Resistant Populations Research Articles

Abstract A032: Uncovering the impact of current therapies on LUAD dormant metastasis

Abstract Despite recent therapeutic advances, Lung Adenocarcinoma (LUAD) remains a leading cause of mortality worldwide, with most deaths attributed to metastasis. Metastasis is mediated by disseminated metastasis initiating cells (MICs) that can persist in a dormant state in distant sites for months to years and ultimately drive metastatic relapse, which is clinically incurable. Adjuvant therapy seeks to prevent cancer relapse, however, efforts to improve adjuvant treatments are hindered by an insufficient understanding of the molecular mechanisms supporting the long-term viability of dormant MICs. We have established that primitive LUAD cells characterized by the spontaneous expression of the pluripotency transcription factor SOX2 can enter an immune-evasive dormant state with downregulation of immune response mediators (STING, NK ligands, MHC-I) to evade immune surveillance during dormancy. Now, we hypothesize that dormant and immune evasive progenitor MICs may also escape therapies targeting growth pathways. We have generated latency competent cells (LCCs) that can remain in a latent state for months by isolating progenitor cells from the Kras LSL-G12D/+ ;Trp53 flox/flox mouse model and screening their metastatic potential and progenitor state in the B6 background. LCCs entering a slow-cycling state in response to dormancy signals remain sensitive to targeted KRAS inhibitors but contain a resistant subpopulation that survives. To specifically characterize the progenitor state in these LCC populations, we have developed and validated two strategies to fluorescently mark SOX2 expression and activity, respectively. As speculated, the resistant population is mostly composed of SOX2+ progenitor LCCs after treatment with KRAS inhibitor under dormancy signaling. Furthermore, induced-dormancy also drives an accumulation of cells in the SOX2+ progenitor state in these LCC-rich populations. Ongoing studies are focused on delineating the emergence of the SOX2+ progenitor state in LCCs during dormancy and the biological mechanisms driving their persistence and resistance to targeted therapies. We aim to define (1) the dependence of dormant LCCs on oncogenic signaling, the (2) effect of targeted therapy on MICs, and (3) strategies to overcome potential resistance mechanisms in dormant MICs. Our ultimate goal is to delineate strategies to clear latent MICs and prevent LUAD recurrence. Citation Format: Inês Godet, Zhenghan Wang, Joan Massagué. Uncovering the impact of current therapies on LUAD dormant metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A032.

Abstract A040: A novel stroma-mediated positive interaction between resistant and sensitive cells in non-small cell lung cancer facilitates drug resistance

Abstract Resistance to targeted therapies, particularly those inhibiting oncogenic tyrosine kinases (TKIs), presents a significant challenge in the treatment of advanced non-small cell lung cancer (NSCLC). Despite initial robust clinical responses, tumors often relapse due to the emergence of resistant cell populations. The origins of this resistance—whether it is pre-existing in a subset of tumor cells or arises de novo during treatment—remains a critical question in understanding and combating therapeutic failure. To investigate this, we developed in silico mathematical models that integrate both pre-existing and de novo resistance mechanisms within a framework that explicitly integrates the stromal niche. Our study focused on the evolutionary dynamics of NSCLC in response to therapy, using a hybrid agent-based spatial modeling framework (HAL) to simulate tumor behavior under treatment. These models were designed to simulate the complex interactions between resistant and sensitive tumor cells, mediated by the stroma, and to predict the timing of relapse based on these interactions. Our findings suggest that stroma-mediated interactions play a crucial role in the evolutionary dynamics of therapy responses, influencing the fitness and survival of both resistant and sensitive cells. Specifically, our models predict that pre-existing resistance is unlikely to be compatible with the long remission periods observed in a substantial subset of patients treated with advanced anaplastic lymphoma kinase (ALK) inhibitors. This conclusion was supported by the observed relapse times and volumetric tumor growth data from subsequent animal models. Moreover, our analyses highlight the importance of ecological factors within the tumor microenvironment in shaping the response to therapy. The spatial models we developed reveal that the stroma can foster positive interactions between resistant and sensitive cells, thereby accelerating the emergence of resistance. These insights underscore the need to consider the stromal niche when developing new therapeutic strategies and when interpreting the dynamics of drug resistance. In conclusion, our study provides new insights into the role of stroma in mediating resistance to TKIs in NSCLC. By combining mathematical modeling with experimental data, we have elucidated how stroma-mediated interactions between tumor cells can influence the evolution of resistance, challenging the assumption that pre-existing resistance alone drives relapses in TKI-treated patients. Our findings emphasize the need for adaptive therapeutic approaches that anticipate and disrupt these microenvironmental interactions to improve patient outcomes. Citation Format: Rishi M. Shah, Sagnik Yarlagadda, Mark Robertson-Tessi, Bina Desai, Tatiana Miti, Daria Miroshnychenko, David Basanta, Andriy Marusyk, Alexander Anderson. A novel stroma-mediated positive interaction between resistant and sensitive cells in non-small cell lung cancer facilitates drug resistance [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A040.

Photodynamic inactivation and its effects on the heterogeneity of bacterial resistance.

Antimicrobial resistance is a growing threat to global public health, requiring innovative approaches for its control. Photodynamic inactivation (PDI) with light-activated photosensitizers has emerged as a strategy to combat resistant bacteria, challenging the intrinsic heterogeneity of bacterial populations. This study evaluates the impact of PDI on both heterogeneity and shape of the distribution profile of resistant bacterial populations, specifically on strains of Staphylococcus aureus resistant to amoxicillin, erythromycin, and gentamicin, for exploring its potential as an adjuvant therapy in the fight against bacterial resistance. Curcumin (10 µM) was used as a photosensitizer and five cycles of PDI were applied on Staphylococcus aureus strains under 450nm irradiation of 10J/cm² energy density. The resistance variations amongst bacterial subpopulations were investigated by calculating the minimum inhibitory concentration (MIC) before and after PDI treatment. MIC was significantly reduced by the antibiotics tested post-PDI and a reduction in the heterogeneity of bacterial populations was recorded, suggesting PDI can effectively decrease the resistance diversity of Staphylococcus aureus. The result reinforces the potential of PDI as a valuable adjuvant therapy, offering a promising avenue for mitigating bacterial resistance and promoting more effective treatment strategies against resistant infections.

Genomic characteristics of Salmonella enterica serovar Blockley.

Non-typhoidal Salmonella (NTS) is a significant cause of foodborne illness worldwide, with increasing antimicrobial resistance posing a public health concern. Salmonella enterica serovar Blockley (S. Blockley) is relatively uncommon, and its antimicrobial resistance profile and population structure have been understudied. This study presents a comprehensive genomic analysis of 264 S. Blockley isolates from diverse geographical regions to elucidate antimicrobial resistance patterns and population structure. Bayesian analysis classified these genomes into 10 distinct groups (BAPS A to BAPS J), further categorized into two lineages, R and S. Lineage R comprised six BAPS clusters (BAPSs A-F), predominantly found in Asia and Africa, all of which harbored the azithromycin resistance gene mph(A) and other resistance determinants. In contrast, lineage S, lacking mph(A), comprised the remaining four BAPS clusters, which were primarily found in Europe and the Americas. Several types of mutations in gyrA were found in lineage R, which were specific to BAPS clusters. These BAPS clusters exhibited distinct geographic distributions, with BAPS B, BAPS D, and BAPS E unique to China, Taiwan, and Japan, respectively, while BAPS H and BAPS I were predominantly found in the United States. Temporal phylogenetic analysis suggested that lineage R diverged in the 1980s, with notable microevolutionary changes. The presence of a genomic island with mph(A), aph(3')-Ia, aph(3")-Ib, aph(6)-Id, and tet(A) in lineage R underscores the public health threat, highlighting a need for continuous surveillance.IMPORTANCEAntimicrobial resistance in Salmonella is a global public health concern. In this study, we focused on serovar Blockley, and a whole-genome analysis revealed its global population structure. The results revealed the existence of azithromycin-resistant strains, which were characterized both phylogenetically and geographically. The resistance genes were transmitted via genomic islands, and their micro-scale evolution was also revealed. Our findings are the first to reveal the dissemination of antimicrobial resistance genes, including azithromycin, in serovar Blockley, and provide valuable insights into understanding the spread of antimicrobial resistance.

RNA sequencing of Beauveria bassiana JEF-350-infected Thrips palmi reveals change of host defense and homeostasis.

Melon thrips, Thrips palmi, represent a significant threat to plants, inducing necrosis and acting as vectors for numerous plant viruses. Entomopathogenic fungi present a promising avenue for the management of melon thrips populations resistant to conventional chemical treatments. In this work, an adult colony of melon thrips was exposed to Beauveria bassiana strain JEF-350, and the ensuing transcriptional response of the infected thrips was scrutinized to elucidate their reactions during fungal pathogenesis. Utilizing Illumina sequencing, RNA samples were extracted from untreated thrips as well as from thrips continuously infected for 2 and 4days, each with three biological replicates. While no notable alterations in gene expression were observed between the untreated control and thrips infected for 2days, those infected for 4days exhibited a plethora of differentially expressed genes. Specifically, in the thrips infected for the extended period, pathways associated with lysosomal function and insect hormone biosynthesis were notably repressed, while others such as serine and glycine metabolism, Toll and Imd, and circadian rhythm pathways displayed heightened activity. Noteworthy downregulation was observed in numerous lysosomal hydrolase genes encoding glycosidases, sulfatases, and lipases, particularly glycosidases. Furthermore, certain genes related to hydrolase precursors within the Golgi apparatus exhibited heightened expression levels but failed to progress toward hydrolase biosynthesis. Upstream regulation of juvenile hormone biosynthesis was augmented, yet downstream genes were significantly downregulated, leading to a disruption in juvenile hormone production. Similarly, while cytochrome P450 genes in the downstream of ecdysone biosynthesis were upregulated, expressions of cholesterol desaturase and cytochrome P450 genes in the upstream were inhibited, consequently dampening ecdysone biosynthesis. The observed differential targeting of organs or pathways by B. bassiana JEF-350, in contrast to conventional chemicals primarily affecting neurotransmission and energy production, suggests its potential efficacy in managing resistant thrips populations. Consequently, integrating JEF-350 into the chemical spray regimen or incorporating it into tank-mix formulations with chemical insecticides emerges as a pragmatic approach within the realm of integrated pest management strategies. KEY POINTS: • Beauveria treatment inhibited lysosomal function and hormone synthesis in thrips. • Thrips serine/glycine metabolism, Toll and Imd, and circadian rhythm pathways were activated. • Upstream functions of thrips hormone biosynthesis increased, while downstream functions were suppressed. • Regarding biosynthesis of metabolites, this fungus targets other pathways with resistance management.

The Mediator complex subunit MoMed15 plays an important role in conferring sensitivity to isoprothiolane by modulating xenobiotic metabolism in M. oryzae.

Rice blast caused by Magnaporthe oryzae is one of the most economically important rice diseases. Fungicides such as isoprothiolane (IPT) have been used extensively for rice blast control, but resistance to IPT in M. oryzae is an emerging threat. In this study, molecular mechanisms of resistance in IPT-resistant mutants were identified. Through whole-genome sequencing and genetic transformation, we identified the gene MoMed15, encoding a transcriptional glutamine-rich co-activator Mediator complex subunit, in which mutations or deletion resulted in moderate IPT resistance. Further research found that MoMed15 physically interacted with the IPT resistance regulatory factor MoIRR to simultaneously regulate both MoIRR expression and the expression of multiple xenobiotic-metabolizing enzymes in response to IPT stress. We hypothesize that some xenobiotic-metabolizing enzymes enhance IPT toxicity by modifying the IPT structure. Variation of MoMed15 affected the recruitment of the transcriptional Mediator complex and decreased the expression of these xenobiotic-metabolizing enzymes, resulting in moderate IPT resistance. We also found that MoPGR1, encoding a protein that activates cytochrome P450 enzymes, was essential to confer IPT sensitivity, and its expression was directly regulated by MoIRR.IMPORTANCEIsoprothiolane (IPT) has been used extensively for the management of rice blast disease and IPT-resistant subpopulations have emerged in Chinese rice fields. The emergence of resistant pathogen populations has led to a steep increase in fungicide use, increasing pesticide risk for the applicator and the environment. The molecular mechanisms of IPT resistance in M. oryzae remain elusive. In this study, we demonstrated that transcriptional co-activator MoMed15 interacts with IPT resistance regulator MoIRR to recruit the Mediator complex, which promotes the expression of xenobiotic-metabolizing enzymes, leading to exacerbated IPT toxicity. The MoMed15 could be used for IPT resistance detection in rice fields.

Biochemistry and Future Perspectives of Antibiotic Resistance: An Eye on Active Natural Products

Antibiotic resistance poses a serious threat to the current healthcare system, negatively impacting the effectiveness of many antimicrobial treatments. The situation is exacerbated by the widespread overuse and abuse of available antibiotics, accelerating the evolution of resistance. Thus, there is an urgent need for novel approaches to therapy to overcome established resistance mechanisms. Plants produce molecules capable of inhibiting bacterial growth in various ways, offering promising paths for the development of alternative antibiotic medicine. This review emphasizes the necessity of research efforts on plant-derived chemicals in the hopes of finding and creating novel drugs that can successfully target resistant bacterial populations. Investigating these natural chemicals allows us to improve our knowledge of novel antimicrobial pathways and also expands our antibacterial repertoire with novel molecules. Simultaneously, it is still necessary to utilize present antibiotics sparingly; prudent prescribing practices must be encouraged to extend the effectiveness of current medications. The combination of innovative drug research and responsible drug usage offers an integrated strategy for managing the antibiotic resistance challenge.

TMIC-62. INVESTIGATING THE ROLE OF OSTEOPONTIN IN RADIORESISTANCE OF H3.3-G34R PEDIATRIC HIGH-GRADE GLIOMA

Abstract Pediatric high-grade gliomas (pHGGs) are currently the leading cause of cancer-related deaths in children. Around 15% of pHGGs harbor a glycine to arginine (G34R) mutation in histone H3.3. Gliomas in general, including H3.3-G34R gliomas, contain cell populations that are resistant to chemotherapy and radiation therapy. These resistant cell populations are responsible for tumor recurrence seen in over 90% of patients within two years after treatment. Uncovering molecular mechanisms responsible for radiation resistance is essential for the development of new targeted therapies against glioma. In our lab’s H3.3-G34R mouse model, we have observed mice that are both radioresistant and radiosensitive. In order to investigate potential mechanisms of resistance leading to this phenotype, we performed single-cell RNA sequencing (scRNA-seq) on 3 non-treated (NT) glioma-bearing mice, 3 mice resistant to treatment (R), and 3 mice susceptible to treatment (S). The scRNA-seq data was processed and filtered using FastQC, Cellranger, CellBender, and DoubletFinder before downstream analysis. Ligand-receptor interaction analysis using CellChat in conjunction with differential expression analysis demonstrated differential expression and secretion of a cytokine known as Secreted Phosphoprotein 1 (SPP1)/Osteopontin (OPN) from tumor-associated microglia and macrophages. Current literature on SPP1 has suggested that its expression may play a role in tumor aggressiveness. However, there is conflicting evidence regarding its mechanism of action when secreted from tumor-associated microglia and macrophages. Additionally, its role in radioresistance has yet to be fully explored. We will present data utilizing in vitro and in vivo experimentation to elucidate the role that differential expression of SPP1 may play in the radioresistance of our H3.3-G34R mouse model. Supported by grants from NIH-NINDS, the Pediatric Brain Tumor Foundation, and Ian’s Friends Foundation

Comparative toxicity of three variant oils and their nanoemulsions on the brown dog tick Rhipicephalus sanguineus

Tick control mainly depends on using chemical acaricides that have led to the emergence of resistant tick populations along with environmental hazards. Natural alternatives including essential oils are now widely used to avoid the undesirable effects of chemicals on human, animals and environment. In this study, three commercial oils (myrrh, patchouli, and cypress) and their nanoemulsions (NEs) were tested against Rhipicephalus sanguineus sensu lato unfed adults. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the nanoemulsions. Four concentrations with three replicates were used in the bioassay of oils and NEs against ticks using an adult immersion test. Furthermore, a toxicity study of the three oils and their NEs using normal fibroblast cells (BJ-1) was performed. TEM revealed particle size ranges from 29 to 211 nm with spherical droplets. The droplet size and polydispersity index were (29.30 nm & 0.367), (211.6 nm & 0.221) and (164.2 nm & 0.237) for myrrh NE, patchouli NE, and cypress NE, respectively. Myrrh and patchouli oils recorded high acaricidal activity followed by cypress oil with LC50 value 5 days after treatment of 9.01, 12.40, and 15.21%, respectively. The acaricidal efficacy of oil was potentiated in the NEs form which was proved by the reduction in LC50 values that were recorded 7 days after treatment 4.17, 8.57, and 5.04%, for myrrh, patchouli, and cypress NE, respectively. As an alternative for lab animals, we applied the cytotoxicity of myrrh, patchouli, and cypress on normal fibroblast cells. The oils showed low cytotoxic activity of 10.6, 21.5, and 23.6% for Myrrh, Patchouli, and Cypress, respectively. The nanoemulsion was revealed to be safe for normal cells up to a concentration of 0.62% (cytotoxicity%= 24.4, 34.4, and 16.3%, respectively), and the moderate cytotoxic effect appeared at around a concentration of 1.25% (cytotoxicity%= 42.2%, 57.0%, and 36.8% respectively). In conclusion, the three oils and their NEs have good acaricidal activity against Rhipicephalus sanguineus unfed adults. Further toxicity studies on mammals are needed to ensure the safe use of these formulations for the control of ticks on infested animals.

Biological performance of Bollgard II® Bt-resistant vs susceptible population of pink bollworm, Pectinophora gossypiella (Saunders) on non-toxic diet

BackgroundThe pink bollworm, Pectinophora gossypiella (Saunders), is a devastating global pest of cotton that has caused substantial economic damage to Bt Bollgard-II® cotton plants in recent years due to the evolution of Bt resistance. The associated fitness cost is assumed to be one of the factors delaying the development of resistance against Bt transgenic crops. Hence, the present study was undertaken to assess the biological performance of pink bollworms by comparing the life history and demographic parameters of a resistant (Field-R) and susceptible (Lab-S) population.ResultsProlonged larval duration (23.40 days in Field-R vs 18.80 days in Lab-S population), total life cycle (male = 50.00 vs 42.80 days; female = 53.60 vs 46.20 days), reduced fecundity (100.60 vs 154.20 eggs/female) and fertility (88.00 vs 138.00 fertile eggs/female) was observed. The demographic parameters indicated a significant reduction in the net reproductive rate (184.27 vs 276.72), innate capacity for increase in number (0.11 vs 0.15), finite rate of increase in number (1.12 vs 1.16 female progenies produced/female/day), weekly multiplication rate (2.16 vs 2.86), potential fecundity (545.06 vs 634.11 eggs), number of hypothetical F2 females (33 955.65 vs 76 572.41), but longer mean length of generation (47.54 vs 37.74 days) and population doubling time (6.30 vs 4.62 days) in Field-R compared with Lab-S population. A stage-specific life table demonstrated the differences in survival rates between susceptible and resistant populations at various life stages, with the resistant population having higher generation mortality (0.22 vs 0.19).ConclusionsThe study confirms the involvement of fitness costs associated with Bt resistance in P. gossypiella. Despite reduced reproductive fitness, the resistant population tried prolonging the larval stage as a compensatory mechanism to repair the damaged host tissues due to Bt intoxication and for accumulation of enough nutrient reserves for normal pupation and adult emergence. Presence of a high proportion of double Bt-resistant larvae in the field coupled with continued noncompliance with refug planting certainly favours the flaring up of this monophagous pest despite the observed fitness costs. The resistance cannot be effectively reversed unless suitable alternative management strategies are deployed.

Fitness Costs in Diamondback Moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) Resistant to Lufenuron, A Chitin-Synthesis Inhibitor Insecticide

The diamondback moth (DBM), Plutella xylostella, is the main pest of Brassicas crops worldwide, and its recorded resistance to 101 active ingredients indicates it is difficult to control. The purpose of this study was to investigate the hypothesis that P. xylostella has fitness costs associated with its resistance to lufenuron, a chitin-synthesis inhibitor insecticide. Thus, concentration–mortality bioassays were performed for susceptible (REC-S), resistant (BZR-R) populations, their progenies F1 and F1′, and one established population without selection pressure (BZR-Rns) after four generations. A fertility life table was used to assess the biological performance of the REC-S and BZR-R. BZR-Rns of P. xylostella. The larval stage, longevity, and survival differed between populations. The reproductive rate (R0) was significantly lower in the F1 (♀R × ♂S) (28.19) and F1′ (♀S × ♂R) (34.06) progenies compared with their parents, but not with the relaxed BZR-Rns (39.39). The mean generation time (T), intrinsic rate of population growth (rm), and doubling time (DT) differed between REC-S and progenies, with fitness of 0.52 and 0.64 for F1 and F1′, respectively. Overall, the results suggest that the resistance of P. xylostella to lufenuron is stable and that low fitness costs appear to be associated with resistance to lufenuron, although heterozygotes showed lower fitness than their parents. Strategies such as preserving refuge areas, rotation of modes of action, etc., are essential for resistance management and prolonging the efficacy of control agents; this highlights the importance of integrated insecticide resistance management.

Characterization of insecticide resistance and their mechanisms in field populations of the German cockroach (Blattodea: Ectobiidae) in Taiwan under different treatment regimes.

This study investigated how management strategies influence resistance profiles in German cockroach (Blattella germanica (L.)) populations and their impact on the performance of commercial gel baits containing fipronil, imidacloprid, and indoxacarb. Field populations from premises managed under 3 different strategies: Baiting, random insecticide (RI) used, and insecticide rotation (IR) were tested. Almost all populations under RI and IR were resistant to deltamethrin, but low to moderate resistance was observed under the Baiting approach. Cytochrome P450 monooxygenases (P450) were involved in deltamethrin resistance in these resistant populations. All individuals under Baiting and RI were homozygous for the L993F mutation, but the populations under IR lacked homozygous-resistant individuals. Eighty-three percent of field populations with complete homozygosity for the Rdl mutation displayed low mortality upon exposure to 3× LD95 fipronil. The effect of P450 and the Rdl mutation conferred high fipronil resistance in populations under the Baiting approach, recording moderate performance indices (PI) of 44-67 in fipronil bait. By contrast, those populations under RI and IR, in which involve glutathione S-transferases in fipronil resistance, had high PIs of 78-93. Almost 80% of populations exhibited over 90% mortality at 3× LD95 indoxacarb treatment, accompanied by high PIs of 90-100 in indoxacarb bait. Partial mortality from 1× LD95 imidacloprid occurred across all field populations due to the involvement of P450. PIs of imidacloprid bait ranged 5-57 and 20-94 in populations under RI and IR, respectively. Field populations demonstrate different resistance profiles depending on the treatment regimes, and the resistance mechanisms involved influenced gel bait's effectiveness.

Cross-sectional Hospital-based Investigation on Clinical Characteristics of Pediatric Staphylococcus aureus Isolates in a Beijing Hospital from 2013 to 2022.

Staphylococcus aureus (S. aureus) was a prevalent pathogenic bacterium among children. Due to the extensive use of antibiotics, the sensitivity of S. aureus to these drugs has gradually declined. Since the 1960s, methicillin-resistant Staphylococcus aureus (MRSA) has emerged and spread worldwide, becoming a primary cause of both healthcare-associated (HA) and community-acquired (CA) infections. This retrospective study aimed to highlight the significance of S. aureus among bacteria isolated from children in Beijing, China, and to elucidate its antimicrobial resistance patterns. Data on all S. aureus infections from 2013 to 2022 were collected from the microbiology department of Beijing Children's Hospital. Only the first isolate from the same kind of specimen was analyzed. Antimicrobial susceptibility tests were carried out by Vitek 2 automated system (bio Mérieux, France) or Kirby-Bauer disc diffusion method, according to the guidelines recommended by the Clinical and Laboratory Standards Institute (CLSI). During the decade-long research period, a total of 47,062 bacterial isolates were isolated from 433,081 submitted specimens, with 6477 of these isolates identified as S. aureus. The majority of patients with S. aureus infections belonged to the age group of infants under one-year-old, accounting for 37.9% of cases. S. aureus isolates were predominantly found in the Pneumology Department, and the most common source of these isolates was lower respiratory tract specimens, comprising 34.3% of the total. The resistance rates of S. aureus to penicillin and erythromycin were notably high, at 89.5% and 73.8%, respectively. In contrast, the resistance rates to linezolid, vancomycin, rifampicin, and moxifloxacin were remarkably low, at 0.0%, 0.0%, 1.3%, and 3.9%, respectively. The detection rate of MRSA was 27.8%. MRSA isolates were predominantly found in the newborn group, ICU, and sterile body fluids. In our study, the most prevalent specimen type was derived from the lower respiratory tract, whereas the highest positive rate was observed in ear secretions. These findings underscored the pressing necessity for ongoing antimicrobial resistance (AMR) surveillance and the revision of treatment guidelines, particularly given the elevated detection of MRSA in ICU wards, sterile body fluids, and the neonatal age group. MRSA exhibited significant resistance to all β-lactam antibiotics, erythromycin, and ciprofloxacin. Therefore, future research endeavors should prioritize examining specific antimicrobial resistance populations and potential intervention strategies, as these were vital in mitigating the dissemination of antimicrobial-resistant isolates.

Resistance ratios and enzyme activity of Tetranychus urticae and Tetranychus turkestani (Acari: Tetranychidae) to commonly used acaricides on cotton in Aydin province, Türkiye

This study aims to determine the resistance ratios of Tetranychus urticae Koch red form (RF) and Tetranychus turkestani (Ugarov & Nikolskii) populations collected from cotton fields in Soke, Germencik, Kocarli and Nazilli districts of Aydin province to commonly used acaricides (abamectin, hexythiazox, etoxazole, spiromesifen). The potential role of detoxification enzymes (esterase, glutathione-s-transferase (GST), P450 monooxygenase (P450)) in acaricide resistance was also assessed. Overall populations of T. urticae RF presented varying ratios of resistance to these acaricides with all three populations (G15R21, K24R21, S3R21) showing significant resistance to abamectin (187.1–223.66 fold), hexythiazox (156.31–168.25 fold), etoxazole (409.58–517.20 fold) and spiromesifen (981.77–1246.11 fold). In contrast, all five T. turkestani populations (G4G21, K16G21, N1G21, N11G21, S19G21) were susceptible to abamectin, etoxazole, and spiromesifen, but exhibited some resistance to hexythiazox (164.34–182.39 fold). The resistance ratios of T. turkestani were however lower compared to T. urticae RF. A relationship was also found between detoxification enzymes and resistance. Esterase activity varied among mite populations, with the highest levels recorded in resistant populations of T. urticae (G15R21 and K24R219) with rates ranging between 6.48 and 7 mOD/min/mg protein. GST activity was highest in resistant mite populations (T. urticae S3R21 and T. turkestani K16G21). T. turkestani N11G21 population exhibited the highest P450 enzyme activity, reaching 4.39 RFU/30 min/mg protein. This study was the first to determine the resistance ratios of T. turkestani to hexythiazox in Türkiye, and on a global scale.

Comparison of Molecularly Identified Resistant and Susceptible Johnsongrass (Sorghum halepense L.) Populations at ALS Gene, in the Absence and Presence of Field Crops

Background/Objectives: Johnsongrass (Sorghum halepense) is an erect tetraploid, perennial, C4 grass weed species categorized among the world’s most noxious weeds due to its high competitive ability against crops and the increased number of field-evolved herbicide-resistant populations. The aim of the present study was to assess the growth rate and performance of resistant (R) johnsongrass genotypes hosting Trp574Leu target-site cross-resistance at ALS gene, inhibiting various herbicides, compared to susceptible (S) conspecific weeds, in the absence and presence of corn or sunflower antagonism. Methods: The aboveground biomass, tiller, and rhizome production ability of one S and one R johnsongrass population with a Trp574-Leu substitution conferring cross-resistance to ALS-inhibiting herbicides were compared under non-competitive conditions. Furthermore, the competitive ability of these two johnsongrass populations against corn or sunflower was determined in a target-neighborhood design. Results: The S and R johnsongrass populations displayed similar growth rates concerning aboveground biomass and tiller number, whereas the R population displayed a slightly greater growth rate for rhizome production compared to the S population. Both populations grown with corn produced more aboveground biomass than the ones grown with sunflowers. The aboveground biomass of corn was reduced to a greater extent than sunflower by the presence of both johnsongrass populations, while both crops were affected more by the S than by the R population. Conclusions: Although the inheritance and the genetic background of plant materls were not addressed, the findings of this study indicate clearly that the growth rate and competitive ability of the ALS-resistant johnsongrass population are not associated with the resistance mechanism involved.

Use of the Micro-Agar Larval Development Test to Differentiate Resistant and Susceptible Cooperia spp. Isolates in Cattle Within the Context of Parasite Population Replacement

Gastrointestinal nematode infections are a global concern in grazing cattle production systems, even more so due to the widespread problem of anthelmintic resistance. In response, early anthelmintic resistance detection methods, such as the micro-agar larval development test (MALDT), and parasite management strategies, such as the replacement of resistant parasite populations with susceptible ones, have been developed. This study aimed to characterize ivermectin-susceptible and -resistant isolates of Cooperia spp. using MALDT in the context of a parasite population replacement strategy. Three Cooperia spp. field isolates were evaluated: a susceptible one (Coop-S), a resistant one (Coop-R), and a post-replacement one (Coop-PR). The MALDT was performed in 96-well plates with 12 known concentrations of eprinomectin (EPR) on an agar base. Each test was performed in quadruplicate. Data analysis included nonlinear regression to determine EC50, EC90, and EC99 values, resistance ratios (RRs), and R2. The results showed clear differentiation between the isolates, with RR values of 5.78 and 1.28 for Coop-R and Coop-PR, respectively, compared to Coop-S. The MALDT proved to be a reliable tool for differentiating ivermectin-susceptible from ivermectin-resistant isolates of Cooperia spp., and future evaluations of this test in mixed nematode populations are recommended for routine diagnosis of anthelmintic resistance.

Evaluation of postharvest age and dormancy-breaking methods on Echinochloa crus-galli seed germination

Barnyardgrass (Echinochloa crus-galli) is one of the most troublesome weeds in irrigated rice cultivation and has increasingly impacted rainfed crops due to the emergence of herbicide-resistant populations. Understanding its germination dynamics is crucial for developing and implementing effective management strategies. Additionally, since barnyardgrass research relies on growing plants from seeds, its dormancy characteristics are of particular interest. The present study aimed to evaluate the influence of postharvest age on barnyardgrass seed germination and the effectiveness of different dormancy-breaking methods in susceptible and herbicide-resistant populations. Germination rate (G), germination speed index (GSI), and seed viability, assessed using the topographic tetrazolium test, were measured in seed lots with four different postharvest ages: two years, one year, two months, and one day postharvest. The seeds were subjected to 15 dormancy-breaking methods, including temperature variation and the use of solutions containing H2SO4, KNO3, and GA3. Seeds that were one or two years old showed germination rates exceeding 90%, regardless of the method used. In contrast, seeds aged two months or one day postharvest only germinated when exposed to 40°C for seven days, with G values of 25.2% and 5.9%, respectively. Both herbicide-susceptible and resistant barnyardgrass populations exhibited similar dormancy levels and responses to dormancy-breaking methods. The results indicate that newly harvested seeds have high dormancy levels, and specific methods are only partially effective in overcoming barnyardgrass seed dormancy.

Evaluation of ALS-Resistant Yellow Nutsedge (Cyperus esculentus) in Georgia Peanut

Abstract Accounting for 53% of United States peanuts (Arachis hypogaea L.), Georgia is the top peanut-producing state with approximately 1.42 billion kg produced in 2023. Peanut producers often use the ALS imidazolinone herbicide imazapic but reduced yellow nutsedge (Cyperus esculentus L.) control was reported in Georgia peanuts after four-years of continuous imazapic use. This study aimed to determine the level of resistance (LD50, I50, and GR50), potential cross-resistance for the suspected resistant population, and identify the associated genetic mutations conferring resistance. A susceptible biotype was treated with 0, 0.0088, 0.0175, 0.035, 0.07, 0.14, 0.28, and 0.56 kg ai ha-1, and a resistant biotype was sprayed with 0, 0.07, 0.14, 0.28, 0.56, 1.13, 2.26, and 4.5 kg ai ha-1 of imazapic. To determine if the suspected resistant biotype was cross-resistant to halosulfuron-methyl, an ALS herbicide used to control nutsedge spp., both biotypes were treated with 0, 0.0117, 0.0233, 0.0466, 0.0933, 0.187, 0.373, and 0.746 g ai ha-1 of halosulfuron-methyl. Plants were rated for injury 7, 14, and 28 days after treatment (DAT), and above-ground biomass harvested at 28 DAT. For imazapic, LD50 was 0.041 and 1.503 kg ai ha-1 and the GR50 was estimated to be 0.0128 and 1.853 kg ai ha-1 for Sus and Res biotypes, respectively, indicating 36 and 145-fold increase in resistance of the Res biotype for I50 and GR50, respectively. Both biotypes responded similarly to applications of halosulfuron-methyl, with biomass reductionat rates greater than 0.023 kg ai ha-1. Transcriptome profiles revealed a mutation in the target-site gene of the resistant biotype, causing an amino acid substitution from Alanine to Valine at position 205 (Ala205Val). Growers should continue to rotate chemistries and implement integrated weed management approaches for control of C. esculentus as the use of imazapic over consecutive years has led to resistance in C. esculentus.

A Trp-574-Leu mutation in acetolactate synthase confers imazamox resistance in barnyardgrass (Echinochloa crus-galli) from China

Abstract Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is increasingly infesting imidazolinone-tolerant (IMI-T) rice fields in China, imazamox resistance of E. crus-galli has become the major concern for weed management in IMI-T rice fields. In this study, the susceptible population JLGY-3 (S) and the suspected resistant population JHXY-2 (R) collected from IMI-T rice fields were used as research subjects. When treated with imazamox, JHXY-2 (R) population showed a high level of herbicide resistance with a resistance index (RI) of 31.2. JHXY-2 (R) was cross-resistant to all five acetolactate synthase (ALS) inhibitors from different chemical families, but sensitive to herbicides inhibiting acetyl-CoA carboxylase (ACCase). In order to understand the reason why JHXY-2 (R) was resistant to imazamox, we performed experiments to characterize potential TSR and NTSR mechanisms. A trp-574-leu amino acid mutation in ALS and low imazamox ALS sensitivity were the main mechanism underlying imazamox resistance in this JHXY-2 (R) population. There was no significant difference in ALS gene expression and ALS protein abundance between R and S populations. High-performance liquid chromatography-tandem mass spectrometry analysis showed enhanced metabolism of imazamox in JHXY-2 (R), which was in contrast to the results of pretreatment with a metabolic enzyme inhibitor. Treatments with the P450/GST inhibitors did not alter the resistance level of JHXY-2 (R) against imazamox. To further clarify the NTSR mechanism of JHXY-2 (R), transcriptome sequencing showed that there was almost no significant difference in the expression of P450 and GST metabolic enzyme genes between R and S populations, and only GST-U1 showed a significant induction in R population. In conclusion, amino acid mutation and higher enzyme activity of ALS are the main causes of imazamox resistance in JHXY-2 (R). However, given the differences in imazamox residues in the leaves of the E. crus-galli, there may still be undetectable NTSR that are causing imazamox resistance in the R population.

PfGSTF2 endows resistance to quizalofop-p-ethyl in Polypogon fugax by GSH conjugation.

Populations of Polypogon fugax have developed resistance to many acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. This resistance threats the effectiveness and sustainability of herbicide use. In our previous research, a field P. fugax population exhibited GST-based metabolic resistance to the widely used ACCase-inhibiting herbicide quizalofop-p-ethyl. Here, in this current study, we identified and characterized two GST genes (named as PfGSTF2 and PfGSTF58) that showed higher expression levels in the resistant than the susceptible population. Transgenic rice calli overexpressing PfGSTF2, but not PfGSTF58, became resistant to quizalofop-p-ethyl and haloxyfop-R-methyl. This reflects similar cross-resistance pattern to what was observed in the resistant P. fugax population. Transgenic rice seedlings overexpressing PfGSTF2 also exhibited resistance to quizalofop-p-ethyl. In contrast, CRISPR/Cas9 knockout of the orthologue gene in rice seedlings increased their sensitivity to quizalofop-p-ethyl. LC-MS analysis of in vitro herbicide metabolism by Escherichia coli-expressed recombinant PfGSTF2 revealed that quizalofop (but not haloxyfop) was detoxified at the ether bond, generating the GSH-quizalofop conjugate and a propanoic acid derivative with greatly reduced herbicidal activity. Equally, these two metabolites accumulated at higher levels in the resistant population than the susceptible population. In addition, both recombinant PfGSTF2 and PfGSTF58 can attenuate cytotoxicity by reactive oxygen species (ROS), suggesting a role in plant defence against ROS generated by herbicides. Furthermore, the GST inhibitor (NBD-Cl) reversed resistance in the resistant population, and PfGSTF2 (but not PfGSTF58) responded to NBD-Cl inhibition. All these suggest that PfGSTF2 plays a significant role in the evolution of quizalofop resistance through enhanced herbicide metabolism in P. fugax.