Analysis of toxin and multilocus sequence typing of Clostridium difficile strains isolated from China-Japan Friendship Hospital

Abstract

Objective To analyze the characteristics of toxin, the PCR-ribotyping(RT) and the multilocus sequence typing(MLST) of Clostridium difficile strains isolated from China-Japan Friendship Hospital in order to provide a basis for monitoring the outbreak of nosocomial Clostridium difficile infection. Methods A total of 321 samples were collected from the patients with suspected Clostridium difficile infection(CDI) in China-Japan Friendship Hospital(CJFH) during 2012 to 2013. All Clostridium difficile strains were isolated and identified by the standard phenotypic culture method. Cytotoxicity test was performed to detect toxin B. Toxin genes (tcdA and tcdB) and binary toxin genes (cdtA and cdtB) harbored by those strains were analyzed. RT and MLST were used for homologous analysis. Clinical data of the patients were collected to analyze the isolation rate of Clostridium difficile in different populations. Results Forty-eight strains of Clostridium difficile were isolated from 46 patients with diarrhea and three of them were isolated from the same patient. The incidence of CDI among all patients, outpatients and inpatients were 14.3%(46/321), 12.8%(5/39) and 14.5%(41/282), respectively. Toxin B was detected in all of the strains as indicated by the cytotoxicity test. Strains of sequence type 1(ST1) showed the strongest cytotoxicity of all the isolated Clostridium difficile strains. Ten out of the 48 strains (20.8%) were tcdA(-)/tcdB(+ ) strains, which belonged to either ST37 or ST81. The results of RT and MLST were consistent in assigning the strains into nine types, in which the predominant type was ST1/RT027 accounting for 27.1% (13/48). All of the ST1/RT027 strains presented a toxin gene profile of tcdA(+ )/tcdB(+ ) and cdtA(+ )/cdtB(+ ). Most of the ST1/RT027 strains were isolated from the Traditional Chinese Medicine Department of Respiratory, where smallnosocomial outbreaks of ST1/RT027 strain infection might happen. Conclusion CDI diagnosed in CJFH mainly belongs to nosocomial infection. Most of the isolated strains harbor tcdA(+ )/tcdB(+ ) genes. Surveillance for the outbreaks of CDI caused by ST1/RT027 strains over producing toxins A and B should be strengthened in hospitals. Key words: Clostridium difficile; Standard phenotypic culture method; Cytotoxicity test; Ribotyping; Multilocus sequence typing