How does antibiotic resistance arise?

Bacteria replicate by binary fission, at a rate of up to one division every 20 minutes. This replication results in genetically identical daughter bacteria to the original, however with each round of genome replication there is a chance of random mutations in the genomic DNA, that may result in a novel protein/function. This rapid duplication and mutation rate, means that antibiotic resistance can arise in a population of bacteria, in which selection pressure caused by the antibiotic means that only those with the new allele for antibiotic resistance survive. These resistant bacteria will be in low concentrations, however the selection pressure means that the resistant alleles will increase In frequency in the population of bacteria, therefore leading to this resistant allele being persistent in the populations as those without the resistance allele are destroyed and those with survive. Bacteria can also exchange genetic information via horizontal gene transfer, in which conjugative transfer of DNA from one bacteria to another may result in the increased prevalence of the resistance allele within the population. Therefore, the antibiotic will no longer be effective in treating the bacteria population within the host, as antibiotic resistance has arisen with the high frequency of the resistance allele within the bacterial population.