Acinetobacter baumannii belongs to a species of gram negative, oxidase negative organisms. It is non motile and on microscopic examination appears as coccobacilli in pairs. Till date, about 25 different varieties of this organism have been identified. These bacteria are commonly found in the water and soil and recent evidence has shown that they are also found to be colonizing the skin, throat and other sites in healthy human individuals (Defense, 2005). These organisms are important in causing outbreaks of infections especially targeted at groups of individuals who are immunocompromised or critically ill especially those who have contracted traumatic injuries either in the context of natural disasters or during war circumstances (Scott, 2007). These organisms can be acquired from the environment through contacts with fomites which have been infected via the environmental reservoir or more commonly via the hands of infected health care personnel and studies have proven that almost one third of health care professionals carry this organism on their hands. Therefore, nosocomial infection of A. baumannii is a common and well established entity and is becoming a major health concern over the past few decades. Moreover, in temperate climates, this organism has also been shown to contaminate wounds and hence cause infections in wounded individuals (Defense, 2005). The most common infections caused by A. baumannii include nosocomial pneumonias, skin and wound infections, urinary tract infections, central nervous system infections (e.g. meningitis) and frank sepsis (Defense, 2005).
Recently, there has been a growing concern over the increasing incidence of A. baumannii infections in military personnel, involved in the Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF), admitted in various health care facilities in Iraq, Kuwait and Afghanistan (Scott, 2007). By August 2004, there were 102 diagnosed cases of A. baumannii infections amongst military individuals involved in OIF and OEF (Prevention, 2006). Similar infections have been noticed in the past and A. baumannii was identified as the most commonly recovered gram negative organism from individuals who had acquired traumatic injury to the extremities during the Vietnam War (Prevention, 2006). Keeping the above mentioned data in mind, the importance of Acinetobacter baumannii infections from the military perspective can be gauged.
Moreover, an important aspect of infections with A. baumannii is the emergence of multidrug resistant strains of this organism. Studies have shown that this organism, in addition to acquiring resistance to antimicrobial therapy as a result of exposure to several antibiotics and single drug therapy, also possesses an intrinsic resistance to certain antimicrobial agents (Prevention, 2006). This makes treatment difficult and poses two main public health concerns viz. the development of stringent strategies for the prevention of the spread of such infections and discovering newer antimicrobial agents to which the resistant strains of A. baumannii are susceptible. Till date, the antimicrobial agents which have been successful in combating A. baumannii infections include the Carbapenems (e.g. Impenem and Meropenem), Amikacin, and Colistin (Defense, 2005). Studies and antimicrobial susceptibility testing has shown that most A. baumannii isolates, including the ones which were found in samples of patients from OEF and OIF, are susceptible only to Colistin (Polymyxin E). However, use of this antimicrobial agent is limited because of its high potential for causing toxicity (Prevention, 2006). Other agents which are under investigation via in vitro testing for effectiveness against Acinetobacter baumannii include piperacillin/tazobactam, most third-generation cephalosporins, aminoglycosides, and fluoroquinolines (Defense, 2005).
The source of acquisition of A. baumannii by military patients is an arena of controversy. Three potential sources have been viz. pre-injury skin colonization, introduction of the organism into the wound at the time of injury, and nosocomial acquisition of the organism after injury during treatment in health care facilities. Scott (2007) in their review of patients from the OIF and OEF found that although the outbreak of multidrug resistant A. baumannii is multifactorial, the most important source of infection is nosocomial spread of infection in patients admitted in the health care facilities (Scott, 2007).
In conclusion, there is a rising concern of the recent increase in the incidence of Acinetobacter baumannii amongst military individuals. Moreover, several multidrug resistant strains have emerged over the past few decades. This has serious public health implications and new strategies to control the further spread of these infections need to be devised.