| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 104 === The emergence of multidrug resistant (MDR) bacteria have become a major threat in public health over the past decades and might cause 10 million deaths every year in 2050. Acinetobacter baumannii is one of the most important nosocomial MDR pathogens and hard to get rid of from medical devices and environment. Multidrug- or Pandrug-resistant A. baumannii infections have contributed significantly to increase difficult-to-treat infection. It is therefore regarded as one of the six top-priority dangerous microorganisms listed by Infectious Disease Society of America. Tigecycline (TGC) has been thought as a last resort to treat MDR A. baumannii. However, TGC-resistant A. baumannii isolates have been increasing reported over the years. For this reason, the development of a novel strategy to combat A. baumannii is urgently needed. Vaccine is the most promising and cost-effective intervention to prevent such superbug infection. In this study, we aimed to identify potential vaccine candidates using two different strategies: (1) reverse vaccinology and (2) target on resistant determinants. First of all, we have analyzed on-line available A. baumannii genome sequences and utilized the in vitro outer membrane proteomic experiment, previous published proteomic information and bioinformatic tools to identify potential extracellular and/or outer membrane proteins. Seventy-seven genes coding for the ideal potential antigens were identified. PubMed and Google Scholar silico software were used to examine whether these antigens have been used as vaccine candidates against A. baumannii and other pathogens. The results suggest that thirteen proteins could potentially be the vaccine targets. We have randomly cloned and expressed three of these antigens. These three antigens were mixed and used to immunize mice. The pneumonia animal model results in partial protection in lethal doses (60% survived). Currently, we are working to discover a more broadly protective vaccine to combat A. baumannii infection.
Secondly, we propose an immunization approach to restore the bactericidal activity of TGC against TGC-resistant A. baumannii infection. Overexpression of resistance-nodulation-cell division (RND) efflux pumps, including AdeABC, AdeIJK, TolC were associated to TGC resistance in clinical isolates of A. baumannii. Thus, we aim to abolish efflux pumps function via immunization strategy. The outer-membrane located efflux protein, AdeK, was found to be the most promising candidate to restore TGC activity after blocking the AdeK with the specific antibody by using in vitro experiments. The bacterial load in the lung of mice that were immunized with AdeK and treated with TGC were significantly lower than those mice that were immunized with AdeK or treated with TGC alone. The results suggested that anti-AdeK antibody could potentially serve as pump inhibitor and restore the TGC activity in TGC-R A. baumannii infected mice.
Collectively, our findings in this study have shed light on vaccinology and chemo-immuno-therapies strategy against MDR pathogens and it is worth of further investigation.
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