Mycoplasma: Tiny bacteria, big risk

Cell line contamination is getting a lot of scrutiny lately, and the urge to prioritize the external threat of cross-contaminated or mislabeled cells is compelling. After all, we can imagine “battening down the hatches” to keep out risks to our work. We’ve covered the rising awareness of cross-contamination and efforts to prevent it in two articles, including the new “Whose line it is, anyway? Contamination draws public attention.”

But the fact is, the more common risk to your work isn’t something slipping in from outside. Like the cliché from horror movies, it comes from inside the lab, from viruses, mold, and bacteria that flourish in unintentionally ideal conditions or from lack of aseptic technique. And today, the most insidious threat—one that may already be affecting your cell cultures—may come from Mycoplasma.

So, how big a threat is Mycoplasma to your lab?

The insidiousness of Mycoplasma

Mycoplasma bacteria are a special risk to lab work because they are hard to detect and can be difficult to eradicate. They’re particularly challenging for two reasons:

1. Their size. Because they are so small (0.15 to 0.3 microns), they frequently pass through sterilization filters that catch other contaminants, and their effects are rarely visible to the naked eye until the damage is done.
2. Their structure. A lack of cell wall makes them resistant to common antibiotics, such as penicillin, that work by targeting the cell wall. Like their size, this structural feature also contributes to their ability to slip through the membranes of many standard sterilization filters.

How bad does it get? Mycoplasma contamination affects the host cells’ metabolism and morphology, causes chromosomal damage and aberrations, and causes cytopathic responses. Therefore, data generated from contaminated cells can be unreliable.

And contamination is pervasive. Data from the 1990s found that, in the United States, 11 to 15 percent of cultures were contaminated, with significantly higher numbers in Europe and Japan. But even today, the numbers are dismaying: A Nucleic Acids Research paper published early in 2015 described a study of rodent and primate samples that determined that 11 percent were contaminated by Mycoplasma.

Like cell line cross-contamination, Mycoplasmas have crossed over into the mainstream news, with reports of a study published in The International Journal of Epidemiology on the prevalence and possible sexual transmission of Mycoplasma genitalium in the United Kingdom.

How can you prevent it?

We recommend you test for Mycoplasmas at least once a month, as part of your regular aseptic practices. Also, look for sterilization filters with a small enough pore size (0.1 microns) to catch the tiny bacteria. Thermo Fisher Scientific has Mycoplasma detection kits and more resources on preventing and detecting contamination on its Mycoplasma Detection page.

If you weren’t concerned about Mycoplasmas before, we hope this opens your eyes to the unique risks they pose to cell culturists.