[zaarn]

Doubt it. Bacteria population is managed by a number of factors, most important ones are food, warmth and predators. Additionally the student is unlikely to follow the strictest ABC-Guidelines so it's probably some samples already leaked if they had any.

If the bacteria only eats plastics then it has an uncontested food supply that nothing else will touch. Other bacteria are unlikely to suffer.

Warmth isn't actively being competed over since it can be obtained fairly easily by non-cooperative means instead.

Predators already exist. Virophages that can kill this bacteria are likely to evolve quickly considering they cover every surface on this planet. If it gets out of control, simply introduce the correct phage. They happily terminate 40% of all marine life every day so I think some plastic bacteria won't be trouble.