Polymer-encapsulated CdSe/CdS core-shell quantum dots, which closely model commercially-available quantum dots, were tested for toxic effects on Pseudomonas aeruginosa. The size, aggregation state, and dissolution of the quantum dots were characterised before and after exposure to bacteria. The physical association of quantum dots with bacterial cells was also examined. The quantum dots were found to have no effect upon bacterial viability. They remained chemically stable and dispersed in solution even with bacterial exposure. It is suggested that the absence of toxicity is the result of the stability of the quantum dots due to their protective polymer coatings, and their apparent lack of association with bacterial cells. The stability of the quantum dots, even in the presence of the bacteria, as well as their non-toxicity has implications for their environmental behaviour and ultimate fate.