title: Monitoring mitochondrial inner membrane potential for detecting early changes in viability of bacterium-infected human bone marrow-derived mesenchymal stem cells.
abstract: BACKGROUND
  One of the most challenging safety issues in the manufacture of cell based medicinal products is the control of microbial risk as cell-based products cannot undergo terminal sterilization. Accordingly, sensitive and reliable methods for detection of microbial contamination are called for. As mitochondrial function has been shown to correlate with the viability and functionality of human mesenchymal stem cells (hMSCs) we have studied the use of a mitochondrial inner membrane potential sensitive dye for detecting changes in the function of mitochondria following infection by bacteria.
  
  
  METHODS
  The effect of bacterial contamination on the viability of bone marrow-derived mesenchymal stem cells (BMMSCs) was studied. BMMSC lines were infected with three different bacterial species, namely two strains of Pseudomonas aeruginosa, three strains of Staphylococcus aureus, and three strains of Staphylococcus epidermidis. The changes in viability of the BMMSCs after bacterial infection were studied by staining with Trypan blue, by morphological analysis and by monitoring of the mitochondrial inner membrane potential.
  
  
  RESULTS
  Microscopy and viability assessment by Trypan blue staining showed that even the lowest bacterial inocula caused total dissipation of BMMSCs within 24 hours of infection, similar to the effects seen with bacterial loads which were several magnitudes higher. The first significant signs of damage induced by the pathogens became evident after 6 hours of infection. Early changes in mitochondrial inner membrane potential of BMMSCs were evident after 4 hours of infection even though no visible changes in viability of the BMMSCs could be seen.
  
  
  CONCLUSIONS
  Even low levels of bacterial contamination can cause a significant change in the viability of BMMSCs. Moreover, monitoring the depolarization of the mitochondrial inner membrane potential may provide a rapid tool for early detection of cellular damage induced by microbial infection. Accordingly, mitochondrial analyses offer sensitive tools for quality control and monitoring of safety and efficacy of cellular therapy products.
authors.forename: Mika
authors.initials: M
authors.lastname: Pietilä
authors.forename: Kaarina
authors.initials: K
authors.lastname: Lähteenmäki
authors.forename: Siri
authors.initials: S
authors.lastname: Lehtonen
authors.forename: Hannu-Ville
authors.initials: HV
authors.lastname: Leskelä
authors.forename: Marko
authors.initials: M
authors.lastname: Närhi
authors.forename: Maarit
authors.initials: M
authors.lastname: Lönnroth
authors.forename: Jaana
authors.initials: J
authors.lastname: Mättö
authors.forename: Petri
authors.initials: P
authors.lastname: Lehenkari
authors.forename: Katrina
authors.initials: K
authors.lastname: Nordström
mesh_terms: D000368:Aged; D001854:Bone Marrow Cells / Q000166:cytology*; D002470:Cell Survival; D002478:Cells, Cultured; D018920:Coculture Techniques; D005260:Female; D006801:Humans; D008297:Male; D053078:Membrane Potential, Mitochondrial; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000382:microbiology; D008875:Middle Aged; D008928:Mitochondria / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity*; D013211:Staphylococcus aureus / Q000472:pathogenicity*; D013212:Staphylococcus epidermidis / Q000472:pathogenicity*