An understanding of how efflux pumps contribute to antibiotic and toxin resistance is crucial for the development of strategies to combat bacterial infection and environmental pollution. One example is the MexAB-OprM efflux pump which is most well known in Pseudomonas aeruginosa for its clinical applications, as well as in other species such as P. fluorescens and P. mendocina for its role in expelling toxins and drugs from the cell. The objective of this experiment was to perform a targeted knockout of the oprM gene using CRISPR-Cas9 technology to interpret the role of OprM in toxin and antibiotic resistance. This study investigates the function of the OprM protein in expelling toxins and antibiotics from multiple Pseudomonas species, using ethidium bromide (EtBr), heavy metals (Cu, Zn), and antibiotics (tetracycline, ciprofloxacin) as model substrates. Following oprM knockout, toxin and antibiotic resistance in these bacterial species will be observed to indicate the role of the OprM subunit in the efflux pump, and thus give insights into its role in bacterial antibiotic resistance and toxin defense.