Antibiotics are not a magic bullet

Contamination in Cell Culture

Contamination with microorganisms, such as mycoplasma that cannot be detected by bright field microscopy, as well as cross-contamination with other eukaryotic cells which results in misidentified cell lines, continue to present the most severe challenges afflicting cell culture laboratories worldwide.

• To this day, many researchers consider antibiotics to be a reliable measure to prevent microbial contaminations. Whereas it may not be widely known that most antibiotics used in cell culture do not affect mycoplasma, even the more obvious drawbacks of using antibiotics to control bacterial infections are often ignored. Antibiotics offer a false sense of security: is the prophylactic use of antibiotics in cell culture worth the ensuing disadvantages?

• Development of antibiotic-resistant bacterial strains.
• Low-level contaminations with partially resistant bacteria which are difficult to detect.
• Longer periods of cultivating cells harboring undetected contaminations increase the risk of spreading the contamination throughout the lab.
• Mycoplasma infections may take hold more easily due to the absence of any visible signs of contamination as well as longer cultivation periods.
• A false sense of security may foster poor aseptic technique.
• Antibiotics can have adverse effects on the metabolism of eukaryotic cells.

Quarantine helps avoid the spread of contamination

Tissue materials and cells which have been transferred between laboratories must be considered a potential source of contamination until the absence of microorganisms has been documented by validated methods, or until authentication of the cell line has been performed. Ideally, such materials should be kept in a separate room that is equipped with its own biosafety cabinet and CO₂ incubator. Only after biological materials have tested negative for contamination and cell lines have been authenticated will they be transferred to the general cell culture laboratory.

In general, primary cells or tissue cultures always bear the risk of endogenous contamination. Therefore they should be separated from continuous cell lines. Again, the ideal solution would be a separate cell culture room. If this is not possible, a separate designated quarantine CO₂ incubator and biosafety cabinet will help reduce the risk of spreading contamination.  If the option of a separate room or separate equipment is not given, it is recommended to confine suspect cells to a separate shelf in the incubator and use them last, at the end of the day, after all "clean" cultures have been maintained and all experimental work has been completed.

Get to know your enemy

It is generally not necessary to identify the exact species of a contaminant.  However, if the same type of contamination becomes a frequent occurrence in the lab, it may be worth taking a detailed look at the creatures ruining your cultures. It is hereby important to recognize the type of contamination you are dealing with (e.g. bacterial or yeast contamination). 

Did you ever wonder about mycoplasma, or why the medium turns yellow if your culture is contaminated with bacteria? Find out about the most common types of contaminants identified in cell culture laboratories worldwide. Learn how to recognize and fight contamination.  What does it look like? What impact does it have on your cells?

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