Vol.68 No.1 January 2020

Evaluation of methods of detection and antimicrobial susceptibility of Clostridioides difficile isolates in Sapporo, Japan

Yuki Sato¹⁾, Masaaki Shinagawa¹⁾, Shinya Nirasawa¹⁾, Masachika Saeki¹⁾, Yuki Yakuwa¹⁾, Makito Tanaka¹⁾, Nozomi Yanagihara^{1, 2)} and Satoshi Takahashi^{1, 2)}

¹⁾Division of Laboratory Diagnosis, Sapporo Medical University Hospital, 291 South-1, West-16 Chuo-ku, Sapporo, Hokkaido, Japan
²⁾Department of Infection Control and Laboratory Medicine, Sapporo Medical University School of Medicine

Abstract

An immunochromatography (IC) assay is widely used for detection of toxigenic Clostridioides difficile. There are few reports on the frequency of C. difficile binary toxin-producing strains and hypervirulent strains. Antimicrobial susceptibility has not been performed in most facilities. We evaluated the detectability of toxigenic C. difficile with the IC assay kit "C. DIFF QUIK CHEK COMPLETE." Additionally, we investigated the toxigenicity and antimicrobial susceptibility in clinical C. difficile strains. Two hundred eighty-five fecal samples were collected from patients suspected as having antibiotic-associated diarrhea between February 2015 and July 2016. C. difficile was detected in 50 samples (17.5%) with selective anaerobic culture. Of 50 C. difficile strains, 35 (70.0%) were positive for toxin A/B. The specific PCR for toxin genes (tcdA, tcdB, cdtA and cdtB) showed 21 (42.0%) of toxin A+B+, 14 (28.0%) of A−B+and 15 (30.0%) of toxin A−B−. The bacterial concentrations in 50 samples ranged from 1.0 × 10¹ to 3.0 × 10⁶ colony forming units per milliliter. The positive and negative concordance rate between the IC assay and toxigenic culture were 22.9% and 99.6%, respectively. Only 1 strain possessed a binary toxin gene. No strains suspected as having a hypervirulent lineage were observed. Fidaxomicin (FDX) had the lowest value of MIC₉₀ (0.12 μg/mL) compared to 4 antimicrobial agents [penicillin G, tazobactam/piperacillin, metronidazole (MNZ) and vancomycin (VCM)]. In conclusion, the IC assay is simple and rapid, but has insufficient sensitivity for toxin detection. Therefore, the combination of this assay and other examination tests would improve the diagnostic accuracy in C. difficile infections. To monitor those strains showing hypervirulence and demonstrating antimicrobial resistance to therapeutic agents like MNZ, VCM and FDX, continuous surveillance is needed.

Received

May 13, 2019

Accepted

August 20, 2019

Jpn. J. Chemother. 68 (1): 155-161, 2020