Antibiotic resistance is a natural phenomenon. Resistant bacteria are found on and in humans, in our environment, on farms, and on animals. They are all around us because resistance happens naturally as bacteria defend themselves against attack; resistant bacteria millions of years old have been found in the ice caps and in the frozen remains of woolly mammoths!
When an antibiotic is used, bacteria that can resist that antibiotic have a greater chance of survival than those that are ‘susceptible’, and those that are not killed quickly multiply. Some resistance occurs without human action, as bacteria can produce and use antibiotics against other bacteria, leading to a low-level of natural selection for resistance to antibiotics. However, the current higher-levels of antibiotic-resistant bacteria are attributed to the overuse and abuse of antibiotics.
Some bacteria are naturally resistant to certain types of antibiotics. However, some mutate to either produce enzymes that ‘deactivate’ antibiotics while other mutations change or close the target area on the bacteria that the antibiotic would normally attack. Some even create mechanisms to push the antibiotic back out of the cell when it attacks. Bacteria can acquire antibiotic resistance genes from other bacteria in several ways. They can transfer genetic material through a simple ‘mating’ process, or through plasmids that ‘reprogramme’ other bacteria to be resistant to antibiotics. They can also pick up stray DNA in their environment or can be infected by viruses.
Antibiotic resistance spreads as bacteria themselves move from place to place via human contact, for example, through coughing, or contact with unwashed hands, as well as animal contact, contaminated materials and in water, food and the wind. You will find resistant bacteria in the same places you find bacteria – it’s just some of them are resistant.
Among humans, human medicine is currently the main source of resistant bacteria.