Persistent Staphylococcus aureus isolates from two independent cases of bacteremia display increased bacterial fitness and novel immune evasion phenotypes.
Bottom Line: Several novel traits were associated specifically with both independent sets of persistent S. aureus isolates compared to both the initial isolates and the isolates from resolved infections (resolved isolates).These traits included (i) increased growth under nutrient-poor conditions; (ii) increased tolerance of iron toxicity; (iii) higher expression of cell surface proteins involved in immune evasion and stress responses; and (iv) attenuated virulence in a Galleria mellonella larva infection model that was not associated with small-colony variation or metabolic dormancy such as had been seen previously.Overall, our data indicate a novel role for MprF function during development of S. aureus persistence by increasing bacterial fitness and immune evasion.
Affiliation: Department of Genetics and Infection, Immunity of Inflammation, University of Leicester, Leicester, United Kingdom.Show MeSH
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Mentions: The formation of SCV has repeatedly been implicated in S. aureus persistence (18, 19, 21, 22); however, no significant differences in colony sizes between the initial, persistent, and resolved isolates examined in this study were observed, therefore indicating that none of the MRSA bacteremia isolates exhibited an SCV phenotype. Moreover, all MRSA bacteremia isolates showed no growth differences when cultured in a nutrient-replete medium (data not shown). In contrast, the EMRSA-15 PB1- and PB3-derived persistent isolates, PB1-15-1, PB1-15-2, and PB3-32-1, showed significantly increased growth compared to the control resolved EMRSA-15 bacteremia isolates when grown in nutrient-deprived, metal ion-restricted medium (Fig. 3A; P < 0.0001), a growth environment which is reflective of conditions in vivo (35). These data also showed that the persistent isolates had a growth advantage in CRPMI medium compared to the respective initial isolates (PB1-1 and PB3-1), although this difference was significant only for the PB3-1-versus-PB3-32-1 comparison (P < 0.01). Viability assays confirmed that persistent isolates showed an increased growth phenotype under nutrient-deprived conditions compared to both the initial infection and the control resolved isolates (data not shown). Interestingly, the measured growth of PB3-74 was equivalent to that of the initial PB3-1 isolate and was significantly lower than that of PB3-32-1 (P < 0.01), which is in agreement with the antibiotic resistance phenotypes.
Affiliation: Department of Genetics and Infection, Immunity of Inflammation, University of Leicester, Leicester, United Kingdom.