There are several causes of antibiotic resistance that have contributed towards the issues experienced today.
Over-prescription by clinicians has led to many more bacteria being exposed to antibiotics than necessary, increasing selection pressures for resistant strains and species. There is some evidence suggesting prescribing antibiotics for too long also leads to resistance arising. Government authorities, such as NICE in the UK, are modifying prescribing guidance to minimise the number of doses prescribed, while also ensuring prescriptions are of the correct antibiotic for the correct duration.
Patients may not complete their full course of antibiotics as prescribed by their clinician (as demonstrated by Terese Coffey, ex-UK health minister). This may lead to resistance developing in a patient, making it harder to resolve an infection. Government authorities, including the NHS in the UK, have information campaigns informing patients to take the complete course of antibiotics as prescribed by their clinician.
The vast majority of antibiotics are used in agriculture, through prophylactic use, as growth promoters, and clinical uses. This is an area of interest for action, due to widespread excessive use and the potential for zoonotic, resistant, bacterial infections to arise. Many legislatures are prohibiting the use of antibiotics prophylactically and as growth promoters, but there is still more work to do here.