, and 91 ST208 strains of Acinetobacter baumannii were collected in this study. The average mortality rate of ST191 in the survival test of Galleria mellonella infection was 23%, and 0 strains had 100% mortality rate; the average mortality rate of ST195 was 53%, and 13 strains had 100% mortality rate; and the average mortality rate of ST208 was 47%, and 4 strains had 100% mortality rate, and the mortality rate of ST191 differed from that of ST195 (P<0.0001) and ST208 (P< 0.0001). The mortality differences were statistically significant. The virulence factor database comparison showed that ST191 was significantly different from ST195 (P<0.0001) and ST208 (P<0.0001) in 12 virulence factors related to the type VI secretion system. Twelve virulence factors above ST195 were present at a rate of 99%; the present rates at ST208 are 92.3%, 91.2%, 93.4%, 93.4%, 91.2%, 82.4%, 91.2%, 91.2%, 94.5%, 93.4%, and 93.4%; at ST191 they are 0.Conclusion The virulence of Acinetobacter baumannii was related to the strain's sequence type, and ST191 has a lower virulence than ST195 and ST208 and does not contain a complete type VI secretion system.