baumannii, capsules are composed of tightly packed repeating oligosaccharide subunits (K units), typically consisting of 4–6 sugars.

Capsules are high-molecular-weight hydrophilic polymers that form a layer enveloping the bacterial cell. While surface carbohydrates influence pathogenicity, studies show that the capsule is the predominant virulence factor in A. These carbohydrates include capsular polysaccharides (capsule), lipooligosaccharide (LOS) and the exopolysaccharide poly-β-(1–6)-N-acetylglucosamine (PNAG). Surface carbohydrates are known to influence virulence and fitness of A. These virulence factors are involved in the pathobiology and infection process, such as binding to host epithelial cells, cellular damage, serum resistance, and invasion. baumannii virulence factors include siderophore-mediated iron acquisition systems, biofilm formation, motility, and a remarkable capacity to acquire and rearrange genetic determinants. Identifying capsulated strains can be useful for directing infection control measures to reduce the spread of hypervirulent strains.Īcinetobacter baumannii is a major cause of hospital-acquired infections. The density-dependent gradient test can be used to verify capsule presence in mucoid-appearing A. Transmission electron microscopy confirmed the presence of a capsule in the six representative strains suspected to be capsulated. Total carbohydrates extracted from strains suspected to be capsulated were significantly higher. There was agreement between the mucoid and the non-mucoid phenotypes and the density-dependent gradient test for all but three isolates. Twenty-three isolates migrated to the bottom phase, indicating thin or non-capsulated strains, and 34 migrated to the top phase, suggesting strains suspected to be capsulated. The density-dependent gradient test was comprised of two phases, with silica concentrations of 30% (top phase) and 50% (bottom phase). baumannii isolates displayed a mucoid phenotype. Here, we describe a density-dependent gradient test to distinguish between capsulated and thin/non-capsulated A. Therefore, it is clinically and epidemiologically important to identify capsulated A. baumannii are associated with increased clinical severity. Infections caused by capsulated or mucoid A. Gram-negative bacterial capsules are associated with production of carbohydrates, frequently resulting in a mucoid phenotype.

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