Background: Clostridium difficile is an anaerobic gram-positive bacillus that is the leading cause of antibiotic-associated diarrhea (AAD) and pseudomembrane colitis. The symptoms of C. difficile infection (CDI) range from mild diarrhea to severe colitis and death. The incidence of CDI is on the increase, and it is a major cause of nosocomial and community-acquired infections. At the Microbiology Laboratory of Rajavithi Hospital, anaerobic culture has not been performed routinely; therefore, the antimicrobial susceptibility of these infections is not known.
Objective: To determine the antimicrobial susceptibility profiles of toxigenic C. difficile isolates at Rajavithi Hospital.
Material and Method: From August 2016 to April 2017, a total of 43 stool samples that were confirmed positive for C. difficile toxin by real-time polymerase chain reaction method were collected. Forty-three toxigenic C. difficile stool samples underwent anaerobic culture and identification using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). All of these were tested to minimum inhibitory concentrations (MICs) of 4 antimicrobial agents; clindamycin (CD), metronidazole (MTZ), moxifloxacin (MXF) and vancomycin (VAN) using gradient diffusion test strips.
Results: All of the 43 toxigenic C. difficile isolates at Rajavithi Hospital were 100.0% susceptible to VAN and MTZ, while susceptibility rates to CD and MXF were 9.3% and 6.9%, respectively. High MIC values of CD (MICs >256 mcg/mL) and MXF (MICs >32 mcg/mL) were found for 55.8% and 81.4%, respectively. Co-resistance to CD and MXF was found in 74.4% of these isolates.
Conclusion: All toxigenic C. difficile isolates identified at Rajavithi Hospital were susceptible to VAN and MTZ but had high resistance rates to CD and MXF, and the antimicrobial susceptibility testing of other antibiotics should therefore be tested to ensure appropriate treatment. Further classification of these toxigenic isolates into PCR genotypes and ribotypes for the detection of hypervilurence strains should be studied because they have high resistance to MXF, fluoroquinolone and CD.

Keywords: Clostridium difficile, Toxin, MALDI-TOF MS, Antimicrobial susceptibility