Antipseudomonal Agents Research Articles

Prevalence of Aminoglycoside Resistance Genes in Clinical Isolates of Pseudomonas aeruginosa from Taif, Saudi Arabia-An Emergence Indicative Study.

Hospital-acquired infections caused by P. aeruginosa contribute to global distress because of the elevated rates of microbial antibiotic resistance. Aminoglycosides are antipseudomonal agents that are effectively and frequently utilized to eradicate this infection. This current study is a retrospective study investigating plasmid-mediated aminoglycoside resistance by focusing on the prevalence of the genes encoding aminoglycoside-modifying enzymes (AMEs) and 16S rRNA methylase among P. aeruginosa clinical isolates from Taif, Saudi Arabia. A hundred clinical isolates of P. aeruginosa were collected. The isolates were identified from February 2021 to February 2022. Antibiotic susceptibility testing and MICs were determined using (DD) and (BM-MIC) testing, respectively. AMEs and 16S rRNA methylase variants in bacterial isolates were amplified via PCR for genetic detection. A relatively high multiple antibiotic resistance rate corresponding to 10-32% was reported. Eighteen percent of P. aeruginosa isolates were gentamicin-amikacin-tobramycin resistant according to the MIC levels. The aminoglycoside-resistant strains were additionally identified via GyrA gene sequencing. The phylogenic relatedness dendrogram of the sequenced GyrA genes was performed using a neighbor-joining method via MEGAX software version 10.2.6. The most prevalent AME encoding gene was aac(6')-Ib, observed in 94.4% of resistant isolates, while a resistance gene cocktail of [aac(6')-Ib and ant(3″)-I] was a highly frequent combination (27.8%). This study updated the knowledge about aminoglycoside resistance mechanisms in P. aeruginosa, which constitutes an urgent need, especially after the COVID-19 crisis, which was associated with increased antimicrobial use and resistance rates.

Changing Genotypic Distribution, Antimicrobial Susceptibilities, and Risk Factors of Urinary Tract Infection Caused by Carbapenemase-Producing Pseudomonas aeruginosa.

Carbapenem-resistant Pseudomonas aeruginosa (CrPA) is a leading cause of healthcare-associated urinary tract infections (UTIs). Carbapenemase production is an important mechanism that significantly alters the efficacy of frequently used anti-pseudomonal agents. Reporting the current genotypic distribution of carbapenemase-producing P. aeruginosa (CPPA) isolates in relation to antimicrobial susceptibility, UTI risk factors, and mortality is necessary to increase the awareness and control of these strains. In total, 1,652 non-duplicated P. aeruginosa strains were isolated from hospitalized patients between 2015 and 2020. Antimicrobial susceptibility, carbapenemase genotypes, risk factors for UTI, and associated mortality were analyzed. The prevalence of carbapenem-non-susceptible P. aeruginosa isolates showed a decreasing trend from 2015 to 2018 and then increased in the background of the emergence of New Delhi metallo-β-lactamase (NDM)-type isolates since 2019. The CPPA strains showed 100.0% non-susceptibility to all tested antibiotics, except aztreonam (94.5%) and colistin (5.9%). Carbapenems were identified as a risk and common predisposing factor for UTI (odds ratio [OR]=1.943) and mortality (OR=2.766). Intensive care unit (ICU) stay (OR=2.677) and white blood cell (WBC) count (OR=1.070) were independently associated with mortality. The changing trend and genetic distribution of CPPA isolates emphasize the need for relentless monitoring to control further dissemination. The use of carbapenems, ICU stay, and WBC count should be considered risk factors, and aggressive antibiotic stewardship programs and monitoring may serve to prevent worse outcomes.

The Art of War with Pseudomonas aeruginosa: Targeting Mex Efflux Pumps Directly to Strategically Enhance Antipseudomonal Drug Efficacy.

Pseudomonas aeruginosa (P. aeruginosa) poses a grave clinical challenge due to its multidrug resistance (MDR) phenotype, leading to severe and life-threatening infections. This bacterium exhibits both intrinsic resistance to various antipseudomonal agents and acquired resistance against nearly all available antibiotics, contributing to its MDR phenotype. Multiple mechanisms, including enzyme production, loss of outer membrane proteins, target mutations, and multidrug efflux systems, contribute to its antimicrobial resistance. The clinical importance of addressing MDR in P. aeruginosa is paramount, and one pivotal determinant is the resistance-nodulation-division (RND) family of drug/proton antiporters, notably the Mex efflux pumps. These pumps function as crucial defenders, reinforcing the emergence of extensively drug-resistant (XDR) and pandrug-resistant (PDR) strains, which underscores the urgency of the situation. Overcoming this challenge necessitates the exploration and development of potent efflux pump inhibitors (EPIs) to restore the efficacy of existing antipseudomonal drugs. By effectively countering or bypassing efflux activities, EPIs hold tremendous potential for restoring the antibacterial activity against P. aeruginosa and other Gram-negative pathogens. This review focuses on concurrent MDR, highlighting the clinical significance of efflux pumps, particularly the Mex efflux pumps, in driving MDR. It explores promising EPIs and delves into the structural characteristics of the MexB subunit and its substrate binding sites.

Implementation of a Rapid Multiplex Polymerase Chain Reaction Pneumonia Panel and Subsequent Antibiotic De-escalation.

Net effects of implementation of a multiplex polymerase chain reaction (PCR) pneumonia panel (PNP) on antimicrobial stewardship are thus far unknown. This retrospective study evaluated the real-world impact of the PNP on time to antibiotic de-escalation in critically ill patients treated for pneumonia at an academic medical center. This retrospective, quasi-experimental study included adult intensive care unit (ICU) patients with respiratory culture results from 1 May to 15 August 2019 (pre-PNP group) and adult ICU patients with PNP results from 1 May to 15 August 2020 (PNP group) at Nebraska Medical Center. Patients were excluded for the following reasons: any preceding positive coronavirus disease 2019 PCR test, lack of antibiotic receipt, or non-respiratory tract infection indications for antibiotics. The primary outcome was time to discontinuation of anti-methicillin-resistant Staphylococcus aureus (MRSA) therapy. Secondary outcomes included time to discontinuation of antipseudomonal therapy, frequency of early discontinuation for atypical coverage, and overall duration (in days) of antibiotic therapy for pneumonia. Sixty-six patients in the pre-PNP group and 58 in the PNP group were included. There were significant differences in patient characteristics between groups. The median time to anti-MRSA agent discontinuation was 49.1 hours in the pre-PNP and 41.8 hours in the PNP group (P = .28). The median time to discontinuation of antipseudomonal agents was 134.4 hours in the pre-PNP versus 98.1 hours in the PNP group (P = .47). Other outcomes were numerically but not significantly improved in our sample. This early look at implementation of a multiplex PNP did not demonstrate a statistically significant difference in antibiotic use but lays the groundwork to further evaluate a significant real-world impact on antibiotic de-escalation in ICU patients treated for pneumonia.

WS07.01 Inter-species interactions alter antimicrobial susceptibility in polymicrobial cultures

People with cystic fibrosis (p/wCF) often develop chronic lung infections punctuated by periods of acute pulmonary exacerbation. One of the pathogens present in many p/wCF is Pseudomonas aeruginosa (PA). In many infection scenarios, PA shares the airway environment with a veritable “zoo” of other microbes, including Gram-negative, Gram-positive and fungal species – yet these are rarely taken into account when testing new anti-pseudomonal agents. The aim of this project is to examine how the presence of other co-habiting species affects the biology of PA during antibiotic challenge.

Patterns of antimicrobial resistance and metal tolerance in environmental Pseudomonas aeruginosa isolates and the genomic characterization of the rare O6/ST900 clone.

Pseudomonas aeruginosa can harbor several virulence and antimicrobial resistance genes (ARGs). In this regard, virulent and multidrug-resistant (MDR) P. aeruginosa strains are closely related to severe infections. In addition, this species can also carry metal tolerance genes, selecting mainly antimicrobial-resistant strains. The action of several pollutants on the environment may favor the occurrence of antimicrobial-resistant and metal-tolerant strains. Therefore, the aim of this study was to characterize potentially pathogenic, antimicrobial-resistant, and/or metal-tolerant P. aeruginosa isolates from different environmental samples (waters, soils, sediments, or sands) and to perform a whole-genome sequence-based analysis of a rare clone from residual water. Environmental isolates carried virulence genes related to adherence, invasion, and toxin production, and 79% of the isolates harbored at least five virulence genes. In addition, the isolates were resistant to different antimicrobials, including important antipseudomonal agents, and 51% of them were classified as MDR, but only ARGs associated with aminoglycoside resistance were found. Furthermore, some isolates were tolerant mainly to copper, cadmium, and zinc, and presented metal tolerance genes related to these compounds. Whole-genome characterization of an isolate with unique phenotype with simultaneous resistance to antimicrobials and metals showed nonsynonymous mutations in different antimicrobial resistance determinants and revealed a classification of O6/ST900 clone as rare, potentially pathogenic, and predisposed to acquire multidrug resistance genes. Therefore, these results draw attention to the dissemination of potentially pathogenic, antimicrobial-resistant, and metal-tolerant P. aeruginosa isolates in environmental niches, alerting to a potential risk mainly to human health.

Management of the febrile neutropenic patient in 2023

Febrile neutropenia (FN) is a well-known complication of chemotherapy (CHT) regimens, which appears more frequently in patients receiving CHT for hematologic malignancies, than those with solid tumors. Given the fact that this condition is life threatening, as well as multiple complications that may happen, rapid intervention is required, administration of empirical antibiotic therapy being necessary in the first hour of admission. Due to the high mortality rate associated with Pseudomonas aeruginosa infections, patients at risk should be given an antipseudomonal antibiotic agent, such as cefepime, carbapenem or piperacillin-tazobactam. Regarding empirical antibiotic coverage for gram-positive microorganisms, this is preserved for hypotensive patients, with skin/soft infections or suspected catheters infection or those taking fluoroquinolone. Considering the fact that a variety of bacterial, viral and fungal pathogens are responsible for high morbidity and mortality among patients with FN, preventable measures like antibiotic, antifungal and antiviral, as well as vaccination and prophylaxis with G-CSF, are crucial components in providing medical treatment for onco-hematological patients.

Inhibitory Potential of Thymus vulgaris Essential Oil against Growth, Biofilm Formation, Swarming, and Swimming in Pseudomonas syringae Isolates

As a follow-up to previous studies, the effects of Thymus vulgaris essential oil on selected virulence factors (growth, sessile cell survival, swimming, swarming, and exopolysaccharide production) were evaluated in phytopathogenic Pseudomonas syringae strains isolated from soybean fields in Argentina; reference strains Pseudomonas savastanoi pv. glycinea B076 and Pseudomonas aeruginosa PAO1. P. syringae are responsible for bacterial blight, a disease that affects crops worldwide. Plant bacterioses are usually treated with antibiotics and copper compounds, which may contribute to the development of resistance in pathogens and damage the environment. For these reasons, eco-friendly alternatives are necessary. Although aromatic plants are a natural source of antimicrobial substances, the effects of these substances on phytopathogenic bacteria remain largely unexplored. Subinhibitory concentrations of the oil significantly reduced the slope and rate of bacterial growth. In addition, biofilm and exopolysaccharide (EPS) production were inhibited, with swimming and swarming motility patterns being affected at all of the oil concentrations tested. Therefore, TEO could potentially be a highly efficient antipseudomonal agent for treating plant infections caused by P. syringae.

In vitro activity of ceftolozane/tazobactam against multidrug-resistant Pseudomonas aeruginosa from patients in Western Europe: SMART 2017-2020

Multidrug-resistant (MDR) Pseudomonas aeruginosa infections compromise both empirical and definitive antimicrobial therapies. The Study for Monitoring Antimicrobial Resistance Trends (SMART) surveillance program identified 943 MDR P. aeruginosa (from a total of 4086 P. aeruginosa isolates [23.1%]) collected at 32 clinical laboratories in six countries in Western Europe from 2017 to 2020. Minimum inhibitory concentrations (MICs) for ceftolozane/tazobactam and 10 comparator agents were determined by broth microdilution and interpreted using 2021 EUCAST breakpoints. β-lactamase genes were identified in selected isolate subsets. Most isolates of P. aeruginosa in Western Europe (93.3%) were ceftolozane/tazobactam-susceptible. A total of 23.1% of P. aeruginosa isolates were MDR. Of these, 72.0% were ceftolozane/tazobactam-susceptible, which is similar to that for ceftazidime/avibactam (73.6%) but >40% higher than for carbapenems, piperacillin/tazobactam, third- and fourth-generation cephalosporins, and levofloxacin. Metallo-β-lactamases (MBLs) were carried by 8.8% of molecularly characterized MDR P. aeruginosa, and 7.6% of molecularly characterized MDR isolates carried Guiana Extended Spectrum (GES) carbapenemases. MBLs were identified in isolates from all six countries, ranging from 3.2% of all P. aeruginosa isolates from Italy to 0.4% of all isolates from the United Kingdom. Acquired β-lactamases were not identified in 80.0% of molecularly characterized MDR P. aeruginosa isolates. Percentages of MDR isolates without detected β-lactamases were higher in the United Kingdom (97.7%), Spain (88.2%), France (88.1%), and Germany (84.7%) than in Portugal (63.0%) and Italy (61.3%), where carbapenemases were more prevalent. Ceftolozane/tazobactam is an important treatment option for patients infected with MDR P. aeruginosa that are not susceptible to first-line antipseudomonal agents.

Leuconostoc lactis Bacteremia and Neutropenic Fever

Abstract The epidemiology of bacteremic infections in neutropenic patients has shifted from a previous majority involving gram-positive cocci to an increasing preponderance of gram-negative Enterobacteriaceae species and Pseudomonas aeruginosa. Recommended empiric antimicrobial treatment regimens include an antipseudomonal β-lactam or carbapenem agent while considering risk factors for the possibility of extended-spectrum β-lactamase– or carbapenemase-producing organisms. The addition of vancomycin is generally reserved for the chance of gram-positive cocci infection, principally in patients with central intravascular catheters or soft tissue infections. Persistent or breakthrough bacteremia despite receiving this glycopeptide drug should prompt the clinician to contemplate not only the possibility of vancomycin-resistant enterococci, but also other organisms that possess intrinsic resistance vancomycin, including Leuconostoc species.

Clinical impact and early prediction of carbapenem-resistant Pseudomonas aeruginosa bacteraemia in allogeneic hematopoietic stem cell transplantation recipients

Although antipseudomonal agents are administered in high-risk patients, no reports have focused on the risk of carbapenem-resistant (CR) Pseudomonas aeruginosa bacteremia in allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients. We retrospectively studied a cohort of adult allo-HSCT recipients with P. aeruginosa bacteremia, focusing on a comparison between carbapenem-sensitive (CS) and CR P. aeruginosa after initiating conditioning chemotherapy at our institute between January 2005 and December 2020. The incidence, all-cause 30-day mortality of P. aeruginosa bacteremia, and risk factors for carbapenem resistance among patients with P. aeruginosa bacteremia in allo-HSCT recipients were evaluated. Forty-eight patients with P. aeruginosa bacteremia were included, with an incidence of 3.84/100 recipients (CS 1.92 vs. CR 1.92). The all-cause 30-day mortality was significantly higher in CR P. aeruginosa bacteremia (CS 4.2% vs. CR 39.1%; p = 0.003). The factor significantly associated with CR P. aeruginosa bacteremia was carbapenem use for at least three days within 30 days before the onset of bacteremia (odds ratio: 9.23, 95% confidence interval: 2.52-33.67). Inappropriate antimicrobial selection was significantly more frequent in CR P. aeruginosa bacteremia (CS 4.2% vs. CR 66.7%; p ˂ 0.001). Empirical combination therapy with reference to antimicrobial susceptibility profiles in each institution should be considered when CR P. aeruginosa bacteremia is suspected in allo-HSCT recipients based on the risk of carbapenem exposure.

Antimicrobial susceptibility of bacterial isolates from clinical specimens in four Pacific Island countries, 2017–2021

There are limited antimicrobial resistance (AMR) surveillance data from low- and middle-income countries, especially from the Pacific Islands region. AMR surveillance data is essential to inform strategies for AMR pathogen control. We performed a retrospective analysis of antimicrobial susceptibility results from the national microbiology laboratories of four Pacific Island countries - the Cook Islands, Kiribati, Samoa and Tonga - between 2017 and 2021. We focused on four bacteria that have been identified as 'Priority Pathogens' by the World Health Organization: Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Following deduplication, a total of 20,902 bacterial isolates was included in the analysis. The most common organism was E.coli (n=8455) followed by S.aureus (n=7830), K.pneumoniae (n=2689) and P.aeruginosa (n=1928). The prevalence of methicillin resistance among S.aureus isolates varied between countries, ranging from 8% to 26% in the Cook Islands and Kiribati, to 43% in both Samoa and Tonga. Ceftriaxone susceptibility remained high to moderate among E.coli (87%-94%) and K.pneumoniae (72%-90%), whereas amoxicillin+clavulanate susceptibility was low against these two organisms (50%-54% and 43%-61%, respectively). High susceptibility was observed for all anti-pseudomonal agents (83%-99%). Despite challenges, these Pacific Island laboratories were able to conduct AMR surveillance. These data provide valuable contemporary estimates of AMR prevalence, which will inform local antibiotic formularies, treatment guidelines, and national priorities for AMR policy. Supported by the National Health and Medical Research Council.

539. Impact of a Rapid Diagnostic Assay for the Detection of Bacterial and Viral Agents on Antimicrobial use in Critically Ill Patients with Pneumonia

Abstract Background Conventional diagnostic methods for pneumonia have a long turnaround time, and a pathogen is isolated in only 33% of cases. As a result, empiric therapy with broad-spectrum antimicrobials often becomes definitive therapy. Rapid molecular diagnostics paired with antimicrobial stewardship intervention have the potential to improve outcomes for patients with lower respiratory tract infections (LRTIs). However, data to support this hypothesis are scarce. This study examined the influence of a rapid multiplex polymerase-chain-reaction (PCR) test on antimicrobial use in critically ill patients with LRTIs. Methods This single-center study consisted of pre-implementation (PrIP, December 1, 2018, to February 28, 2019) and post-implementation periods (PoIP, December 1, 2021, to February 28, 2022). Both groups included intensive-care unit (ICU) patients with respiratory cultures from bronchoalveolar lavage (BAL), mini-BAL, or tracheal aspirates. Interventions during the PoIP included concurrent testing of specimens with the BioFire® Pneumonia Panel and clinical decision support tools to streamline treatment recommendations from ICU pharmacists. The primary outcome was the difference in time to optimal therapy (TTOT). Secondary outcomes included time to effective therapy (TTET) and duration of therapy (DOT) for antipseudomonal and anti-MRSA agents. Results A total of 163 patients were included (n = 80, PrIP; n = 83, PoIP). The mean age was 57 + 16 years, and medical ICU patients accounted for 60% (n = 97) of cases. The median APACHE II score was the only significant baseline difference between the two arms (22 vs. 18, interquartile range [IQR] 16, 28 vs. 12, 25, p = 0.01). The median TTOT was 38 hours in the PrIP and 21 hours in the PoIP (p < 0.001). TTET was 5.7 hours in the PrIP and 4.9 hours in the PoIP (p = 0.106). The median DOT for antipseudomonal agents decreased by 52% (4.4 days in the PrIP and 2.1 days in the PoIP, p < 0.001), and anti-MRSA agent DOT was 53% shorter in the PoIP (1.9 days vs. 0.9 days, p < 0.001). Conclusion Implementation of a rapid multiplex PCR panel for lower respiratory-tract pathogens significantly reduced the time to optimal therapy in critically ill patients with pneumonia. Clinically meaningful reductions in anti-MRSA and anti-pseudomonal agent duration were also noted. Disclosures Blake W. Buchan, PhD, Accelerate: Advisor/Consultant|Accelerate: Honoraria|BioFire: Honoraria|ChromaCode: Advisor/Consultant|ChromaCode: Honoraria|Pattern: Advisor/Consultant|Pattern: Honoraria.

165. Biofire pneumonia panel use in severe pneumonia and antibiotic treatment in COVID-19 patients

Abstract Background Hospitalized COVID-19 patients with severe pneumonia are commonly treated for secondary bacterial pneumonia. The Biofire pneumonia panel, a rapid molecular diagnostic tool with 18 bacterial, 8 viral and 7 resistance gene targets, was made available to critical care and infectious disease clinicians in May 2020 at our institution. We sought to describe its utilization and influence on antibiotic use in patients hospitalized with COVID-19 lower respiratory tract infection (LRTI). Methods Eligible patients with COVID-19 LRTI (positive PCR test and abnormal chest imaging) had sputum or bronchoalveolar lavage pneumonia panel (PNP) paired with a respiratory tract culture between May 4 and Dec. 8, 2020, were included. Demographics, comorbidities, clinical data including microbiologic testing, PNP indication(s), and antibiotic use after testing were abstracted through chart review. Descriptive statistics were utilized. Results Characteristics of 133 patients are provided in Table 1. Median age was 61 years, 93 (70%) were male, 93 (70%) were mechanically ventilated, and 68 (51%) died within 30 days on PNP testing. PNP results, including culture results are listed in Table 2. No target was identified in 63 (47%) patients. Staphylococcus aureus was the most common bacterial isolate identified (MSSA in 32 [24%], MRSA in 8 [6%]) with culture growth in 21 specimens. More than 1 target was identified in 29 patients (22%). Empiric antibiotics and subsequent modifications within 24h hours of pneumonia panel are provided in Table 3. Vancomycin and cefepime were most frequently prescribed. Antibiotic modifications were made in 71/133 patients. Cessation of the anti-MRSA agent occurred in 39/72 (54%) of eligible patients and the anti-Pseudomonal agent in 21/78 (27%). Conclusion The PNP is a useful tool to evaluate secondary bacterial pneumonia in critically ill COVID-19 patients and may assist clinicians and antimicrobial stewardship programs in expedited antibiotic discontinuation or de-escalation particularly where rates of secondary bacterial infection are low, such as COVID-19 LRTI. Disclosures Erica J. Stohs, MD, MPH, bioMerieux: Grant/Research Support Paul D. Fey, PhD, BioFire: Advisor/Consultant|BioFire: Grant/Research Support|Merck: Grant/Research Support Trevor C. Van Schooneveld, MD, bioMerieux: Advisor/Consultant|bioMerieux: Grant/Research Support|Insmed: Grant/Research Support|Merck: Grant/Research Support|Thermo-Fischer: Advisor/Consultant.

986. Pseudomonas Prosthetic Joint Infections: Is there a role for monotherapy?

Abstract Background Pseudomonas species are a less common but devastating pathogen family in prosthetic joint infections (PJI). Despite advancements in management, Pseudomonas PJI remains particularly difficult to treat due to fewer antibiotic options and robust biofilm formation. The purpose of this study was to better evaluate outcomes after Pseudomonas PJI treatment. Methods All hip or knee PJIs, at a single institution, with positive Pseudomonas culture were analyzed. 51 patients (29 hips and 22 knees) meeting inclusion criteria were identified. The primary outcome of interest was infection clearance at 1-year after surgical treatment, defined as reassuring aspirate without ongoing antibiotic treatment or death within one year post-operatively. Monomicrobial and polymicrobial infections were evaluated separately. Results Among monomicrobial PJIs, ten (50.0%) patients were clear of infection at one year post-operatively. Patients treated with 2-stage exchange (n=11) had a 1-year clearance rate of 54.5% compared to 60.0% with DAIR (n=5) and 25.0% with resection or amputation (n=4). Two of six patients treated with fluoroquinolone monotherapy met 1-year infection clearance, despite fluoroquinolone sensitivity, compared to four of five patients meeting 1-year clearance when treated with combined intravenous and oral therapy for at least 6 weeks. Resistance to anti-pseudomonal agents was infrequent (20%, n=4/20), and three of ten mono- and polymicrobial PJI patients with recurrent Pseudomonas PJI developed resistance to anti-pseudomonal therapy. Polymicrobial infections were the most common presentation (54.9%) of Pseudomonas positive PJI with a mortality rate of 46.4% (n=13/28) at a median follow-up of 4.2 years [IQR: 3.4-5.7]. Conclusion Despite surgical and antibiotic treatment regimens consistent with traditional treatment algorithms, our data portrays poor clearance rate of Pseudomonas PJI with relatively poor outcomes in patients treated with oral or intravenous monotherapy. Pseudomonas infections are difficult to eradicate and likely require deviations from classical therapeutic protocols to improve treatment success. Disclosures William A. Jiranek, MD, Biomech Holdings LLC: Stocks/Bonds|DePuy, A Johnson & Johnson Company: IP royalties Thorsten M. Seyler, MD, PhD, Heraeus: Paid consultant|Pattern Health: IP royalties|Restor3d: IP royalties|Smith & Nephew: Paid consultant|Total Joint Orthopedics: Paid consultant|Zimmer: research.

125. Induction of Resistance Against Antipseudomonal Agents: Comparison of Novel b-Lactam/b-Lactamase Inhibitor (BL/BLI) Combinations and Other b-lactam Agents

Abstract Background The acquisition of mutations is the main driver of β-lactam resistance in Pseudomonas aeruginosa isolates. New BL/BLIs, such as ceftazidime-avibactam (CAZ-AVI), ceftolozane-tazobactam (C/T), and imipenem-relebactam (IMI-REL), are active against most P. aeruginosa isolates from US hospitals, but the ability of these agents to induce resistance have not been explored. We subjected 8 P. aeruginosa isolates, including ATCC 27853 and 7 clinical isolates, to a 10-day serial passage with 6 antipseudomonal agents to evaluate resistance levels and mechanisms in terminal mutant strains. Fold change in MIC results from parent isolate to terminal mutant Methods Serial passaging was performed in broth microdilution (BMD) for CAZ-AVI, IMI-REL, C/T, meropenem (MEM), cefepime (FEP), and piperacillin-tazobactam (P/T). The MIC of the terminal mutants was determined after 2X passaging on drug-free agar. Parent strains and terminal mutants were subjected to short-read whole genome sequencing (WGS) at 100X coverage. Parent isolates were sequenced using long-read WGS and the data was combined with short-reading sequencing for single nucleotide polymorphism (SNP) analysis. Results Overall, IMI-REL (1- to 4-fold) and CAZ-AVI (2- to 8-fold) displayed lower fold increases in MIC values when compared to other agents tested (Figure). Of the CAZ-AVI terminal mutants, 3 displayed a nalD regulator alteration, and 1 of these had a clpA chaperone missense substitution. FEP terminal mutants exhibited alterations in ampD, mexB, and the TetR family transcriptional regulator AmrR. C/T mutants had ampG and ftsI missense alterations. MEM mutants had nalC, ftsI, and phoP missense alterations. Mutations in merR, nalC, and ampD were observed in the P/T terminal mutants. Among 2 IMI-REL terminal mutants displaying a SNP alteration, 1 displayed a nonsense mutation in pilF, a pilus forming protein. Many terminal mutants displayed alterations in genes not commonly associated to β-lactam resistance. Conclusion MEM, FEP, and P/T terminal mutants displayed high MIC values compared to those obtained after exposure to C/T, CAZ-AVI, and IMI-REL. This data might indicate a benefit of using these newer agents to prevent the emergence of high-level resistance. Disclosures Mariana Castanheira, PhD, AbbVie: Grant/Research Support|Cidara: Grant/Research Support|GSK: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Jill Lindley, BS, AbbVie: Grant/Research Support Timothy Doyle, MS, AbbVie: Grant/Research Support John H. Kimbrough, PhD, AbbVie: Grant/Research Support|GSK: Grant/Research Support Jessica Ewald, PhD, AbbVie: Grant/Research Support Helio S. Sader, MD, PhD, AbbVie: Grant/Research Support|Cidara: Grant/Research Support|Melinta: Grant/Research Support|Nabriva Therapeutics: Grant/Research Support|Pfizer: Grant/Research Support.

Cefiderocol resistance genomics in sequential chronic Pseudomonas aeruginosa isolates from cystic fibrosis patients

ObjectiveTo evaluate the activity of cefiderocol against sequential P. aeruginosa isolates from chronically-infected cystic fibrosis patients as well as to investigate the potential mechanisms involved in resistance through whole genome sequencing. MethodsThree sequential P. aeruginosa isolates from each of 50 chronically-colonized cystic fibrosis patients were studied. MICs for novel and classical antipseudomonal agents were determined by broth microdilution and whole genome sequences (n = 150) were obtained to investigate the presence of mutations within a set of chromosomal genes involved in P. aeruginosa antibiotic resistance (n = 40) and iron uptake (n = 120). ResultsCefiderocol showed the lowest MIC50/90 values and its susceptibility rate was comparable to other novel antipseudomonal agents. Clinical resistance was documented in 9 isolates from 6 patients. Resistance genes associated with a statistically significant increase in cefiderocol MICs included ampC, pmrAB, galU, fusA1 and those coding the penicillin-binding proteins PBP2 and PBP3. Likewise, mutations within several genes participating in different iron-uptake systems were found to be significantly associated with resistance, including genes participating in the pyochelin and pyoverdin biosynthesis and several tonB-dependent receptors. Mutator and small colony variants isolates were also associated with increased cefiderocol MICs. DiscussionCefiderocol resistance is modulated by a complex mutational resistome, potentially conferring cross-resistance to novel beta-lactam beta-lactamase combinations, as well as an extended list of mutated iron-uptake genes. Monitoring the acquisition of mutations in all these genes will be helpful to guide treatments and mitigate the emergence and spread of resistance to this novel antibiotic.

Antimicrobial Activity of Ceftolozane-Tazobactam, Ceftazidime-Avibactam, and Cefiderocol against Multidrug-Resistant Pseudomonas aeruginosa Recovered at a German University Hospital.

ABSTRACTMultidrug-resistant (MDR) Pseudomonas aeruginosa increasingly causes health care-associated infections. In this study, we determined the activity of ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol against 223 MDR P. aeruginosa clinical isolates recovered from 2013 to 2017 at the University Hospital Frankfurt by using MIC test strips. Furthermore, we evaluated the presence of genes encoding major β-lactamases, such as VIM, IMP, NDM, GIM, SPM, and KPC; the extended spectrum β-lactamase (ESBL)-carbapenemase GES; and the virulence-associated traits ExoS and ExoU, as in particular ExoU is thought to be associated with poor clinical outcome. For MDR P. aeruginosa isolates, the MIC50/MIC90 values of ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol were 8/>256 mg/L, 16/>256 mg/L, and 0.25/1 mg/L, respectively. Cefiderocol showed the highest susceptibility rate (97.3%) followed by ceftazidime-avibactam (48.4%) and ceftolozane-tazobactam (46.6%). In 81 (36.3%) isolates, carbapenemase gene blaVIM was detected, and in 5 (2.2%) isolates, blaGES was detected (with a positive association of exoU and blaVIM). More than half of the isolates belong to the so-called international P. aeruginosa “high-risk” clones, with sequence type 235 (ST235) (24.7%) being the most prevalent. This study underlines that ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol are important options for the treatment of infections due to MDR P. aeruginosa, with cefiderocol currently being the most active available antipseudomonal β-lactam agent. According to our clinical experience, the outcome of cefiderocol therapy (8 patients) was favorable especially in cases of MDR P. aeruginosa-associated complicated urinary tract infections.IMPORTANCE After testing ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol against a collection of 233 multidrug-resistant (MDR) Pseudomonas aeruginosa, we showed that cefiderocol is the most active antipseudomonal β-lactam agent (susceptibility rates were 46.6%, 48.4%, and 97.4%, respectively). The most prevalent one was sequence type 235 (ST235) (24.7%), followed by ST244, ST175, and ST233, with all belonging to the top 10 P. aeruginosa high-risk clones with worldwide distribution. Our data indicate that during surveillance studies special attention should be paid to the MDR and highly virulent VIM- and ExoU-producing variant of ST235. Furthermore, in the case of infections caused by carbapenemase-producing MDR P. aeruginosa, cefiderocol is the preferred treatment option, while outcomes of complicated urinary tract infections and hospital-acquired pneumonia with cefiderocol were favorable.

Spectrum scores: Toward a better definition of de-escalation.

Spectrum scores measure antimicrobial utilization while also quantifying the spectrum of activity. Accordingly, changes in spectrum score can be used to identify antimicrobial de-escalation. We show that spectrum-score-based de-escalation has a 95.7% positive percentage agreement and 81.6% negative percentage agreement versus de-escalation defined as stopping either antistaphylococcal or antipseudomonal agents.

Impact of the antimicrobial stewardship program on hospital-acquired candidemia

Antibiotic stewardship programs reduce antibiotic use without negative clinical outcomes. However, epidemiological data describing the relationship between implementing antimicrobial stewardship and candidemia incidence are scarce. This study aimed to evaluate the effect of antibiotic stewardship on the incidence of hospital acquired candidemia. We conducted a retrospective study from April 2017 to September 2020. We reviewed patients that were treated with three broad-spectrum antipseudomonal agents: carbapenem, tazobactam/piperacillin, and cefepime. Monthly aggregated hospital antimicrobial consumption was measured as days of therapy (DOTs) per 1000 patient-days, and the monthly incidence of hospital acquired candidemia was recorded. The median monthly carbapenem-DOTs during pre-intervention and intervention were 28.4 and 10.0, respectively. Time-series analysis showed significant level changes after intervention: − 10.0 DOTs (p = 0.02). There was a downward trend in the monthly carbapenem-DOTs after intervention. The median hospital-acquired candidemia incidence was 0.17 and 0.08 per 1000 patient-days during pre-intervention and intervention periods, respectively. Time-series analysis showed a significant level change after intervention (− 0.16 per 1000 patient-days; p = 0.048). The trend in the incidence of hospital-acquired candidemia did not significantly change between pre-intervention and intervention. Decreased broad-spectrum antibiotic use (particularly carbapenem) by our antimicrobial stewardship term may reduce hospital-acquired candidemia incidences.