Current Perspectives on Proteus Species: From Morphology to Multidrug Resistance

Proteus species are Gram-negative, highly motile opportunistic pathogens belonging to the family Enterobacteriaceae and are widely distributed in the environment, including the human digestive tract and animals. Among them, Proteus mirabilis is the most clinically significant species and is commonly associated with catheter-associated urinary tract infections (CAUTIs), wound infections, gastrointestinal disorders, and other nosocomial infections. The pathogenicity of Proteus is attributed to several virulence factors, including swarming motility, urease production, fimbriae, adhesins, hemolysin, lecithinase, and biofilm formation, which facilitate colonization, tissue invasion, immune evasion, and persistence within the host. The genus also possesses complex antigenic structures involving O, H, and K antigens that contribute to serological diversity and pathogenic variability. Increasing antimicrobial resistance among Proteus isolates, particularly through the production of extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, and carbapenemases, has become a major clinical concern. These resistance mechanisms significantly limit therapeutic options and complicate infection control measures. This review highlights the classification, morphology, virulence factors, pathogenicity, clinical manifestations, antimicrobial resistance mechanisms, and phenotypic characteristics of Proteus species, emphasizing their growing importance as multidrug-resistant (MDR) opportunistic pathogens.