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The Battlefield Bacterium

By Barbara L. Fox, MS, MPH, MT (ASCP)

he horrors of combat includemany dangers both physical andbiological. One of the most

deadly bacterial threats to combatpersonnel has been the environmentallyresilient organism found in nosocomialand community-acquired infections,

Acinetobacter baumannii .

This organism, in the FamilyMoraxellaceae, is a gram negative,aerobic, non fermenting coccobacilli,oxidase negative, that grows onMacConkey agar and is non motile.

Figure 1: A. baumannii has emerged as an important multi-drug resistant organism. For this reason the resistant strains are known as MDRAB.

Although other species of Acinetobacter such as lwoffi are found in soil andwater, a natural reservoir for A.

baumannii outside of the hospitalenvironment has not been found. Insettings such as hospitals and long termcare facilities, Acinetobacter organismscan colonize the skin, respiratory andgastrointestinal tracts of patients, as wellas surgical and respiratory careequipment, catheters, or personalprotective gowns or gloves.

Figure 2: A. baumanii has earned itself the nickname Iraqnobacter due to the high incidence in wounded soldiers from the Middle East. Field hospitals are often the source of infection. Although A. baumanii infections were seen during the Viet Nam war,widespread drug resistance had not

been seen.

Infections in these compromised patientpopulations include pneumonia,endocarditis, meningitis, peritonitis,

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osteomyelitis, endopthalmitis, urinarytract infections, and skin and woundinfections.

Figure 3: The word, Acinetobacter, comes from the Greek word formotionless rod, since the bacilli have

no flagella.

A. baumannii is very adept at developingresistance to all existing classes of antibiotics, becoming what is calledMDR, or multi drug resistant ,due tofactors including plasmid insertion of resistance genes. Effective drugs haveincluded the carbapenems (imipenemand meropenem), but the organism isnow showing resistance to this class of antibiotics as well. More than one-third

of A. baumannii infections are multidrugresistant (MDRAB), which means thepathogens are resistant to at least threedifferent classes of antibiotics.

Figure 4: A study in 2004 at the Indiana University School of Medicine Burn Unit revealed that a patient with an MDRAB infection incurred costs of $98,575 more than similar patients whowere not infected.

Figure 5: The first line treatment iswith a carbapenem antibiotic such asimipenem or meropenem, but

carbapenem resistance is increasingly common. Other treatment optionsinclude polymyxins, tigecycline and

aminoglycosides.

This organism has caused numerousoutbreaks globally, being reported fromhospitals in Europe, North and SouthAmerica, Asia and elsewhere.

Recently, MDR Acinetobacter

baumannii has emerged as a problem forwounded military personnel returningfrom Iraq and Afghanistan. Thisalarming increase prompted the CDC tosend a team of ID specialists to Iraq in2004 to determine the source of theseinfections. Soil was ruled out as areservoir; however, one strain found incombat wound infections was found tobe the same strain circulating inhospitalized patients in Europe. Some

studies suggest field hospitals may alsobe contributing to the organisms spread.Additional factors contributing tocolonization, virulence, and infection arestill being investigated.

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Infection control measures in health carefacilities both abroad and in the U.S cando much to control the spread of superbugs such as MDR Acinetobacter

baumannii . As part of the health careteam, we microbiologists must bevigilant about washing our hands,wearing personal protective equipmentwhile working with microorganisms, andwearing only our street clothes when inother areas of the health care facility.We will be helping in the war against avery tenacious enemy and doing our partto improve patient care.

Figure 6: Soil analysis in Iraq failed to find it as a source of the infection. However, many isolates were found on

surfaces and in solutions within field hospitals. Acinetobacter is a waterloving organism that can be found in

catheters, respiratory equipment, and irrigation solutions.

Barbara L. Fox, MS, MPH, MT (ASCP) Infectious Disease Consultant