C. difficile wears chain-mail armour and poisons its gut rivals
Clostridioides difficile survives by a mix of armour and chemical warfare. A mesh-like protein coat shields it from saliva enzymes and some antibiotics, it releases a compound that stunts neighbouring microbes, and its spores shrug off even strong bleach. Usually, though, the friendly bacteria in a healthy gut keep it in check.
The microbe is a rod-shaped, spore-forming bacterium that shuns oxygen and is common in soil, sewage, animal dung and retail meat. Under a microscope its cells often look like drumsticks, swollen at one end. It was moved out of the genus Clostridium in 2016, and as of 2025 it is the only member of its new genus. In the United States in 2017 it caused an estimated 223,900 infections among hospital patients and 12,800 deaths.
Its reputation as a hospital bug is only partly deserved. At most a third of cases trace back to spread from an infected patient in hospital, and most are caught elsewhere. It lives quietly in many guts, outcompeted for food by other bacteria. When an antibiotic suddenly wipes out those competitors, it can take over, typically within 5 to 10 days. Carriers who have had earlier bouts of diarrhoeal illness seem to be the main reservoir, and their shedding can swing from undetectable to heavy overnight. Young children often carry toxin-producing strains yet rarely fall ill.
Disease comes from toxins, chiefly two called A and B, which disable signalling proteins in gut cells and can inflame the colon severely. Toxin output is not constant: a sensor protein called CodY holds it back while favoured amino acids such as proline and glycine are plentiful and releases the brake when they run short. The bacterium also produces para-cresol, which inhibits other microbes nearby.
A 2005 report described a highly toxic strain resistant to fluoroquinolones spreading across North America, and by 2018 up to 12 per cent of clinical samples resisted metronidazole. Researchers writing in Nature Communications traced much of its toughness to the S-layer; stripping one region, called D2, left cells open to lysozyme, the saliva enzyme that rips bacteria open.
Source: Clostridioides difficile
