CRISPR-Cas associated adaptive immune system likely plays a role in the pathogenesis of Clostridium difficile infection and may alter resistance to commonly used antimicrobials. This study aims to assess the differences in antimicrobial susceptibility patterns based on presence/absence of the CRISPR-Cas system in clinical C. difficile strains.
A total of 60 clinical C. difficile isolates were included. The antibiotic sensitivity and resistance pattern of 7 antibiotics (metronidazole, vancomycin, fidaxomicin, levofloxacin, meropenem, clindamycin and cefepime) were tested. Previously ribotyped C. difficile isolates were CRISPR typed based on the presence of Cas1 gene. 48-hour MIC was determined from the overnight culture of each of the C. difficile strains using microdilution method and MIC50, MIC90, and Geomean calculated.
The 48-hour MIC for 60 C. difficile strains of different ribotypes (52 CRISPR-positive and 8 CRISPR negative) were determined and compared with that of a standard strain R20291.The range of MICs for various antibiotics were - Vancomycin (0.25 to 16 g/ml), Metronidazole (0.24 to 7.66 mg/ml), Fidaxomicin (0.03 to 1.92 mg/ml), Meropenem (2 to 16 mg/ml), Cefepime (8 to 500mg/ml), Clindamycin (4 to 250 mg/ml) and Levofloxacin (0.5 to 250 mg/ml). The Geomean of MIC for C. difficile specific antibiotics (Vancomycin, Metronidazole, Fidaxomicin) was higher among the CRISPR negative (0.85, 1.87, 0.24) compared to CRISPR positive strains (0.90, 0.48, 0.06). Similar results were also seen for C. difficile non-selective antibiotics (Meropenem, Cefepime, Clindamycin and Levofloxacin) with CRISPR negative being (5.28, 143.59, 36.41) and CRISPR positive (4.13, 163.14, 18.77). There was no significant difference in the MIC by ribotypes.
The presence of CRISPR in C. difficile might have the potential to protect against the development of antibiotic resistance against commonly used antibiotic with specific mechanism of action.
K. Begum, None
M. J. Alam, None
K. Garey, None