Antimicrobial resistance in bacterial microorganisms has emerged as a considerable challenge to human well-being in the twenty-first century. Bacteria resistant to multiple drugs are becoming responsible for increased morbidity and mortality, and this trend is expected to grow phenomenally in the next two decades. Among various antimicrobials critically important for treating bacterial infections, quinolones represent one of the most prescribed classes of antimicrobials in treating multiple gram-negative bacterial infections in humans. Although colistin is not a preferred antibiotic for human treatment because of its toxicity, the recent emergence of extended-spectrum β-lactamase (ESBL)-producing, carbapenem-resistant Enterobacterales has necessitated a reevaluation of its clinical efficacy. However, the emergence of mobile colistin-resistant plasmids is gradually jeopardizing its potential use in treatment. Quinolone- and colistin-resistant ESBL-producing Escherichia coli are increasingly being reported worldwide. Due to genetic alterations in elements of the quinolone resistance–determining region (QRDR) and the acquisition of plasmids harboring quinolone- and colistin-resistant genes via horizontal gene transfer, E. coli may display varying degrees of quinolone and colistin resistance. The emergence of multidrug-resistant E. coli recalcitrant to β-lactams, carbapenems, quinolones, and colistin can jeopardize antibiotic chemotherapy, potentially leading to an unprecedented health crisis in the future. This chapter discusses the genetic molecular mechanisms underlying colistin and quinolone resistance in E. coli, the role of new clonal groups in the spread of resistance, and the potential strategies needed to mitigate their public health implications.