Veterans Affairs

Acinetobacter baumannii vaccine

VIR-O subpopulation likely underlies a worrisome cycle present in hospital wards, accounting for the difficulty in eradicating A. baumannii as well as the high virulence of many of these infections. Vaccines based on this subpopulation show promise in creating immunity

Medical & Biotechnology

A highly virulent opaque (VIR-O) population (right) is responsible for causing disease during in vivo pulmonary infection of mice. The avirulent, translucent AV-T is shown at left.

Antibiotic-resistant infections lead to 700,000 deaths per year worldwide and the roles of phenotypically diverse subpopulations of clonal bacteria in the progression of diseases are unclear. Acinetobacter baumannii, a gram-negative bacterium is one such opportunistic pathogen, affecting people with compromised immune systems.  A. baumannii is also notoriously difficult to eradicate in hospital settings and contamination of intensive care wards is a frequent problem. The remarkable ability of A. baumannii to persist in this environment is due to both its intrinsic resistance to commonly used disinfectants and its ability to survive long periods of desiccation.

VA researchers have developed an A. baumannii vaccine from an attenuated or heat-killed form of A baumannii. The researchers identified a high-frequency phenotypic switch in multidrug-resistant A. baumannii. Phenotypic switching is a type of switch that occurs between multiple cellular morphologies. As a result, two different phenotypic subpopulations can be present in an isogenic strain culture. These subpopulations are genetically identically and can interconvert. They exist in A. baumannii and contribute to its ability to survive in a hars environment.

VA researchers have found that one of the subpopulations is remarkably more virulent and ddrug-resistantthan the other. In fact, data suggest that the more virulent subpopulation is dominanatly found in the bloodstream of human patients. This subpopulation is resistant to hospital used disinfectants including benzethonium chloride, benzalkonium chloride, and chlorhexidine gluconate and can survive on dry surfaces.

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