Virulence-associated chromosome locus J, VacJ, an outer membrane lipoprotein elicits protective immunity against Acinetobacter baumannii infection in mice

Abstract

Acinetobacter baumannii is a Gram-negative, strictly aerobic nonmotile bacterium with a DNA G-C content of 39% to 47%. A. baumannii is an important opportunistic nosocomial pathogen that causes pneumonia, bacteremia, urinary tract infections, meningitis, skin, and soft tissue infections. The major concern about A.baumannii is the emergence of resistant strains which necessitates the development of new prevention, control, and treatment methods. Recently the bacterial lipoproteins have attracted the attention of the researchers for the induction of protective immunity against infectious diseases. VacJ is a highly conserved outer membrane lipoprotein that exists in many A. baumannii strains that deserves research on its immunogenicity. The gene encoding mature vacJ of A. baumannii ATCC19606 was cloned and over-expressed in Escherichia coli as a fusion protein. The recombinant VacJ (rVacJ) was purified. 20 and 40 µg of the purified ∼ 31 kDa rVacJ were used for immunization of mice along with Freund’s or Alum adjuvants. Antibody titres raised against the recombinant protein were determined by indirect ELISA. Whole A.baumannii cell was detected at 1:200 serum dilution. Bacterial challenges of mice groups with varying doses of A. baumannii were performed in the active, passive, and intranasal forms. The bacterial load in the mice lungs was determined in both control and immunized groups. A high antibody titre was noted as a result of immunization with rVacJ. The rVacJ-Freund’s adjuvant elicited a higher antibody level compared to the rVacJ-Alum adjuvant. The mice groups challenged intraperitoneally with live A. baumannii did not survive while the intranasally challenged group exhibited a significant reduction of 600 fold of the bacterial load in the lungs. The findings are of significant value in the development of novel adjuvanted vaccines and precise routes of administrations in combat against the notorious multidrug-resistant A.bauamnnii .