Mucoidy

Mucoidy refers to the property of a substance or organism to produce a mucus-like, viscous, slippery mass. In biology, mucoidy often describes the appearance of colonies or the extracellular matrix produced by microorganisms.

In microbiology, mucoidy most commonly describes a mucoid phenotype where bacteria produce large amounts of extracellular polysaccharides, forming a slimy, protective layer around cells. The archetypal example is Pseudomonas aeruginosa, which overproduces alginate, creating a thick slime that supports biofilm formation. Other bacteria may be mucoid due to capsule synthesis or other exopolysaccharides.

Clinical relevance: Mucoid strains are associated with chronic infections, particularly in patients with cystic fibrosis, where mucoid P. aeruginosa colonizes airways and forms biofilms within mucus. The mucoid biofilm can impede immune clearance and contribute to antibiotic tolerance, prolonging infection and complicating treatment.

Mechanisms: Mucoidy often results from altered regulation of polysaccharide biosynthesis. In P. aeruginosa, mutations in regulatory genes relieve repression of alginate production, leading to constitutive synthesis of alginate in the alginate biosynthetic pathway, promoting biofilm formation and resistance to host defenses.

Laboratory and clinical implications: Mucoid colonies appear more viscous and slippery on culture media. Observing mucoidy can inform prognosis and treatment planning; however, antibiotic susceptibility testing should be interpreted in the context of biofilm-associated tolerance rather than planktonic susceptibility alone.