Genomic heterogeneity underlies multidrug resistance in Pseudomonas aeruginosa: A population-level analysis beyond susceptibility testing.

BACKGROUND: Pseudomonas aeruginosa is a persistent and difficult-to-treat pathogen in many patients, especially those with Cystic Fibrosis (CF). Herein, we describe a longitudinal analysis of a series of multidrug resistant (MDR) P. aeruginosa isolates recovered in a 17-month period, from a young female CF patient who underwent double lung transplantation. Our goal was to understand the genetic basis of the observed resistance phenotypes, establish the genomic population diversity, and define the nature of sequence evolution over time. METHODS: Twenty-two sequential P. aeruginosa isolates were obtained within a 17-month period, before and after a double-lung transplant. At the end of the study period, antimicrobial susceptibility testing, whole genome sequencing (WGS), phylogenetic analyses and RNAseq were performed in order to understand the genetic basis of the observed resistance phenotypes, establish the genomic population diversity, and define the nature of sequence changes over time. RESULTS: The majority of isolates were resistant to almost all tested antibiotics. A phylogenetic reconstruction revealed 3 major clades representing a genotypically and phenotypically heterogeneous population. The pattern of mutation accumulation and variation of gene expression suggested that a group of closely related strains was present in the patient prior to transplantation and continued to change throughout the course of treatment. A trend toward accumulation of mutations over time was observed. Different mutations in the DNA mismatch repair gene mutL consistent with a hypermutator phenotype were observed in two clades. RNAseq performed on 12 representative isolates revealed substantial differences in the expression of genes associated with antibiotic resistance and virulence traits. CONCLUSIONS: The overwhelming current practice in the clinical laboratories setting relies on obtaining a pure culture and reporting the antibiogram from a few isolated colonies to inform therapy decisions. Our analyses revealed significant underlying genomic heterogeneity and unpredictable evolutionary patterns that were independent of prior antibiotic treatment, highlighting the need for comprehensive sampling and population-level analysis when gathering microbiological data in the context of CF P. aeruginosa chronic infection. Our findings challenge the applicability of antimicrobial stewardship programs based on single-isolate resistance profiles for the selection of antibiotic regimens in chronic infections such as CF

Real-world, Multicenter Experience With Meropenem-Vaborbactam for Gram-Negative Bacterial Infections Including Carbapenem-Resistant Enterobacterales and Pseudomonas Aeruginosa

Background: We aimed to describe the clinical characteristics and outcomes of patients treated with meropenem-vaborbactam (MEV) for a variety of gram-negative infections (GNIs), primarily including carbapenem-resistant Enterobacterales (CRE). Methods: This is a real-world, multicenter, retrospective cohort within the United States between 2017 and 2020. Adult patients who received MEV for ≥72 hours were eligible for inclusion. The primary outcome was 30-day mortality. Classification and regression tree analysis (CART) was used to identify the time breakpoint (BP) that delineated the risk of negative clinical outcomes (NCOs) and was examined by multivariable logistic regression analysis (MLR). Results: Overall, 126 patients were evaluated from 13 medical centers in 10 states. The most common infection sources were respiratory tract (38.1%) and intra-abdominal (19.0%) origin, while the most common isolated pathogens were CRE (78.6%). Thirty-day mortality and recurrence occurred in 18.3% and 11.9%, respectively. Adverse events occurred in 4 patients: nephrotoxicity (n = 2), hepatoxicity (n = 1), and rash (n = 1). CART-BP between early and delayed treatment was 48 hours (P = .04). MEV initiation within 48 hours was independently associated with reduced NCO following analysis by MLR (adusted odds ratio, 0.277; 95% CI, 0.081-0.941). Conclusions: Our results support current evidence establishing positive clinical and safety outcomes of MEV in GNIs, including CRE. We suggest that delaying appropriate therapy for CRE significantly increases the risk of NCOs

1611. Evaluating Clinical Outcomes and Efficacy of Daptomycin in Combination with a Beta-Lactam for the Treatment of Vancomycin-Resistant Enterococcus (VRE) Bacteremia

Abstract Background In-vitro studies have shown synergistic bactericidal activity with daptomycin (DAP) plus β-lactam antimicrobials against vancomycin resistant enterococci (VRE). There is a paucity of data regarding clinical outcomes with this combination in VRE bloodstream infections (BSI). The purpose of this study was to assess the efficacy of DAP plus a β-lactam with in-vitro activity vs. other therapies for treatment of VRE BSI. Methods IRB-approved, single-center, retrospective study of patients with VRE BSI from 01/2018-09/2019. Patients were excluded if < 18 years old, pregnant, or incarcerated. The primary outcome was time-to-microbiological clearance. Secondary outcomes included infection-related mortality, 30-day all-cause mortality, and incidence of recurrent BSI within 30 days of index culture. Targeted DAP doses were ≥ 8mg/kg and based on MIC. Factors associated with significance for outcomes, via univariate analysis, were evaluated with multivariable logistic regression (MLR), removed in a backward-step approach. Results A total of 85 patients were included, 23 of which received DAP plus a β-lactam. The comparator arm included linezolid or DAP monotherapy. Patients with combination therapy had significantly higher Charlson Comorbidity Index (CCI) (p=0.013) and numerically higher Pitt Bacteremia scores (PBS) (p=0.087) (Table 1). There was no difference seen in the primary outcome (Table 2). Secondary outcomes are provided in Table 2. The presence of polymicrobial infection and higher PBS were significantly associated with infection-related mortality (p=0.008 and p=0.005, respectively) by MLR. A Mann Whitney U test indicated that presence of infection-related mortality was greater for patients with higher MICS (U=20.5, p=0.06). The presence of an underlying source may be related to recurrence of BSI (p=0.075). Table 1: Patient Characteristics Table 2. Primary and Secondary Outcomes Conclusion We did not find a significant difference in time-to-microbiological clearance, although patients treated with DAP and a β-lactam had higher CCI and PBS. These results are limited by retrospective design, small sample size, and potential selection bias. Prospective randomized studies are needed to further validate these findings. Disclosures All Authors: No reported disclosure

670. Real-life Experience of Imipenem-cilistatin-relebactam for the Treatment of Extensively Drug-resistant and Difficult-to-treat Pseudomonas Infections

Abstract Background Imipenem-cilistatin-relebactam (Recarbrio) is recommended to treat extensively drug-resistant (XDR) and difficult-to-treat (DTR) Pseudomonas aeruginosa (PA). Since approval in 2019, there remains limited literature describing real-world use. We describe our experience and evaluate the efficacy and safety of Imipenem-cilistatin-relebactam for the treatment of XDR and DTR Pseudomonas infections. Methods This was a retrospective, observational study at a 1,550 licensed-bed academic hospital. Adults receiving ≥72 hours of Imipenem-cilistatin-relebactam for Pseudomonas infections between January 2020-February 2022 were included. The primary outcome was clinical success. Secondary outcomes included 30-day all-cause mortality, 30-day recurrence, 60-day infection-related hospital readmission, and adverse effects. Descriptive statistics were used to analyze our findings. Results Ten patients were included, with 60% being male and a median age of 63 years (range 31-85). The median duration of treatment was 7 days (range 4-14). Sources of infection included ventilator-associated pneumonia (70%), empyema (20%), and bacteremia (20%). Two isolates were XDR, and seven DTR, including an isolate positive for Verona-integron-borne Metallo-β-lactamase (VIM). At the time of index culture, the median APACHE II score was 25.5 and 60% had at least one concomitant infection. For our primary outcome, 7 patients (70%) achieved clinical success. All-cause mortality at 30 days was 30% and 3 out of 8 patients had recurrent infection within 30 days. Conclusion Our study demonstrates the real-life use of Imipenem-cilistatin-relebactam for the treatment of XDR and DTR Pseudomonas infections. While the majority of patients achieved clinical success, a high mortality and recurrence rate was still observed. Larger studies are needed to validate our initial findings. Disclosures All Authors: No reported disclosures

Clinical pharmacist input on HIV management may improve antiretroviral prescribing for psychiatric patients

Abstract Purpose The results of a study to determine the difference in HIV management with clinical pharmacist input in an adult psychiatric hospitalized patient population are reported. Methods Single-center, retrospective study of patients admitted to a psychiatric hospital on antiretroviral (ARV) medication(s) from October 2016 to March 2017 (phase I: no pharmacist involvement), October 2017 to March 2018 (phase II: partial pharmacist involvement), and November 2018 to January 2019 (phase III: consistent pharmacist involvement). Patients were excluded if less than 18 years of age, pregnant, incarcerated, or taking ARV medication(s) for non-HIV indications. The primary outcome was difference in appropriateness of ARV therapy prior to and during pharmacist involvement. Secondary outcomes were appropriateness of opportunistic infection (OI) prophylaxis, laboratory testing, and comprehensive HIV management. Results Thirty-seven patients were included per phase. An increased number of appropriate ARV regimens were initiated in phase II compared to phase I (62% vs 32%; P = 0.01) and in phase III compared to phase II (84% vs 62%; P = 0.036). Increased laboratory monitoring was seen with partial and consistent pharmacist involvement. Among the patients requiring OI prophylaxis, appropriate prophylaxis was initiated in more patients in phase III (57%) than in phase II (50%) or phase I (11%). More patients had comprehensive HIV management in phase II compared to phase I (38% vs 5%; P < 0.001) and in phase III compared to phase II (46% vs 38%; P = 0.48). Conclusion Pharmacist involvement in HIV management in a psychiatric patient population increased appropriateness of ARV therapy, laboratory testing, and OI prophylaxis

1304. Pharmacist Impact on HIV Management in a Psychiatric Patient Population

Abstract Background Patients with mental illnesses are more than four times more likely to have human immunodeficiency virus (HIV) compared with the general population. HIV management can be especially challenging in these patients due to potential substance abuse, drug interactions, and nonadherence. The purpose of this study was to determine the impact of pharmacist management of antiretroviral (ARV) therapy in a psychiatric patient population. Methods This is an institutional review board-approved, single-center, retrospective study of patients admitted to a psychiatric hospital with an order for one or more ARV medication(s) between October 2016 and March 2017 (no pharmacist involvement), October 2017 and March 2018 (partial pharmacist involvement), and November 2018 and January 2019 (consistent pharmacist involvement). Patients were excluded if less than 18 years of age, pregnant, incarcerated, or taking ARV medication(s) for a non-HIV indication. The primary outcome was difference in appropriateness of ARV therapy prior to and during pharmacist involvement. Secondary outcomes were appropriateness of opportunistic infection (OI) prophylaxis and laboratory testing. Results A total of 37 patients were included per group. A greater number of appropriate ARV regimens were initiated with partial pharmacist involvement compared with no pharmacist involvement (62% vs. 32%, P = 0.0096), as well as with consistent pharmacist involvement compared with partial pharmacist involvement (84% vs. 62%, P = 0.0327). There was a trend toward increased HIV viral load draws with partial vs. no pharmacist involvement (54% vs. 43%, P = 0.24) and additionally with consistent vs. partial pharmacist involvement (62% vs. 54%, P = 0.32). With consistent pharmacist involvement, more patients had a resulted CD4 cell count (65%) than with both partial and no pharmacist involvement (57%). Of the patients requiring OI prophylaxis, appropriate prophylaxis was initiated in more patients with consistent pharmacist involvement (57%) than with partial pharmacist involvement (50%) or no pharmacist involvement (11%). Conclusion Pharmacist involvement in HIV management in a psychiatric patient population increased appropriateness of ARV therapy, laboratory testing, and OI prophylaxis. Disclosures All authors: No reported disclosures

Difficult-to-treat (DTR) Pseudomonas aeruginosa harboring Verona-Integron metallo-β-lactamase (blaVIM): infection management and molecular analysis

Pseudomonas aeruginosa harboring Verona Integron-encoded metallo-β-lactamase enzymes (VIM-CRPA) have been associated with infection outbreaks in several parts of the world. In the US, however, VIM-CRPA remain rare. Starting in December 2018, we identified a cluster of cases in our institution. Herein, we present our epidemiological investigation and strategies to control/manage these challenging infections. This study was conducted in a large academic healthcare system in Miami, FL, between December 2018 and January 2022. Patients were prospectively identified via rapid molecular diagnostics when cultures revealed carbapenem-resistant P. aeruginosa. Alerts were received in real time by the antimicrobial stewardship program and infection prevention teams. Upon alert recognition, a series of interventions were performed as a coordinated effort. A retrospective chart review was conducted to collect patient demographics, antimicrobial therapy, and clinical outcomes. Thirty-nine VIM-CRPA isolates led to infection in 21 patients. The majority were male (76.2%); the median age was 52 years. The majority were mechanically ventilated (n = 15/21; 71.4%); 47.6% (n = 10/21) received renal replacement therapy at the time of index culture. Respiratory (n = 20/39; 51.3%) or bloodstream (n = 13/39; 33.3%) were the most common sources. Most infections (n = 23/37; 62.2%) were treated with an aztreonam–avibactam regimen. Six patients (28.6%) expired within 30 days of index VIM-CRPA infection. Fourteen isolates were selected for whole genome sequencing. Most of them belonged to ST111 (12/14), and they all carried blaVIM-2 chromosomally. This report describes the clinical experience treating serious VIM-CRPA infections with either aztreonam–ceftazidime/avibactam or cefiderocol in combination with other agents. The importance of implementing infection prevention strategies to curb VIM-CRPA outbreaks is also demonstrated

110. Impact of Diagnostic and Antimicrobial Stewardship on Time-to-Appropriate Therapy and Clinical Outcomes in Multi-Drug Resistant Pseudomonas Infections

Abstract Background Timely effective therapy in multi-drug resistant (MDR) Pseudomonas (PsA) infections has a direct impact on patient survival. We aimed to determine the impact of diagnostic and antimicrobial stewardship (AMS) on time-to-appropriate therapy (TAP) and clinical outcomes of patients with MDR PsA infections utilizing novel beta-lactam/beta-lactamase inhibitors (BL/BLIs). Methods Retrospective cohort study of adult patients with MDR PsA infections at a 1,500-bed University-affiliated public hospital in Miami, Florida who received ≥72 hours of ceftazidime-avibactam (C/A) or ceftolozane-tazobactam (C/T). During the pre-intervention period (12/2017-12/2018), additional susceptibilities for C/A and C/T were performed upon providers’ request. In the post intervention period (01/2019 – 12/2019), we implemented automatic reflex algorithms (Figure 1) for faster identification and susceptibilities for MDR PsA, including carbapenemase producers. Results were communicated in real-time to the AMS team. Figure 1. Reflex Testing Algorithm for MDR Pseudomonas Isolates from Any Source Results Seventy-six patients were included; median age was 56 years (IQR 37.5–67.0), 40 (52.6%) were in an intensive care unit at time of culture collection; median APACHE II score was 20 (IQR 15.0 – 26.0). Three isolates were carbapenemase producers (VIM = 2; KPC = 1). The most common infections were pneumonia (56.6%) and bacteremia (18.4%). We found a significant decrease in median TAP (120.1 [IQR 82.5–164.6] vs 75.9 [IQR 51.3–101.7] hours, p = 0.003). Median time from culture collection to final susceptibility results was shorter in the post-intervention group (122.2 vs 90.5 hours; p < 0.001). Median length-of-stay after culture collection was numerically lower in the post-intervention group (26.0 [11.6–59.4] vs 19.7 [12.9–37.8] days; p = 0.33). Controlling for ICU admission, our intervention was not associated with decreased 30-day inpatient mortality (OR = 1.62, 95% CI 0.45–5.79). Conclusion Our study identified an improvement in TAP in MDR PsA infections with implementation of diagnostic and AMS initiatives. In an adequately powered study, our intervention could potentially impact patient survival through timely initiation of effective therapy with novel BL/BLIs. Disclosures All Authors: No reported disclosure

Impact of a Real-Time Diagnostic and Antimicrobial Stewardship Workflow on Time-to-Appropriate Therapy for Infections Caused by Multidrug-Resistant Gram-negative Organisms

•Multidisciplinary collaboration plus RDTs can improve outcomes in GNR infections•We focused on both CRE and MDR Pseudomonas infections•We implemented reflex susceptibility testing and real-time alerts to ASP/IP•We found a significant decrease in TAP and LOS post-AMS intervention Introduction: Multi-drug resistant (MDR) Gram-negative organisms (GNR) cause life-threatening infections and incidence is rising globally. Timely therapy in these infections has a direct impact on patient survival. We aimed to determine the impact of a multi-disciplinary diagnostic and antimicrobial stewardship (AMS) workflow on time-to-appropriate therapy (TAP) of these infections using novel beta-lactam/beta-lactamase inhibitors (BL/BLIs). Methods: This was a retrospective quasi-experimental study of adult patients with carbapenem-resistant Enterobacterales (CRE) and multidrug-resistant Pseudomonas (MDR PsA) infections at a 1,500-bed University hospital. Included patients received ≥72 hours of ceftazidime-avibactam (CZA) or ceftolozane-tazobactam (C/T) from 12/2017-12/2019. During the pre-intervention period (12/2017-12/2018), additional susceptibilities (including CZA and C/T) were performed only upon providers’ request. In 2019, we implemented reflex algorithms for faster identification and testing of all CRE/MDR PsA isolates. Results were communicated in real-time to the AMS team to tailor therapy. Results: A total of 99 patients were included with no differences at baseline between groups; median age 60 years, 56 (56.7%) were in intensive care at time of culture collection. Organisms identified included 71 (71.7%) MDR PsA and 26 CRE, of which 18 were carbapenemase producers (KPC=12, NDM=4, VIM=2). The most common infections were pneumonia (49.5%) and bacteremia (30.3%). We found a decrease in median TAP (103 [IQR 76.0–156.0] vs 75 [IQR 56–100] hours, p < 0.001). Median time from culture collection to final susceptibility results was shorter in the post-intervention group (123 vs 93 hours; p < 0.001). Conclusion: Our study identified improvement in TAP in MDR PsA and CRE infections with implementation of a reflex microbiology workflow and multidisciplinary antimicrobial stewardship initiatives