AUTHOR=Van den Bossche Sara , Vandeplassche Eva , Ostyn Lisa , Coenye Tom , Crabbé Aurélie 

TITLE=Bacterial Interference With Lactate Dehydrogenase Assay Leads to an Underestimation of Cytotoxicity

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2020.00494

DOI=10.3389/fcimb.2020.00494

ISSN=2235-2988

ABSTRACT=<p>Models to study host-pathogen interactions <italic>in vitro</italic> are an important tool for investigating the infectious disease process and evaluating the efficacy of antimicrobial compounds. In these models, the viability of mammalian cells is often determined using the lactate dehydrogenase (LDH) cytotoxicity assay. In the present study we evaluated whether bacteria could interfere with the LDH assay. As a model for host-pathogen interactions, we co-cultured lung epithelial cells with eight bacteria encountered in the lower respiratory tract. We show that LDH activity is affected by <italic>Pseudomonas aeruginosa, Klebsiella pneumoniae, Stenotrophomonas maltophilia</italic>, and <italic>Streptococcus pneumoniae</italic>, and that this depends on the density of the start inoculum and the duration of infection. Two different mechanisms were discovered through which bacteria interfered with LDH activity, i.e., acidification of the cell culture medium (by <italic>K. pneumoniae</italic> and <italic>S. pneumoniae</italic>) and protease production (by <italic>P. aeruginosa</italic> and <italic>S. maltophilia</italic>). In addition, we developed and validated a modified protocol to evaluate cytotoxicity using the LDH assay, where bacterial interference with LDH quantification is avoided.</p>