Enhanced expression of dltABCD is associated with the development of daptomycin nonsusceptibility in a clinical endocarditis isolate of Staphylococcus aureus

Abstract

Using isogenic clinical bloodstream Staphylococcus aureus strains from a patient with relapsing endocarditis, we investigated the transcriptional profiles of the mprF and dlt genes in the context of cell-surface charge and daptomycin nonsusceptibility. As in prior studies, a point mutation within mprF was observed in the daptomycin-nonsusceptible strain. However, neither the transcriptional profile of mprF nor the membrane phospholipid analyses were compatible with the anticipated mprF gain-in-function phenotype. In contrast, we demonstrated enhanced dlt expression coincident with increased positive surface charge and reduced daptomycin binding.

Figure 1

Population analyses of study strains to vancomycin (A) or daptomycin (B); expression of mprF (C) and dlt operon (D). Population analyses data represent the means (±SD) for at least two separate assays. Total cellular RNA samples were isolated from exponential- and stationary-phase cultures of BOY755 (lane 1) and BOY300 (lane 2) and were subjected to RT-PCR to detect expression of mprF, dltA, and gyrA.

Figure 1

Population analyses of study strains to vancomycin (A) or daptomycin (B); expression of mprF (C) and dlt operon (D). Population analyses data represent the means (±SD) for at least two separate assays. Total cellular RNA samples were isolated from exponential- and stationary-phase cultures of BOY755 (lane 1) and BOY300 (lane 2) and were subjected to RT-PCR to detect expression of mprF, dltA, and gyrA.

Figure 1

Population analyses of study strains to vancomycin (A) or daptomycin (B); expression of mprF (C) and dlt operon (D). Population analyses data represent the means (±SD) for at least two separate assays. Total cellular RNA samples were isolated from exponential- and stationary-phase cultures of BOY755 (lane 1) and BOY300 (lane 2) and were subjected to RT-PCR to detect expression of mprF, dltA, and gyrA.

Figure 1

Population analyses of study strains to vancomycin (A) or daptomycin (B); expression of mprF (C) and dlt operon (D). Population analyses data represent the means (±SD) for at least two separate assays. Total cellular RNA samples were isolated from exponential- and stationary-phase cultures of BOY755 (lane 1) and BOY300 (lane 2) and were subjected to RT-PCR to detect expression of mprF, dltA, and gyrA.