Detection of Mollicutes in bioreactor samples by real-time transcription-mediated amplification

Diagnosis and treatment of HEp-2 cells contaminated with mycoplasma

Contamination of primary and cell cultures by mycoplasmas is one of the main economic and biological pitfalls in basic research, diagnosis and manufacture of biotechnological products. It is a common issue which may be difficult to conduct surveillance on. Mycoplasma presence may affect several physiological parameters of the cell, besides being considered an important source of inaccurate and/or non-reproducible scientific results. Each cell type presents characteristical symptoms, mainly morphological, that indicate a contamination by mycoplasma. HEp-2 cells originate from carcinoma of the larynx and are, therefore, part of the respiratory tract, which is one of mycoplasma habitats. Despite the importance these cells in several biological research (evaluation of cell proliferation and migration, apoptosis, antiviral and antitumor compounds), the alterations induced by mycoplasma contamination in HEp-2 cells have not yet been described. Here, we describe the progressive morphological alterations in culture of HEp-2 cells infected with mycoplasma, as well as the-diagnosis of the infection and its treatment. Mycoplasma contamination described within this work led to cytoplasm elongation, cell-to-cell spacing, thin plasma membrane projections, cytoplasmic vacuoles, fusion with neighboring cells, and, finally, cell death. Contamination was detected by fluorescence imaging (DAPI) and PCR reactions. The cultures were treated with BM-Cyclin antibiotic to eliminate contamination. The data presented here will be of relevance to researchers whose investigations involve cell culture, especially respiratory and HEp-2 cells.

Impacts of intentional mycoplasma contamination on CHO cell bioreactor cultures

Mycoplasma contamination events in biomanufacturing facilities can result in loss of production and costly cleanups. Mycoplasma may survive in mammalian cell cultures with only subtle changes to the culture and may penetrate the 0.2 µm filters often used in the primary clarification of harvested cell culture fluid. Culture cell‐based and indicator cell‐based assays that are used to detect mycoplasma are highly sensitive but can take up to 28 days to complete and cannot be used for real‐time decision making during the biomanufacturing process. To support real‐time measurements of mycoplasma contamination, there is a push to explore nucleic acid testing. However, cell‐based methods measure growth or colony forming units and nucleic acid testing measures genome copy number; this has led to ambiguity regarding how to compare the sensitivity of the methods. In addition, the high risk of conducting experiments wherein one deliberately spikes mycoplasma into bioreactors has dissuaded commercial groups from performing studies to explore the multiple variables associated with the upstream effects of a mycoplasma contamination in a manufacturing setting. Here we studied the ability of Mycoplasma arginini to persist in a single‐use, perfusion rocking bioreactor system containing a Chinese hamster ovary (CHO) DG44 cell line expressing a model monoclonal immunoglobulin G1 (IgG1) antibody. We examined M. arginini growth and detection by culture methods, as well as the effects of M. arginini on mammalian cell health, metabolism, and productivity. We compared process parameters and controls normally measured in bioreactors including dissolved oxygen, gas mix, and base addition to maintain pH, to examine parameter changes as potential indicators of contamination. Our work showed that M. arginini affects CHO cell growth profile, viability, nutrient consumption, oxygen use, and waste production at varying timepoints after M. arginini introduction to the culture. Importantly, how the M. arginini contamination impacts the CHO cells is influenced by the concentration of CHO cells and rate of perfusion at the time of M. arginini spike. Careful evaluation of dissolved oxygen, pH control parameters, ammonia, and arginine over time may be used to indicate mycoplasma contamination in CHO cell cultures in a bioreactor before a read‐out from a traditional method.

Cell lines authentication and mycoplasma detection as minimun quality control of cell lines in biobanking

Establishment of continuous cell lines from human normal and tumor tissues is an extended and useful methodology for molecular characterization of cancer pathophysiology and drug development in research laboratories. The exchange of these cell lines between different labs is a common practice that can compromise assays reliability due to contamination with microorganism such as mycoplasma or cells from different flasks that compromise experiment reproducibility and reliability. Great proportions of cell lines are contaminated with mycoplasma and/or are replaced by cells derived for a different origin during processing or distribution process. The scientific community has underestimated this problem and thousand of research experiment has been done with cell lines that are incorrectly identified and wrong scientific conclusions have been published. Regular contamination and authentication tests are necessary in order to avoid negative consequences of widespread misidentified and contaminated cell lines. Cell banks generate, store and distribute cell lines for research, being mandatory a consistent and continuous quality program. Methods implementation for guaranteeing both, the absence of mycoplasma and authentication in the supplied cell lines, has been performed in the Andalusian Health System Biobank. Specifically, precise results were obtained using real time PCR detection for mycoplasma and 10 STRs identification by capillary electrophoresis for cell line authentication. Advantages and disadvantages of these protocols are discussed.

World Health Organization International Standard To Harmonize Assays for Detection of Mycoplasma DNA

Nucleic acid amplification technique (NAT)-based assays (referred to here as NAT assays) are increasingly used as an alternative to culture-based approaches for the detection of mycoplasma contamination of cell cultures. Assay features, like the limit of detection or quantification, vary widely between different mycoplasma NAT assays. Biological reference materials may be useful for harmonization of mycoplasma NAT assays. An international feasibility study included lyophilized preparations of four distantly related mycoplasma species (Acholeplasma laidlawii, Mycoplasma fermentans, M. orale, M. pneumoniae) at different concentrations which were analyzed by 21 laboratories using 26 NAT assays with a qualitative, semiquantitative, or quantitative design. An M. fermentans preparation was shown to decrease the interassay variation when used as a common reference material. The preparation was remanufactured and characterized in a comparability study, and its potency (in NAT-detectable units) across different NATs was determined. The World Health Organization (WHO) Expert Committee on Biological Standardization (ECBS) established this preparation to be the "1st World Health Organization international standard for mycoplasma DNA for nucleic acid amplification technique-based assays designed for generic mycoplasma detection" (WHO Tech Rep Ser 987:42, 2014) with a potency of 200,000 IU/ml. This WHO international standard is now available as a reference preparation for characterization of NAT assays, e.g., for determination of analytic sensitivity, for calibration of quantitative assays in a common unitage, and for defining regulatory requirements in the field of mycoplasma testing.

A specific statistical model and algorithm related to the detection of Mollicutes in contaminated biological samples by Real-Time Transcription Mediated Amplification

Among all nucleic acid amplification technologies, Real-Time Transcription Mediated Amplification (Real-Time TMA) is an isothermal method that can amplify RNA targets a billion-fold in less than one hour's time. By using this method, a new assay was developed for detecting the presence of Mollicutes in mammalian cell cultures and biologics. Production of amplicons is monitored in real time by measuring continuously a fluorescence signal during the reaction. The shape of this signal curve is a sigmoid, where an initial baseline phase precedes an exponential phase ending with a maximum followed by a linear decreasing phase. The aim of this study was to develop a curve-analysis tool to unambiguously assign a Mollicutes positive or negative status to a biological sample. In this context, a statistical analysis of the data combined with the selection of the best predictors allowed the development of an algorithm which removes erroneous data and applies the best predictors to generate the Mollicutes status prediction. Our results demonstrate that this algorithm assigns positive/negative/invalid status coming from Real-Time TMA fluorescence signal analysis with a confidence (true predictions) in the results close to 100%.