231 ISSN 1478-7210 © 2013 Expert Reviews Ltd 10.1586/ERI.13.11 www.expert-reviews.com Editorial Acinetobacter baumannii is one of the most prevalent causes of severe hospital-acquired infections, such as ventilator-associated pneumonia, bacteremia and meningitis, among others, with a high rate of morbid- ity and mortality [1] . This microorganism has turned, in recent years, from an oppor- tunistic bacterium, even with controversial pathogenicity [2] , to be included in the top- seven list of ‘bad bugs’ with a lack of appro- priate treatment by the Infectious Diseases Society of America [3] . Besides other char- acteristics, such as its ability to survive on dry surfaces for 5 months and its high tol- erance to wide ranges of pH, temperatures and humidity, it is its array of intrinsic and acquired antibiotic-resistance genes that has prompted A. baumannii to be a major cause of concern, changing from being suscepti- ble to almost all antimicrobials in the early 1970s to the accumulation of numerous outbreaks of resistant strains to all com- mercially available antibiotics nowadays [4] . In this article, we try to review the main works of a new approach to circumvent the lack of treatment against A. baumannii by blocking its virulence factors. Virulence mechanisms in A. baumannii Recent whole-genome sequencing stud- ies involving A. baumannii have demon- strated not only a vast array of antibiotic drug resistance determinants but also many pathogenicity islands [5] . Studies of specific virulence mechanisms have recently been reviewed [6] , focusing on biofilm forma- tion – more related to the ability to persist on surfaces and host rather than on infec- tiveness; siderophore-mediated iron acqui- sition systems, including acinetobactin, which allows A. baumannii to acquire ferric ions under the iron-limited host conditions – bacterial quorum sensing used to assess their local population densities through molecule signals; adherence to, and inva- sion of host cells, to escape the host immune system and to cross the epithelia of tissues to increase its replication; cytotoxicity depend- ent on outer membrane proteins and outer membrane vesicles that are involved in the first contact with the host; phospholipase D, which plays an important role in hematog- enous dissemination; and lipopolysaccha- rides that induce inflammatory responses. These studies demonstrate the contribu- tion of a few factors in the pathogenesis of A. baumannii, suggesting that these mech- anisms would be possible candidates for targets of novel antimicrobial agents. Virulence factor blocking agents Some studies have already been performed in order to investigate the role of block- ers of A. baumannii virulence factors as potential antimicrobials. Several of them have focused on the inhibition of biofilm formation by different approaches, such as the use of a new phage (AB7-IBB2) that is able to lyze 49% of clinical isolates of Treating multidrug-resistant Acinetobacter baumannii infection by blocking its virulence factors Expert Rev. Anti Infect. Ther. 11(3), 231–233 (2013) “This microorganism has turned, in recent years, from an opportunistic bacterium, even with controversial pathogenicity, to be included in the top-seven list of ‘bad bugs’…” KEYWORDS: Acinetobacter baumannii • antimicrobial resistance • therapeutic alternatives • virulence factors Rafael López-Rojas Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/ University of Seville, Seville, Spain Younes Smani Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/ University of Seville, Seville, Spain Jerónimo Pachón Author for correspondence: Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/ University of Seville, Seville, Spain pachon@us.es For reprint orders, please contact reprints@expert-reviews.com Expert Review of Anti-infective Therapy Downloaded from informahealthcare.com by Universidad de Sevilla on 11/05/14 For personal use only.