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The bacterium Clostridium difficile, the pathogen that most often causes antibiotic-associated diarrhoea, has genetically specialised in hospital survival. According to a recent study by Nature Genetics1, a strain that forms resistant spores is spreading among in-patient settings.
It is normally a harmless bacterium: Found among other microbiota in human gastrointestinal flora, Clostridium difficile rarely occurs as a pathogen. However, when bacterial flora present in patients’ intestines – which include E. coli – have been killed off by antibiotics, then C. difficile can spread rapidly throughout the intestine and cause severe diarrhoea.
C. difficile has adapted particularly well to the conditions in hospitals. Here the spores of the pathogen have an important selection advantage because they are very resistant to disinfectants. This makes it easier for the bacterium to spread. C. difficile infections (CDI) are the most common cause of nosocomial2 and antibiotic-associated diarrhoea today. In Germany alone, a total of around 70,000 people suffer from a CDI every year.
Researchers at the Wellcome Sanger Institute in Hinxton near Cambridge have now genetically studied 906 C. difficile isolates to obtain a precise understanding of the properties and evolution of this pathogen. The researchers discovered that the C. difficile strains commonly found in hospitals differ genetically from other C. difficile isolates to such an extent that they seem to be evolving their own bacterial species. Today, the Clade A bacterial strain accounts for roughly 70 percent of the C. difficile isolated in hospitals. The researchers attribute this to genes that enable Clade A to better utilise glucose and other simple sugars. Experiments on mice have confirmed this. When the food of the animals was enriched with sugar, C. difficile spread more rapidly in the intestine.
For clinical medicine, this means that the patient’s diet following antibiotic treatment could directly affect the risk of contracting a CDI infection. Faecal transplant can be used to treat disorders In many cases, a stool transplant improves the patient’s condition. In a “faecal microbiota transplantation (FMT)”, a small amount of faeces is transplanted from the stool of a healthy donor into the patient’s intestine. The goal is to encourage a healthy balance of bacterial flora to colonise the damaged intestine of the patient, so as to supress the dominating Clostridia. For patients with a Clostridia infection who have not responded to standard therapy with an antibiotic, FMT leads to a cure in up to 90 percent of cases.
Although researchers suspect that Clade A may have formed 76,000 years ago, the bacterium was not widespread for a long time. Its increase in hospitals will make the role of hygiene and prevention even more important in the future.