605. Identification of a Novel CMY-Variant Enzyme in a Clinical Escherichia coli Strain with Treatment-Emergent Ceftazidime–Avibactam Resistance

Background

Ceftazidime–avibactam (CZA) is a novel β-lactam / β-lactamase inhibitor with in vitro activity against multidrug-resistant Gram-negatives, including those harboring CMY-2 enzymes. Treatment-emergent resistance to CZA has been described in KPC-producing Klebsiella pneumoniae but has not been described in non-carbapenemase-producing, carbapenem-resistant Enterobacteriaceae (CRE).

Methods

A patient with an intra-abdominal infection due to a carbapenem-resistant E. coli (ertapenem MIC 16 µg/mL; meropenem MIC 2 µg/mL; CZA MIC 2 µg/mL; carbapenemase negative) was treated with CZA. On day 48 of therapy, a CZA resistant, carbapenem-sensitive E. coli was identified from abdominal drainage (CZA MIC ≥256 µg/mL; meropenem MIC 0.19 µg/mL). Illumina MiSeq whole-genome sequencing (WGS) was performed on both isolates to identify potential resistance mechanisms. The ResFinder database was used to identify known β-lactamase enzymes, and in silico modeling of β-lactamase structure was assessed.

Results

WGS revealed that both isolates were ST410 E. coli, with the sole difference in β-lactam resistance determinants between the two being a novel CMY β-lactamase harbored on an Inc1-type conjugative plasmid in the second isolate. The novel CMY has 4 amino acid substitutions relative to CMY-2: A134E, Q140K, V231S, and N366Y. The V231S substitution is found in CMY-42 and has previously been associated with increased ceftazidime hydrolysis. The remaining three substitutions have not previously been identified. Previous studies have identified that substitutions at position 366 influence the rate of ceftazidime hydrolysis rate. Preliminary protein structure analysis suggests that positions 140 and 366 are in the active site. No other differences in β-lactam resistance determinants were identified between the first and second isolates.

Conclusion

To our knowledge, we have identified the first case of CMY-associated CZA resistance. Given the widespread and transferrable nature of CMY enzymes, this finding raises concern for additional cases of resistance with increasing usage of CZA. Further analysis is needed to identify the mechanism by which this enzyme confers CZA resistance.

Disclosures

Samuel L. Aitken, PharmD, Melinta Therapeutics: Grant/Research Support, Research Grant; Merck, Sharpe, and Dohme: Advisory Board; Shionogi: Advisory Board.

89. Efficacy and Tolerability of Voriconazole (VOR) vs. Isavuconazole (ISA) Prophylaxis (px) in Preventing Invasive Fungal Infections (IFI) in Lung Transplant Recipients (LTR)

Background

IFI is a significant complication following lung transplant (LT). VOR was universal antifungal px in our LT program from 2004 to October 2015, at which time px was changed to ISA. We compared the efficacy and tolerability of VOR vs. ISA px in LTR.

Methods

We reviewed all LTR from September 2013 to February 2018 who received VOR or ISA Px. The standard duration of px was 3 or 4 months following basiliximab and alemtuzumab induction, respectively. All patients were followed for ≥1 years post-Tx. IFI was defined by revised EORTC/MSG criteria.

Results

In total, 310 LTR were included, 149 and 161 of whom received ISA and VOR px, respectively. There was no difference in demographics, underlying diseases, single vs. double LT, or induction therapy (alemtuzumab vs. basiliximab) between the 2 groups. At 1-year after LT, 9% (14) and 8% (13) of patients in ISA and VOR groups developed IFI, respectively (P = 0.5). 5% (7) and 3% (5) of patients developed breakthrough (BT) IFI during ISA and VOR px, respectively (P = 0.6; Figure 1, P = 0.4, Kaplan-–Meier). ISA BT included pneumonia (PNA, 2), endobronchial IFI (2), mediastinitis (1), chest wall IFI (1), and candidemia (1). ISA BT patients were infected with Aspergillus fumigatus (3; 2 with ISA MIC = 0.5 µg/mL, 1 MIC = 1 µg/mL), black mould (1), and yeasts (3; 2 C. glabrata, 1 C. albicans). VOR BT IFI included PNA (2), endobronchial IFI (1), empyema (1), and chest wall IFI (1). VOR BT IFIs were due to A. ustus, A. niger, A. lentulus, black mould, and Rhizopus spp (1 each). All Aspergillus VOR BT isolates exhibited VOR MIC ≥2 µg/mL. Patients with IFI were more likely to have positive pre-LT respiratory fungal culture (P = 0.01) and grade ≥3 ischemic reperfusion injury (IRI) post-LT (P = 0.01). VOR and ISA were prematurely discontinued in 53% (85) and 14% (21) of patients due to adverse events, respectively (P < 0.0001). Hepatotoxicity was more common with VOR (22%, 35) than ISA (5%, 7) (P < 0.0001). IFI was an independent risk factor for death at 1 year (Figure 2, P < 0.0001, Kaplan–Meier).

Conclusion

ISA was as effective as VOR in preventing IFI in LTR, and significantly better tolerated. Pre-LT fungal culture positivity and grade ≥3 IRI post-LT were risk factors for the development of IFI. IFI within 1-year post-LT had a significant impact on mortality

Disclosures

Fernanda P. Silveira, MD, MS, FIDSA, Ansun: Grant/Research Support; Qiagen: Grant/Research Support; Shire: Grant/Research Support; Whiscon: Grant/Research Support.

2667. Does Ceftazidime–Avibactam (CAZ-AVI) Improve Short- and Long-Term Outcomes Among Solid-Organ Transplant (SOT) Recipients with Carbapenem-Resistant Enterobacteriaceae (CRE) Infections?

Background

SOT recipients are an ideal population in which to study the impact of new antibiotics, since they are particularly dependent upon drug activity to clear infections. In 3/15, FDA approved CAZ-AVI, the first new anti-CRE agent to arrive in the clinic. Our objective was to determine whether CAZ-AVI improves short- and long-term outcomes of CRE-infected SOT recipients.

Methods

We performed a retrospective study of SOT recipients infected with CRE since 2012, who were treated with CAZ-AVI or salvage agents for ≥ 3 days.

Results

35 CRE-infected SOT recipients (14 liver, 11 lung, 6 kidney, 3 intestine, 1 heart) with bacteremia (20), pneumonia (11), intra-abdominal abscess (3) and soft-tissue infection/osteomyelitis (1) were enrolled. 16 and 19 patients (pts) were treated with CAZ-AVI and salvage agents, respectively. Types of infection or SOT, APACHE II and McCabe scores did not differ significantly between patients treated with CAZ-AVI or salvage agents. 30- and 90-d mortality rates were significantly lower among SOT recipients treated with CAZ-AVI (0% and 6%, respectively) compared with salvage agents (26% and 37%; P = 0.049 and 0.047). Among patients who survived 90 days, recurrent CRE infections were diagnosed in 53% and 17% of those treated with CAZ-AVI and a salvage regimen, respectively (P = 0.10). Median time from end of therapy for the 1st CRE infection to recurrent infection was 116 days (max 1,242) and 361 days (max 799) for CAZ-AVI and salvage regimens, respectively. Survival and recurrence-free survival were greater for treatment with CAZ-AVI and salvage agents, respectively, as measured by Kaplan–Meier (Figures). CAZ-AVI resistance developed in 37% (n = 3) of patients with recurrent infections. Recurrent isolates were genetically indistinguishable from parent isolates by core genome SNP phylogeny (< 15 SNP).

Conclusion

CAZ-AVI significantly reduced short-term mortality among SOT recipients with CRE infections compared with salvage regimens, but was limited by recurrent infections and emergence of resistance. The same strains caused recurrent and initial infections, suggesting that CAZ-AVI did not eliminate CRE from GI sites that serve as sources of recurrence. Optimizing outcomes in SOT recipients with CRE infections will require new agents like CAZ-AVI, and strategies to eliminate long-term colonization.

Disclosures

All authors: No reported disclosures.

2247. Real-world Experience with Meropenem–Vaborbactam (M/V) for Treatment of Carbapenem-Resistant Enterobacteriaceae (CRE) Infections

Background

M/V demonstrates in vitro activity against KPC-producing CRE, but real-world clinical experience is limited.

Methods

Patients treated for > 48 hours with M/V for CRE infections were included. Success was defined as improved symptoms, absence of recurrent infection, and survival at 30 days. Microbiologic failures (MF) were defined as isolation of the same species post-treatment (tx). KPC and ompK36 mutations were detected by sequencing of PCR products.

Results

19 patients were included; 58% were men; median age was 53. 11% were transplant recipients and median Charlson score was 3 (range: 0–10). Infection types included bacteremia (n = 7), pneumonia (6; 5 ventilator-associated), soft tissue (2), tracheobronchitis (2), intra-abdominal (1), and pyelonephritis (1). 68% of patients were in the ICU; median APACHE II and SOFA scores were 18 (7–40) and 4 (1–13), respectively. CR pathogens included K. pneumoniae (14), K. oxytoca (2), E. coli (2), and C. freundii (1); 89% harbored KPC, including KPC-2 (6), KPC-3 (10), and KPC-3 with a D179Y mutation (1). All were susceptible to M/V (median MIC = 0.03 µg/mL [0.015–0.12]). Median duration of tx was 8 days (3 – 28); 89% received monotherapy. Success and survival rates at 30d were 63% and 89%, respectively. Failures were due to death (2), recurrent infection (2), worse symptoms (2), and persistent bacteremia (1). Success rates for bacteremia and pneumonia were 57% and 67%, respectively. MF within 90 days occurred in 32% due to K. pneumoniae (5) or E. coli (1). MF were classified as intra-abdominal abscess (3), pneumonia (1), and respiratory (1) or urinary (1) colonization. The median time to MF was 32 days (15 – 67). M/V MICs were increased ≥8-fold against 67% (4/6) of recurrent isolates. 1 pt developed intra-abdominal infection due to M/V non-susceptible KPC-3 K. pneumoniae isolate (MIC = 8) following a 12-day of M/V; the recurrent isolate differed from the parent by an IS5 insertion in the ompK36 gene promoter. M/V was well-tolerated, 1 patient developed eosinophilia.

Conclusion

In this cohort of critically-ill patients with CRE infection, tx with M/V yielded outcomes comparable to prior cohorts treated with ceftazidime–avibactam. M/V non-susceptibility emerged in 1 isolate. Our findings require validation in future studies.

Disclosures

All authors: No reported disclosures.

1709. Epidemiology of Invasive Fungal Infection (IFI) after Severe Influenza Requiring Intensive Care Unit (ICU) Admission: 10-Year Experience at a Tertiary Care Center in the United States

Background

Despite increasing recognition of aspergillosis complicating severe influenza and its associated high fatality in Europe, incidence and features of the disease in the United States are unknown.

Methods

We reviewed all influenza cases requiring ICU admission from 2009 to 2019 at our center.

Results

262 patients with influenza required ICU admission. 4% (10) developed IFI at median 2d after influenza diagnosis. 80% (8/10) of patients with IFI were infected with influenza A vs. 88% (221/252) without IFI. 20% were on steroids at the time of IFI diagnosis. 70% of IFI required mechanical ventilation. Types of IFI were pneumonia (70%, 6 Aspergillus and 1 Wangiella), endobronchial IFI (20%, 1 each with Aspergillus and Lictheimia), and Coccidioides fungemia (10%). 4% (10) of patients were fungal colonized, but did not have IFI (5 A. fumigatus, 1 A. terreus, 4 Penicillium). CT findings of IFI included nodules (4), cavitation (3), and ground-glass opacities (2). Serum galactomannan (GM) was positive in 3 (43%). Median time to antifungal therapy (AF) was 2 days. Triazoles were prescribed to all 7 patients with aspergillosis. Posaconazole and amphotericin B were AF for patients with Wangiellaand Lichteimia, respectively. Patients with C. immitis fungemia died before AF. Median duration of AF was 60 days among survivors. Patients with IFI required acute hemodialysis more frequently than colonized patients (60% vs. 0%, P = 0.01). 30-day mortality was 60% (6/10) and 20% 92/10) in patients with IFI and colonization, respectively (P = 0.2). Patients with IFI had significantly higher in-hospital and 60-day mortality than those without IFI (Fig 1, P = 0.009).

Conclusion

Our rate of post-influenza IFI (4%) was lower than reported in Europe (~15%), which might stem from a lack of systematic BAL GM testing at our center, over-reliance on GM to make diagnoses in Europe, and/or differences in pt populations and clinical practices in treating severe influenza. IFI and fungal colonization rates were similar at our center, highlighting the importance of using well-defined criteria to define disease. Given the high mortality of post-influenza IFI, priority should be given to defining risk factors that might identify patients for targeted AF prophylaxis. In using AF, it is important to recognize that Aspergillus is not the only cause of IFI.

Disclosures

All authors: No reported disclosures.

656. Prioritizing Gram-Negative Bacteremia (GNB) Cases for Rapid Detection by β-Lactam Resistance (BLR) and Patient Outcomes

Background

GNB is associated with significant morbidity and mortality. The availability of rapid diagnostic tests (RDTs) provides an opportunity to improve outcomes. Our goal was to review GNB and its empiric treatment at our center in order to devise rational approaches to diagnostic stewardship and use of RDTs.

Methods

All patients with GNB from 2010 to 2018 were evaluated. BLR was defined by 2019 CLSI breakpoints; phenotypes are shown in Table 1.

Results

A total of 2795 GNB cases were included (Table 2); 57% occurred within the first 24 hours of hospitalization and 29.3% in the ICU. The median length of stay (LOS) was 12 days; 17.2% of patients were re-admitted within 30 days. Fourteen- and 30-day mortality rates were 13.7% and 19.5%, respectively. Rates of death were higher (30 days; 26.3% vs. 17.1%; P < 0.001) and median LOS longer (17 vs. 11 days; P < 0.001) among patients with BLR compared with susceptible GNB. Thirty-day mortality rates were highest for CRE (30.1%) and BLR P. aeruginosa (BLR-Pa; 32.8%, Figure 1). 47.7% of BLR GNB were non-CRE/ESBL, which demonstrated higher mortality rates than CRE/ESBL (30 days; 27.6% vs. 21.2%; P = 0.048). Most common empiric regimens prescribed were piperacillin–tazobactam (TZP; 50.3%), cefepime (FEP; 24.2%), carbapenem (9.3%), or other agents (16.2%). 21.6% of GNB patients received inactive empiric treatment (IET). Empiric TZP (21.9%) was more likely to be inactive than FEP (17.5%; P = 0.05), but not a carbapenem (20.7%; P = NS). 57.6% of patients with inhibitor-resistant Enterobacteriaceae (IRE) received TZP empirically. Receipt of IET was associated with higher rates of death (30 days; 22.5% vs. 16.7, P = 0.03) and longer LOS (14 vs. 11 days; P < 0.001) than receipt of active ET. Rates of IET varied by pathogen (Figure 1).

Conclusion

IET is common against BLR GNB and associated with poor pt outcomes, highlighting the potential for RDTs and diagnostic stewardship teams (DSTs) to improve care. Genotypic RDTs detect most CRE/ESBL, but may miss nearly 50% of BLR GNB cases at our center. BLR-Pa and IRE are pathogens associated with prolonged LOS, and high rates of IET and death. These pathogens could be detected earlier by phenotypic RDTs and prioritized by DSTs to optimize early treatment regimens.

Disclosures

All authors: No reported disclosures.

1458. Burden of Illness in Patients with Urinary Tract Infections With or Without Bacteremia Caused by Carbapenem-Resistant Gram-Negative Pathogens in US Hospitals (2014 to 2018)

Background

Urinary tract infections (UTIs) are the most frequent infections caused by Gram-negative (GNB) bacteria in the USA. We aimed to characterize the burden of UTIs caused by carbapenem-resistant (CR) or -susceptible (CS) GNB in hospitalized patients with or without bacteremia.

Methods

Data from the Premier Healthcare Database of adult patients hospitalized between January 1, 2014 and June 30, 2018 with UTIs (defined as positive urine culture and receipt of GN antibiotics within −2 to 3 days of the index urine culture) with bacteremia (defined as positive blood culture with the same pathogen from the urine) or without bacteremia caused by CR or CS GNB were analyzed retrospectively. Stenotrophomonas maltophilia were presumed to be CR but rarely tested. Patient characteristics and outcomes (mortality, different types of length of hospital stay [LOS], ICU admission, discharge status and hospitalization charges) were compared.

Results

A total of 46,076 UTI patients were included. 11,212 patients with bacteremia were significantly more likely to have UTI index culture on the day of the admission vs. 34,864 patients without bacteremia (82.0% vs. 65.9%, P < 0.001, respectively). The same results were seen when stratified by CR status (CR: 68.59% vs. 61.23%, P < 0.047; CS: 82.29% vs. 66.19%, P < 0.001, respectively). UTI patients with bacteremia were also more likely to have a positive blood culture for the same pathogen on the same day of index urine culture (CR: 85.86%; CS: 95.45%). Pseudomonas aeruginosa was the most frequent CR pathogen (50.03%), followed by K. pneumoniae (14.28%) and Stenotrophomonas maltophilia (10.76%), and CR patients with bacteremia were more likely to die in the hospital and less likely to be discharged home than other groups. They also had longer median overall and infection-associated LOS, were more likely to be admitted to the ICU and had higher hospitalization charges (table).

Conclusion

UTIs complicated by bacteremia exacerbates the burden of illness in patients hospitalized with UTIs, increasing mortality, LOS, and hospitalization charges. The presence of CR pathogens further exacerbates this burden.

Disclosures

All authors: No reported disclosures.

1829. The Paradox of KPC Bearing Strains of Klebsiella pneumoniae with the D179Y Substitution: Resistance to Ceftazidine/Avibactam (CZA) and Susceptibility to Meropenem (MEM)

Background

Resistance to CZA is a serious limitation of treatment for KPC bearing Enterobacteriaceae infections. Recently, a single amino acid substitution (D179Y) was described in KPC-2 and KPC-3 bearing CZA-resistant K. pneumoniae recovered from patients failing treatment. In class A β-lactamases the D179 residue is located at the neck of the omega loop and is critical for KPC catalytic activity. In attempts to understand the evolution of substrate specificity in KPC-2, the D179Y variant of KPC-2 was shown to be resistant to CZA (ceftazidime forms a long-lived acyl enzyme with in KPC-2), but susceptible to MEM. A similar observation was made in clinical and laboratory-generated K. pneumoniae and E. coli strains bearing D179Y KPC-3. We were compelled to explore the catalytic mechanisms of susceptibility to MEM of the D179Y variants in KPC-2 vs. KPC-3.

Methods

KPC-2, KPC-3, and D179Y in the respective KPC were cloned into an expression vector and the β-lactamase proteins were purified. 5 mg of each β-lactamase with and without MEM (1:1 molar ratio) was incubated for the time indicated and analyzed using the Quadrupole Time-of-Flight (QTOF) timed mass spectrometry for the reaction intermediates. To assess thermal stability, denaturation melting curves were run for 2 hours using 12 µM β-lactamase.

Results

The D179Y variant forms prolonged acyl-complexes with meropenem in KPC-3 and KPC-2, which can be detected up to 24 hours (Figure 1). This prolonged trapping of meropenem by D179Y variants is not evident with the respective KPCs. Further, the tyrosine substitution at the D179 position (Tm = 48–52°C) destabilizes the KPC β-lactamases (TmKPC-2/3 = 52–56°C).

Conclusion

These data suggest that MEM acts as a covalent β-lactamase inhibitor more than as a substrate for KPC-2 and -3. The mechanistic basis of paradoxical susceptibility to carbapenems provides an impetus to develop better therapeutic approaches to the increasing threat of carbapenem resistance and highlights how the rational design of novel β-lactam/β-lactamase inhibitors must consider mechanistic bases of resistance.

Disclosures

All Authors: No reported Disclosures.

1580. Colistin Potentiates the In Vitro Activity of Meropenem–Vaborbactam (M/V) Against Some, but not All KPC-producing Klebsiella pneumoniae (KPC-Kp)

Background

M/V demonstrates potent in vitro activity against KPC-producing organisms. It is unclear whether the combination interacts synergistically with other active agents.

Methods

We tested isolates for responses to M/V alone (1 and 4x MIC; V fixed at 8 µg/mL), and in combination with colistin (COL; 2 µg/mL), fosfomycin (FOS; 100 µg/mL + 25 µg/mL G6P), gentamicin (GEN; 2 µg/mL), and tigecycline (TGC; 2 µg/mL) by time-kill using a starting inoculum of 1 × 10⁸ cFu/mL. 24h was the primary endpoint.

Results

16 KPC-Kp isolates were studied (7 KPC-2 and 9 KPC-3); all were M/V-susceptible (MIC range: 0.015 – 4 µg/mL). 44% harbored ompK36 mutations (4 IS5 promoter insertion, 2 134–135 DG duplication, and 1 premature stop codon). Median M/V MICs were higher against isolates with mutant ompK36 (0.25 vs. 0.03; P = 0.002). Mean log-kills by M/V at 1x and 4x were -0.50 and -2.41, respectively; M/V was bactericidal (≥3-log kill) against 6% and 56%, respectively (Figure 1). Mean log-kills at 4× were greater against KPC-2 (-3.79) than KPC-3 (−1.33) isolates (P = 0.09), and among isolates with (−3.31) vs. without (−1.71) ompK36 mutations (P = 0.11). GEN was the most active single agent (bactericidal against 56%, mean log-kill = −3.04). In combo with M/V, rates of synergy (>2-log kill in combo) with COL, FOS, GEN, and TGC were 44%, 19%, 12.5%, and 12.5%, respectively (Figure 2). Corresponding rates of bactericidal activity were 44%, 25%, 69%, and 31%, respectively. Antagonism (> 1-log kill by most active single agent) was identified for each combo against 2 isolates. Mean log-kills by M/V + GEN were greater against isolates with GEN MICs ≤1 (−7.16) vs. ≥2 (−1.66; P = 0.001), reflecting the activity of GEN alone. Mean log-kills by M/V + COL were greater against isolates with IS5 insertions (-6.32) compared with wild type (−2.38) or other mutations (−1.77) in ompK36. Responses to M/V + FOS were not dependent upon FOS MIC, but log-kills were greater against mutant (-2.13) vs. wild-type (0.01) ompK36 (P = 0.03).

Conclusion

M/V + GEN is rapidly cidal if GEN MICs are ≤1, while M/V + COL resulted in highest rates of synergy against diverse KPC-Kp. Mean log-kills were highest among isolates with IS5 promoter insertions suggesting a potential role for COL combination therapy against KPC-Kp isolates with decreased outer membrane permeability.

Disclosures

All authors: No reported disclosures.

Evolution of Outbreak-Causing Carbapenem-Resistant Klebsiella pneumoniae ST258 at a Tertiary Care Hospital over 8 Years

Carbapenem-resistant Klebsiella pneumoniae (CRKP) strains belonging to sequence type 258 (ST258) are frequent causes of hospital-associated outbreaks and are a major contributor to the spread of carbapenemases. This genetic lineage emerged several decades ago and remains a major global health care challenge. In this study, genomic epidemiology was used to investigate the emergence, evolution, and persistence of ST258 carbapenem-resistant K. pneumoniae outbreak-causing lineages at a large tertiary care hospital over 8 years. A time-based phylogenetic analysis of 136 ST258 isolates demonstrated the succession of multiple genetically distinct ST258 sublineages over the 8-year period. Ongoing genomic surveillance identified the emergence and persistence of several distinct clonal ST258 populations. Patterns of multidrug resistance determinants and plasmid replicons were consistent with continued evolution and persistence of these populations. Five ST258 outbreaks were documented, including three that were caused by the same clonal lineage. Mutations in genes encoding effectors of biofilm production and iron acquisition were identified among persistent clones. Two emergent lineages bearing K. pneumoniae integrative conjugative element 10 (ICEKp10) and harboring yersiniabactin and colibactin virulence factors were identified. The results show how distinct ST258 subpopulations have evolved and persisted within the same hospital over nearly a decade.IMPORTANCE The carbapenem class of antibiotics is invaluable for the treatment of selected multidrug-resistant Gram-negative pathogens. The continued transmission of carbapenem-resistant bacteria such as ST258 K. pneumoniae is of serious global public health concern, as treatment options for these infections are limited. This genomic epidemiologic investigation traced the natural history of ST258 K. pneumoniae in a single health care setting over nearly a decade. We found that distinct ST258 subpopulations have caused both device-associated and ward-associated outbreaks, and some of these populations remain endemic within our hospital to the present day. The finding of virulence determinants among emergent ST258 clones supports the idea of convergent evolution of drug-resistant and virulent CRKP strains and highlights the need for continued surveillance, prevention, and control efforts to address emergent and evolving ST258 populations in the health care setting.

706. Ceftazidime-Avibactam (CZA) and Meropenem (MER) Are Synergistic and Bactericidal Against Genetically Diverse KPC-Producing Klebsiella pneumoniae (Kp)

Background

We previously showed that CZA MICs are higher among KPC-3 Kp and KPC-2 Kp with porin mutations. Clinical resistance has emerged among KPC-3 Kp. Here, we tested various agents in combination with CZA for synergistic and bactericidal activity.

Methods

We tested isolates for responses to CZA alone (1 and 4× MIC; avibactam fixed at 4 µg/mL), and in combination with colistin (COL; 2 µg/mL), fosfomycin (FOS; 100 µg/mL + 25 µg/mL G6P), gentamicin (GEN; 2 µg/mL), MER (8 µg/mL), and tigecycline (TGC; 2 µg/mL) by time-kill using a starting inoculum of 1 × 10⁸ cFu/mL. Log-kills were calculated as log cFu/mL decrease from time 0; 24 hours was the primary endpoint.

Results

Thirty KPC-Kp isolates were studied (22 KPC-2 and 8 KPC-3); all isolates were CZA-susceptible (MIC range: 0.125–4 µg/mL). Fifty-three percent harbored ompK36 mutations (eight each with IS5 and 134–135 DG insertions). Mean log-kills by CZA at 1× and 4× MIC were 2.00 and 2.35, respectively; CZA was bactericidal (≥3-log kill) at 24 hours against 33% and 50%, respectively. CZA mean log-kills at 4× MIC were greater for KPC-3 (3.81) than KPC-2 (1.82) isolates (P = 0.03), but did not vary by porin genotype (P = 0.44). GEN was the most active single agent and was bactericidal against 57%; the mean log-kill was 3.06. In combination with CZA, rates of synergy (>2-log kill in combo) with COL, FOS, GEN, MER, and TGC were 83%, 60%, 40%, 87%, and 7%, respectively. The corresponding rates of bactericidal activity were 87%, 77%, 80%, 100%, and 30%, respectively. Antagonism (>1-log kill by most active single agent) was identified in 7%, 23%, 20%, 0%, and 27% with CZA + COL, FOS, GEN, MER, and TGC, respectively. Mean log-kills by CZA + MER were greater among isolates with wild-type (6.58) vs. mutant (5.48) ompK36 (P = 0.0006), and isolates harboring KPC-3 (7.02) vs. KPC-2 (5.63; P = 0.0004). CZA + COL responses were attenuated among isolates with COL MICs ≥2 (log-kills 2.88 vs. 7.94; P = 0.0009), but not affected by ompK36 genotype (P = 0.53). Among isolates with COL MICs <2; log-kills were greater for CZA + COL (7.94) than CZA + MER (6.44; P < 0.0001).

Conclusion

A two-drug combination of CZA + MEM results in high rates of synergy and bactericidal activity against genetically diverse KPC-Kp. Mean log-kills were less among isolates with mutations in ompK36. CZA + COL was highly active against isolates ompK36 mutations, but contingent on COL susceptibility.

Disclosures

M. H. Nguyen, Merck: Grant Investigator, Research grant. Astellas: Grant Investigator, Research grant. R. K. Shields, Allergan: Grant Investigator, Research grant. Pfizer: Consultant and Scientific Advisor, Speaker honorarium. Shionogi: Scientific Advisor, Consulting fee. Roche: Grant Investigator, Research grant. Venatorx: Grant Investigator, Research grant. Medicines Company: Grant Investigator and Scientific Advisor, Consulting fee and Research grant. Accelerate Diagnostics: Scientific Advisor, Consulting fee.

383. An Increased Rate of Candida parapsilosis Infective Endocarditis Is Associated With Injection Drug Use

Background

Methods

Results

Conclusion

Disclosures

1378. Evaluation of the In vitro Activity of Meropenem-Vaborbactam Against Carbapenem-Resistant Enterobacteriaceae, Including Isolates Resistant to Ceftazidime–Avibactam

Background

Methods

Results

Conclusion

Disclosures

2033. Incorporating T2Candida Testing into Rational Antifungal (AF) Management: A Successful Pilot Study of Diagnostic Stewardship (DS) Directed Toward Specific Intensive Care Unit (ICU) Patients At-Risk for Sepsis due to Invasive Candidiasis (IC)

Background

Blood cultures (BC) are ~50% sensitive for diagnosing IC. T2Candida (T2) detects five leading Candida spp. directly in blood and was ≥90%/90% sensitive/specific (S/Sp) for candidemia in clinical trials. Optimal use of T2 in clinical practice is unclear. We targeted T2 to specific ICU patients at-risk for IC, and implemented AF management algorithms developed with ICU teams.

Methods

A DS team ordered concurrent T2 and BC, and used results to guide AF in patients fulfilling pre-specified criteria for septic shock (medical ICU (MICU)), sepsis after abdominal surgery (trauma ICU), or sepsis with mechanical circulatory support (cardiothoracic ICU). We focused on groups with anticipated pre-test IC probabilities of ~3–15%. Proven IC was defined if BC+ and possible IC if BC- but a compatible clinical picture was observed.

Results

Seven percent (6/88) of BC in ICU patients with sepsis were Candida +. T2 and BC results are shown in the table. Using BC as gold standard, T2 S/Sp and PPV/NPV were 50%/87% and 33%/96%, respectively. Including possible IC, T2 S/Sp increased to 69%/96%, and 67% (4/6) of T2+/BC− results were likely true positive; two false-positive results were for C. parapsilosis. We focused on MICU outcomes initially since 75% (66/88) of tests were performed here. Empiric AFs were discontinued in 12 patients following a T2- result; AFs were avoided in all others. Median combined days of therapy (DOT)/month for caspofungin and fluconazole as empiric or definitive treatment prior to and after introducing DS were 26 (range: 10–53) and 15 (3–32), respectively (P = 0.0047). AF consumption was decreased 47% (figure).

Conclusion

Targeted DS using T2 in select ICU patients with sepsis significantly reduced AF usage. 14% of patients with sepsis were diagnosed with IC using either T2+ or BC+, compared with 7% with BC+ alone, as would be expected if BC S was 50%. T2 S and T2−/BC+ results were lower and higher, respectively, than previously reported, indicating that treatment decisions should be based on results of both tests. Most T2+/BC− results were ascribed to possible IC.

Disclosures

M. H. Nguyen, Merck: Grant Investigator, Research grant. Astellas: Grant Investigator, Research grant.

2438. Ceftolozane/Tazobactam (C/T) Against Multidrug-Resistant Pseudomonas aeruginosa (MDR-Pa) Infections: Clinical Efficacy, and Baseline and Emergent Resistance

Background

Experience is mounting for C/T against MDR-Pa infections. More data are needed on efficacy for different infections, and baseline and emergent resistance.

Methods

We retrospectively reviewed patients receiving >48 hours of C/T for MDR-Pa infections. Clinical success was defined at 30 days as survival, improved symptoms, and absence of recurrent infection. Microbiologic failures were defined as isolation of MDR-Pa following ≥7 days of C/T. Minimum inhibitory concentrations (MICs) were determined by broth microdilution.

Results

63 patients were included. Median age was 58 (range: 23–91), 54% were men, and median Charlson score was 4 (0–12). 35% were transplant recipients. At onset of infection, median APACHE II and SOFA scores were 21 (2–49) and 5 (0–17), respectively. Infections included pneumonia (n = 45), tracheobronchitis (n = 4), intra-abdominal (n = 4), skin/soft tissue (n = 3), urinary tract (n = 3), bacteremia (n = 2), endocarditis and empyema (n = 1 each). Median duration of C/T was 13 days (3–52). 58% of patients with pneumonia received concomitant inhaled antibiotics. 30% patients received concomitant intravenous antibiotics. Overall rates of clinical success and survival at 30 days were 57% and 78%, respectively. Failures were due to death (n = 14), recurrent infection (n = 7), lack of clinical improvement (n = 5), or early discontinuation of C/T (n = 1). Rates of success and survival for pneumonia were 53% and 71%, respectively. Success rates were 67% and 51% among patients receiving C/T mono- vs. combination therapy (P = 0.29). Among surviving patients (n = 49), microbiologic failures occurred in 49% at a median of 23 days (7–64) from C/T initiation. Micro failures were due to recurrent pneumonia (n = 6) or colonization (n = 18). 56% of patients survived at 90 days. Median C/T MIC vs. baseline MDR-Pa isolates was 2 µg/mL (range: 0.5–>256); 10% of patients had C/T resistant isolates at baseline. Among patients with microbiologic failures infected by C/T susceptible isolates at baseline (n = 21), 38% developed resistance. The median duration of treatment prior to the emergence of resistance was 17 days (6–53).

Conclusion

C/T was effective for treatment of various MDR-Pa infections. MDR-Pa cannot be assumed to be C/T susceptible at baseline, and MICs should be measured before treatment and following microbiologic failure.

Disclosures

R. K. Shields, Allergan: Grant Investigator, Research grant. Pfizer: Consultant and Scientific Advisor, Speaker honorarium. Shionogi: Scientific Advisor, Consulting fee. Roche: Grant Investigator, Research grant. Venatorx: Grant Investigator, Research grant. Medicines Company: Grant Investigator and Scientific Advisor, Consulting fee and Research grant. Accelerate Diagnostics: Scientific Advisor, Consulting fee. M. H. Nguyen, Merck: Grant Investigator, Research grant. Astellas: Grant Investigator, Research grant.

1064. Clinical Outcomes of Daptomycin in Combination With Ceftaroline or Anti-Staphylococcal Penicillins for Patients With Persistent MRSA Bacteremia

Background

Daptomycin-β-lactam (DAP-BL) combinations demonstrate in vitro synergy against MRSA; however, the clinical efficacy of combo is limited. Our objective was to compare the outcomes of patients with persistent MRSA bacteremia treated with DAP-BL combinations.

Methods

Retrospective, cohort study of hospitalized patients receiving DAP with ceftaroline (CPT) or oxacillin (OXA) between March 2012 and February 2018. Patients with persistent MRSA bacteremia despite ≥4 days of vancomycin therapy were included. Clinical success was defined as resolution of signs and symptoms of infection, microbiological eradication and in hospital survival.

Results

Thirty-two patients included. Forty-four percent were male, median age was 61 (range: 26–78), and the median Charlson score was 2 (range: 0–11). Sixteen percent were IVDU. Sources of bacteremia included endocarditis (31%), bone/joint (31%), skin soft tissue (28%), and catheter (25%); 53% had more than one source. At the onset of combo therapy, median Pitt Bacteremia score was 1 (0–7). ID was consulted in all patients. Twenty-three and nine patients received DAP in combo with CPT or OXA, respectively. Baseline demographics, underlying disease, and clinical characteristics were comparable between groups. Patients receiving DAP-CPT had higher median Pitt Bacteremia scores (2 vs. 1; P = 0.04) and shorter median durations of prior vancomycin (8 vs. 10 days; P = 0.02) than did patients receiving DAP-OXA. Source control was pursued equally between groups. Median time to clearance of bacteremia following combo therapy was 3 (0–24) vs. 2 (−1–16) days in the DAP-CPT and DAP-OXA groups, respectively (P = 0.45). Corresponding rates of clinical success (43% vs. 56%) and microbiologic eradication (78% for both) did not vary between groups (figure). In hospital mortality occurred in 39% of patients receiving DAP-CPT and 0% of patients receiving DAP-OXA (P = 0.03). Adverse events occurred in 35% and 44% of patients, respectively.

Conclusion

We have demonstrated high rates of microbiologic eradication and reasonable clinical success rates with DAP-BL combination therapy. Patients receiving DAP-CPT had higher severity of illness at baseline, which paralleled with higher mortality. These data provide compelling evidence for future studies designed to determine the optimal BL in combination with DAP for persistent MRSA bacteremia.

Disclosures

R. K. Shields, Allergan: Grant Investigator, Research grant. Pfizer: Consultant and Scientific Advisor, Speaker honorarium. Shionogi: Scientific Advisor, Consulting fee. Roche: Grant Investigator, Research grant. Venatorx: Grant Investigator, Research grant. Medicines Company: Grant Investigator and Scientific Advisor, Consulting fee and Research grant. Accelerate Diagnostics: Scientific Advisor, Consulting fee.

247. Sustaining Excellence of Care During a Fluid Shortage: Snapshot of Antibiotic Mitigation Strategies Following Hurricane Maria

Background

Intravenous (IV) antibiotics (ABX) are standard for treatment of many inpatient infections. A devastating Puerto Rico hurricane in September 2017 resulted in critical shortages of IV ABX and fluids. In response, a comprehensive review of viable mitigation strategies related to antimicrobials was coordinated at our center to ensure continued excellence in care was provided to all patients.

Methods

A multidisciplinary mitigation task force (MTF) was established to begin immediate fluid conservation efforts from an antimicrobial perspective.

Results

First, ABX regimens were converted to oral equivalents where clinically appropriate. Second, the ABX stewardship team (ASP) offered alternatives to IV ABX that required a large volume of fluid for reconstitution (e.g., ampicillin-sulbactam (A/S, 400 mL fluid/day), meropenem (MER, 300 mL fluid/day). Third, through prospective audit and feedback (PAF), we transitioned patients from A/S (n = 37), cefazolin (n = 21), and IV doxycycline (n = 4) to either oral or alternative IV therapies. We completed additional PAF transitions of IV metronidazole (n = 15) and MER (n = 7). Lastly, 24 ABX products were transitioned to alternative routes of delivery or to diluent fluids. Products were transitioned from mini bags to IV push (n = 10) and IV syringe pump (n = 10). Each product transition required coordinated efforts from over 10 teams including electronic ordering. Education consisted of 20 newsletters created for nursing and 10 order verification packets created for pharmacists. Metrics were established to ensure sustained impact through bi-weekly ABX scorecards. After 6 days of IV metronidazole ASP restriction, use decreased 52% from baseline. With the transitions in place, an average of approximately 100 liters of fluid was conserved per week.

Conclusion

The immediate and collective response of the MTF allowed for the continued capability to provide IV ABX for patient care as supplies fluctuated. Continued education supported safe transitions. Further data will determine the impact of the fluid shortage on patient outcomes once critical supply levels have resolved. These efforts establish a foundation for ongoing initiatives after shortages are resolved.

Disclosures

M. H. Nguyen, Merck: Grant Investigator, Research grant

Astellas: Grant Investigator, Research grant

2421. Tedizolid Is Well-Tolerated Among Patients Receiving Prolonged Treatment Courses

Background

Tedizolid (TED) is a newly-approved oxazolidinone antibiotic that may be better tolerated than linezolid; however, real-world clinical data are limited, particularly among patients receiving prolonged treatment courses. Our objective was to review our clinical experience with TED and describe rates of adverse events.

Methods

Retrospective review of patients receiving >24 hours of TED between June 2015 and April 2018. Adverse events were determined according to standard definitions.

Results

55 patients receiving 60 different TED treatment courses were included. The median duration of treatment was 7 days (range: 2–141 days); 42% and 16% of patients received courses ≥10 and ≥30 days, respectively. 44% of patients were male, the median age was 58 (20–88), and 35% were immunosuppressed, including 22% of patients who received a solid-organ transplant. Indications for TED were skin/soft-tissue infections (n = 23), bacteremia (n = 10), osteomyelitis/septic arthritis (n = 7), endocarditis/endovascular infection (n = 5), pneumonia (n = 4), M. abscessus treatment (n = 3), intra-abdominal infection (n = 2) and urinary tract infection (n = 1). 60% of patients failed alternative therapies prior to TED treatment. Specifically, 31% of patients had documented adverse events to linezolid (n = 8), daptomycin (n = 3), vancomycin (n = 3), quinupristin/dalfopristin, televancin, or tigecycline (n = 1 each). At initiation of TED, the median platelet (PLT) count (per 1000 cells/L) was 205 (range: 16–674); 20% had baseline thrombocytopenia (PLT <100). Overall, 11% of patients experienced an adverse event or intolerability leading to TED discontinuation, including 3 patients with thrombocytopenia (>50% decrease in PLT) and 1 patient each with a rash, vomiting, and confusion. 67% of patients with thrombocytopenia were previously intolerant of linezolid. No patients experienced lactic acidosis, peripheral neuropathy, or neutropenia. Notably, TED was well tolerated for treatment courses up to 141 days and among 2 patients with repeated, prolonged courses.

Conclusion

Among acutely and chronically-ill patients, TED was well-tolerated. This includes patients who received long-term treatment with TED, and those who were intolerant of alternative antibiotics.

Disclosures

R. K. Shields, Allergan: Grant Investigator, Research grant. Pfizer: Consultant and Scientific Advisor, Speaker honorarium. Shionogi: Scientific Advisor, Consulting fee. Roche: Grant Investigator, Research grant. Venatorx: Grant Investigator, Research grant. Medicines Company: Grant Investigator and Scientific Advisor, Consulting fee and Research grant. Accelerate Diagnostics: Scientific Advisor, Consulting fee.

1370. Cefepime/VNRX-5133 Broad-Spectrum Activity Is Maintained Against Emerging KPC- and PDC-Variants in Multidrug-Resistant K. pneumoniae and P. aeruginosa

Background

VNRX-5133 is a cyclic boronate β-lactamase inhibitor (BLI) currently in clinical development with cefepime to treat multidrug-resistant (MDR) infections caused by ESBL- and carbapenemase-producing Enterobacteriaceae (ENT) and P. aeruginosa (PSA). VNRX-5133 has direct inhibitory activity against serine-active site β-lactamases (Ser-BL) and emerging VIM/NDM metallo-β-lactamases (MBL). We show herein that cefepime/VNRX-5133 is highly active against MDR-K. pneumoniae and P. aeruginosa clinical isolates producing BL-variants evolved during therapy that compromise activity of ceftazidime/avibactam and ceftolozane/tazobactam.

Methods

Susceptibility testing was performed according to CLSI methods with cefepime, ceftolozane, and ceftazidime alone or in combination with VNRX-5133, avibactam, or tazobactam, respectively, fixed at 4 mg/L. Five clinical isolates of K. pneumoniae producing KPC variants impacting ceftazidime/avibactam and five clinical isolates of P. aeruginosa producing Pseudomonas-derived cephalosporinase variants impacting ceftolozane/tazobactam activity were collected in 2016 and 2017, respectively, from United States and Spanish hospitals. All other clinical isolates of Enterobacteriaceae and P. aeruginosa (n = 40) were collected in 2016.

Results

Cefepime/VNRX-5133 was highly active against five ceftazidime/avibactam-resistant K. pneumoniae clinical isolates producing KPC variants with MIC ranging from 0.5 to 4 mg/L relative to ceftazidime/avibactam MIC range of 16 to >128 mg/L. Cefepime/VNRX-5133 was also active against all five clinical isolates of ceftolozane/tazobactam-resistant P. aeruginosa, where 4/5 isolates had MIC of 4–8 mg/L relative to ceftolozane/tazobactam MIC range of 32–128 mg/L. The elevated cefepime/VNRX-5133 MIC (16 mg/L) in the remaining P. aeruginosa isolate was not due to the PDC-221 variant, as an engineered strain of P. aeruginosa producing this enzyme had a cefepime/VNRX-5133 MIC of 1 mg/L.

Conclusion

VNRX-5133 is a potent BLI possessing a unique broad spectrum of activity, including Class A, C, and D Ser-BLs, clinically evolving variants of Ser-BLs (e.g., KPC, PDC) and emerging VIM/NDM-type MBLs. Cefepime/VNRX-5133 is highly active against emerging multidrug-resistant Enterobacteriaceae and P. aeruginosa.

Disclosures

D. Daigle, VenatoRx Pharmaceuticals Inc.: Employee and Shareholder, Salary. J. Hamrick, VenatoRx Pharmaceuticals Inc.: Employee, Salary. C. Chatwin, VenatoRx Pharmaceuticals Inc.: Employee, Salary. N. Kurepina, VenatoRx Pharmaceuticals Inc.: Research Contractor, Research support. B. N. Kreiswirth, VenatoRx Pharmaceuticals Inc.: Research Contractor, Research support. R. K. Shields, VenatoRx Pharmaceuticals Inc.: Research Contractor, Research support. A. Oliver, VenatoRx Pharmaceuticals Inc.: Research Contractor, Research support. C. J. Clancy, VenatoRx Pharmaceuticals Inc.: Research Contractor, Research support. M. H. Nguyen, VenatoRx Pharmaceuticals Inc.: Research Contractor, Research support. D. Pevear, VenatoRx Pharmaceuticals Inc.: Employee, Salary. L. Xerri, VenatoRx Pharmaceuticals Inc.: Employee and Shareholder, Salary.

2420. A Real-World Perspective on the Efficacy of Fosfomycin for Treatment of Multidrug-Resistant Pathogens Causing Urinary Tract Infections

Background

Methods

Results

Conclusion

Disclosures

2403. Comparison of Daptomycin Combination Therapy With Ceftaroline or Oxacillin Against Methicillin-Resistant Staphylococcus aureus (MRSA) Isolates Causing Persistent Bacteremia

Background

Increasing evidence suggests that daptomycin (DAP) demonstrates in vitro synergy in combination with other anti-staphylococcal agents, including ceftaroline (CPT) and oxacillin (OXA), against MRSA. Nevertheless, optimal combinations remain undefined. Here, our objective was to compare DAP in combination with CPT or OXA against MRSA bloodstream isolates collected from patients with persistent bacteremia despite >7 days of vancomycin treatment.

Methods

Minimum inhibitory concentrations (MICs) for DAP, CPT, and OXA were determined in duplicate by reference broth microdilution methods. We used time-kill analyses (TKA) to test free peak concentrations (fC_max) of DAP (8 µg/mL), CPT (16 µg/mL), and OXA (4 µg/mL) alone and in combination against 1 × 10⁸ CFU/mL to simulate high-inocula infections. Bactericidal and synergistic activity were defined as a ≥3-log₁₀ decrease in CFU/mL and >2-log₁₀ decrease in CFU/mL in combination compared with the most active single agent, respectively, at 24 hours.

Results

A representative isolate was selected from 12 patients with persistent MRSA bacteremia. Median (range) MICs were 0.5 (0.5–1), 0.5 (0.5–1), and 64 (64–≥128) µg/mL for DAP, CPT, and OXA, respectively. By TKA (n = 5 isolates), median log-kills were −3.81, −1.90, and +1.99 log₁₀CFU/mL for DAP, CPT, OXA, respectively. Corresponding rates of bactericidal activity were 80%, 20%, and 0%, respectively. In combination, median log-kills were −7.83 and −4.82 log₁₀CFU/mL for DAP+CPT and DAP+OXA, respectively (P = 0.111; Figure 1). DAP was synergistic in combination with CPT or OXA against 80% and 60% of isolates, respectively. Median log-kills in combination with CPT or OXA were higher than DAP alone (P = 0.003 and P = 0.0497, respectively). At 24 hours, colony counts were below the lower limit of detection (50 CFU/mL) against 60% and 20% of isolates exposed to DAP+CPT or DAP+OXA, respectively.

Conclusion

Among persistent MRSA bloodstream isolates, combinations of DAP + CPT or OXA demonstrates synergy and statistically greater killing effects in vitro at fCmax concentrations than DAP alone. Log-kills were greatest with DAP+CPT, which merits further validation in pre-clinical models.

Disclosures

All authors: No reported disclosures.

357. Aspergillus Isolates Remain Largely Susceptible to Azoles and Other Antifungals at a Large Transplant Program Using Azole Prophylaxis

Background

The emergence of azole resistance globally among Aspergillus species has major clinical and agricultural implications. At our center, isavuconazole (ISA), posaconazole (POS), and voriconazole (VOR) have been used as antifungal prophylaxis in solid-organ transplant recipients. We determined susceptibility to azoles and other antifungals among Aspergillus isolates from our center.

Methods

Fifty-two patient isolates of Aspergillus species were collected from the UPMC Microbiology Laboratory between December 2016 and April 2018. Minimum inhibitory concentrations (MICs) of ISA, POS, VOR, amphotericin B (AmB), and caspofungin (CAS) were measured using EUCAST Antimicrobial Susceptibility Testing methods. Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 were used as quality control.

Results

Seventy-one percent (37/52) of isolates were from solid-organ transplant recipients (34 lungs, two liver, and one heart). Aspergillus spp. were A. fumigatus (29), A. terreus (At, 6), A. niger, A. flavus and Aspergillus calidoustus (five of each species), and A. lentulus and A. thermomutatus (one of each species). Thirteen breakthrough (BT) isolates were recovered from patients on azoles: A. calidoustus (5), A. niger (4), A. flavus (2), A. fumigatus (1) and At (1). A. calidoustus, A. flavus, and A. niger were more likely than other species to be recovered from azole BT (75% (12/16) vs. 5% (2/36), P = 0.06). For all isolates, ISA, VOR, and POSA MIC₅₀ were 0.25 µg/mL, 0.04 µg/mL, and 0.25 µg/mL, respectively. One A. calidoustus and one At were resistant to all antifungals (azoles, AmB, and caspofungin MICs were >16 µg/mL); both were associated with azole BT. ISA, POS, and VOR MIC₅₀ vs. azole BT isolates (0.5, 0.125, and 0.5 µg/mL, respectively) were higher than those vs. non-BT isolates (0.25, 0.03, and 0.25 µg/mL, respectively; P < 0.01 for all).

Conclusion

Despite widespread use of azole prophylaxis in transplant recipients at our center, we did not observe high rates of resistance to azoles or other antifungals among Aspergillus isolates, although azole MICs were higher against BT isolates. Azole BT isolates were more likely to be non-A. fumigatus species. Clinicians should understand that antifungal resistance rates can vary by center and geographical location, and use their local epidemiology to guide decisions about the utility of specific agents in their populations.

Disclosures

All authors: No reported disclosures.

1528. A Real-World Perspective on Treatment of CRE UTIs With Oral Agents

Background

Methods

Results

Conclusion

Disclosures

Whole-Genome Sequencing Accurately Identifies Resistance to Extended-Spectrum β-Lactams for Major Gram-Negative Bacterial Pathogens

Background

There is marked interest in using DNA-based methods to detect antimicrobial resistance (AMR), with targeted polymerase chain reaction (PCR) approaches increasingly being incorporated into clinical care. Whole-genome sequencing (WGS) could offer significant advantages over targeted PCR for AMR detection, particularly for species where mutations are major drivers of AMR.

Methods

Illumina MiSeq WGS and broth microdilution (BMD) assays were performed on 90 bloodstream isolates of the 4 most common gram-negative bacteria causing bloodstream infections in neutropenic patients. The WGS data, including both gene presence/absence and detection of mutations in an array of AMR-relevant genes, were used to predict resistance to 4 β-lactams commonly used in the empiric treatment of neutropenic fever. The genotypic predictions were then compared to phenotypic resistance as determined by BMD and by commercial methods during routine patient care.

Results

Of 133 putative instances of resistance to the β-lactams of interest identified by WGS, only 87 (65%) would have been detected by a typical PCR-based approach. The sensitivity, specificity, and positive and negative predictive values for WGS in predicting AMR were 0.87, 0.98, 0.97, and 0.91, respectively. Using BMD as the gold standard, our genotypic resistance prediction approach had a significantly higher positive predictive value compared to minimum inhibitory concentrations generated by commercial methods (0.97 vs 0.92; P = .025).

Conclusions

These data demonstrate the potential feasibility of using WGS to guide antibiotic treatment decisions for patients with life-threatening infections for an array of medically important pathogens.

Therapeutic Drug Monitoring (TDM) of Suspension (SUS), Extended-Release (ER), and Intravenous (IV) Posaconazole (POS) at a Large Transplant Center

Background

Data on ER and IV POS among organ transplant recipients (OTRs) are limited, and the role of TDM is unclear.

Methods

Retrospective study of patients (pt) receiving any formulation of POS who had serum troughs checked. Therapeutic was defined as ³ 1 mcg/mL.

Results

We analyzed 88 pt and 340 levels (SUS: 88, ER: 197, IV: 55). Eighty-five pt were OTRs (97%), 73 were lung transplant recipients (LT) (83%), 17 had cystic fibrosis (CF) (19%). POS was used for treatment (70%) (probable aspergillosis (38%), possible aspergillosis (10%), mucormycosis (16%), other mycoses (6%)), prophylaxis (19%), and pre-emptive therapy (14%). POS was given for intolerance of or contraindication to other azoles (47%), salvage therapy (10%), resistance (19%), and failure to achieve therapeutic levels with other azoles (6%). Serum concentration/dose ratios were lower with SUS vs. ER/IV (P < 0.0001) but were similar in ER/IV groups (P = 0.51) (Figure). There was no difference in serum levels between pt receiving ER vs. IV POS at 300 mg once daily (median 1.2 vs. 1.3 mcg/mL, therapeutic 70% vs. 73%, P = 0.57 and >0.99, respectively). 3 pt had levels £ 0.2 mcg/mL on 300 mg ER: 2 had CF and had undergone LT (0.2 and 0 mcg/mL) and 1 had short-gut syndrome (0.1 mcg/mL). Sixty-six percent and 67 % of pt receiving ER or IV POS (300 mg once daily) achieved initial therapeutic levels, respectively; of these, 87% and 83% had median therapeutic follow-up levels, respectively. Serial levels were available for 7 pt whose dose was increased from 300 to 400 mg ER once daily for subtherapeutic levels. 4/7 pt achieved therapeutic levels on 400 vs. 0/7 on 300 mg ER once daily (P = 0.069). Metoclopramide use and CF were associated with subtherapeutic vs. therapeutic levels (25% vs. 4% and 37% vs. 13%, respectively, P = < 0.05). When pt with CF were excluded, neither age nor body mass index were associated with POS levels. CF pt had lower levels than non-CF pt on a dose of 300 mg ER once daily (median 0.8 vs. 1.3 mcg/mL, P = 0.018).

Conclusion

Therapeutic levels are more reliably achieved with ER & IV POS compared with SUS POS. Serial TDM is unnecessary for most, but is recommended for pt with CF or those on metoclopramide. Dose increases may effectively increase levels. Novel dosing strategies are needed for CF.

Disclosures

R. K. Shields, Astellas: Received research funding, Research support. Merck: Received research funding, Research support. C. J. Clancy, Merck: Received research funding, Research support. Astellas: Received research funding, Research support. Cidara: Received research funding, Research support. Astellas: Scientific Advisor, Advisory board. Merck: Scientific Advisor, Advisory board. Cidara: Scientific Advisor, Advisory board. Medicines Company: Scientific Advisor, Advisory board.