217. Combination Salvage Therapy with Cefazolin Plus Ertapenem for Refractory Methicillin-Susceptible Staphylococcus aureus Bacteremia

Background

Suboptimal therapy against methicillin-sensitive Staphylococcus aureus (MSSA) may have catastrophic consequences in severe infections such as endocarditis or epidural abscess. High MSSA inocula have been associated with clinical failure in patients receiving cefazolin (CZ), particularly when used at low doses, associated with a CZ inoculum effect. We previously described that adding ertapenem (ETP) to CZ led to synergism against MSSA and sensitized the pathogen to host innate immune factors. Here we expand our experience with CZ plus ETP as salvage therapy for 11 cases of refractory MSSA bacteremia (lacking source control problems) and explore CZ+ETP combination in vitro and in vivo.

Methods

Six available MSSA strains from patients treated with CZ+ETP for refractory bacteremia were tested in Mueller–Hinton Broth or RPMI media at standard (10⁵ CFU/mL) or high (10⁷ CFU/mL) inocula by MIC, checkerboard, and time-kill assays using ETP, CZ or nafcillin (NAF) alone vs. ETP+NAF or ETP+CZ. Disk diffusion synergy assays between CZ and ETP were also performed. CZ, ETP and CZ+ETP were tested in a rat endocarditis model using well described MSSA, TX0117 and TX0117c.

Results

11 consecutive patients with MSSA bacteremia (6 confirmed endocarditis) refractory to standard CZ or NAF rapidly cleared with CZ+ETP. 9 patients had daily positive blood cultures, and 8 cleared in ≤24 hr, including those with ≥2 cm vegetations. All 11 survived hospitalization. In MHB, 3/6 MSSA exhibited a CZ inoculum effect (CZ MIC >3 log₂ in 10⁷ vs. 10⁵ CFU/mL), but only 1 showed a significant CZ inoculum effect in RPMI. CZ+ETP was significantly more efficacious than CZ in a rat model of MSSA endocarditis utilizing a strain displaying a CZ inoculum effect, despite only modest benefit observed in vitro for 6 MSSA isolates.

Conclusion

CZ+ETP combination therapy yielded profound clinical success in severe MSSA infections with high bacterial densities, as demonstrated by rapid bacteremia clearance. Enhanced efficacy was also observed in a rat endocarditis model. The anti-staphylococcal activity of CZ+ETP in vivo exceeded that observed in vitro, consistent with our prior observations of host innate immune cooperativity with the regimen. CZ+ETP warrants further study for the treatment of refractory MSSA bacteremia and endocarditis.

Disclosures

All authors: No reported disclosures.

2390. Avibactam Sensitizes NDM Klebsiella pneumoniae to Innate Immune Killing by Human Cathelicidin LL-37, Serum, Neutrophils, and Platelets

Background

Avibactam (AVI) is a broad-spectrum intravenous non-β-lactam/β-lactamase inhibitor with no reported activity against metallo-β-lactamases such as New Delhi metallo-β-lactamases (NDM). Structural similarities between β-lactamases and bacterial penicillin-binding proteins (PBPs) have led investigators to explore and confirm the hypothesis that AVI may interact with PBPs of several Gram-negative and -positive bacterial species. Potent synergy has also been observed between AVI and peptide antibiotics such as polymyxin B. We hypothesized that sub-bacteriostatic concentrations of AVI may bind PBPs to weaken cell wall integrity and enhance lysis by the membrane attack complex of complement and by endogenous cationic antimicrobial peptides (AMPs) such as human cathelicidin LL-37. Sensitization to endogenous AMPs could improve killing by neutrophils and platelets that release these effectors upon degranulation.

Methods

Using NDM K. pneumoniae (NDM-KP) as a model, we performed LL-37 kill curves and killing assays with human serum, neutrophils and platelets in the presence or absence of AVI 4 μg/mL against NDM-KP.

Results

AVI alone lacked in vitro activity against NDM-KP. Addition of AVI to a physiological achievable concentration of LL-37 (2 mM) was bactericidal and resulted in an 8-log₁₀ reduction (below detection limit) in recoverable NDM-KP CFU at 6 and 24 h; no bactericidal activity was seen in bacteria treated with LL-37 or AVI alone (P < 0.0001). AVI pretreatment dramatically sensitized NDM-KP to neutrophil and platelet killing (P < 0.0001 and P < 0.01, respectively). AVI also sensitized NDM-KP to 20% human serum, resulting in 8-log₁₀ reduction in recoverable NDM-KP CFU within 6 h (P < 0.0001), an effect abrogated by heat treatment to inactivate complement.

Conclusion

AVI demonstrates potent synergy with peptide antibiotics and the innate immune system in vitro. Since AVI alone has scant direct antimicrobial activity and no direct inhibitory effect on metallo-β-lactamases, it is less likely to increase selective pressures toward antibiotic resistance. The use of AVI in combination with other antibiotics against drug-resistant bacterial pathogens warrants further study.

Disclosures

G. Sakoulas, Allergan: Consultant and Speaker, Consulting fee and Speaker honorarium. Sunovion: Speaker, Speaker honorarium. The Medicines Company: Speaker, Consulting fee. Paratek Pharmaceuticals: Consultant, Consulting fee. Cidara Therapeutics: Scientific Advisor, None. Arsanis Pharmaceuticals: Scientific Advisor, None.

Long-term follow-up of IPEX syndrome patients after different therapeutic strategies: An international multicenter retrospective study

Background

Immunodysregulation polyendocrinopathy enteropathy x-linked(IPEX) syndromeis a monogenic autoimmune disease caused by FOXP3 mutations. Because it is a rare disease, the natural history and response to treatments, including allogeneic hematopoietic stem cell transplantation (HSCT) and immunosuppression (IS), have not been thoroughly examined.

Objective

This analysis sought to evaluate disease onset, progression, and long-term outcome of the 2 main treatments in long-term IPEX survivors.

Methods

Clinical histories of 96 patients with a genetically proven IPEX syndrome were collected from 38 institutions worldwide and retrospectively analyzed. To investigate possible factors suitable to predict the outcome, an organ involvement (OI) scoring system was developed.

Results

We confirm neonatal onset with enteropathy, type 1 diabetes, and eczema. In addition, we found less common manifestations in delayed onset patients or during disease evolution. There is no correlation between the site of mutation and the disease course or outcome, and the same genotype can present with variable phenotypes. HSCT patients (n = 58) had a median follow-up of 2.7 years (range, 1 week-15 years). Patients receiving chronic IS (n = 34) had a median follow-up of 4 years (range, 2 months-25 years). The overall survival after HSCT was 73.2% (95% CI, 59.4-83.0) and after IS was 65.1% (95% CI, 62.8-95.8). The pretreatment OI score was the only significant predictor of overall survival after transplant (P = .035) but not under IS.

Conclusions

Patients receiving chronic IS were hampered by disease recurrence or complications, impacting long-term disease-free survival. When performed in patients with a low OI score, HSCT resulted in disease resolution with better quality of life, independent of age, donor source, or conditioning regimen.

Effects of histamine H1- and H2-receptor antagonists on thyrotrophin secretion in the rat

The effects of histamine H1- and H2-receptor antagonists on the pituitary-thyroid axis were studied in normal and thyroxine (T4)-treated rats. Acute administration (120 min before the test) of the H2 antagonist cimetidine induced a significant (P less than 0.01) increase in the TSH response to TRH, whereas treatment with histamine (30 min before the test) or with the H1-receptor blocker diphenhydramine (120 min before the test) was without effect. Treatment with cimetidine or ranitidine (another H2-receptor antagonist) for 5 days induced a marked decrease in basal plasma TSH concentrations (P less than 0.01), with no changes in pituitary concentrations of TSH. Plasma prolactin concentrations were similarly decreased by cimetidine (P less than 0.01), though not by ranitidine. Neither antihistaminic altered pituitary prolactin concentrations. Despite decreasing basal concentrations of plasma TSH, cimetidine augmented the response to TRH above baseline values (P less than 0.01) in control rats as well as in animals with T4-induced suppression of plasma TSH. Administration of cimetidine or ranitidine for 5 days was followed by a reduced concentration of plasma T4 and triiodothyronine (T3) (P less than 0.05 and P less than 0.01 respectively), perhaps as a result of the declining plasma TSH levels. These results provide the first evidence for the reduction of plasma TSH concentrations by H2-receptor blockers, and may indicate that histamine can physiologically regulate TSH and prolactin secretion through H2 receptors in the anterior pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)