**4.1. Genetics of antibiotic resistance**

Resistance can be an intrinsic property of the bacteria themselves or it can be acquired. There are two main ways of acquiring antibiotic resistance: i) chromosomal mutations and ii) horizontal gene transfer. But the question is where the horizontal gene comes from? Some of these genes have an environmental origin and began their evolution before the antibiotic era; most likely, the primary genes originated and diversified within the environmental bac‐ terial communities, then mobilized and penetrated into pathogens. [27; 28]

#### *4.1.1. Mutations*

Acinetobacterbaumannii (A. baumannii), E. coli, and Klebsiellapneumoniae (K. pneumo‐ niae), producing extended-spectrum β-lactamases (ESBL), vancomycin-resistant enterococci Enterococcus faecium (E. faecium) (VRE), MRSA, vancomycin-resistant S. aureus VRSA, ex‐ tensively drug-resistant (XDR) Mycobacterium tuberculosis (M. tuberculosis), Salmonella enterica (S. enterica) serovar Typhimurium, Shigelladysenteriae (S. dysenteriae), Haemophi‐

Great amount of antibiotic is used in nonhuman niches, leading to the spread of resistant bacteria too. Antibiotics have been used for improving the production of livestock and poul‐ try for more than 50 years [25]. The Institute of Food Technologists (IFT), once convened a panel of internationally renowned experts to address the concern that, the emergence of an‐ timicrobial resistance may result from abuse in food production, manufacturing, and else‐

Over the past several years, people struggled to search for the mechanisms of resistance. Therefore today there is a large pool of information about how drug resistances come out. Biochemical and genetic aspects of antibiotic resistance mechanisms are shown in Fig. 1.

lusinfluenzae (H. influenzae), Stenotrophomonas, and Burkholderia [23; 24].

where [26].

292 Drug Discovery

**Figure 1.** Kinds of antibiotic resistance mechanisms [85].
