The perplexing interactions between an organism and it’s gut commensal microbiota have both potentiating and detrimental effects on innate and adaptive immunity and consequentially the development of several immune-mediated diseases. Juvenile idiopathic (JIA) and reactive arthritis (ReA) are two adverse outcomes of such disorder in children. This study aimed to assess the differences in the presence of subtypes of Escherichia coli (E coli), one of the most abundant bacteria in the microbiota, in the stool of JIA and ReA patients.

Stool samples of 14 patients with joint swelling were collected during their first visit to Pediatric Rheumatology Clinic in Sestre milosrdnice University Hospital Center in Zagreb, Croatia. Three months later, the diagnosis of JIA was made in seven patients, while the others were classified as ReA. The samples were analyzed by mass spectrometry on nanoLC-Synapt G2 Si instrument. To identify the most abundant E coli subtypes, specialized software named Protein Reader with implemented Dust algorithm have searched through the NCBI nr database, that contains the records of more than 400 E coli subtypes. The median age of patients was 7.14 and 7.11, respectively.

Various E coli subtypes (P0301867.1-10, O104:H4, O103:H25, O111:H11, KTE and K) were three times more abundant in patients with JIA, while in children with ReA, the abundance of diarrheagenic E. coli (DEC) was detected.

Many studies have speculated the influence of gut microbiota in the development of arthritis in children. Despite the technological advancements in the examination of microbiota composition, there are still many limitations imposed by patient selection, methodology and data analysis.

Besides, without the proper definition of ‘healthy’ microbiome as a reference standard, it is challenging to distinguish alterations responsible for diseases development. In our proof-of-the-concept study microbiota was therefore compared in two groups of patients both presenting with arthritis.

Since E coli is one of the paramount bacteria in gut microbiota with more than 600 recognized subtypes, it is reasonable to assume that described differences can have a potential impact on the gut environment, with the contribution to the development of the chronic disease in JIA patients or the resolution of symptoms in children with ReA. While this observation needs conformation in multiple time points and larger patient cohorts, it pinpoints gut microbiota as a potential new therapeutic target in the treatment of chronic inflammatory diseases.