Lipopolysaccharide (LPS), the outermost component of Gram-negative bacterial cells, is critical to bacterial pathogenicity, functioning as an endotoxin that activates the human immune system and induces an inflammatory response during infection. LPS comprises three primary components: lipid A, the oligosaccharide core, and the O-antigen. The O-antigen, in particular, is highly variable and strain-specific, playing a pivotal role in how the host immune system recognizes bacterial cells. This study focuses on the Proteus mirabilis 1B-m strain, belonging to serogroup O78, the most prevalent serogroup in hospitals in Lodz, Poland. Given the increasing hospitalization rates, particularly among the elderly and catheterized patients, understanding the common strains and their virulence factors is crucial. This work presents bioinformatics analyses based on next-generation sequencing data (both short and long reads), aimed at elucidating the structure of the gene cluster responsible for O-antigen biosynthesis in the 1B-m strain. Our results suggest the presence of a unique wzx flippase in the strain, alongside the characterization of role of the licD gene, which was most often assigned a role in the phosphocholine decoration process of LPS. The function of licD in this strain appears to be linked to the ispD gene, potentially involved in the biosynthesis of CDP-ribitol. Additionally, we explored other genomic features, including the strain's genetic similarity to closely related microorganisms, the presence of antimicrobial resistance genes, and prophage elements. This study provides valuable insights into the genetic factors underlying the pathogenicity of the P. mirabilis 1B-m strain and its potential implications for hospital-acquired infections.