Fluorescence in situ hybridization (FISH) combined with 16S rRNA gene amplification and sequencing allowed researchers to make a definitive diagnosis of human intestinal spirochetosis (HIS) and further identify the causative pathogens.

Pablo Rojas, PhD, of Charité Universitätsmedizin Berlin, and his colleagues evaluated 149 paraffin-embedded or native intestinal biopsies from 91 consecutive patients with histologically diagnosed HIS. The reasons for endoscopy and histological investigation included chronic diarrhea, cancer/adenoma screening, inflammatory bowel disease, and endoscopic detection of polyps or colitis. In all, 12 patients were HIV-positive.

The researchers used a FISH probe to confirm Brachyspira spp. HIS for 77 of the 91 patients. A polymerase chain reaction (PCR) analysis of part of the bacterial 16S rRNA gene confirmed the presence of Brachyspira spp. in 75 patients. The sequencing allowed the researchers to drill down on the pathogen, identifying both the B. aalborgi and B. pilosicoli species lineage among the samples.

There were 14 cases in which researchers could not confirm the diagnosis of HIS with either FISH or RNA sequencing, but they noted that these cases were likely misdiagnosed by histopathology.

“FISH at the interface of histopathology and molecular biology is a valuable diagnostic tool for the diagnosis of HIS. The bright FISH signal in most cases already allowed rapid localization of Brachyspira spp. at 400 magnification. All samples that could be tested via PCR were consistent with the FISH results, whereas 14 cases were diagnosed false positive by histopathology,” the researchers wrote. “On these grounds, we propose to include FISH for the diagnosis and follow-up observation of HIS in routine practice.”

Find the full study in Anaerobe (2017 Oct. doi: 10.1016/j.anaerobe.2017.03.012 ).