In the antibiotic testing on the bacteria lawn, it is found that the Staphylococcus aureus (S. aureus) is less resistant than Pseudomonas aeruginosa (P. aeruginosa) as S. aureus is susceptible to three kinds of antibiotics (susceptible: CO, GM and S; resistant: AP, KF, ST, T and TS) compared to P. aeruginosa which is susceptible to two types (susceptible: GM and FC; resistant: PG, CD, SMX, T and EM). The reason P. aeruginosa is so particularly so resistant is to most of the modern antibiotics is because of its intrinsic resistance that arises from the permeability and secondary resistance mechanisms such as energy-dependent multidrug efflux and chromosomally encoded periplasmic Î²-lactamase. At such level of natural resistance, mutational resistance to most classes of antibiotics can readily arise (Hancock & Speert, 2000). For instance, the resistance of P. aeruginosa towards PG is because of de-repression of chromosomal Î²-lactamase and also the overexpression of the MexAB-OprM multidrug efflux pump due to a NalB mutation. Specific plasmid-mediated Î²-lactamases also infer that the resistance to PG could be a form of introduction of foreign DNA from surroundings or via conjugation with other bacteria (Hancock & Speert, 2000).