Risk Factors for Recurrent Staphylococcus aureus Bacteremia.

BACKGROUND: To understand the clinical, bacterial, and host characteristics associated with recurrent Staphylococcus aureus bacteremia (R-SAB), patients with R-SAB were compared to contemporaneous patients with a single episode of SAB (S-SAB). METHODS: All SAB isolates underwent spa genotyping. All isolates from R-SAB patients underwent pulsed-field gel electrophoresis (PFGE). PFGE-indistinguishable pairs from 40 patients underwent whole genome sequencing (WGS). Acute phase plasma from R-SAB and S-SAB patients was matched 1:1 for age, race, sex, and bacterial genotype, and underwent cytokine quantification using 25-analyte multiplex bead array. RESULTS: R-SAB occurred in 69 (9.1%) of the 756 study patients. Of the 69 patients, 30 experienced relapse (43.5%) and 39 reinfection (56.5%). Age, race, hemodialysis dependence, presence of foreign body, methicillin-resistant Staphyloccus aureus, and persistent bacteremia were individually associated with likelihood of recurrence. Multivariate risk modeling revealed that black hemodialysis patients were nearly 2 times more likely (odds ratio [OR] = 9.652 [95% confidence interval [CI], 5.402-17.418]) than white hemodialysis patients (OR = 4.53 [95% CI, 1.696-10.879]) to experience R-SAB. WGS confirmed PFGE interpretations in all cases. Median RANTES (regulated on activation, normal T cell expressed and secreted) levels in acute phase plasma from the initial episode of SAB were higher in R-SAB than in matched S-SAB controls (P = .0053, false discovery rate < 0.10). CONCLUSION: This study identified several risk factors for R-SAB. The largest risk for R-SAB is among black hemodialysis patients. Higher RANTES levels in R-SAB compared to matched controls warrants further study.

Human genetic variation in GLS2 is associated with development of complicated Staphylococcus aureus bacteremia.

The role of host genetic variation in the development of complicated Staphylococcus aureus bacteremia (SAB) is poorly understood. We used whole exome sequencing (WES) to examine the cumulative effect of coding variants in each gene on risk of complicated SAB in a discovery sample of 168 SAB cases (84 complicated and 84 uncomplicated, frequency matched by age, sex, and bacterial clonal complex [CC]), and then evaluated the most significantly associated genes in a replication sample of 240 SAB cases (122 complicated and 118 uncomplicated, frequency matched for age, sex, and CC) using targeted sequence capture. In the discovery sample, gene-based analysis using the SKAT-O program identified 334 genes associated with complicated SAB at p<3.5 x 10-3. These, along with eight biologically relevant candidate genes were examined in the replication sample. Gene-based analysis of the 342 genes in the replication sample using SKAT-O identified one gene, GLS2, significantly associated with complicated SAB (p = 1.2 x 10-4) after Bonferroni correction. In Firth-bias corrected logistic regression analysis of individual variants, the strongest association across all 10,931 variants in the replication sample was with rs2657878 in GLS2 (p = 5 x 10-4). This variant is strongly correlated with a missense variant (rs2657879, p = 4.4 x 10-3) in which the minor allele (associated here with complicated SAB) has been previously associated with lower plasma concentration of glutamine. In a microarray-based gene-expression analysis, individuals with SAB exhibited significantly lower expression levels of GLS2 than healthy controls. Similarly, Gls2 expression is lower in response to S. aureus exposure in mouse RAW 264.7 macrophage cells. Compared to wild-type cells, RAW 264.7 cells with Gls2 silenced by CRISPR-Cas9 genome editing have decreased IL1-ß transcription and increased nitric oxide production after S. aureus exposure. GLS2 is an interesting candidate gene for complicated SAB due to its role in regulating glutamine metabolism, a key factor in leukocyte activation.

Candidate genes on murine chromosome 8 are associated with susceptibility to Staphylococcus aureus infection in mice and are involved with Staphylococcus aureus septicemia in humans.

We previously showed that chromosome 8 of A/J mice was associated with susceptibility to S. aureus infection. However, the specific genes responsible for this susceptibility are unknown. Chromosome substitution strain 8 (CSS8) mice, which have chromosome 8 from A/J but an otherwise C57BL/6J genome, were used to identify the genetic determinants of susceptibility to S. aureus on chromosome 8. Quantitative trait loci (QTL) mapping of S. aureus-infected N2 backcross mice (F1 [C8A] × C57BL/6J) identified a locus 83180780-88103009 (GRCm38/mm10) on A/J chromosome 8 that was linked to S. aureus susceptibility. All genes on the QTL (n~ 102) were further analyzed by three different strategies: 1) different expression in susceptible (A/J) and resistant (C57BL/6J) mice only in response to S. aureus, 2) consistently different expression in both uninfected and infected states between the two strains, and 3) damaging non-synonymous SNPs in either strain. Eleven candidate genes from the QTL region were significantly differently expressed in patients with S. aureus infection vs healthy human subjects. Four of these 11 genes also exhibited significantly different expression in S. aureus-challenged human neutrophils: Ier2, Crif1, Cd97 and Lyl1. CD97 ligand binding was evaluated within peritoneal neutrophils from A/J and C57BL/6J. CD97 from A/J had stronger CD55 but weaker integrin α5ß1 ligand binding as compared with C57BL/6J. Because CD55/CD97 binding regulates immune cell activation and cytokine production, and integrin α5ß1 is a membrane receptor for fibronectin, which is also bound by S. aureus, strain-specific differences could contribute to susceptibility to S. aureus. Down-regulation of Crif1 with siRNA was associated with increased host cell apoptosis among both naïve and S. aureus-infected bone marrow-derived macrophages. Specific genes in A/J chromosome 8, including Cd97 and Crif1, may play important roles in host defense against S. aureus.

Long-term survival of tuberculosis complex mycobacteria in soil.

While there is evidence for the persistence of Mycobacterium bovis in soil, there are no reports for the other Mycobacterium tuberculosis complex (MTC) mycobacteria. Here, soil was inoculated with 10(8) c.f.u. g(-1) M. tuberculosis, M. bovis and M. canettii and subcultured monthly for 12 months. The pathogenicity of mycobacterial colonies, identified by using matrix-assisted laser desorption/ionization time of flight mass spectrometry, was assessed in a mouse model. Moreover, mice were fed with food that contained 16.7% M. tuberculosis-contaminated soil. The three tested MTC species survived in soil for 12 months with a final inoculum of 2 × 10(3) c.f.u. g(-1) for M. tuberculosis, 150 c.f.u. g(-1) for M. bovis and 2 × 10(4) c.f.u. g(-1) for M. canettii. In an experiment that included negative controls, all (5/5) mice inoculated with such M. tuberculosis and M. canettii developed 0.03-0.3 granulomas mm(-2) in their lungs and spleen and grew mycobacteria; five mice that were inoculated with M. bovis from soil did not develop granulomas but grew mycobacteria. Furthermore, 0.2-0.4 granulomas mm(-2) were observed in the lungs and spleen of 3/5 mice fed with M. tuberculosis-contaminated soil in the presence of two negative control mice. M. tuberculosis grew in the stomach, intestine, spleen and lung in 5/5 challenged mice, whereas the negative controls remained M. tuberculosis-free (P = 0.008, Fisher exact test). This study provides clear evidence that MTC mycobacteria survive in soil, and that M. tuberculosis remains virulent while in the soil, outside its hosts, for extended periods of time.