Bacterial contamination is one of the most common cell culture contamination.
Poor aseptic culture condition, including handling, incubator and laminar flow hood, or culture media, can be common source of bacterial contamination.
Contaminated culture often becomes turbid and the medium turns yellow (phenol red containing medium).
Microscopic inspection of such culture is often sufficient to confirm the presence of bacteria. Motile bacteria and bacterial clumps are often observed in contaminated culture, which can easily be distinguished from cell debris. However, low level of contamination may go undetectable in the presence of antibiotics in culture.
In such cases, suspected contaminated culture can be grown in absence of antibiotics, which will allow the bacteria to grow, thus contamination can be detected easily.
Usually a contaminated culture once confirmed is discarded immediately. In case of precious culture, one can try to rescue the culture by treating the culture in presence of high concentration of antibiotics. Frequently replacing the culture medium containing high concentration bactericidal antibiotics may help to eliminate the bacterial contamination.