A young laboratory technician was puzzled by his plates when he pulled them out of the warm room. They never looked that cloudy and fuzzy before. He brought them to his lab director, who shook her head sadly; together, they threw the plates away. Does this story sound familiar? What probably happened was an all-too common problem in cell culture: a bacterial infection. Bacteria are just one example of a handful of microbes that can invade your cell culture, and set your research back weeks. Some are easy to detect; others, not so much. But microbial contamination ranks as one of the top three quality control concerns in tissue culture.
What are the most common microbial contaminants in cell culture? And how can you keep them out of your lab?
Bacteria are some of the most common contaminants, but also probably the easiest to spot. You usually will see a change in turbidity (like our young tech did earlier) and color. The pH of the medium will also drop. Using a light microscope, you should be able to see tiny moving bacterial cells. A daily look using a microscope will usually let you detect early contamination.
Yeast is another common bug-a-boo in the soup. You’ll also see a change in turbidity, but very little change in pH. Yeasts are also visible under a light microscope, which is useful for early detection. Molds can also pose a contamination threat, with similar symptoms as yeast contamination. Mold spores, however, are able to survive harsh conditions (including some antiseptic procedures), only to become active when growth conditions improve.
Viruses are more difficult to detect and remove. Their small size and survival tactics of taking over host cell’s genetics, metabolism and machinery make them a particularly pernicious contaminant. Viruses can be detected, but with more sophisticated equipment such as electron microscopy, immunostaining, ELISA, or PCR.
Mycoplasma are estimated by some as the most common contaminant. Simplified bacteria, Mycoplasma are the smallest self-replicating organism known. They survive by attaching to the cell wall or membrane of other organisms and acting as a parasite. Infections often can progress without any changes to cell cultures; by the time you see changes in cell behavior, the contamination is widespread. Many mycoplasma detection kits are available, and are based largely on PCR, ELISA, or autoradiography.
How can you stop contamination? By remembering that the principal cause of contamination by microbes is probably you. Our young lab tech probably infected his cell cultures early in the process. But by using aseptic techniques (washing your hands, wearing gowns and gloves, and using disposable pipettes, for example), you can help save off these common lab bugs.
How do you prevent cell culture contamination?
Sources:
Life Technologies (2012). Biological contamination.
Sigma-Aldrich (2010). Quality Control Considerations in Cell Culture.
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