Methicillin-resistant Staphylococcus aureus (MRSA) clusters are considered epidemic or nonepidemic based on their ability to spread effectively. Successful transmission could be influenced by dehydration tolerance. Current methods for determination of dehydration tolerance lack accuracy. Here, a climate-controlled in vitro dehydration assay using isothermal microcalorimetry (IMC) was developed and linked with mathematical modeling to determine survival of 44 epidemic versus 54 nonepidemic MRSA strains from France, the United Kingdom, and the Netherlands after 1 week of dehydration. For each MRSA strain, the growth parameters time to end of first growth phase (tmax [h]) and maximal exponential growth rate (m m) were deduced from IMC data for 3 experimental replicates, 3 different starting inocula, and before and after dehydration. If the maximal exponential growth rate was within predefined margins (636% of the mean), a linear relationship between tmax and starting inoculum could be utilized to predict log reduction after dehydration for individual strains. With these criteria, 1,330 of 1,764 heat flow curves (data sets) (75%) could be analyzed to calculate the post-dehydration inoculum size, and thus the log reduction due to dehydration, for 90 of 98 strains (92%). Overall reduction was;1 log after 1 week. No difference in dehydration tolerance was found between the epidemic and nonepidemic strains. Log reduction was negatively correlated with starting inoculum, indicating better survival of higher inocula. This study presents a framework to quantify bacterial survival. MRSA strains showed great capacity to persist in the environment, irrespective of epidemiological success. This finding strengthens the need for effective surface cleaning to contain MRSA transmission. IMPORTANCE Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of infections globally. While some MRSA clusters have spread worldwide, others are not able to disseminate successfully beyond certain regions despite frequent introduction. Dehydration tolerance facilitates transmission in hospital environments through enhanced survival on surfaces and fomites, potentially explaining differences in transmission success between MRSA clusters. Unfortunately, the currently available techniques to determine dehydration tolerance of cluster-forming bacteria like S. aureus are labor-intensive and unreliable due to their dependence on quantitative culturing. In this study, bacterial survival was assessed in a newly developed assay using isothermal microcalorimetry. With this technique, the effect of drying can be determined without the disadvantages of quantitative culturing. In combination with a newly developed mathematical algorithm, we determined dehydration tolerance of a large number of MRSA strains in a systematic, unbiased, and robust manner.
Bibliographical noteFunding Information:
This work was part of the MACOTRA project, which was financially supported by JPIAMR 3rd call, AMR Transmission Dynamics, and Dutch ZonMw (grant no. 547001006). G.M.K.was supported by an UK MRC Skills Development Fellowship (MR/P014658/1).
We are grateful to all members of the MACOTRA study group for their input. We thank Jean-Philippe Rasigade for his assistance on statistical analysis. This work was part of the MACOTRA project, which was financially supported by JPIAMR 3rd call, AMR Transmission Dynamics, and Dutch ZonMw (grant no. 547001006). G.M.K.was supported by an UK MRC Skills Development Fellowship (MR/P014658/1). The MACOTRA study group consists of Valérie O. Baede, Mehri Tavakol, Margreet C. Vos, and Willem J. B. van Wamel (Department of Medical Microbiology and Infectious Diseases, Erasmus MC University Medical Center Rotterdam, Rotterdam, the Netherlands); Anaïs Barray, Gérard Lina, and Jean-Philippe Rasigade (CIRI, Centre International de Recherche en Infectiologie, Université de Lyon, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, Lyon, France; Centre National de Référence des Staphylocoques, Institut des Agents Infectieux, Hospices Civils de Lyon, Lyon, France); Sake J. de Vlas and Anneke S. de Vos (Department of Public Health, Erasmus MC University Medical Center Rotterdam, Rotterdam, the Netherlands); Arya Gupta, Jodi A. Lindsay (email@example.com), and Adam A. Witney (Institute for Infection and Immunity, St George’s, University of London, London, United Kingdom); Antoni P. A. Hendrickx and Leo M. Schouls (Center for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands); Mirjam E. E. Kretzschmar (Center for Infectious Disease Control, National Institute for Public Health and the Environment Bilthoven, the Netherlands; Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands); and Gwenan M. Knight (Centre for Mathematical Modelling of Infectious Diseases, Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom).
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