How do I detect bacterial cell culture contamination?

Bacterial cell culture contamination is relatively easy to detect by visually inspecting the culture a few days after it is infected. An infected cell culture will appear turbid or cloudy and may have a thin film on the surface. When observed under a low-power microscope, the bacteria can be seen as tiny, granules moving between the cells. The shapes of individual bacteria are easily discernible under a high-power microscope. The change in appearance of the infected cell culture is often accompanied by a sudden drop in pH of the culture medium.