Abstract
Farm animals are a potential reservoir for human Clostridium difficile infection (CDI), particularly PCR ribotype 078 which is frequently found in animals and humans. Here, whole genome single-nucleotide polymorphism (SNP) analysis was used to study the evolutionary relatedness of C. difficile 078 isolated from humans and animals on Dutch pig farms. All sequenced genomes were surveyed for potential antimicrobial resistance determinants and linked to an antimicrobial resistance phenotype. We sequenced the whole genome of 65 C. difficile 078 isolates collected between 2002 and 2011 from pigs (n = 19), asymptomatic farmers (n = 15) and hospitalised patients (n = 31) in the Netherlands. The collection included 12 pairs of human and pig isolates from 2011 collected at 12 different pig farms. A mutation rate of 1.1 SNPs per genome per year was determined for C. difficile 078. Importantly, we demonstrate that farmers and pigs were colonised with identical (no SNP differences) and nearly identical (less than two SNP differences) C. difficile clones. Identical tetracycline and streptomycin resistance determinants were present in human and animal C. difficile 078 isolates. Our observation that farmers and pigs share identical C. difficile strains suggests transmission between these populations, although we cannot exclude the possibility of transmission from a common environmental source.
Highlights
In the past decade Clostridium difficile has emerged rapidly to become the most common cause of antibioticassociated diarrhoea in healthcare facilities worldwide
The human isolates (n = 46) were obtained either from hospitalised patients suffering from C. difficile infection (CDI) (n = 31) or from asymptomatic colonised humans working on Dutch pig farms (n = 15)
We initially compared the genotypes of the C. difficile 078 isolates with multilocus sequence typing (MLST), the traditional gold standard for epidemiological typing of bacterial pathogens
Summary
In the past decade Clostridium difficile has emerged rapidly to become the most common cause of antibioticassociated diarrhoea in healthcare facilities worldwide. Antibiotic treatment, advanced age and hospitalisation are the major risk factors for developing C. difficile infection (CDI) leading to diarrhoea, pseudomembranous colitis or death [1,2]. C. difficile virulence is primarily mediated by two potent enterotoxins, TcdA and TcdB, which are encoded in a pathogenicity locus (PaLoc) [9,10,11]. The binary toxin may contribute to the virulence of C. difficile as well [12], but its role in CDI is still under debate [13,14,15,16]. C. difficile produces highly resistant and infectious spores, which can survive in the environment for a long time and facilitate environmental transmission within the healthcare setting [17]
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