• A widespread Gram-negative bacterium found in soil and water is Acinetobacter baumannii. It can also be found on the skin of healthy individuals and in hospital settings. A. baumannii infections can range from mild skin infections to life-threatening bloodstream infections, pneumonia, and meningitis. 
• One of the reasons that  A. baumannii has become a concern in healthcare settings is its ability to develop antibiotic resistance. This makes infections difficult to treat, leading to increased morbidity and mortality. 
• The prevalence of  A. baumannii infections varies by region and healthcare setting. According to projections, A. baumannii causes 3% of healthcare-associated infections in the US. The prevalence may be substantially higher in other parts of the world, such as the Middle East and the Mediterranean nations. 
• Risk factors for  A. baumannii infections include prolonged hospital stays, mechanical ventilation, urinary catheterization, and antibiotic exposure. Preventative measures such as hand hygiene, infection control protocols, and antibiotic stewardship programs can help to reduce the spread of A. baumannii infections in healthcare settings. 

Here is an overview of its structure: 

• Cell shape: Acinetobacter baumannii is a rod-shaped bacterium. 
• Cell wall: The cell wall of Acinetobacter baumannii is composed of peptidoglycan, lipopolysaccharides, and various proteins. 
• Outer membrane: The outer membrane of Acinetobacter baumannii contains porins, which allow for the diffusion of small molecules across the membrane. 
• Capsule: Some Acinetobacter baumannii have a capsule that surrounds the cell wall, which can protect the bacterium from host defenses and antibiotics. 
• Flagella: Acinetobacter baumannii can have multiple flagella, which enable the bacterium to move. 
• Pili: Acinetobacter baumannii can have pili, proteinaceous appendages that facilitate adherence to surfaces and host cells. 

Classification  

In terms of classification, Acinetobacter baumannii is classified as follows: 

Domain: Bacteria  

Phylum: Proteobacteria  

Class: Gammaproteobacteria  

Order: Pseudomonadales  

Family: Moraxellaceae  

Genus: Acinetobacter  

Species: baumannii 

Acinetobacter baumannii is a highly diverse species, and different strains of the bacteria can have different genetic characteristics and cause different types of infections. Therefore, further classification of Acinetobacter baumannii strains can be done using molecular techniques such as whole-genome sequencing or multi-locus sequence typing. 

• Acinetobacter baumannii can be classified into different types based on its genetic and antigenic characteristics. One commonly used classification system is the multilocus sequence typing (MLST) scheme, which identifies distinct sequence types (STs) based on the DNA sequence of seven housekeeping genes. This system has identified over 700 different STs of Acinetobacter baumannii. 
• Another classification system is based on the O antigen, a component of the bacterial cell wall used by the immune system to recognize and mount a response against the bacteria. Acinetobacter baumannii can be classified into different O antigen types based on the specific structure of its O antigen. There are currently 33 recognized O antigen types of Acinetobacter baumannii. 

• There have been five main pathogenic mechanisms identified so far: 
• Biofilm creation: the subsequent formation of biofilms and attachment via pili increase colonization of environmental surfaces. The formation and maintenance of biofilms depend on the biofilm-associated protein (Bap). Bap is essential for colonization because it helps cells adhere to one another. Acinetobacter has a well-documented ability to live in dry circumstances, and strains that produce more biofilm appear less vulnerable to desiccation than strains that produce less biofilm. 
• About one-third of strains synthesize the K1 capsule, a polysaccharide that collaborates with the cell wall oligosaccharide to block complement activation. The capsule may postpone phagocytosis. 
• Acinetobacter can endure iron-deficient conditions for a considerable time [68] thanks to the siderophore-mediated iron-acquisition pathway. Its “acinetobacter,” a catechol siderophore that can sequester iron from the host, is the cause of this. 
• Fimbriae: As was already noted, fimbriae aid in the organism’s attachment to environmental surfaces. Moreover, they aid in colonizing biotic surfaces such as bronchial epithelial cells. 

Here are some host defenses against Acinetobacter baumannii: 

• Hand hygiene: One of the most excellent strategies to stop the spread of Acinetobacter baumannii is to practice good hand hygiene. Regular hand washing with soap and water or using a hand sanitizer with alcohol can help lower the risk of illness. 
• Use of antibiotics: Antibiotics are often used to treat Acinetobacter baumannii infections. However, overuse or misuse of antibiotics can lead to antibiotic resistance, making infections more difficult to treat. Therefore, it is crucial to use antibiotics only when necessary and as directed by a healthcare professional. 
• Immune system response: The body’s immune system is also an essential defense against Acinetobacter baumannii. A robust immune system can aid in the prevention of illnesses as well as the treatment of existing ones. 
• Isolation precautions: Patients infected or colonized with Acinetobacter baumannii may be placed in isolation to help prevent the spread of the bacteria to others. 
• Environmental cleaning: Proper cleaning and disinfection of surfaces and equipment in healthcare settings can also help prevent the spread of Acinetobacter baumannii. 

The clinical manifestations of Acinetobacter baumannii infection can vary depending on the site of infection and the patient’s underlying health status. 

Some common clinical manifestations of Acinetobacter baumannii infection include: 

• Pneumonia: Acinetobacter baumannii can cause severe pneumonia, particularly in patients on mechanical ventilation or with other underlying respiratory conditions. 
• Bloodstream infection: Acinetobacter baumannii can enter the bloodstream and cause sepsis, a life-threatening condition characterized by fever, chills, and low blood pressure. 
• Urinary tract infection: Urinary tract infections brought on by Acinetobacter baumannii can be characterized by frequent urination, the urge to urinate even when the bladder is empty, and pain or burning during urinating. 
• Skin and soft tissue infection: Acinetobacter baumannii can cause skin and soft tissue infections, such as cellulitis and wound infections, particularly in patients with compromised immune systems. 
• Meningitis: Acinetobacter baumannii can cause meningitis, a severe infection of the membranes surrounding the brain and spinal cord.

• It is commonly found in hospitals and healthcare settings and can lead to severe infections such as pneumonia, bloodstream infections, and meningitis. 
• Diagnosing Acinetobacter baumannii typically involves a combination of clinical evaluation, laboratory testing, and imaging studies. Laboratory testing may include blood cultures, wound cultures, or other tests to identify the specific strain of bacteria causing the infection. 

The bacterium is notorious for its ability to resist many types of antibiotics, making it a difficult pathogen to treat.

Here are some ways to control Acinetobacter baumannii: 

• Hand hygiene: Acinetobacter baumannii must be stopped from spreading by regularly washing hands with soap and water or using a hand sanitizer containing alcohol as the active ingredient. 
• Environmental cleaning: Proper cleaning and disinfection of surfaces and equipment in healthcare facilities are essential in reducing the risk of Acinetobacter baumannii transmission. 
• Antibiotic stewardship: Limiting the use of antibiotics can help prevent the development and spread of antibiotic-resistant bacteria like Acinetobacter baumannii. 
• Contact precautions: Patients infected with or colonized by Acinetobacter baumannii should be placed under contact precautions, which include wearing gowns and gloves to prevent transmission to other patients or healthcare workers. 
• Surveillance and screening: Regular surveillance and screening of patients in healthcare facilities can help identify and isolate those colonized with Acinetobacter baumannii, even if they are not showing symptoms. 
• Improved infection control practices: Healthcare facilities can improve their infection control practices by implementing policies and procedures to reduce the spread of Acinetobacter baumannii, such as using dedicated equipment for infected or colonized patients and adequately disposing of contaminated materials. 
• Development of new antibiotics: Developing new antibiotics that are effective against Acinetobacter baumannii is an ongoing area of research and can help control its spread. 

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3442836/ 
• https://www.uptodate.com/contents/acinetobacter-infection-epidemiology-microbiology-pathogenesis-clinical-features-and-diagnosis