Pathogenic bacteria species have been resistant to antibiotics before humans even made antibiotics. These bacterial samples which have displayed natural antibiotic resistance are as such due to genetic variation and mutations. When a bacterial species is exposed to an antibiotic, there is a selective pressure working against the majority which is not resistant. This leads to a decrease in the population of non-resistant bacteria yet an increase in the population of resistant bacteria since they are able to thrive and reproduce. This is how a resistant strain within the pathogenic bacteria can develop and multiply. This adaption of bacteria to be able to be resistant in the presence of antibiotics is an agent of natural selection and allows
