Antibiotic resistance profiles and molecular characteristics of Clostridioides difficile PCR ribotypes in patients...

The present study aimed to survey the antibiotic resistance patterns and toxin gene expression levels in different PCR ribotypes and sequency types of C.difficile isolated from patients with colorectal polyps.

A total of 305 stool specimens were collected from patients with colorectal polyps. The antimicrobial susceptibility of C. difficile isolates was determined using the Liofilchem^® MIC Test Strips and disk diffusion method (DDM). The prevalence of toxin-encoding genes (tcdA, tcdB, cdtA, cdtB) was determined by PCR assay. PCR ribotyping was performed on all C. difficile isolates that tested positive for at least one of the toxin-encoding genes. SYBR Green based qRT-PCR was employed to determine the relative expression of toxin-encoding genes in C. difficile Ribotypes (RTs). Multilocus sequence typing (MLST) analysis was performed to investigate the genetic relationships of the C. difficile RTs.

A total of 37 C. difficile isolates were isolated from 305 stool samples (12.1%). Overall, 35.1% (n = 13/37), 48.6% (n = 18/37), 35.1% (n = 13/37), and 43.2% (n = 16/37) of C. difficile isolates were positive for tcdA, tcdB, cdtA, and cdtB genes, respectively. Out of 23 toxin gene-positive C. difficile isolates, 8 isolates were tcdA-/tcdB+/cdtA+/cdtB+, 5 isolates were tcdA+/tcdB+/cdtA+/cdtB-, and 4 isolates were tcdA+/tcdB-/cdtA-/cdtB+. The most prevalent RTs among C. difficile isolates were 012 (34.78%; n = 8), 126 (21.73%; n = 5), and 001 (17.39%; n = 4). The most frquenctly detected sequence types were ST-2 (n = 9; 39.13%), followed by ST-54 (n = 6; 26%). Toxigenic C. difficile isolates showed the lowest resistance rate to vancomycin (8.7%; n = 2/23) and metronidazole (13%; n = 3/20), respectively. The rates of vancomycin resistance in RT001 (25%) and RT126 (20%) C. difficile isolates were higher than those in other RTs. tcdB gene expression was significantly high in RT027 (8.15 fold), and RT078 (6.25 fold). Meanwhile, the tcdA relative expression level was significantly high in RT027 (6.25 fold), RT078 (4.75 fold) and RT126 (4.35 fold).

The significant increase in toxin gene expression observed in RT012, in addition to the hypervirulent ribotypes RT027 and RT078, is particularly concerning and highlights the potential for RT012 to become an emerging clinical challenge.