Importance of Mycoplasma Testing

While bacterial and fungal infections of cultures are relatively easy to detect, prevent and treat, a contamination with mycoplasma represents a much bigger problem in terms of incidence, detectability, prevention, eradication and its effects on the final product. It has been estimated that approximately 11% of cell cultures in current use are infected with mycoplasma.

Most common contaminating mycoplasma species

While a large number of species have been isolated from contaminated cell lines, detailed investigations on the identity of the contaminating species showed that by far the largest portion of infections is caused by a relatively small number of mycoplasma and acholeplasma species: 90 – 95% of the contaminants were identified as either M. orale, M. hyorhinis, M. arginini, M. fermentans, M. hominis or A. laidlawii (table 3) (Drexler and Uphoff, 2002). 

 

Species

Frequency

Host

M. orale

20-40%

Human

M. hyorhinis

10-40%

Swine

M. arginini

20-30%

Bovine

M. fermentans

10-20%

Human

M. hominis

10-20%

Human

A. laidlawii

5-20%

Bovine

 

Source of mycoplasma Conamination

1.       Laboratory staff

2.       Cross-contamination from infected cultures

3.       Culture reagents

4.       Original (primary) tissue isolate (<1%)

 

Tissue specimens used to initiate cell cultures do not appear to represent a major source of mycoplasma infection (table 2). The frequency of infection in primary cell cultures is low, around 1% (Barile and Rottem, 1993).

The high incidence of bovine mycoplasma species, mainly A. laidlawii and M. arginini, implicates fetal or newborn bovine serum. While bovine serum contamination has certainly significantly decreased over time due to intense efforts of the suppliers with regard to prevention and testing, serum lots absolutely free from mycoplasma cannot be guaranteed.

Because the largest percentage of mycoplasmas found in cell cultures are of human origin, one may assume that laboratory personnel are one of the major sources of contamination. In laboratories with contaminated cells, most or all cultures are positive containing the same mycoplasma species (McGarrity et al., 1992). Mycoplasma –infected cell lines are themselves the single most important source for further spreading of the contamination. This is due to the ease of droplet generation during handling of cell cultures, and the prolonged survival of dried mycoplasmas. Operator-induced contamination is a multifaceted problem. Mycoplasmas are spread by using laboratory equipment, media, or reagents that have been contaminated by previous use in processing mycoplasma-infected cells.