part of Future Microbiol. (2011) 6(4), 407–422 407 10.2217/FMB.11.23 © 2011 Future Medicine Ltd ISSN 1746-0913 Future Microbiology Acinetobacter spp. are glucose nonfermentative Gram-negative coccobacilli that have emerged in recent years as a major cause of nosocomial infections associated with high morbidity and mortality [1,2] . The genus Acinetobacter currently contains up to 32 described named and unnamed (genomic) species [1] . Acinetobacter baumannii, genomic species 3 and 13TU, three of the most clinically relevant species, are genetically and phenotypically very similar to an environmen- tal species, Acinetobacter calcoaceticus, and are therefore grouped together into the so-called A. calcoaceticus–Acinetobacter baumannii complex [1] . However, because A. calcoaceticus is not clin- ically relevant, the designation A. baumannii complex might be more appropriate if used in a clinical context [2] . Because phenotypic iden- tification of Acinetobacter isolates to the species level has proven to be insufficient, several geno- typic methods have been developed for genomic species identification, which include amplified 16S rRNA gene restriction analysis, high-res- olution fingerprint analysis by amplified frag- ment length polymorphism, sequence analysis of the 16S–23S rRNA gene spacer region, rpoB sequencing and gyrB multiplex PCR [1–6] . The species that is most frequently recognized as a pathogen is A. baumannii, which causes a vari- ety of healthcare-associated infections, compris- ing hospital-acquired and ventilator-associated pneumonia, bacteremia, urinary tract infection and surgical-site infection, especially in inten- sive care unit patients [1,2,7–9] . A. baumannii has simple growth requirements and can survive in dry conditions. This might contribute to the fitness of A. baumannii in the hospital environ- ment, which represents the main reservoir of this bacterium [1,2,10] . Hand carriage by healthcare workers has also been implicated as a mode of A. baumannii transmission in the hospital set- ting [1,2,10] . Although A. baumannii has been classically recognized as a hospital-acquired pathogen, an increased prevalence of multidrug- resistant A. baumannii isolates has been recently observed among older adults in community hospitals and nursing homes in the USA [11] . Drug-resistant Acinetobacter baumannii Resistance to antimicrobial agents is the main advantage of A. baumannii in the nosocomial environment. Multidrug resistance (MDR) in A. baumannii has been defined as resist- ance to more than two of the following five drug classes: antipseudomonal cephalosporins (ceftazidime or cefepime), antipseudomo- nal carbapenems (imipenem or meropenem), ampicillin-sulbactam, fluoroquinolones (cipro- floxacin or levofloxacin), and aminoglycosides (gentamicin, tobramycin or amikacin) [2] . Pandrug resistance was originally defined as Global spread of drug-resistant Acinetobacter baumannii : molecular epidemiology and management of antimicrobial resistance Emanuele Durante-Mangoni 1 & Raffaele Zarrilli † 1 Chair of Internal Medicine & Unit of Transplant Medicine, Second University of Naples, Monaldi Hospital, Naples, Italy † Author for correspondence: Department of Preventive Medical Sciences, Hygiene Section, University of Naples ‘Federico II’, Via Pansini 5, 80131, Naples, Italy n Tel.: +1 39 081 746 3026 n Fax: +1 39 081 746 3352 n rafzarri@unina.it Acinetobacter baumannii is an opportunistic Gram-negative pathogen with increasing relevance in a variety of hospital-acquired infections especially among intensive care unit patients. Resistance to antimicrobial agents is the main reason for A. baumannii spread. A. baumannii outbreaks described worldwide are caused by a limited number of genotypic clusters of multidrug-resistant strains that successfully spread among hospitals of different cities and countries. In this article, we will focus on the mechanisms responsible for resistance to antimicrobials and disinfectants in A. baumannii and the epidemiology of drug-resistant A. baumannii in healthcare facilities. We will also discuss the therapeutic and infection control strategies for management of drug-resistant A. baumannii epidemics. Keywords n Acinetobacter baumannii n antimicrobial therapy n antiseptics n infection control n molecular epidemiology n resistance genes Review