**2.1 Development and spread of antimicrobial resistance**

The development of resistance in microbes arises in two ways: (i) intrinsic resistance, which occurs when the microbial species is able to innately resist the activity of an antimicrobial agent (by preventing either the entry or binding of the antimicrobial agent); and (ii) acquired resistance, in which once-susceptible microbial species mutate or obtain genes from other microbe, to acquire resistance. Antimicrobial resistance cannot be prevented because every time antimicrobials are used, the effective lifespan of that antimicrobial drug is shortened [10]. In general, few categories of pathogen are responsible for a large portion of resistant infections in humans. One of them is New Delhi metallo-β-lactamase-1 (NDM-1) gene which confers broad resistance to most antibiotics, including carbapenems, and can be transferred to a wide variety of bacterial species [11]. Another is resistant Gram-negative bacteria which carry extended-spectrum beta-lactamase enzymes (ESBLs), responsible for high levels of resistance to some of the most commonly prescribed antibiotics [12].
