The Acinetobacter are a group of bacteria from the genus Gammaproteobacteria, all of which are gram-negative and encompass many different life forms. Acinetobacter is one of the best-known aerobic bacteria and is best known as a multidrug-resistant hospital germ. For immunodeficient patients, an infection can be fatal.

What are Acinetobacter?

Acinetobacter baumannii bacteria are aerobic short-rod bacteria. © Robert Kneschke - stock.adobe.com

Gammaproteobacteria are also referred to as γ-Proteobacteria. It is a class of the phylogenetic bacterial system. This system was constructed based on the base sequence of ribosomal 16S ribonucleic acid, also known as 16S rRNA. The proteobacteria strain contains 5 genera of Alphaproteobacteria to Epsilonproteobacteria. Every single member of this bacterial strain is gram-negative. Gammaproteobacteria are the species-richest class from the group of the Proteobacteria and are physiologically as extremely diverse.

Also bacteria of the genus Acinetobacter belong to the Grammaproteobakterien. They are gram-negative and are considered to be one of the most common types of bacteria. In most cases, the bacteria are multi-drug resistant and for this reason can cause serious diseases that are not conventionally treatable. For example, Acinetobacter baumannii is pathogenic to humans and therefore always associated with disease in humans. Due to its resistance, this disease germ is one of the most dreaded germs worldwide. The germ is one of the most common hospital germs. Other species of the genus are Acinetobacter johnsonii, junii, lwoffii and Acinetobacter towneri. In total, around 20 species from the group are known.

Occurrence, distribution & characteristics

Acinetobacter baumannii bacteria are aerobic short-rod bacteria. The bacterium needs oxygen to survive and is therefore one of the aerobic bacteria. This differentiates the species from most other types of bacteria. Many of them are not necessarily dependent on oxygen or even experience oxygen as deadly. Aerobics is chemically characterized by oxidation. If the individual processes within the bacterial organisms use oxygen, aerobic organisms are mentioned. The Acinetobacter baumanii can not survive without oxygen.

In addition, it is one of the short-rod bacteria. As such, species are designated which have a length less than twice their width. The bacteria of the species Acinetobacter baumanii are also known as environmental germs whose preferred habitat is the interior of the soil and the water. Acinetobacter baumanii often colonize the skin of humans. They also occur in this context on the skin of healthy people. This colonization is, however, to be understood as temporary, since healthy human skin is colonized by various skin bacteria. These naturally occurring bacteria on the skin create an unfavorable environment for Acinetobacter baumanii.

The spread of bacteria in the human body is therefore possible only under certain circumstances. An infection with the Acinetobacter baumannii therefore usually affects at most strongly defensive weakened people. The infection is classified as a nosocomial infection, as it appears to be increasing in hospitalization. An infection is not necessarily mentioned after contact with the germ. For healthy people, the contacts usually remain inconsequential, as their immune system kills the bacteria in time. Since the bacteria can not sufficiently proliferate before the rapid intervention of a healthy immune system, no symptoms occur.

In people with a weakened immune system, such as in AIDS patients or deliberately immunosuppressed patients (for example, after organ transplantation), the immune system does not intervene quickly enough. The germ can propagate through division and spreads through the bloodstream. It comes to an infection. The bacteria of this species colonize due to their milieu preferences especially wounds or organs such as the lungs.

Diseases & complaints

Acinetobacter baumanii can cause serious wound infections and pneumonia in immunosuppressed or otherwise immunocompromised people. The most serious complication of these phenomena is sepsis. It is an inflammatory reaction of the whole organism, also known as blood poisoning, which can have fatal consequences.

Other types of Acinetobacter mainly cause meningitis, in particular the Acinetobacter lwoffii, junii, haemolyticus and johnsonii. The spread of the pathogens to the brain takes place in this context via the bloodstream.

While some other medicines help against other Acinetobacter species, the Acinetobacter baumannii are multi-resistant. A multidrug-resistant strain was first reported in the Dutch Intensive Care Unit of Enschede Hospital. In 2015, a multidrug-resistant strain was also reported at Kiel University Hospital after 31 patients had become infected with Acinetobacter baumannii. The strain was classified in the 4-MRGN group: all four groups of antibiotics could not harm the bacterium. In 12 cases, the infection resulted in death. At the end of 2015, the Linz Women's and Children's Hospital reported a germ of the species Acinetobacter, which had infected a total of five babies, three of whom had died.

The use of broad-spectrum antibiotics is now believed by scientists to be the main reason for the increased occurrence of Acinetobacter. According to the Robert Koch Institute, the multidrug-resistant proportion of tribes increased between 2009 and 2011 to 10.7 percent. Multidrug resistance results from the evolutionary adaptability and learning ability of bacteria. Most of the time, at least one of four groups of antibiotics initially acts against the germs. However, the more frequently they come into contact with the drugs, the faster they develop resistance to the relevant active ingredients. Multi-resistance is only mentioned when a bacterium has already become resistant to several active substances.

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