A method of producing a vaccine against multi-drug resistant (MDR) Acinetobacter baumannii comprises the step of isolating a whole cell material of inactivated antibiotic-exposed A. baumannii cultured in presence of an antibiotic at early logarithmic (log) phase of bacterial growth, inactivating the bacteria with chemical and heat at late log phase of bacterial growth and mixing the isolated whole cell material with a preservative. The antibiotic in the culture medium is at an effective concentration hindering the growth of the A. baumannii without substantially killing the A. baumannii and enhances expression of A. baumannii proteins conferring resistance to the antibiotics and virulence. Preferably, imipenem is used.