**1. Introduction**

Infections caused by bacteria of genus Acinetobacter pose a significant health care challenge worldwide (Munoz-Price & Weinstein, 2008; Visca et al., 2011). Acinetobacter infections in the past were sporadically identified in hospitalized patients and hospital infection outbreaks in intensive care units. But, nowadays Acinetobacter has emerged as an important healthcareassociated and multidrug-resistant microorganism (Peleg at al., 2008).

Acinetobacter was first described in 1911 by Beijerinck as Micrococcus calco-aceticus. The name "Acinetobacter" originates from the Greek word "akinetos" meaning "unable to move", as these bacteria are not motile. A. baumannii, A. calcoaceticus, A. haemolyticus and A. lwoffii are the most important species in clinical practice.

Acinetobacter species are ubiquitous in nature and have been found in soil, water, animals and humans. Some strains of Acinetobacter can survive for weeks in environment, promoting transmission within the hospital settings (Doughari et al., 2011). Acinetobacter baumannii was recovered from the skin, throat, rectum and respiratory tract of humans. The species A. baumannii accounts for nearly 80% of reported Acinetobacter infections (CDC,2007). This feature along with antimicrobial resistance, colonization potential and contact transmission are main challenges for prevention and control activities (Maragakis et al., 2008). Some strains of Acinetobacter produce verotoxins and others have been identified to have an impact on removal of biological phosphorus from wastewater.

© 2013 Raka et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **2. Taxonomy and main features**

Genus Acinetobacter belongs to the family Moraxellaceae and order Pseudomonadales.

Based on molecular studies, 32 species of Acinetobacter have now been recognized; 22 of them have assigned valid names, whereas other species are described as a "genomic" group. The most important clinical species in medicine is Acinetobacter baumannii. This micro-organism has phenotypicall similarities with a group of species known as A.calcoaceticus-A.baumannii complex (Vaneechoutte et al., 2011). In healthcare settings, this group is implicated in major outbreaks and healthcare-associated infections.

The genus Acinetobacter consists of strictly aerobic Gram-negative coccobacilli rods, which are nonmotile, catalase-positive, indole-negative, oxidase-negative, non-fermentative. The bacilli are 0.9 to 1.6 μm in diameter and 1.5 to 2.5 μm in length, often in pairs or assembled into longer chains. Acinetobacter spp. are non-fastidious and can be grown on standard laboratory media.

**Figure 1.** Colonies of Acinetobacter spp. on sheep's blood agar after 24 hours at 37°C. CDC/ Pete Seidel. Public Health

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Acinetobacter species are widely distributed in nature and can be found in soil, sewage, water, consumables (including fruits and vegetables), and on healthy skin and other body sites. A. baumannii can be found also in some unusual reservoirs, such as food or arthropods. The majority of A. baumannii strains survive longer than Escherichia coli on dry surfaces, and some

About 25% of adults carry this organism on their skin, whereas about 7% carry it in their pharynx. Hospitalized patients may become easily colonized. Half of the patients with tracheostomy may be colonized with Acientobacter. Isolation of this microorganism from feces, urine, vaginal secretions is often considered as colonization or contamination. But, their presence from immunocompromised persons may have significant clinical impact

Clinical infections with Acinetobacter in healthcare settings are related to the use of invasive procedures (mechanical ventilation, vascular catheters) and patient's underlying conditions (Fournier & Richet, 2006). The most important risk factors for acquiring Acinetobacter infections are: prior antibiotic use (third-generation cephalosporins, fluoroquinolones or carbapenems), prolonged hospitalization, high APACHE II (Acute Physiology and Chronic Health Evaluation) score, recent surgical intervention, central vascular catheterization,

Acinetobacter can contaminate many surfaces and medical equipment, such are: suctioning equipment, washbasins, bedrails, bedside tables, ventilators, sinks, pillows, mattresses, hygroscopic bandages, resuscitation equipment, and trolleys (Bernards et al., 2004). The hands

Image Library

(Mahon et al., 2010).

strains survive for more than 4 months.

tracheostomy, mechanical ventilation and enteral feeding.

Acinetobacter is relatively nonreactive in many biochemical tests used to differentiate among gram-negative bacilli. Most clinical microbiology laboratories identify members of the genus Acinetobacter at the level of the following three groups with corresponding metabolic attributes (Allen et al., 2006):


**2. Taxonomy and main features**

84 Infection Control

outbreaks and healthcare-associated infections.

laboratory media.

attributes (Allen et al., 2006):

mannii can be identified by OXA-51 serotyping)

**•** Acinetobacter haemolyticus: hemolytic.

**•** Acinetobacter lwoffii: non glucose-oxidizing, non-hemolytic

Genus Acinetobacter belongs to the family Moraxellaceae and order Pseudomonadales.

Based on molecular studies, 32 species of Acinetobacter have now been recognized; 22 of them

have assigned valid names, whereas other species are described as a "genomic" group. The

most important clinical species in medicine is Acinetobacter baumannii. This micro-organism

has phenotypicall similarities with a group of species known as A.calcoaceticus-A.baumannii

complex (Vaneechoutte et al., 2011). In healthcare settings, this group is implicated in major

The genus Acinetobacter consists of strictly aerobic Gram-negative coccobacilli rods, which

are nonmotile, catalase-positive, indole-negative, oxidase-negative, non-fermentative. The

bacilli are 0.9 to 1.6 μm in diameter and 1.5 to 2.5 μm in length, often in pairs or assembled

into longer chains. Acinetobacter spp. are non-fastidious and can be grown on standard

Acinetobacter is relatively nonreactive in many biochemical tests used to differentiate among

gram-negative bacilli. Most clinical microbiology laboratories identify members of the genus

Acinetobacter at the level of the following three groups with corresponding metabolic

**•** Acinetobacter calcoaceticus-baumannii complex: glucose-oxidizing non-hemolytic (A.bau‐

**Figure 1.** Colonies of Acinetobacter spp. on sheep's blood agar after 24 hours at 37°C. CDC/ Pete Seidel. Public Health Image Library

Acinetobacter species are widely distributed in nature and can be found in soil, sewage, water, consumables (including fruits and vegetables), and on healthy skin and other body sites. A. baumannii can be found also in some unusual reservoirs, such as food or arthropods. The majority of A. baumannii strains survive longer than Escherichia coli on dry surfaces, and some strains survive for more than 4 months.

About 25% of adults carry this organism on their skin, whereas about 7% carry it in their pharynx. Hospitalized patients may become easily colonized. Half of the patients with tracheostomy may be colonized with Acientobacter. Isolation of this microorganism from feces, urine, vaginal secretions is often considered as colonization or contamination. But, their presence from immunocompromised persons may have significant clinical impact (Mahon et al., 2010).

Clinical infections with Acinetobacter in healthcare settings are related to the use of invasive procedures (mechanical ventilation, vascular catheters) and patient's underlying conditions (Fournier & Richet, 2006). The most important risk factors for acquiring Acinetobacter infections are: prior antibiotic use (third-generation cephalosporins, fluoroquinolones or carbapenems), prolonged hospitalization, high APACHE II (Acute Physiology and Chronic Health Evaluation) score, recent surgical intervention, central vascular catheterization, tracheostomy, mechanical ventilation and enteral feeding.

Acinetobacter can contaminate many surfaces and medical equipment, such are: suctioning equipment, washbasins, bedrails, bedside tables, ventilators, sinks, pillows, mattresses, hygroscopic bandages, resuscitation equipment, and trolleys (Bernards et al., 2004). The hands of healthcare workers are in frequent contact with these objects in patient surroundings. Hands become an important vectors of transmission in case of non-compliance with hand hygiene recommendations (Pittet et al., 2006). The ability of Acinetobacter to participate in biofilm formation promotes durability in surfaces and may contribute to continuation of environmen‐ tal presence during outbreaks (Fournier et al., 2006).

Recent disasters suggested that Acinetobacter infections should be taken in consideration in

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Many Acinetobacter infections have a seasonal variation with 50% infection rates higher from July to October than at other times of the year. This variation was explained by warmer, more humid ambient air, which favors growth of Acinetobacter and potentially preventable

The main challenge with A. baumannii is it's ability to acquire antimicrobial-resistance genes extremely rapidly, leading to multidrug resistance. Widespread use of antimicrobials within hospitals resulted to the emergence and increase of antimicrobial resistance among Acineto‐ bacter strains, in particular, the wide use of extended-spectrum cephalosporins and quinolones

Acinetobacter spp. are intrinsically less susceptible to antimicrobial agents than other repre‐ sentatives from the family Enterobacteriaceae. Various mechanisms played a role in the acquisition of a multiresistance phenotype amongst Gram-negative bacteria, including Acinetobacter strains such as: loss of porins, production of β-lactamases, increased expression of efflux pumps, presence of antibiotic-modifying enzymes, target site mutations, ribosomal mutations or modifications, metabolic bypass mechanisms and a mutation in the lipopolysac‐ charide (Poirel et al, 2011). The role of plasmids in the acquisition of antimicrobial resistance

Acinetobacter spp have ability to acquire antimicrobial-resistance genes rapidly, leading to multidrug resistance. As a result, the clinical management of these infections has become a public health challenge in many countries. Nowadays, the most serious problem in the treatment of Acinetobacter infection is acquired multidrug-resistance, leaving only few antimicrobial agents as treatment options. This resistance is attributed to the presence of multiple resistant determinant among bacteria, which confers resistance to many groups of antimicrobial agents (Livermore, 2012). One of the main concerns about antimicrobial resist‐ ance in A.baumannii has been the resistance to the last line of antimicrobials through acquis‐ ition of carbapenem resistance - mainly through the acquisition of B and D class

Infection or colonization with Acinetobacter is usually diagnosed by the culture of clinical samples and samples from environment. The most frequent clinical samples include blood, cerebrospinal fluid, endotracheal aspirate, wounds, sputum, urine, catheter tips, stool or sterile body fluid, skin, cordon of newborns, nasal swabs, hand swabs of hospital workers. The most

differential diagnosis of soft-tissue infections (Asia tsunami on 2004).

environmental contaminants, such as condensate from air-conditioners.

in A. baumannii is mostly related to their integron structures.

**4. Antimicrobial resistance**

carbapenemases(Bou et al., 2012).

**5. Detection and typing systems**

(Imperi et al, 2011).

Acinetobacter species posses the following virulence factors which enable transmission within health care settings: cell surface hydrophobicity, enzymes, toxic slime polysaccharides, verotoxins, siderophores and outer membrane proteins.
