Amino acid alterations in fibronectin binding protein A (FnBPA) and bacterial genotype are associated with cardiac device related infection in Staphylococcus aureus bacteraemia

Objectives: Staphylococcus aureus initiates cardiac device-related infection (CDI) by binding of fibronectin binding protein A (FnBPA) to the device's surface. In FnBPA, specific binding enhancing amino acid alterations are associated with CDI. However, no study has investigated whether these mutations also occur in geographically different regions and whether they arise during infection or are inherent properties of the infecting isolate. Methods: We analysed bacterial isolates from 34 patients with S. aureus bacteraemia and implanted cardiac devices for association with CDI, FnBPA sequence, classification into a clonal complex (CC), and binding to fibronectin (Fn). Results: We confirmed that amino acid alterations at positions 652, 782, and 786 in FnBPA were associated with CDI (p = 0.005). Furthermore, CC15 and CC45 isolates were associated with CDI (p = 0.004). All isolates within a CC exhibited a characteristic mutation pattern, with major changes occurring in CC45 including a duplication of D1 and an altered immunogenic epitope in the D3 repeat. Isolates harbouring the binding enhancing mutations showed a slightly increased Fn binding capability, whereas Fn binding was decreased in CC45 isolates, according to a microtiter plate assay. Conclusions: FnBPA sequence variations are lineage specific and display inherent properties of the infecting isolate. Sequence analysis of FnBPA, as well as the bacterial genotype, may be used to predict the risk for device-related infection. (C) 2014 The British Infection Association. Published by Elsevier Ltd. All rights reserved

Determining vancomycin Etest MICs in patients with MRSA bloodstream infection does not support switching antimicrobials

Objectives: Elevated vancomycin minimum inhibitory concentrations (MIC) have been reported to adversely affect clinical outcome in methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI). We therefore examined the association between vancomycin MIC and outcome considering various potential confounders. Methods: Clinical data and bacterial isolates were prospectively collected from patients with MRSA BSI from 2006 to 2012 as part of the Invasive Staphylococcus aureus Infection Cohort (INSTINCT) study. Antimicrobial susceptibility was assessed by Etest, broth microdilution (BMD) and VITEK 2. Bacterial genotypes were determined by spa typing. Using univariate and Cox regression analyses, we investigated the impact of low (= 1.5 mg/L) vancomycin Etest MIC on clinical outcomes. Results: Ninety-one MRSA BSI episodes were included, of which 79 (86.8%) were caused by spa types t003, t032 and t045. High vancomycin MICs were seen only if using Etest but not confirmed using standard reference BMD. When episodes were stratified into low and high vancomycin Etest MIC groups, 30-day overall mortality was 34.5% and 27.3%, respectively (P = 0.64, OR 0.71; 95% confidence interval [CI] 0.27-1.79). Variables significantly associated with all-cause mortality in the Cox model were age (P = 0.003), acute physiology score (P = 0.0006), and Charlson comorbidity index (P = 0.018). Conclusions: Vancomycin MICs may vary dependent on testing methodologies and local MRSA epidemiology. The patients' underlying disease and individual comorbidities rather than elevated vancomycin MICs determine adverse clinical outcomes in MRSA BSI. Routine Etest MIC testing of MRSA isolates is of limited value for treatment decisions. (C) 2016 The British Infection Association. Published by Elsevier Ltd. All rights reserved

Polymorphisms in Fibronectin Binding Proteins A and B among Staphylococcus aureus Bloodstream Isolates Are Not Associated with Arthroplasty Infection

Background Nonsynonymous single nucleotide polymorphisms (SNPs) in fibronectin binding protein A (fnbA) of Staphylococcus aureus are associated with cardiac device infections. However, the role of fnbA SNPs in S. aureus arthroplasty infection is unknown. Methods Bloodstream S. aureus isolates from a derivation cohort of patients at a single U.S. medical center with S. aureus bacteremia (SAB) and prosthetic hip or knee arthroplasties that were infected (PJI, n = 27) or uninfected (PJU, n = 43) underwent sequencing of fnbA and fnbB. A validation cohort of S. aureus bloodstream PJI (n = 12) and PJU (n = 58) isolates from Germany also underwent fnbA and fnbB sequencing. Results Overall, none of the individual fnbA or fnbB SNPs were significantly associated with the PJI or PJU clinical groups within the derivation cohort. Similarly, none of the individual fnbA or fnbB SNPs were associated with PJI or PJU when the analysis was restricted to patients with either early SAB (i.e., bacteremia occurring 1 year after placement or manipulation of prostheses). Conclusions In contrast to cardiac device infections, there is no association between nonsynonymous SNPs in fnbA or fnbB of bloodstream S. aureus isolates and arthroplasty infection. These results suggest that initial steps leading to S. aureus infection of cardiovascular and orthopedic prostheses may arise by distinct processes

Comparison of the fibronectin binding capacity of <i>S</i>. <i>aureus</i> isolates from prosthetic joint infection (PJI) and uninfected prosthetic joint (PJU) groups.

<p>Values were calculated as percentage capacity to bind fibronectin relative to <i>S</i>. <i>aureus</i> control strain 8325–4. Box ends represent the 25^th and 75^th percentiles, and whisker ends represent the minimum and maximum. There was no difference in fibronectin binding capacity between isolates in the PJI and PJU groups.</p

Single Nucleotide Polymorphisms (SNPs) in fibronectin binding protein B (<i>fnbB)</i> in <i>fnbB-</i>containing isolates.

<p>*When false discovery rate control is applied, this raw p-value no longer maintains statistical significance (p = 1.00).</p><p>No SNP was associated with the prosthetic joint infected (PJI) or uninfected (PJU) isolates in the derivation cohort, external validation cohort, or late <i>S</i>. <i>aureus</i> bacteremia (SAB) group. Late SAB was defined as SAB occurring >1 year after placement or manipulation of prostheses.</p

Demographic and clinical characteristics of patients in the derivation cohort with <i>S</i>. <i>aureus</i> bacteremia and infected or uninfected prostheses.

<p>*Late infection is defined as bloodstream infection occurring >1 year after the prostheses was implanted or surgically manipulated.</p><p>Demographic and clinical characteristics of patients in the derivation cohort with <i>S</i>. <i>aureus</i> bacteremia and infected or uninfected prostheses.</p

Comparison of the biofilm-forming capacity of <i>S</i>. <i>aureus</i> isolates from prosthetic joint infection (PJI) and uninfected prosthetic joint (PJU) groups.

<p>Values were calculated as percentage capacity to form biofilms relative to <i>S</i>. <i>aureus</i> control strain UAMS-1. Box ends represent the 25^th and 75^th percentiles, and whisker ends represent the minimum and maximum. There was no difference in biofilm-forming capacity between isolates in the PJI and PJU groups.</p

Single Nucleotide Polymorphisms (SNPs) in fibronectin binding protein A (<i>fnbA)</i> in the derivation cohort, external validation cohort, and late <i>S</i>. <i>aureus</i> bacteremia (SAB) group.

<p>*When false discovery rate control is applied, this raw p-value no longer maintains statistical significance (p = 0.22).</p><p>In the derivation cohort, no SNPs occurred with greater frequency in the prosthetic joint infection group (PJI) relative to the uninfected prosthetic joint group (PJU). In the external validation cohort, one SNP (S839N) was significantly associated with the PJU group, though when the two cohorts were combined the S839N association did not reach statistical significance (p = 0.22). Late SAB was defined as bacteremia occurring >1 year after placement or manipulation of prostheses, and here contains data from both the derivation and external validation cohorts. In the late SAB group, no SNPs occurred with greater frequency in PJI or PJU.</p

Single Nucleotide Polymorphisms (SNPs) in the binding regions (Repeats 1–11) of fibronectin binding protein B (FnBPB) in the derivation cohort (A) and the external validation cohort (B).

<p>Red boxes indicate SNPs that were only present in isolates from the prosthetic joint infection group (PJI), blue boxes indicate SNPs that were only present in the uninfected (PJU) group, and purple boxes indicate SNPs that were present in both PJI and PJU isolates.</p