Enterococcus faecalis is typically described as a commensal bacterium – one of our “good bacteria” – but in patients with weakened immune systems, it can transfer DNA to other bacteria, in this case, providing genes for vancomycin resistance to MRSA – Methicillin-resistant Staphylococcus aureus, a bacterium that causes infections in different parts of the body. It’s tougher to treat than most strains of staphylococcus aureus — or staph — because it’s resistant to some commonly used antibiotics.
Antibiotic resistance is spreading fast all over the world. When infectious bacteria mutate in a certain way and then multiply, they can become resistant to even the most powerful drugs.
But research has revealed a worrying alternative way that antibiotic resistance can spread: an organism that passes on its resistance on to other living bacteria.
In June 2012, a 35-year old man from São Paulo found himself in hospital with a myriad of problems. Alongside a diagnosis of skin cancer, he was told he harboured a potentially lethal bacterial infection. The doctors placed him on a course of chemotherapy and antibiotics, and the bacteria-killing treatment appeared to do its work. But within a month the microbe-driven fever had returned.
The patient had contracted the well-known superbug MRSA (methicillin-resistant Staphylococcus aureus). So the medical team turned to one of the “last line of defence” antibiotics, the powerful compound vancomycin. This strain of MRSA originally had no natural defence against vancomycin, but by August that year it had become resistant, rendering the treatment ineffective.
Scientists would later uncover that rather than acquiring resistance through a simple mutation, the MRSA had instead been gifted a huge chunk of new DNA. Within this string of donated genetic code were the instructions for proteins that would keep the bacteria safe from the destructive work of the antibiotic.
MRSA had been dealt a winning hand, but where had this DNA come from?