3 research outputs found

    Dehydration Tolerance in Epidemic versus Nonepidemic MRSA Demonstrated by Isothermal Microcalorimetry.

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    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 (μm) 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 (±36% 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

    Memory Th1 Cells Are Protective in Invasive <i>Staphylococcus aureus</i> Infection

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    <div><p>Mechanisms of protective immunity to <i>Staphylococcus aureus</i> infection in humans remain elusive. While the importance of cellular immunity has been shown in mice, T cell responses in humans have not been characterised. Using a murine model of recurrent <i>S</i>. <i>aureus</i> peritonitis, we demonstrated that prior exposure to <i>S</i>. <i>aureus</i> enhanced IFNÎł responses upon subsequent infection, while adoptive transfer of <i>S</i>. <i>aureus</i> antigen-specific Th1 cells was protective in naĂŻve mice. Translating these findings, we found that <i>S</i>. <i>aureus</i> antigen-specific Th1 cells were also significantly expanded during human <i>S</i>. <i>aureus</i> bloodstream infection (BSI). These Th1 cells were CD45RO<sup>+</sup>, indicative of a memory phenotype. Thus, exposure to <i>S</i>. <i>aureus</i> induces memory Th1 cells in mice and humans, identifying Th1 cells as potential <i>S</i>. <i>aureus</i> vaccine targets. Consequently, we developed a model vaccine comprising staphylococcal clumping factor A, which we demonstrate to be an effective human T cell antigen, combined with the Th1-driving adjuvant CpG. This novel Th1-inducing vaccine conferred significant protection during <i>S</i>. <i>aureus</i> infection in mice. This study notably advances our understanding of <i>S</i>. <i>aureus</i> cellular immunity, and demonstrates for the first time that a correlate of <i>S</i>. <i>aureus</i> protective immunity identified in mice may be relevant in humans.</p></div
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