Fry those mollicutes!

By Dr. Ray Nims

It is not only viruses that may be introduced into biologics manufactured in mammalian cells using bovine sera in upstream cell growth processes. The other real concern is the introduction of mollicutes (mycoplasmas and acholeplasmas). Mollicutes, like viruses, are able to pass through the filters (including 0.2 micron pore size) used to sterilize process solutions. Because of this, filter sterilization will not assure mitigation of the risk of introducing a mollicute through use of contaminated bovine or other animal sera in upstream manufacturing processes.

Does mycoplasma contamination of biologics occur as a result of use of contaminated sera? The answer is yes. Most episodes are not reported to the public domain, but occasionally we hear of such occurrences. Dehghani and coworkers reported the occurrence of a contamination with M. mycoides mycoides bovine group 7 that was proven to have originated in the specific bovine serum used in the upstream process (Case studies of mycoplasma contamination in CHO cell cultures. Proceedings from the PDA Workshop on Mycoplasma Contamination by Plant Peptones. Pharmaceutical Drug Association, Bethesda, MD. 2007, pp. 53-59). Contamination with M. arginini and Acholeplasma laidlawii attributed to use of specific contaminated lots of bovine serum have also occurred.

Fortunately, the risk of introducing an adventitious mollicute into a biologics manufacturing process utilizing a mammalian cell substrate may be mitigated by gamma-irradiating the animal serum prior to use. This may be done in the original containers while the serum is frozen. Unlike the case for viruses, in which the efficacy of irradiation for inactivation may depend upon the size of the virus, mollicute inactivation by gamma irradatiion has been found to be highly effective (essentially complete), regardless of the species of molicute. The radiation doses required for inactivation are relatively low compared to those required for viruses (e.g., 10 kGy or less, compared to 25-45 kGy for viruses). The gamma irradiation that is performed by serum vendors is typically in the range of 25-40 kGy. This level of radiation is more than adequate to assure complete inactivation of any mollicutes that may be present in the serum. For instance, irradiation of calf serum at 26-34 kGy resulted in ≥6 log10 inactivation of M. orale, M. pneumoniae, and M. hyorhinis. In the table below I have assembled the data available on inactivation of mollicutes in frozen serum by gamma-irradiation.

So, the good news is that gamma irradiation of animal serum that is performed to mitigate the risk of introducing a viral contaminant will also mitigate the risk of introducing a mollicute contaminant. If the upstream manufacturing process cannot be engineered to avoid use of animal serum, the next best option is to validate the use of gamma irradiated serum in the process.  In fact, the EMEA Note for guidance on the use of bovine serum in the manufacture of human biological medicinal products strongly recommends the inactivation of serum using a validated and efficacious treatment, and states that the use of non-inactivated serum must be justified.


References: Gauvin and Nims, 2010; Wyatt et al. BioPharm 1993;6(4):34-40; Purtle et al., 2006