Objective      To determine the effect of nanobacteria (NB) and nano hydroxyapatite (nHAP) on breast cancer cells.       Methods      Breast cancer MDA-MB-231 cells were treated by 100 μg/mL nHAP with a turbidity of 2 M and NB at a same turbidity for 12

24 and 48 h

respectively. The MDA-MB-231 cells receiving no treatment served as normal control. CCK-8 assay was used to determine the toxic effect of NB and nHAP on t

he cells. The activity of lactate dehydrogenase (LDH) in the supernatant was measured after the treatment for 12

24

48 and 72h

respectively. In 72 h after the treatment

flow cytometry (FCM) was used to measure the apoptotic rates

and transmission electron microscopy (TEM) was employed to observe the ultrastructure of the cells.       Results      CCK-8 assay revealed that NB showed significantly stronger inhibition on the proliferation of MDA-MB-231 cells than nHAP treated and normal control cells after 24

48 and 72 hours’ treatment (

P

0.01). NB also resulted in significantly higher LDH activity than normal control after 24

48 and 72 hours’ treatment (

P

0.05). The activity level was still higher in NB treated cells than in nHAP treated ones

but there were statistical differences only in 24 and 48 hour’s treatment (

P

0.05). Significant difference was also found in the LDH levels between nHAP treatment cells and control cells in 72 h (

P

0.01). In 72 h after treatment

the apoptotic rates of the breast cancer cells were obviously higher in NB treated group than in nHAP treated group (

P

0.01). TEM displayed that the MDA-MB-231 cells in NB group had cytoplasmic cavities

karyopyknosis and obvious apoptotic bodies. But no such change was found in the cells in the nHAP group.       Conclusion      NB inhibits the growth and promotes the apoptosis in breast cancer cells. It is due to not only hydroxyl apatite shell components

but also other components or metabolic products of NB.