Monday, July 22, 2013

Why Is There Antibiotic in Cell Culture Media?

Answer: Antibiotic is there to kill microbes, if any.

That's the short-answer.

Question: Why would there microbes in the cell culture?

Answer: Poor aseptic practices.

So if you have good aseptic procedure, then you ought not have antibiotics in the media, right?

Answer: Right, but we still keep it in just in case.

This type of thinking pervades large-scale cell culture. And ironically, it's backwards.

I'm sure there are smart ways of using antibiotics in cell culture, but I'm not aware of any.

Antibiotic Resistance

antibiotic gentamicin
Molecular structure of Gentamicin
The first problem with antibiotics is that they select for resistance: over time, the organisms that are susceptible to antibiotics die off leaving the antibiotic resistant organisms to remain. These organisms may become slow-growing, low-level contaminations that are difficult to detect.


The second problem with antibiotics is that they interfere with detection. QC Microbiology tells us their tests are sensitive to 1 colony-forming unit (CFU) in the sample, which means if there is 1 CFU in a 40mL sample bottle, they'll find it. But 1 CFU/40mL is 25 CFU/L... and for a 12,000L bioreactor, you need a contamination of ~300,000 CFUs in order for QC to detect contamination.

The sooner the culture hits 300,000 CFUs (assuming you have a 12kL), the sooner you know there's a problem, and antibiotics slow things down.

Poor Aseptic Technique

The third problem with antibiotics is that it lets you get away with sloppy procedure. Back in 1973, M.F. Barile's study of mycoplasma contamination in cell culture found that 72% of cultures grown continuously in antibiotics were contaminated versus 7% of cultures without antibiotics. The conclusion was that over-reliance on antibiotics leads to poor aseptic technique.

Happily, we are coming across more and more customers who don't use antibiotics at the production scale, and generally speaking, these contamination investigations are mercifully straightforward.

Those other guys have long weeks of meetings ahead of them.

See also:

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