Final answer:
The blue contaminant in the Mycobacterium smegmatis liquid culture is likely Pseudomonas aeruginosa, identifiable by its characteristic blue-green pigment production. Contamination could have been prevented with the addition of carbenicillin to the culture medium.
Step-by-step explanation:
The likely identity of the blue contaminant in the Mycobacterium smegmatis liquid culture is Pseudomonas aeruginosa. This bacterium is known for producing distinctive blue-green pigments, such as pyocyanin on cetrimide agar, which is a telltale sign of its presence. This pigment is a common identifier for P. aeruginosa in laboratory tests, as it is one of the few organisms that not only survives but thrives on media with cetrimide, a selective agent that inhibits the growth of other species.
As for the prevention of this contamination, the correct measure, according to the original protocol, would be the addition of carbenicillin. Carbenicillin is effective against a broad range of gram-negative bacteria, including Pseudomonas aeruginosa, and would help suppress its growth within the culture.
Contamination can be a major issue in microbial cultures and, besides following strict aseptic techniques, the use of antibiotics like carbenicillin for the containment of Pseudomonas aeruginosa is a common practice. When culturing sensitive species like Mycobacterium, additional care must be taken to ensure that the sample stays pure and uncontaminated to arrive at an accurate diagnosis or research outcome.