OBJECTIVE To evaluate the immunoprotection effect of a novel inactivated whole cell vaccine against Acinetobacter baumannii based on ultrasonic microbubble physical damage technique (IWC) and explore its potential of clinical transformation.

METHODS Totally 48 C57BL/6 mice were randomly assigned to divide into three groups and receive the nasal inoculation of corresponding preparations, the IWC group and the paraformaldehyde inactivated vaccine group were inoculated with 20 μl of 1×10⁷ CFU vaccine, the control group was treated with 20 μl phosphate buffered salt solution. The infection models were established 7 days after intraperitoneal injection of a lethal dose of A. baumannii. The 7-day mortality rates of the mice were statistically analyzed after toxin attack. The counts of colonized bacterial colonies on lung and spleen tissues were determined by plate count method after toxin attack for 24 hours. The levels of inflammatory factors interleukin (IL)-6, tumor necrosis factor α(TNF-α) and IL-1β in the lung tissues were detected by enzyme-linked immunosorbent assay (ELISA), and the pathological damage was observed.

RESULTS The survival rate of the IWC group was higher than that of the control group, and the counts of colonized bacterial colonies on lung and spleen tissues were less in the IWC group than those in the control group (P < 0.05). As compared the paraformaldehyde inactivated vaccine group, the survival rate of the IWC group increased by 10.00%, and the counts of colonized bacterial colonies on the lung tissues were slightly less in the IWC group than those in the paraformaldehyde inactivated vaccine group (P < 0.05), and the counts of colonized bacterial colonies on spleens were basically the same. The levels of lung tissue inflammatory factors of the IWC group were lower than those of the other two groups (P < 0.05). The pathological damage was alleviated, and the IWC group was superior to the control group in the integrity of alveolar structure.

CONCLUSIONS IWC can maintain the immunogenicity of pathogens through physical damage technique, effectively activate the immune response of the hose, and reduce the bacterial load and inflammatory injury, showing better immunoprotection effect than the traditional chemical inactivation method. The study has provided experimental bases for development of novel, specific, safe and highly efficient vaccine as well as new ideas and strategies for clinical prevention and treatment of A. baumannii infection.