Inhibitory effect of yoghurt and soya yoghurt containing bifidobacteria on the proliferation of Ehrlich ascites tumour cells in vitro and in vivo in a mouse tumour model.

The effect of yoghurt and soya yoghurt containing Bifidobacterium lactis Bb-12 or B. longum Bb-46 on Ehrlich ascites tumour cell proliferation was investigated in vitro and in vivo. Tumour cells were incubated with B. lactis Bb-12 or B. longum Bb-46 cultivated in de Mann Rogosa Sharpe (MRS) broth medium, or with their centrifuged supernatant fractions or sediments, for 2 h at 37 degrees C. Treatment resulted in the inhibition of tumour cell proliferation by 85.42 (SD 0.78) and 85.10 (SD 1.28) % by intact micro-organisms, 77.61 (SD 0.29) and 71.43 (SD 1.75) % by their supernatant fractions, but only 4.00 (SD 0.19) and 9.09 (SD 1.24) % by the two sedimented bacteria, respectively. The incubation of tumour cells with yoghurt and soya yoghurt containing Bb-12 for 2 h resulted in 83.01 (SD 0.11) and 88.23 (SD 0.06) % inhibition, respectively, while it was 83.82 (SD 0.24) and 86.36 (SD 0.06) %, respectively for the same products containing Bb-46. Corresponding values for plain yoghurt and soya milk (without bifidobacteria) were 32.81 (SD 0.14) and 5.55 (SD 0.12) %, respectively. The differences between yoghurt or soya yoghurt containing Bb-12 or Bb-46 and plain yoghurt, soya milk or control treatments were statistically significant (n 3; P<0.05). Female Swiss albino mice were injected intraperitoneally with the same tumour cells. The lifespan of mice fed diets supplemented with yoghurt or soya yoghurt containing Bb-12 or Bb-46 was prolonged by 16, 23, 34 and 39 %, respectively compared with that of the positive control group (n 6; P<0.05). The lifespan of groups fed plain yoghurt or soya milk was prolonged by 15 and 8 %, respectively. Prolongation of lifespan was positively correlated with faeces bifidobacterial count in the groups fed yoghurt or soya yoghurt containing bifidobacteria (r 0.917; P<0.05).