Pseudomonas A. are resistant to many disinfectants and antimicrobials. B. are mostly harmless except for the opportunistic P. aeruginosa. C. require nutrient rich environments. D. do not contain plasmids. E. are resistant to many disinfectants and antimicrobials AND are mostly harmless except for the opportunistic P. aeruginosa.

The best answer is option E.

Explanation:

Pseudomonas are gram-negative bacteria which is present almost everywhere air, soil, water and even indoors. These gammaproteobacteria are also present in some of the healthy people.

Pseudomonas is resistance to many antimicrobials and disinfectants. These bacteria are generally harmless but some opportunistic species like P. aeruginosa are infectious.

Thus, the correct answer is option E.