The Main Source of Clostridium difficile in the Community is Nature

Introduction: Clostridium difficile is considered the leading cause of antibiotic associated disease worldwide. In the last decade a large number of studies were focused on identifying the main sources of contamination and natural reservoirs in order to elucidate the complete life cycle of the infection. Hospitals environments, food animals, pets and retail foods have been considered as potential vectors. However, the prevalence of C. difficile in these types of samples was found to be rather low, suggesting that other contamination routes must exist.

Purpose: This study is one of the few to explore the presence of C. difficile in the natural environment, and specifically away from the urban cores.

Methods: Farmlands and surroundings, residential, walking areas, and forests were studied. Samples, including mud, water, grass, roots, and stones, were collected from soils (top soil: organic debris partly decomposed). Sampling was performed from November to December 2016 with an outside temperature ranging between 2 and 8°C. Clostridium difficile was isolated from the samples by direct and enrichment broth.

Results: An unexpected, very high prevalence was found in this study. A total of 29 out of 59 samples were positive for the bacterium (50.8%). The viable spore count from soils varied between 50 and 250 cfu/g. Spores were detected more frequently on the roadsides than into the forests and farmlands. These findings may indicate that animals, including dogs, foxes, wild boards and birds among others are responsible of the spread of C. difficile spores. Furthermore, the high prevalence found indicates that the bacterium probably forms part of the normal gut microbiota of some animals. Further work should address if the presence of spores in this environment increases in spring and/or summer and the factors associated with this increase.

Significance: Results of this study reveal that humans are continuously exposed to the bacterium by a highly contaminated natural environment and only a disruption in the gut causes the disease.