Mucoid phenotype in clinical isolates of Escherichia coli: an underexplored phenomenon

Escherichia coli is an important clinical pathogen that requires urgent attention. Although a commensal bacterium, E. coli can cause serious infections ranging from enterohaemorrhagic diarrhoea to neonatal meningitis. The pathogenesis of E. coli is characterized by a complex interplay of virulence factors that facilitate its colonization, invasion, and evasion of host immune responses. The adaptive capability of the pathogen to varying host environment is facilitated by its genetic plasticity leading to patho-adaptive mutations. Production of mucoid capsule represents a way of such phenotypic adaptation. Mucoid phenotype is commonly found and associated with enhanced virulence in Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. However, mucoid colony types are not common in clinical E. coli isolates and their correlation to virulence, biofilm formation and antibiotic resistance is not thoroughly studied. A majority of studies are based on laboratory-generated mutants, while information on clinical mucoid strains is limited. Hence, understanding the challenges posed by mucoid E. coli in clinical settings might play a crucial role in treatment and infection control measures. This review compiles information on the phenotypic characteristics, virulence determinants, and associated diseases of mucoid E. coli, and aims to address the gaps in knowledge for a better understanding of its clinical implications.