Fig. 6

Mechanisms responsible for the development of antimicrobial resistance in bacteria. Bacteria naturally acquire new genes (including antimicrobial-resistant genes) to survive in a new environment or host. The antimicrobial-resistant genes produce enzymes (e.g., extended-spectrum β-lactamase in E. coli) to destroy or inactivate antibiotics. For example, penicillin-resistant bacteria synthesize β-lactamase, which breaks down the β-lactam ring of penicillin to an inactive degradation product. Through this mechanism, the bacteria cannot be killed by penicillin, leading to antimicrobial resistance in infected animals and humans. The sign (X) denotes an inability to kill bacteria