Members of the genus Acinetobacter are involved in a wide spectrum of infections. Although this organism is mainly associated with nosocomial infections, these bacteria have been recently shown involved in community-acquired infection. Over 1,000 published papers refer to “infections by antibiotic resistant acinetobacter in the international literature.” This opportunistic commensal bacterium was initially considered a relatively low-grade pathogen and frequently ignored until the 1960s, even when isolated from clinical samples. However, marked improvement in culture techniques in the last 30 years increased awareness of infections due to acinetobacter. Prior to the 1970s, nosocomial infections by this organism were mainly detected after surgical procedures or in the urinary tract from patients hospitalized in intensive care units (ICU), but since the 1980s, acinetobacters were found rapidly spread among ICU patients. At the present time, this bacterium represents about 9–10% of all nosocomial infections, but the majority are due to respiratory tract infection. The origin of such infections is known to be both endogenous and exogenous, and the introduction of single-use disposable patient items is now known to limit endogenous infection. Nevertheless, transmission of the bacteria by the hands of hospital staff is now known to be an important risk factor for patient colonization. Of the many different microbial species isolated from various environments, Acinetobacter baumannii is known to be the most frequently involved in human infections. Although the reservoirs outside of hospital environments are not clearly defined, community acquired infection and infection related to war or earthquakes have been recognized and may be due to presence of these microbes in the soil. The severity of such infection by this bacterium depends on the site of infection and the degree of a patient’s immune competence related to underlying disease. Acinetobacter may cause mild to severe illness and can be fatal. However, a consensus whether this organism is indeed highly pathogenic is not established since this organism is thought to be mainly a low-grade pathogen. It is likely that increased pathogenesis by this microbe involves numerous factors, including virulence factors that are not yet clear. However, there is now increased interest in this pathogen the last 30 years (Livermore, 2003), since recognition of antibiotic multiresistant strains, including pan resistance, emerged in an outbreak in a clinical unit (Del Mar et al., 2005; Fierobe et al., 2001; Mah et al., 2001; Rello, 2003; Simor et al., 2002; Smolyakov et al., 2003). In hot and humid areas such as the tropics, acinetobacter infections are usually community acquired, in general bacteremias, or primary infections (Anstey et al., 2002).