Our results revealed that faecal shedding of C. difficile is not common among healthy pets in Eastern China. The samples used in this study were collected from 18 pet shops. In pet shops, animals are kept in close contact with each other and may also be exposed to C. difficile from their handlers or visitors to the shop. Since the animals were kept in close proximity with each other, the low prevalence found in this study and the fact that no MLST types were shared between animals imply that the transmission of C. difficile is not common among animals. These results agree with observations in previous reports on the epidemiology of C. difficile in pets from Spanish veterinary teaching hospitals and veterinary clinics in the Madrid region [13, 20]. In the current study, colonization and transient passage of C. difficile were not differentiated. In further studies, the repeat collection of stool samples could be performed to reveal whether the isolated C. difficile colonize in or transiently pass through pets’ gut. The majority of samples were collected from dogs and the rest were from cats in this study, which may result in a bias of C. difficile prevalence in cats. Thus, due to the limited number of samples from cats, the results reported here may not completely represent the prevalence of C. difficile in cats in Eastern China. The age of the animal is important for C. difficile prevalence, since the pathogen has been isolated more frequently in the faecal samples of juvenile animals. In this study, faecal samples were collected from adult pets. In a future study, faecal samples from juvenile pets could be included, and an analysis of samples from juvenile and adult animals could be performed in a larger survey in China. Notably, one isolate recovered from dog faeces, D141–1, was resistant to three kinds of antibiotics and carried toxin genes (tcdA and tcdB). Since there is intimate contact between humans and their pets, this result suggests the possibility of transmission of toxigenic C. difficile from pets to humans during contact with pets.

Vancomycin and metronidazole have long been used as first-line drugs for the treatment of CDI [21, 22]. In this study, one isolate displayed high-resistance to vancomycin (MIC> 8 μg/ml). All isolates were susceptible to metronidazole (Table 1). A few isolates with low resistance or reduced susceptibility to vancomycin have been were reported in China [23,24,25]. All C. difficile isolates in this study showed resistance to clindamycin and cefoxitin, similar to clinical C. difficile in China and other countries [23, 24, 26, 27]. All C. difficile isolates in this study exhibited high susceptibility to tetracycline, consistent with clinical isolates in China [23]. Few studies have tested the susceptibility of C. difficile to chloramphenicol and ampicilin. The results in this study showed that all three isolates were susceptible to chloramphenicol. Isolate D141–1, which contained toxin genes, showed resistance to 3 different antibiotics, including ampicillin, clindamycin and cefoxitin, which are known to promote CDI [28, 29]. Some studies abroad have reported high resistence of C. difficile isolates from food or community patients, with resistance rates of 72.22 and 100%, respectively [28, 30]. Some domestic studies have shown that C. difficile isolated from hospitals also displays high resistance to clindamycin (88.1%) and cefoxitin (86.67%) [18, 23].

C. difficile can be classified into 5 major clades (Clade 1–5) and 2 novel clades (Clade 6, C-I) using MLST [31]. Clade 1 represents a highly heterogeneous cluster of toxigenic and nontoxigenic STs. This clade includes the majority of human isolate STs, such as ST-2, ST-14, ST-49, ST-8 and ST-17 [17, 31]. Jin et al. and Chen et al. identified more than 30 STs in stool specimens of patients with diarrhoea or patients suspected by clinicians to have CDI in hospitals located in Eastern China. Among them, ST2, ST3, ST35, ST37 and ST54 were the most prevalent types [22, 32]. In the current study, the three isolates were assigned to ST-3, ST-15 and ST129, which have been identified in patients with diarrhoea in Eastern China [22, 32]. These results indicate the potential for C. difficile to be transmitted from pets to humans.

Since there is intimate contact between humans and their pets, the isolation of C. difficile from pets in this study suggests a possibility that humans may be colonized by C. difficile carried by pets, although faecal shedding of pathogenic C. difficile was not common among healthy dogs and cats. Given that Clade 1 contains the majority of human isolate STs [17, 31], these results further imply that domesticated pets may be possible community reservoirs of C. difficile infection in humans, potentially due to the intimate contact between these pets and their owners.