Infectious Disease

PURPOSE: Secukinumab, a fully human anti-interleukin-17A monoclonal antibody, exhibited promising activity in a proof-of-concept study when administered in intravenous (IV) doses to patients with active, chronic, noninfectious uveitis. This study compared the efficacy and safety of different IV and subcutaneous (SC) doses of secukinumab in patients with noninfectious uveitis. DESIGN: Multicenter, randomized, double-masked, dose-ranging, phase 2 clinical trial. PARTICIPANTS: Thirty-seven patients with active noninfectious intermediate uveitis, posterior uveitis, or panuveitis who required corticosteroid-sparing immunosuppressive therapy. METHODS: Patients were randomized to secukinumab 300 mg SC every 2 weeks for 4 doses, secukinumab 10 mg/kg IV every 2 weeks for 4 doses, or secukinumab 30 mg/kg IV every 4 weeks for 2 doses. Intravenous or SC saline was administered to maintain masking. Efficacy was assessed on day 57 (2-4 weeks after last dose). MAIN OUTCOME MEASURES: Percentage of patients with treatment response, defined as (1) at least a 2-grade reduction in vitreous haze score or trace or absent vitreous haze in the study eye without an increase in corticosteroid dose and without uveitis worsening or (2) reduction in corticosteroid dosages to prespecified levels without uveitis worsening. Percentage of patients with remission, defined as anterior chamber cell and vitreous haze scores of 0 or 0.5+ in both eyes without corticosteroid therapy or uveitis worsening. RESULTS: Secukinumab 30 mg/kg IV and 10 mg/kg IV, compared with the 300 mg SC dose, produced higher responder rates (72.7% and 61.5% vs. 33.3%, respectively) and remission rates (27.3% and 38.5% vs. 16.7%, respectively). Statistical and clinical superiority for the 30 mg/kg IV dose compared with the 300 mg SC dose was established in a Bayesian probability model. Other measures, including time to response onset, change in visual acuity, and change in vitreous haze score, showed numeric trends favoring IV dosing. Secukinumab, administered in IV or SC formulations, appeared safe and was well tolerated. CONCLUSIONS: Intravenous secukinumab was effective and well tolerated in noninfectious uveitis requiring systemic corticosteroid-sparing immunosuppressive therapy. Greater activity with IV dosing suggests that patients may not receive sufficient drug with SC administration. High-dose IV secukinumab may be necessary to deliver secukinumab in therapeutic concentrations.

Available at http://www.ncbi.nlm.nih.gov/books/NBK190422/

Microarrays were used to investigate the transcriptional response of Enterococcus faecalis to photostress. E. faecalis are Gram-positive bacteria used as indicators of water quality and have been shown to vary diurnally in response to sunlight. E. faecalis in filtered seawater microcosms were exposed to artificial sunlight for 12h and then placed in the dark for 12h. Transcript abundance was measured at 0, 2, 6, 12, and 24h in the sunlit microcosm and a dark control using microarrays. Culturable E. faecalis concentrations decreased 6-7 orders of magnitude within the first 6h of light exposure. After 12h in the dark, no evidence of dark-repair was observed. Expression data collected after 12h of sunlight exposure revealed a difference in transcript abundance in the light relative to dark microcosms for 35 unique ORFs, 33 ORFs showed increased transcript abundance and 2 ORFs showed reduced transcript abundance. A majority (51%) of the ORFs with increased transcript abundance in the sunlit relative to dark microcosms encoded hypothetical proteins; others were associated with protein synthesis, oxidative stress and DNA repair. Results suggest that E. faecalis exposed to sunlight actively transcribe RNA in response to photostress.

CD80 plays a critical role in stimulation of T cells and subsequent control of infection. To investigate the effect of CD80 on HSV-1 infection, we constructed a recombinant HSV-1 virus that expresses two copies of the CD80 gene in place of the latency associated transcript (LAT). This mutant virus (HSV-CD80) expressed high levels of CD80 and had similar virus replication kinetics as control viruses in rabbit skin cells. In contrast to parental virus, this CD80 expressing recombinant virus replicated efficiently in immature dendritic cells (DCs). Additionally, the susceptibility of immature DCs to HSV-CD80 infection was mediated by CD80 binding to PD-L1 on DCs. This interaction also contributed to a significant increase in T cell activation. Taken together, these results suggest that inclusion of CD80 as a vaccine adjuvant may promote increased vaccine efficacy by enhancing the immune response directly and also indirectly by targeting to DC.

Staphylococcus aureus contains two distinct teichoic acid (TA) polymers, lipoteichoic acid (LTA) and wall teichoic acid (WTA), which are proposed to play redundant roles in regulating cell division. To gain insight into the underlying biology of S. aureus TAs, we used a small molecule inhibitor to screen a highly saturated transposon library for cellular factors that become essential when WTA is depleted. We constructed an interaction network connecting WTAs with genes involved in LTA synthesis, peptidoglycan synthesis, surface protein display, and D-alanine cell envelope modifications. Although LTAs and WTAs are synthetically lethal, we report that they do not have the same synthetic interactions with other cell envelope genes. For example, D-alanylation, a tailoring modification of both WTAs and LTAs, becomes essential when the former, but not the latter, are removed. Therefore, D-alanine-tailored LTAs are required for survival when WTAs are absent. Examination of terminal phenotoypes led to the unexpected discovery that cells lacking both LTAs and WTAs lose their ability to form Z rings and can no longer divide. We have concluded that the presence of either LTAs or WTAs on the cell surface is required for initiation of S. aureus cell division, but these polymers act as part of distinct cellular networks.

PURPOSE: To define global transcriptional responses of Staphylococcus aureus and its codY mutant (CodY is a transcription regulator of virulence and metabolic genes in response to branched-chain amino acids) when growing in bovine aqueous (AH) and vitreous humor (VH) in vitro, and to investigate the impact of codY deletion on S. aureus virulence in a novel murine anterior chamber (AC) infection model. METHODS: For the in vitro model, differential transcriptomic gene expression of S. aureus and its codY mutant grown in chemically defined medium (CDM), AH, and VH was analyzed. Furthermore, the strains were inoculated into the AC of mice. Changes in bacterial growth, electroretinography and inflammation scores were monitored. RESULTS: Bovine AH and VH provide sufficient nutrition for S. aureus growth in vitro. Transcriptome analysis identified 72 unique open reading frames differentially regulated ≥10-fold between CDM, AH, and VH. In the AC model, we found comparable growth of the codY mutant and wild type strains in vivo. Average inflammation scores and retinal function were significantly worse for codY mutant-infected eyes at 24 h post-infection. CONCLUSION: Our in vitro bovine AH and VH models identified likely nutrient sources for S. aureus in the ocular milieu. The in vivo model suggests that control of branched-chain amino acid availability has therapeutic potential in limiting S. aureus endophthalmitis severity.

The enterococci are an ancient genus that evolved along with the tree of life. These intrinsically rugged bacteria are highly adapted members of the intestinal consortia of a range of hosts that spans the animal kingdom. Enterococci are also leading opportunistic hospital pathogens, causing infections that are often resistant to treatment with most antibiotics. Despite the importance of enterococci as hospital pathogens, the vast majority live outside of humans, and nearly all of their evolutionary history took place before the appearance of modern humans. Because hospital infections represent evolutionary end points, traits that exacerbate human infection are unlikely to have evolved for that purpose. However, clusters of traits have converged in specific lineages that are well adapted to colonize the antibiotic-perturbed gastrointestinal tracts of patients and that thrive in the hospital environment. Here we discuss these traits in an evolutionary context, as well as how comparative genomics is providing new insights into the evolution of the enterococci.

The enterococci evolved over eons as highly adapted members of gastrointestinal consortia of a wide variety of hosts, but for reasons that are not entirely clear, emerged in the 1970s as leading causes of multidrug resistant hospital infection. Hospital-adapted pathogenic isolates are characterized by the presence of multiple mobile elements conferring antibiotic resistance, as well as pathogenicity islands, capsule loci and other variable traits. Enterococci may have been primed to emerge among the vanguard of antibiotic resistant strains because of their occurrence in the GI tracts of insects and simple organisms living and feeding on organic matter that is colonized by antibiotic resistant, antibiotic producing micro-organisms. In response to the opportunity to inhabit a new niche--the antibiotic treated hospital patient--the enterococcal genome is evolving in a pattern characteristic of other bacteria that have emerged as pathogens because of opportunities stemming from anthropogenic change.

Enterococcus faecalis is a Gram-positive commensal member of the gut microbiota of a wide range of organisms. With the advent of antibiotic therapy, it has emerged as a multidrug resistant, hospital-acquired pathogen. Highly virulent strains of E. faecalis express a pore-forming exotoxin, called cytolysin, which lyses both bacterial and eukaryotic cells in response to quorum signals. Originally described in the 1930s, the cytolysin is a member of a large class of lanthionine-containing bacteriocins produced by Gram-positive bacteria. While the cytolysin shares some core features with other lantibiotics, it possesses unique characteristics as well. The current understanding of cytolysin biosynthesis, structure/function relationships, and contribution to the biology of E. faecalis are reviewed, and opportunities for using emerging technologies to advance this understanding are discussed.

FasL was recently shown be required for bacterial clearance in C57BL/6 mice that express the FasL.1 allotype. The FasL.2 allotype is expressed in BALB/c mice and exhibits increased binding affinity to and increased cytotoxic activity against Fas(+) target cells. Therefore, we hypothesized that BALB/c mice would be more resistant to Staphylococcus aureus-induced endophthalmitis. To test this hypothesis, C57BL/6, BALB/c, and BALB(gld) mice received intravitreal injections of 2,500 CFU of S. aureus (RN6390). Clinical examinations, electroretinography (ERG), histology, and bacterial quantification were performed at 24, 48, 72, and 96 h postinjection. The myeloperoxidase (MPO) assay was used to quantitate neutrophil infiltration. At 96 h postinfection, 86% of C57BL/6 mice presented with complete destruction of the eye, compared to only 29% of BALB/c mice with complete destruction. To our surprise, in the absence of Fas ligand, BALB(gld) mice showed no difference in bacterial clearance compared to BALB/c mice. However, histology and ERG analysis revealed increased retinal damage and significant loss of retinal function. MPO analysis revealed equal numbers of neutrophils in BALB(gld) and BALB/c mice at 24 h postinfection. However, at 48 h, the neutrophil numbers remained significantly elevated in BALB(gld) mice, correlating with the increased retinal damage observed in BALB(gld) mice. We conclude that the increased resistance to S. aureus induced endophthalmitis in BALB/c mice is not dependent upon the FasL. However, in contrast to C57BL/6 mice, FasL is required for resolution of inflammation and protecting host tissue from nonspecific damage in BALB/c mice.