When an antibiotic is taken to combat a bacterial infection, some bacterial cells may possess mutations which make them resistant to the drug. As with natural selection, those bacterial cells which are resistant to the drug will survive even after a full course of antibiotics. You are likely to feel better, and not notice the infection anymore as the number of resistant cells would be negligible. However, these cells will remain, divide and reproduce. Therefore, the next time you get this infection, there are more of the resistant cell type present, and as a result, the symptoms you experience may not clear as the antibiotic will not have the desired effect,  (i.e. destroying the bacterial cell wall). Eventually, your doctor will give you another antibiotic which appears to combat the infection, and you continue as usual. However, new mutations in the bacteria may have arisen as the infection grew, and so the resistance continues. Overall, you are left with resistant bacteria which are much harder to target as fewer and fewer antibiotics can destroy the bacterial cell walls. To make matters worse, antibiotics may not affect human cells but they do kill the 'good' bacteria which help to prevent infection and regulate our microbiomes. Therefore, alongside more resistant bacteria, our immune systems are less able to cope with future infections.  
Antibiotic-resistant bacteria also work their way into our systems from the ingestion of livestock. Many farmers use antibiotics to deter disease and promote growth in their stock. However, these animals are not immune to antibiotic resistance. As a result, there has been a rise in the number of resistant bacteria seen in livestock and thus, through ingestion of this stock, we have yet more antibiotic-resistant bacteria. Not only do humans need to stop taking antibiotics unnecessarily, so do animals! In 2017, WHO published new guidelines for the use of antimicrobials in food-producing livestock in a bid to educate those administering them but also, in an attempt to reduce the instances of unnecessary antibacterial resistance. \citep{resistance}

How can we Overcome Resistance? 

To overcome resistance research is underway into developing new antibiotics which aim to address different bacterial processes than those currently targeted. A novel approach, however, is looking to go back to basics and utilise something that has shown antibacterial properties for thousands of years: metals. Silver is regularly used in plasters to prevent bacterial infections in cuts (etc.), so now, scientists are investigating the use of silver in antibiotics. The exact mechanism is not known, but it is thought that as metals are not naturally found in a bacteria’s environment, bacterial cells are not able to form resistance towards them (yet!) and thus, silver can protect against bacterial infections \citep{Owens_2013}. Other research into the use of phages which naturally target bacteria, is also currently underway. Georgia uses phages widely for bacterial infections, but the more rigorous standards in countries such as the UK and USA, mean a much longer time frame until such research could be administered to the general public.