Microbe Selection for the SER-TAIN™ Gamma Irradiation FBS Validation Process

Validating gamma irradiation as a method for reducing bovine viral contaminants in FBS

A requirement for designing a process for validation of extraneous agent inactivation is the selection of specific microbes to evaluate. Those used in the SER-TAIN™ Gamma Irradiation Serum Validation were carefully selected to represent a wide range of organisms that are potential contaminants of serum products. These arise from either from the starting material itself or from the processing environment.

Model bovine viruses for testing FBS contamination

When considering potential endogenous microbes in bovine serum, viruses are of significant concern. Several viruses that commonly affect cattle are listed in Table 1; all of these are represented in the SER-TAIN™ validation. BVD, PI3, IBR, BTV and BLV (Table 1) are all bovine viral species of significant industrial importance. Although Porcine Parvovirus (PPV) does not cause disease in cattle under typical conditions, it has been isolated from bovine herds2. MvM is included as a potential environmental contaminant.

Viruses of the same type and similar physical characteristics have been shown to have comparable susceptibility to inactivation by gamma irradiation. This allows model viruses to be used as a substitute for viruses that are difficult or hazardous to grow and titer in culture. The use of viral models in validation studies is a common practice and is recommended by the Food and Drug Administration (FDA) in evaluating the safety of human therapeutics3. For example, Bovine Leukemia Virus (BLV) is utilized in studies as a model for Human Immunodeficiency Virus (HIV).

In some cases, appropriate model viruses were used to validate the SER-TAIN™ process. For example, consistently propagating bovine leukemia virus (BLV) in vitro has proven to be difficult or impossible. By using inactivated Feline Leukemia Virus (FeLV) as a model, a categorically-similar virus that is less fastidious, the amount of protection gamma radiation provides against contamination of biosubstances by BLV can be accurately assessed. Based on the irradiation information gathered about PI3 (of the family Paramyxoviridae), assessments can be made about the inactivation of serum-relevant paramyxoviruses, such as Bovine Respiratory Syncytial Virus (BRSV).

Similarly, the use of porcine parvovirus (PPV) as a model provides confirmation about effectiveness of the Ser-Tain™ process Bovine Parvovirus (BPV).

Table 1. Viruses Used for the SER-TAIN™ Gamma Irradiation Serum Validation

Common bacteria, fungi, and mycoplasma contaminants in fetal bovine serum (FBS)

Non-viral contaminants from the environment—like bacteria, fungi and mycoplasma—are also a major concern for users of serum products. Table 2 shows those non-viral organisms used in the SER-TAIN™ Validation.

Table 2.Non-viral Organisms Used in the SER-TAIN™ Gamma Irradiation Serum Validation

These bacterial and fungal species were selected for validation of gamma irradiation efficacy based on those recommended for sterility testing in the United States Pharmacopeia4. Although there are many types of mycoplasma, A. laidlawii was chosen because it is the variety that specifically affects cattle. Additionally, an E. coli-specific bacteriophage (JH Strauss, Strain MS2) was included as a representative potential contaminant from the environment. The use of these organisms provides scope for the protection SER-TAIN™ processing provides against a broad range of potential environmental agents.

The unique SER-TAIN™ radiation process provides assurance against the presence of microbial contaminants in serum products. The validation of this process has been fortified by the selection of a wide spectrum of organisms that have the greatest impact on serum products and are of predominant industry concern. Our experience with the SER-TAIN™ process allows the validation to be expanded as new extraneous agents emerge that have the potential for transmission through bovine serum.


Fenner F, Gibbs E, Murphy Fea. 1993. Veterinary Virology. Academic Press, Inc., .622-623.
Fenner F, Gibbs E, Murphy Fea. 1993. Veterinary Virology. Academic Press, Inc., .308.
Guide To Inspections of Viral Clearance Processes For Plasma Derivatives. [cited 2020]. Federal Drug Administration Internet homepage. . [Internet]. Available from: https://www.fda.gov/media/73834/download.
Section 71 – Sterility Tests, United States Pharmacopeia. 1995 Edition, pp. 1686-1687.