## 1 Historical Overview of Antibiotic Use
Penicillinase, which is able to dissolve penicillin, was first identified in a bacterium in 1940; it was the first reported enzyme able to destroy the structure of an antibiotic drug. In the following years, more research reported the presence of this deactivating enzyme in some other microbes, and over the subsequent decades, the exposure of bacterial populations to a high concentration of different antibiotics exacerbated the resistance situation [11; 12; 13]. This issue needs to be addressed publicly in order to raise awareness about antibiotic resistance, and the overuse of antibiotics should be reassessed, because the consequences are irreparable. For instance, infections that were once easily managed with standard antibiotic treatments have now developed resistance, making them significantly more challenging to treat. This growing resistance has resulted in prolonged hospital stays for affected patients, increasing the risk of severe complications and mortality [4; 5]. Dueto the severity of the problem, the World Health Organization (WHO) released a list of the 12 most health-threatening families of bacteria in 2017, which included _Pseudomonas_, _Acinetobacter_, _E. coli_, _K. pneumoniae_, etc. These families were reported as multidrug-resistant (MDR) pathogens with a great risk of causing severe infections in the bloodstream and respiratory system [12, 14]. However, developing a new antibiotic is a long process, and pharmaceutical companies are reluctant to invest because of the poor profitability and protractedness of the process [4] Figure 1.  
Mechanisms of Antibiotic Resistance: Genetic Mutations and Their Implications in Bacterial Evolution  
The first report regarding antibiotic resistance was produced back in 1930, when sulfonamides were first introduced. At the time, this predicted the inevitable occurrence of antibiotic resistance, despite the presence of fatal pathogens. Microbial strains obtain resistance genes from another bacterium via transgenes, phages, or plasmids, or through instability and mutations in chromatin, all of which lead to cross-resistance. Over the years, bacteria have utilized different ways to evade the various mechanisms of action executed by different classes of antibiotics, such as interfering with protein synthesis, dissolving the components of bacterial cell walls, and disrupting the metabolic pathways or nucleic acid production [15]. One resistance mechanism is genetic mutation, forming a \"resistance\" that leads to primary resistance without drug exposure; this acquired resistance, resulting from DNA mutations, is transferred through the vertical pathway [4, 12]. These mutations can happen through addition, deletion, inversion, substitution, or duplication, and be easily transferred to the next generation; for instance, mutations in the DNA gyrase coding genes \(gyrA\) and \(gyrB\) can result in resistance against fluoroquinolones, or resistance to macrolides can be caused by mutations in ribosomal RNA 23S sequences [16]. Plasmid transfer is another mechanism by which resistance-containing genes are transferred to another bacterium and its offspring. These mutations have the ability to change the target site's structure, which reduces the antibiotic's affinity and effectiveness. The inhibition of _Mycobacterium tuberculosis_, for instance, is caused by mutations in the RNA polymerase gene, which is the binding site for the antibiotic rifampicin [4]. Another significant consequence of these mutations is the upregulation of efflux pumps, which are specialized protein transporters capable of actively expelling antibiotics from the cell. This mechanism prevents antibiotics from reaching their intracellular targets, thereby reducing their efficacy and contributing to the development of antimicrobial resistance. MexAB-OprM is an example of efflux pump in _Pseudomonas aeruginosa_ (_P. aeruginosa_) that can pump out  
Figure 1: Significant events in antibiotic evolution, including the discovery of new antibiotics and the emergence of resistance to various types.