This is a true statement because we are dependent on the use of antibiotics to treat infections. More resistance means it is harder to treat infections and infections that we no longer think of as harmful will once again become deadly. Surgical procedures will become much more dangerous because post-operative infections will become more common and harder to treat. Many non-surgical therapies also rely on the ability of antibiotics to defeat infections. Modern clinical medicine is essentially built on the effectiveness of antibiotics.
Recall that mutations can occur randomly in bacteria and are also influenced by environmental and chemical conditions. Mutations are a mechanism that allow for survival in the face of antibiotics. When a resistance gene is present in a population subjected to antibiotics, the bacteria that have it will survive and rapidly reproduce so that all remaining organisms have the resistant gene. These genes are often on plasmids that can easily be shared with other bacteria thereby promoting resistance in multiple species through horizontal gene transfer.
The mechanisms of antibiotic resistance are inactivation of the antibiotic, efflux pumping of the antibiotic, modification of the antibiotic target, and alteration of the targeted metabolic pathway. Inactivation of the antibiotic usually involves bacterial production of an enzyme, such as beta lactamase, that breaks down the antibiotic molecules. This requires expression of, and may involve acquisition of, the gene that codes for the modifying enzyme. Efflux pumping does not require changes in bacterial cell structure or function as efflux pumps are part of the normal cellular apparatus that removes molecules from the cell. Target modification and destruction of the antibiotic require special cellular activity.