Susceptible Strains Research Articles

Agar-Dilution Is Comparable to Broth Dilution for MIC Determination in Streptococcus agalactiae

Background: Streptococcus agalactiae (Group B Streptococcus, GBS) is a leading cause of neonatal sepsis in high-income countries. While intrapartum antibiotic screening reduces this risk, increasing resistance to macrolides and lincosamides in Europe since the 1990s has limited therapeutic options for penicillin-allergic patients. Reports of reduced beta-lactam susceptibility in GBS further emphasise the need for robust antimicrobial resistance (AMR) surveillance. However, broth microdilution (BMD) methods are unsuitable for large-scale antimicrobial susceptibility testing (AST). Objective: To demonstrate that agar-dilution AST provides equivalent results to broth dilution methods, with superior capacity for high-throughput screening. Methods: Agar-dilution and microdilution AST methods were compared using a panel of 24 characterised susceptible and resistant GBS strains for benzylpenicillin, chloramphenicol, clindamycin, erythromycin, gentamicin, levofloxacin, tetracycline, and vancomycin. Minimum inhibitory concentration (MIC) agreements were evaluated, and resistance profile correlations were assessed using Cohen’s kappa values. Results: Agar-dilution demonstrated >90% agreement with BMD MIC for most antimicrobials, except vancomycin (87.5%), erythromycin (83.33%), and tetracycline (52.78%). Cohen’s kappa values indicated strong agreement (0.88–1.00) for resistance determination. Agar-dilution avoided “trailing growth” issues associated with BMD and facilitated easier detection of non-GBS contaminants. Conclusions: Agar-dilution is a valid method for high-throughput AMR surveillance of retrospective cohorts (96 isolates per plate) and is critical for identifying emerging GBS resistance trends and informing therapeutic guidelines. However, due to the large number of plates required per antimicrobial, it is impractical for routine clinical diagnostics.

Exposure to copper metal enhances the tolerance of An. gambiae s.s. over multiple generations while reducing both fertility and fecundity in this primary malaria vector.

Background Anopheles s.l. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness. This study investigated the larval metal exposure on larval development and reproduction of An. gambiae s.s., a laboratory susceptible strain, kisumu. Methods Stage 2 larvae of Anopheles gambiae, Kisumu were exposed to C1 = 484 μg L-1, C2 = 300 μg L-1 and 0 μg L-1 (control) of copper chloride. Larval mortality, pupation time, pupation rate, gonotrophic cycle length, fecundity and fertility of larvae/adults were assessed over six generations. Results Results revealed that larval mortality rate was significantly higher in the C1 groups of each group (p = 0.000), but this mortality rate decreased over generations. Pupation time was extended to 13 and 14 days respectively for C2 and C1 groups (p = 0.000) compared to the control group. Similar results were observed for the gonotrophic cycle, which increased from 4 days at G0 to more than 6 days at generation 5 in adults of C1. The pupation rate in generation 4 (C1) and generation 5 of the same group (p = 0.000) as well as the emergence rate in generation 4 (C2, p = 0.000) and generation 5 (C1 and C2, p = 0.000) decreased significantly compared to the control group. The average number of eggs laid was lower in the test groups from generation 4 to generation 5 (C1 and C2, p = 0.00) and egg fertility was also negatively affected by exposure of the larval stage of An. gambiae s.s. to copper. Conclusion This study showed that copper not only exhibits larvicidal properties in Anopheles gambiae s.s. larvae, it also revealed the potential of this metal to reduce fecundity and fertility in these malaria vectors.

Comparative growth kinetics and drug susceptibility of Mycobacterium tuberculosis lineages prevalent in Ethiopia: implications for tuberculosis treatment and management

Tuberculosis (TB) remains a global health challenge, with treatment outcomes influenced by the genetic diversity of Mycobacterium tuberculosis (Mtb) strains. This study examines the growth kinetics and drug susceptibility of Mtb strains from different lineages in Ethiopia to understand their impact on disease management. Mtb strains, including sub-lineages 4.1.2.1, 4.2.2.2, 4.6.3, lineages 3 and 7, and the reference strain H37Rv (ATCC 27294), were cultured in liquid 7H9 Middlebrook broth. Growth began on day 6 post-inoculation. Sub-lineage 4.1.2.1 showed rapid exponential growth by day 9, reaching the stationary phase by day 15. Sub-lineage 4.1.2.1 followed by sub-lineage 4.2.2.2 had the highest maximum growth concentration (Cmax), indicating enhanced growth efficiency and adaptive traits that may increase their pathogenicity or resistance to host defenses or anti-TB drugs. To support this observation, the minimum inhibitory concentrations (MIC) for first-line anti-TB drugs were assessed for all the studied Mtb strains using the microdilution broth method. While all strains were susceptible, MIC values varied. Sub-lineages 4.1.2.1 and 4.2.2.2 had MIC values matching WHO’s critical concentrations (except for rifampicin). Lineage 3 showed increased sensitivity to rifampicin, isoniazid, and streptomycin, requiring only half the standard concentration. Lineage 7 also exhibited higher sensitivity to rifampicin and streptomycin. These findings highlight the importance of considering lineage-specific differences in Mtb strains for optimizing treatment regimens and improving TB control strategies, particularly in regions with diverse Mtb populations like Ethiopia.

Genetic analysis of chlorantraniliprole resistance in the non-target bio-control agent Trichogrammachilonis.

Trichogramma chilonis (Ishii) (Hymenoptera: Trichogrammatidae), a widely used egg parasitoid of lepidopteran pests in various crops, has developed very high levels of resistance when treated with chlorantraniliprole under laboratory conditions. This study assessed and characterized its mode of inheritance, degree of dominance, realized heritability (h2), and cross-resistance. Toxicity bioassays were performed on T. chilonis adults using a dry film residue method. The chlorantraniliprole resistant strain (Chlr-R) of T. chilonis showed >25000-fold resistance as compared with chlorantraniliprole susceptible strain (Chlr-S). The chlorantraniliprole resistance in T. chilonis was characterized as incompletely dominant and governed by multiple autosomal genes. Additionally, the resistance of T. chilonis to chlorantraniliprole shifted from functionally dominant (at lower applied doses) to functionally recessive (at highest applied dose). Parameters regarding the h2 of chlorantraniliprole resistance in T. chilonis predicted 10-fold rise in the initial LC50 after 14.28 generations with continuous selections (at h2=0.24). No obvious cross-resistance to cypermethrin and chlorpyrifos and a very low cross-resistance to flonicamid were detected. These findings are helpful to improve the field-based effectiveness and integration of these wasps with chemical control.

P-1997. Real-world Effectiveness of Tixagevimab/cilgavimab for COVID-19 Pre-exposure Prophylaxis in Solid Organ Transplant Recipients during the BA.2.75 and BQ.1 Omicron Variant Period: A matched Case-control Dtudy

Abstract Background Solid organ transplant recipients (SOTRs) develop poor immunogenicity after SARS-CoV-2 immunization. The neutralizing monoclonal antibody combination of tixagevimab/cilgavimab (T/C) has been shown to reduce the risk of COVID-19 among this vulnerable population. We assessed the effectiveness and safety of T/C pre-exposure prophylaxis (PrEP) for COVID-19 protection after transplantation. Methods We conducted a matched case-control study at a single transplant center during the Omicron lineages BA.2.75 and BQ.1 period (August 2022 to February 2023). T/C doses of 150/150 mg were provided from August 2022 until February 2023, and doses of 300/300 mg were administered thereafter (December 2022 to February 2023). All patients were followed for up to 6 months, and adverse events (AEs) from T/C were assessed. Results A total of 143 SOTRs were included, with 115 and 28 SOTRs in the T/C and control groups, respectively. Transplants included kidney (n=108), liver (n=28), and heart (n=9). Over 6 months, 18 (15.7%) in T/C developed COVID-19, with onset at median 3 months. All had mild infections without respiratory failure. Mild and reversible adverse events (AEs) were reported in 25.2% of cases. No rejection occurred. Non-significantly lower COVID-19 within 3 months during BA.2.75 Omicron (8.7% vs. 17.9% in control; p=0.128; effectiveness: 51.4%). At 6 months (BQ.1 Omicron), COVID-19 incidence was 15.7% in T/C vs. 17.9% in control (p=0.667; effectiveness: 12.3%). The occurrence of COVID-19 was not significantly different after adjustment for the number of vaccine doses, history of prior COVID-19, or the dose of T/C. Conclusion The effectiveness of T/C tends to be protective against susceptible strains, although the severity of breakthrough infections tends to be mild. Short-term safety as PrEP appears tolerable. TCTR20220801004. Disclosures All Authors: No reported disclosures

The genetic architecture of resistance to flubendiamide insecticide in Helicoverpa armigera (Hübner).

Insecticide resistance is a major problem in food production, environmental sustainability, and human health. The cotton bollworm Helicoverpa armigera is a globally distributed crop pest affecting over 300 crop species. H. armigera has rapidly evolved insecticide resistance, making it one of the most damaging pests worldwide. Understanding the genetic basis of insecticide resistance provides insights to develop tools, such as molecular markers, that can be used to slow or prevent the evolution of resistance. We explore the genetic architecture of H. armigera resistance to a widely used insecticide, flubendiamide, using two complementary approaches: genome-wide association studies (GWAS) in wild-caught samples and quantitative trait locus (QTL) mapping in a controlled cross of susceptible and resistant laboratory strains. Both approaches identified one locus on chromosome 2, revealing two SNPs within 976 bp that can be used to monitor field resistance to flubendiamide. This was the only region identified using linkage mapping, though GWAS revealed additional sites associated with resistance. Other loci identified by GWAS in field populations contained known insecticide detoxification genes from the ATP-binding cassette family, ABCA1, ABCA3, ABCF2 and MDR1. Our findings revealed an oligogenic genetic architecture, contrasting previous reports of monogenic resistance associated with the ryanodine receptor. This work elucidates the genetic basis of rapidly evolving insecticide resistance and will contribute to developing effective insecticide resistance management strategies.

P-1538. Analyzing Trends and Outcomes of Clindamycin Resistant Invasive Group A Streptococci Infections

Abstract Background Streptococcus pyogenes (Group A Streptococci; GAS) is a gram-positive bacterium that is a leading cause of life-threatening infections. For invasive infections, IDSA recommends high-dose penicillin and clindamycin (DA). However, increasing resistance to DA has been reported. The aim of this study was to determine the prevalence of DA-resistant GAS and evaluate if DA resistance was associated with worse outcomes. Table Comparison of clindamycin susceptible and clindamycin resistant strains of invasive GAS infections Methods This was a retrospective cohort study from June 2013 to December 2023 across a five-hospital health system in Southeast Michigan of patients with positive blood cultures for GAS who received DA for anti-toxin therapy identified through Microsoft SQL. Children, polymicrobial bacteremia, incomplete data, receiving linezolid empirically, or those who died within 48 hours of admission were excluded. Patients with DA susceptible (DA-S) GAS isolates were compared to patients with DA resistant (DA-R) GAS isolates. Variables included demographics, infection characteristics, microbiologic data, therapy, and clinical outcomes. Figure Cases of GAS bacteremia and percent of clindamycin resistant strains Results 390 cases were reviewed, and 215 were included in the cohort study [Table]. There was no difference in age, sex, or race among the groups. People who use injection drugs (51.7% vs 48.3%, p=0.07), people experiencing homelessness (PEH; 63.2% vs 36.8%, p=0.001), and chronic hepatitis C infection (HCV; 54.2% vs 45.8%, p=0.007) were more prevalent in the DA-R group; chronic kidney disease was more frequent in the DA-S group (57.1% vs 42.9%, p=0.029). Uncomplicated SSTI was more common in the DA-S group (64.2% vs 35.8%, p=0.022). There was no significant difference in the severity of illness, duration of bacteremia, surgical management, treatment duration, length of stay, readmission or mortality between the two groups. There was an increased incidence of invasive GAS infections beginning in 2022, and 50% of isolates were DA-R in 2023 [Figure]. Conclusion Although there is an increase in DA-R in invasive GAS infections, there was no significant difference in outcomes among patients with DA-R and DA-S who received standard of care treatment in addition to DA antitoxin therapy. Further research is needed to determine the clinical significance of these findings to inform optimal therapy for these groups. Disclosures Rachel M. Kenney, PharmD, BCIDP, Medtronic Inc: Spouse is an employee, stockholder

P-300. Antimicrobial Resistance Focus in French ICU: A national surveillance network analysis on Pseudomonas aeruginosa nosocomial infections

Abstract Background The aim of this study was to perform a comprehensive description on a cohort of Pseudomonas aeruginosa infected patients in ICU, comparing their characteristics between susceptible and resistant strains, to understand the impact of resistance on clinical decisions and to characterize patients at risk of MDR. Site of infection of Pseudomonas aeruginosa Methods Adult patients hospitalized in France for at least 48 hours in ICU participating to REA-REZO surveillance between 2018 and 2021 were included in the data base used to create this cohort. Resistance patterns of Pseudomonas aeruginosa Results 4196 patients with nosocomial Pseudomonas aeruginosa infections were included in this cohort. Most infections were identified in patients with pneumonia, with a consistently high prevalence ranging from 71.5% to 74.5% depending on the year. Among the Pseudomonas, 1734 (31.0%) were resistant to piperacillin/tazobactam, 1331 (23.8%) were resistant to ceftazidime, and 1191 (21.3%) were carbapenem resistant. A statistically significant difference (p< 0.001) in resistance patterns between the first and subsequent infections is seen, notably for resistance to carbapenems which rose markedly from initial to subsequent infections, from 16.3% to 27.8% (p< 0.001). Regarding occurrence of resistant Pseudomonas strains, statistically significant differences in age distribution among the resistance groups are noted (p< 0.001), particularly evident in patients under 55, where 24.0% of those with dual resistance are under this age threshold, compared to 19.7% with no resistance. The SAPS II score was higher among resistant strains, as well as the duration in ICU stay, suggesting more challenging infections. Description of the patient with Pseudomonas aeruginosa infections Conclusion These results reaffirm the critical challenge posed by resistant Pseudomonas in the ICU. It highlights the need for comprehensive antibiotic strategies that address the clinical, psychological, and economic dimensions of this issue. Disclosures Xavier Bourge, PharmD, MSD France: Employee Arnaud Friggeri, MD, MSD France: Advisor/Consultant Alain Lepape, MD, MSD France: Grant/Research Support Claire Prevot, n/a, MSD France: Employee Anais Machut, n/a, MSD France: Grant/Research Support Charles-Hervé Vacheron, MD, MSD France: Grant/Research Support

82. Comparative Evaluation of Low Versus High Doses of Rifampin for the Treatment of Staphylococcal Bone and Joint Infections: an open-label, randomized, controlled non-inferiority trial (EVRIOS)

Abstract Background The antibiotic management of staphylococcal bone and joint infection usually relies on rifampin associated with another antibiotic for susceptible strains. The appropriate dose of rifampin remains unclear and diverges in international recommendations. 543 patients were randomized, 530 were included in the Intent-to-Treat analysis and 327 in the per-protocol analysis. Methods We performed an open-label, randomized, controlled, noninferiority trial to compare a daily dose of 10 mg/kg (Low-dose) qd and 20 mg/kg (High-dose, divided in 10mg/kg bid for high BMIs) of rifampin in association with another antibiotic in patients with microbiologically confirmed bone and joint infections due to Staphylococcus sp. Surgical procedures were performed as needed. The primary outcome was persistent infection, defined as the persistence or recurrence of infection with the initial causative bacteria within 1 year after the completion of antibiotic therapy. Results A total of 543 patients from 18 French centers were randomly assigned to receive either Low-dose (252 patients) or High-dose (291 patients) of rifampin associated with another antibiotic. Thirteen patients who withdrew consent were not included in the analysis. The main antibiotics associated with rifampin were levofloxacin/ofloxacin (82%, 435 out of 530 patients). Mean age was 59.8 ± 16.4 years, and mean BMI 27.9 ± 5.8 kg/m2; 24.6% [n=130] had osteosynthesis and 34% [n=180] prostheses at the site of infection. Staphylococcus aureus was present in 75.8% of patients [n=402]. In the ITT analysis, persistent infection occurred in 8 of 227 patients (3.5%) in the Low-dose group and in 10 of 265 patients (3,8%) in the High-dose group (risk difference, 0.0019; 95% confidence interval [-0.032 – 0.036], thus, noninferiority was shown. Serious adverse events linked to rifampin where more frequent in the High-dose group (7%) than in the Low-dose group (1.6%, p=0.0043). Patients in the High-dose group were less likely to remain in the per-protocol analysis (57%, versus 67% in the Low-dose group). Noninferiority was also shown in the per-protocol analysis. Conclusion Among patients with confirmed Staphylococcus sp. bone and joint infection that were managed with standard surgical procedures, antibiotic therapy with daily 10 mg/kg of rifampin was shown to be noninferior to 20 mg/kg. Severe adverse events linked to rifampin where more frequent in the 20 mg/kg group. Disclosures Cedric Arvieux, MD, GILEAD: Advisor/Consultant|ViiV: Advisor/Consultant Florian Lemaitre, PharmD, Astellas: Grant/Research Support|Chiesi: Grant/Research Support|Pfizer: Scientific meeting fees|ViiV: Scientific meeting fees Aurélien Lorleac'h, MD, Gilead: Hospitality|GSK: Hospitality|Nestlé Home Care: Hospitality|ViiV Healthcare: Hospitality Thomas Guimard, MD, Gilead: Convention invitation|Menarini France: Hospitality|MSD: Hospitality|Pfizer: Advisor/Consultant|Shionogi BV: Hospitality Gwenael Lemoal, MD, Gilead: Hospitality|MSD: Hospitality|Viiv Heathcare: Advisor/Consultant

P-1241. Cefepime Pharmacodynamics Against Pseudomonas aeruginosa Evaluated in a Chemostat Infection Model: Do Generalized Cephalosporin Targets Translate?

Abstract Background Cefepime (FEP) is used widely to treat infections caused by susceptible strains of Pseudomonas aeruginosa. However, nonclinical pharmacokinetic-pharmacodynamic (PK/PD) relationships for this drug-bug combination are not fully characterized. An in vitro chemostat (CS) model was used to assess the translatability of broadly established cephalosporin PK/PD targets to support development of FEP combined with taniborbactam (TAN), a novel serine- and metallo-β-lactamase inhibitor.Table.Antimicrobial susceptibility testing results and summary of cefepime pharmacodynamics against strains evaluated in the chemostat (CS) modelAR, denotes strains sourced from the CDC & FDA Antimicrobial Resistance Isolate Bank; FTB, cefepime-taniborbactam Methods Cefepime-taniborbactam (FTB) and FEP minimum inhibitory concentrations (MIC) were determined by reference broth microdilution (BMD) against P. aeruginosa isolates with no known acquired β-lactamases (N=6). Cefepime MICs were also assessed in 125 mL of TAN-supplemented media (4 µg/mL) to simulate CS conditions (CS MIC, Figure). In FEP dose-ranging studies in the dynamic CS model, bioreactors were inoculated with ≥ 5 log10 CFU/mL. FEP was dosed every 8 h for 24 h while media was infused to achieve a 2-h half-life. FEP concentrations were determined by a qualified bioanalytical method and used to calculate the percentage of time concentrations exceeded MIC values (T > MIC). Viable bacteria were quantified by serial dilution and plating at time points from 0 to 24 h. CS qualification was performed with Enterobacterales to confirm that the model recapitulated in vivo PD profiles reported previously by others.Figure.Schematic of the chemostat MIC (CS MIC) assay for an example strain with a CS MIC of 4 µg/mL. Results P. aeruginosa strains were FEP-susceptible (n=5) and -nonsusceptible (n=1) and BMD MICs ranged from 2 to 16 µg/mL. CS MICs were equal to (n=2), 2x (n=3), or 8x (n=1) the FTB BMD MIC (Table). All strains grew in the CS model to an average (standard deviation) bacterial burden of 7.3 (0.6) log10 CFU/mL. In composite PD models fit to dose-ranging data, change in bacterial burden from 0 to 24 h was best described by T > CS MIC versus T > BMD MIC. Reductions in bioburden were observed at T > CS MICs of 41-49% (Table). Conclusion In a dynamic in vitro model of P. aeruginosa infection, efficacious FEP exposures were similar to those established for Enterobacterales when indexed to CS MIC values. The results also indicate that differences between BMD and CS MIC should be considered when performing in vitro PK/PD profiling of discovery-phase antibacterials to prevent underestimation of therapeutic potential. Disclosures All Authors: No reported disclosures

P-2041. In Vitro Resistance Profiling of S-892216, a Second Generation SARS-CoV-2 3CLpro Inhibitor for the Treatment of COVID-19

Abstract Background S-892216 is a candidate for the treatment of COVID-19 that has 3CLpro inhibitory activity and antiviral activity. In this study, the susceptibility of S-892216 was evaluated against SARS-CoV-2 with 3CLpro substitution associated with reduced susceptibility to other 3CLpro inhibitors, ensitrelvir and nirmatrelvir. Additionally, in vitro selection of SARS-CoV-2 with reduced susceptibility to S-892216 was conducted. Methods Reverse genetics-derived SARS-CoV-2 (rgSARS-CoV-2) with 3CLpro substitutions including M49L and E166V were generated using circular polymerase extension reaction (CPER) system The susceptibility of S-892216 was assessed using rgSARS-CoV-2 infected VeroE6/TMPRSS2 cells. For the selection of SARS-CoV-2 with reduced susceptibility to S-892216 in vitro, VeroE6/TMPRSS2 cells infected with SARS-CoV-2 Omicron BE.1/BA.5-like variant (hCoV-19/Japan/TY41-702/2022) were cultured in the presence of S-892216 and passaged 10 times. Genotyping analysis of 3CLpro and its cleavage sites in the isolated SARS-CoV-2 were then conducted. The susceptibility of S-892216 and nirmatrelvir against the isolated viruses were assessed. Results Fold change (FC) values of S-892216 against rgSARS-CoV-2 with 3CLpro substitutions M49L and E166V were < 2-fold. SARS-CoV-2 with 3CLpro substitutions of D48E, M49K, L50F, N221K, and P252L were isolated from the in vitro virus selection. The FC values of each compound against the isolated SARS-CoV-2 were 3.51- to 28.7-fold for S-892216 and 0.736- to 3.25- fold for nirmatrelvir. Conclusion The isolated SARS-CoV-2- strains with reduced susceptibility to S-892216 carried 3CLpro mutation - indicating that the target site is 3CLpro, did not show cross-resistance to nirmatrelvir. Furthermore, S-892216 did not show cross-resistance against nirmatrelvir and ensitrelvir-reduced susceptibility strains. These data suggest S-892216 might be effective if described ensitrelvir- and nirmatrelvir-resistant SARS-CoV-2 variants become relevant in the clinical setting. Disclosures Sho Kawashima, Shionogi & Co., Ltd.: Employee Haruaki Nobori, PhD, Shionogi & Co., Ltd.: Employee|Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Miyako Okane, n/a, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company)|Shionogi TechnoAdvance Research CO., Ltd.: employee Takashi Hashimoto, n/a, Shionogi TechnoAdvance Research CO., Ltd.: employee Kae Inoue, n/a, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company)|Shionogi TechnoAdvance Research CO., Ltd.: employee Yuko Yamano, n/a, Shionogi TechnoAdvance Research CO., Ltd.: employee Keiko Funabiki, n/a, Shionogi TechnoAdvance Research CO., Ltd.: ex-employee Michie Watanabe, n/a, Shionogi TechnoAdvance Research CO., Ltd.: employee Kaoru Baba, n/a, Shionogi TechnoAdvance Research: Employee Keita Fukao, MD, SHIONOGI and CO., LTD.: Stocks/Bonds (Private Company) Teruhisa Kato, PhD, Shionogi & Co., Ltd.: employee|Shionogi & Co., Ltd.: Stocks/Bonds (Private Company)

P-1110. The Impact of Xeruborbactam on in vitro Activity of Cefiderocol against a Panel of Enterobacterales Enriched with Isolates with Reduced Cefiderocol Susceptibility

Abstract Background Cefiderocol (CFDC) is a siderophore cephalosporin with potent activity against resistant gram-negative bacteria. According to recent SIDERO-WT surveillance studies that involved testing of > 30,000 Enterobacterales (ENT) isolates collected in North America and Europe, 99.8% of ENT were susceptible (S) to CFDC (by CLSI breakpoint) (MIC90=1 µg/mL). For carbapenem-resistant Enterobacterales (CRE), S to CFDC was as high as 96.5% (MIC90=4 µg/mL). In ENT, resistance to CFDC is multifactorial and seems to require production of either a serine (SBL) or metallo (MBL) carbapenemase. Xeruborbactam (XER) is a novel beta-lactamase inhibitor that inhibits multiple SBL and MBL enzymes. In this study, we evaluated the impact of XER on activity of CFDC against a challenge panel of β-lactamase-producing ENT (BL-ENT) enriched in CFDC-resistant isolates. MIC50/90 of cefiderocol (CFDC) alone and with xeruborbactam (XER) against Enterobacterales Methods A challenge panel of 165 BL-ENT isolates that included 139 CRE was used for this study. 79 (56.8%) and 41 (24.8%) of isolates had CFDC MIC values > 1 µg/mL and > 4 µg/mL (non-S by CLSI/FDA breakpoint), respectively. The β-lactamase profile for each isolate was determined by PCR or whole genome sequencing. MICs were determined for CFDC alone and in combination with 1, 2 or 4 μg/mL of XER according to CLSI guidelines for CFDC using iron-depleted CAMHB. Results MIC50/MIC90 of CDFC alone and XER alone against 165 ENT were 2/16 and 16/ > 16 μg/mL, respectively. Dose-dependent shifts of CFDC MICs to the more susceptible range in the presence of increasing concentrations of XER were observed. XER at ≥ 1 μg/mL reduced the MIC90 of CFDC to ≤ 1 μg/mL, which is below the MIC90 for CFDC alone for all ENT in surveillance studies. XER at ≥ 2 μg/mL reduced CFDC MIC90 of MBL producers to ≤ 1 μg/mL For isolates with CFDC MIC > 4 μg/mL, 4 μg/mL of XER reduced the CFDC MIC90 from 32 to 1 μg/mL; the MIC50 for this subset of isolates were reduced from 16 to 0.25 µg/mL, the same MIC50 that were observed for all surveillance isolates. Conclusion XER significantly improved the activity of CFDC against rarely encountered isolates of Enterobacterales with elevated CFDC MICs. The potency of CFDC/XER against these isolates was as high as potency of CFDC alone against CFDC susceptible strains. Disclosures Takafumi Hara, MSc, SHIONOGI & CO., LTD.: Employee Naoki Ishibashi, MD, SHIONOGI & CO., LTD.: Employee Dai Miyagawa, n/a, SHIONOGI & CO., LTD.: Employee Motoyasu Onishi, PhD, Shionogi & Co., Ltd.: Employee Olga Lomovskaya, PhD, Qpex Biopharma Inc.: Board Member|SHIONOGI & CO., LTD.: Employee Yoshinori Yamano, PhD, Shionogi & Co., Ltd.: Employee

Modeling the Efficacy of Phosphine on Eggs of Major Stored-Product Insect Species: Investigating Strains with Varying Susceptibility Levels

Phosphine is a widely utilized fumigant insecticide in stored-product facilities; however, its excessive application and improper usage have contributed to the emergence of resistance in insect populations. Although phosphine resistance is globally recognized, limited studies address its effects across different developmental stages. This research investigates the efficacy of phosphine on the eggs of major stored-product pests, including Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), Tribolium castaneum, and T. confusum (Coleoptera: Tenebrionidae), focusing on strains with varying levels of phosphine susceptibility. Egg hatching rates were analyzed following exposure to phosphine concentrations ranging from 50 to 1000 ppm for durations of 1 to 7 days. Predictive models were constructed to correlate phosphine concentration and exposure time, facilitating the determination of optimal pest control strategies. The findings reveal significant differences in efficacy among species and strains, with eggs from susceptible strains experiencing complete hatch failure at 50 ppm, while resistant strains showed higher tolerance. Lethal time (LT50 and LT99) values were determined, with LT99 ranging from 6.91 to 12.95 days at 50 ppm, highlighting species-specific and age-related differences in phosphine susceptibility. Lethal concentration (LC50 and LC99) values could only be estimated for T. castaneum, with LC99 for 1-day-old eggs ranging from 773.67 ppm to 923.03 ppm after 2.5 days of exposure. Furthermore, egg age influenced susceptibility, with 2-day-old eggs exhibiting greater mortality compared to 1-day-old eggs. This study underscores the critical role of phosphine concentration, exposure duration, and developmental stage in resistance management, providing valuable insights for enhancing fumigation protocols and improving the control of stored-product pests.

Characterization of resistance to Bacillus thuringiensis toxin Cry1Ac in Crocidosema sp. (Lepidoptera: Tortricidae) from Brazil.

Crocidosema aporema (Walsingham 1914) has historically been the main bud borer species in soybean in Brazil; however, a recent study reported that this species is not C. aporema but an undescribed species. In recent seasons, injury by Crocidosema sp. has been reported in soybean expressing the Bacillus thuringiensis Berliner (Bt) toxin Cry1Ac. In this study, we investigated the genetic basis of Cry1Ac resistance and assessed the fitness costs of resistance in a field-derived Cry1Ac-resistant Crocidosema sp. strain selected through an F2 screen. The Cry1Ac-resistant strain of Crocidosema sp. developed from neonate to pupae fed on Cry1Ac soybean leaves and adults produced viable offspring. The resistance ratio to Cry1Ac in this strain was >500 000-fold relative to the susceptible strain. Results from leaf and diet-overlay bioassays indicated that the inheritance pattern of Cry1Ac resistance in Crocidosema sp. is sex-linked, with a lethal dose compensation in the F1 progeny from R♂ × S♀ (making resistance incompletely recessive), whereas the F1 progeny from R♀ × S♂ had complete mortality on Cry1Ac soybean (making resistance completely recessive). The mortality of backcrosses on Cry1Ac soybean varied significantly, suggesting that the resistance is controlled by multiple genes. Life-history results revealed that the Cry1Ac-resistant strain had lower pupal weight, reproductive performance and population growth on non-Bt soybean compared with the susceptible strain. The inheritance patterns of Cry1Ac resistance in Crocidosema sp. are sex-linked, incompletely or completely recessive depending on the direction of the reciprocal cross, polygenic and associated with fitness cost. © 2025 Society of Chemical Industry.

Clinical considerations on antimicrobial resistance potential of complex microbiological samples.

Antimicrobial resistance (AMR) is one of our greatest public health challenges. Targeted use of antibiotics (ABs) can reduce the occurrence and spread of AMR and boost the effectiveness of treatment. This requires knowledge of the AB susceptibility of the pathogens involved in the disease. Therapeutic recommendations based on classical AB susceptibility testing (AST) are based on the analysis of only a fraction of the bacteria present in the disease process. Next and third generation sequencing technologies allow the identification of antimicrobial resistance genes (ARGs) present in a bacterial community. Using this metagenomic approach, we can map the antimicrobial resistance potential (AMRP) of a complex, multi-bacterial microbial sample. To understand the interpretiveness of AMRP, the concordance between phenotypic AMR properties and ARGs was investigated by analyzing data from 574 Escherichia coli strains of five different studies. The overall results show that for 44% of the studied ABs, phenotypically resistant strains are genotypically associated with a 90% probability of resistance, while for 92% of the ABs, the phenotypically susceptible strains are genotypically susceptible with a 90% probability. ARG detection showed a phenotypic prediction with at least 90% confidence in 67% of ABs. The probability of detecting a phenotypically susceptible strain as resistant based on genotype is below 5% for 92% of ABs. While the probability of detecting a phenotypically resistant strain as susceptible based on genotype is below 5% for 44% of ABs. We can assume that these strain-by-strain concordance results are also true for bacteria in complex microbial samples, and conclude that AMRP obtained from metagenomic ARG analysis can help choose efficient ABs. This is illustrated using AMRP by a canine external otitis sample.

Abstract B013: Autoimmunity mechanisms in combined radiotherapy and immune-checkpoint inhibitor therapy-induced myocarditis

Abstract Immuno-checkpoint inhibitors (ICI) are frequently used as a major cancer therapy, frequently combined with radiotherapy, particularly among patients with lung cancer. There is an increasing awareness of potential cardiotoxicities from either therapy, thus raising concerns when both therapies are combined. It is likely that radiation-induced cardiac inflammation becomes unchecked when ICIs are administered, contributing to myocarditis although the underlying specific mechanisms have not been characterized. We developed a mouse model of ICI and cardiac irradiation-induced myocarditis through an image-guided small animal irradiator in the A/J mice, which is prone to ICI-induced myocarditis. Our results showed that 20 % of ICI treated mice developed mild myocarditis, whereas 40 to 50% of mice with ICI plus irradiation treatment showed severe myocarditis, characterized by lots of infiltration of CD4+ T cells, CD8+ T cells, B cells and macrophages in hearts. Flow cytometry analysis showed that the number of infiltrated CD4+ T cells is 2 to 3 folds of CD8+ T cells in the heart tissue with disease. Severe fibrosis in hearts was associated with severe myocarditis. The levels of cardiomyocyte-specific protein troponin I in serum was correlated well with the severity of myocarditis, implicating that ICI and irradiation caused many cardiomyocyte damages. ELISA assay showed that serum IL-17 was dramatically increased in mice treated with ICI alone or ICI plus radiation, implying Th17 cells may play a pathogenic role in ICI & irradiation-induced myocarditis. In addition, we compared the myocarditis induced by ICI and irradiation in less susceptible prone of C57 mice with the more susceptible strain of A/J mice. The incidence of myocarditis was significantly lower in C57 mice compared with A/J Mice. Overall, our study indicates that irradiation promotes the pathogenesis of ICI-induced myocarditis, and individuals with autoimmune tendency have a high risk to develop severe myocarditis after administration of combined ICIs and irradiation. (This work is supported by NIH grant R01) Citation Format: Shiguang Yu, Nhan T Vu, Tyler Verburg, Bo Lu. Autoimmunity mechanisms in combined radiotherapy and immune-checkpoint inhibitor therapy-induced myocarditis. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr B013.

Metabolic resistance to pyrethroids with possible involvement of non-coding ribonucleic acids in Anopheles funestus, the major malaria vector in western Kenya

BackgroundThe resurgence of Anopheles funestus, a dominant vector of human malaria in western Kenya was partly attributed to insecticide resistance. However, evidence on the molecular basis of pyrethroid resistance in western Kenya is limited. Here, we reported metabolic resistance mechanisms and demonstrated that multiple non-coding Ribonucleic Acids (ncRNAs) could play a potential role in An. funestus resistance to pyrethroid in western Kenya. Anopheles funestus mosquitoes were sampled using aspiration methods in Bungoma, Teso, Siaya, Port Victoria and Kombewa in western Kenya. The F1 progenies were exposed to deltamethrin (0.05%), permethrin (0.75%), DDT (4%) and pirimiphos-methyl (0.25%) following WHO test guidelines. A synergist assay using piperonyl butoxide (PBO) (4%) was conducted to determine cytochrome P450s’ role in pyrethroid resistance. RNA-seq was conducted on a combined pool of specimens that were resistant and unexposed, and the results were compared with those of the FANG susceptible reference strain. This approach aimed to uncover the molecular mechanisms underlying the observed phenotypic pyrethroid resistance.ResultsPyrethroid resistance was observed in all sites with an average mortality rate (MR) of 57.6%. Port Victoria had the highest level of pyrethroid resistance to permethrin (MR = 53%) and deltamethrin (MR = 11%. Teso had the lowest level of resistance to permethrin (MR = 70%) and deltamethrin (MR = 87%). Resistance to DDT was observed only in Kombewa (MR = 89%) and Port Victoria (MR = 85%). A full susceptibility to P-methyl (0.25%) was observed in all sites. PBO synergist assay revealed high susceptibility (> 98%) to pyrethroids in all the sites except for Port Victoria (MR = 96%). Whole transcriptomic analysis showed that most gene families associated with pyrethroid resistance comprised non-coding RNAs (67%), followed by immunity proteins (10%), cytochrome P450s (6%), cuticular proteins (5%), olfactory proteins (4%), glutathione S-transferases (3%), UDP-glycosyltransferases (2%), ATP-binding cassettes (2%) and carboxylesterases (1%).ConclusionThis study unveils the molecular basis of insecticide resistance in An. funestus in western Kenya, highlighting for the first time the potential role of non-coding RNAs alongside metabolic detoxification in pyrethroid resistance. Targeting non-coding RNAs for intervention development could help in insecticide resistance management.

Chemical structure-biological activity of 1,4-naphthoquinone analogs as potential Aedes aegypti larvicides.

1,4-Naphthoquinone compounds have shown pesticidal activity against Aedes aegypti larvae, a key vector of diseases such as dengue and Zika. However, limited knowledge of their structure-activity relationships has hindered their optimization for pesticide development. This study investigates the structure-activity relationships of 1,4-naphthoquinone, particularly 2-hydroxy-1,4-naphthoquinone and its derivatives. A series of 1,4-naphthoquinones with modifications at the C-2, C-5, and C-8 positions were synthesized and tested for larvicidal activities against Ae. aegypti. The presence of chlorine substituents at the C-2 position significantly increased mosquito larval mortality. In contrast, 2-hydroxy and 2-methoxy groups were less effective, highlighting the importance of the C-2 substituent in determining larvicidal activity. The compounds were tested on both pyrethroid-susceptible Orlando 1952 (ORL1952) and permethrin-resistant Puerto Rico (PR) strains of Ae. aegypti. While compound 1d exhibited the lowest median lethal concentration (LC50) against ORL1952 larvae, it showed minimal activity against the PR strain, which is resistant. The most promising compounds, 1 and 4a, showed LC50 values of 2.764 and 4.916 ppm in the ORL strain, and 2.548 and 4.878 ppm in the PR strain, respectively. Chlorine substitution at the C-2 position of 1,4-naphthoquinones enhances larvicidal activity against Ae. aegypti, while 2-hydroxy and 2-methoxy substitutions reduce efficacy. Certain compounds, such as 1 and 4a, show potential as broad-spectrum agents effective against both susceptible and resistant strains of Ae. aegypti, highlighting their promise for further development as mosquito control agents. © 2025 Society of Chemical Industry.

Cis-regulation of the CYP6CS1 gene and its role in mediating cross-resistance in a pymetrozine-resistant strain of Nilaparvata lugens.

Pymetrozine is currently one of the primary insecticides used to control the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae), but the long-term effectiveness of this chemical is threatened by growing issues of resistance. Previous studies in a laboratory selected strain of N. lugens, Pym-R, have shown that resistance to pymetrozine can evolve without target-site mutations. A key candidate gene identified is the cytochrome P450 gene CYP6CS1, which is overexpressed in the resistant Pym-R strain compared to the laboratory susceptible strain, Pym-S. In this study, we provide a deeper characterization of the regulatory mechanism and phenotypic effects of CYP6CS1 by comparing the resistant and susceptible variants of this gene. Using artificial constructs in Luciferase activity assays, we elucidate the role of indels in the overexpression of CYP6CS1 in the resistant strain. Additionally, transgenic Drosophila experiments also revealed that the CYP6CS1 gene not only contributes to resistance against pymetrozine, but is able to confer moderate to low cross-resistance to several other pesticides. This research provides vital insights into the possible genetic mechanisms that may contribute to pymetrozine resistance in field populations. Future work will aim to examine the relevance of CYP6CS1 variation in the field with the aim of developing diagnostic markers of resistance.

Deletion of bZIP Transcription Factor PratfA Reveals Specialized Metabolites Potentially Regulating Stress Response in Penicillium raistrickii.

Fungal secondary metabolism (SM) is highly correlated with physiological processes that are typically regulated by pleiotropic regulators. In this study, we purposefully altered PratfA, a crucial regulator associated with oxidative stress in Penicillium raistrickii CGMCC 3.1066. After the knockout of PratfA, a novel polyketide (PK) raistrilide A (1) and the known nonribosomal peptide (NRP) tunicoidine (2) subsequently disappeared. Notably, compound 1 is a rare octaketone derivative and contains two unsubstituted cis-double bonds, demonstrating its unique biosynthetic mechanism. The knockout of PratfA resulted in the disappearance of 1-2 and greatly increased the susceptibility of ΔPratfA mutant strain to oxidative stress, rendering it nearly impossible to survive in such environments. At present, the OE⸬PratfA strain showed no phenotypic or oxidative stress sensitivity differences compared to the wild-type strain. Our findings highlight that the oxidative-stress-related transcription factor (TF) PratfA influences SM pathways in P. raistrickii. The manipulation of regulatory factors can guide the discovery of novel natural products (NPs).