Mechanism Of Cross-resistance Research Articles

Sublethal Sodium Hypochlorite Exposure: Impact on Resistance-Nodulation-Cell Division Efflux Pump Overexpression and Cross-Resistance to Imipenem

Sodium hypochlorite (NaOCl) is widely used in public healthcare facilities; this exposure can result in the development of bacterial tolerance to disinfectants, which has known links to antibiotic cross-resistance. However, the mechanism through which cross-resistance to antibiotics and disinfectants develops remains ambiguous. Therefore, this study aimed to examine the phenotypic and transcriptomic changes caused by disinfectant exposure in Gram-negative bacteria and determine the cause of cross-resistance to antibiotics. The results demonstrated that the misuse of disinfectants plays an important role in the emergence of disinfectant resistance and in the increase in antibiotic resistance. Antibiotic resistance may occur from the exposure of Gram-negative bacteria to subminimal inhibitory concentrations (MICs) of NaOCl. Ten passages of Gram-negative bacteria in increasingly higher subMICs of the NaOCl disinfectant were sufficient to increase the MIC to >2500 µg/mL NaOCl, particularly in K. pneumoniae and P. aeruginosa. To determine the development of cross-resistance to antibiotics due to NaOCl exposure, the MICs for each antibiotic before and after the exposure of each strain to sublethal concentrations of NaOCl were compared. After overnight incubation with a sublethal concentration of NaOCl, a statistically significant increase in MIC was only observed for imipenem (p < 0.01). An investigation of the mechanism of cross-resistance by means of transcriptome analysis revealed that 1250 µg/mL of NaOCl-adapted K. pneumoniae and P. aeruginosa strains increased resistance to imipenem due to the increased expression of resistance-nodulation-cell division (RND) efflux pumps, such as AcrAB-TolC and MexAB/XY-OprM. Therefore, we suggest that exposure to NaOCl can influence the expression of RND efflux pump genes, contributing to imipenem cross-resistance.

Indoor residual spraying of experimental huts in Cameroon highlights the potential of Fludora® Fusion to control wild pyrethroid-resistant malaria vectors

Elevated resistance to pyrethroids in major malaria vectors has led to the introduction of novel insecticides including neonicotinoids. There is a fear that efficacy of these new insecticides could be impacted by cross-resistance mechanisms from metabolic resistance to pyrethroids. In this study, after evaluating the resistance to deltamethrin, clothianidin and mixture of clothianidin + deltamethrin in the lab using CDC bottle assays, the efficacy of the new IRS formulation Fludora® Fusion was tested in comparison to clothianidin and deltamethrin applied alone using experimental hut trials against wild free-flying pyrethroid-resistant Anopheles funestus from Elende and field An. gambiae collected from Nkolondom reared in the lab and released in the huts. Additionally, cone tests on the treated walls were performed each month for a period of twelve months to evaluate the residual efficacy of the sprayed products. Furthermore, the L1014F-kdr target-site mutation and the L119F-GSTe2 mediated metabolic resistance to pyrethroids were genotyped on a subset of mosquitoes from the EHT to assess the potential cross-resistance. All Anopheles species tested were fully susceptible to clothianidin and clothianidin + deltamethrin mixture in CDC bottle assay while resistance was noted to deltamethrin. Accordingly, Fludora® Fusion (62.83% vs 42.42%) and clothianidin (64.42% vs 42.42%) induced significantly higher mortality rates in EHT than deltamethrin (42.42%) against free flying An. funestus from Elende in month 1 (M1) and no significant difference in mortality was observed between the first (M1) and sixth (M6) months of the evaluation (P > 0.05). However, lower mortality rates were recorded against An. gambiae s.s from Nkolondom (mortality rates 50%, 45.56% and 26.68%). In-situ cone test on the wall showed a high residual efficacy of Fludora® Fusion and clothianidin on the susceptible strain KISUMU (> 12 months) and moderately on the highly pyrethroid-resistant An. gambiae strain from Nkolondom (6 months). Interestingly, no association was observed between the L119F-GSTe2 mutation and the ability of mosquitoes to survive exposure to Fludora® Fusion, whereas a trend was observed with the L1014F-kdr mutation. This study highlights that Fludora® Fusion, through its clothianidin component, has good potential of controlling pyrethroid-resistant mosquitoes with prolonged residual efficacy. This could be therefore an appropriate tool for vector control in several malaria endemic regions.

Kinesin Facilitates Phenotypic Targeting of Therapeutic Resistance in Advanced Prostate Cancer.

Understanding the mechanisms underlying resistance is critical to improving therapeutic outcomes in patients with metastatic castration-resistant prostate cancer. Previous work showed that dynamic interconversions between epithelial-mesenchymal transition to mesenchymal-epithelial transition defines the phenotypic landscape of prostate tumors, as a potential driver of the emergence of therapeutic resistance. In this study, we use in vitro and in vivo preclinical MDA PCa patient-derived xenograft models of resistant human prostate cancer to determine molecular mechanisms of cross-resistance between antiandrogen therapy and taxane chemotherapy, underlying the therapeutically resistant phenotype. Transcriptomic profiling revealed that resistant and sensitive prostate cancer C4-2B cells have a unique differential gene signature response to cabazitaxel. Gene pathway analysis showed that sensitive cells exhibit an increase in DNA damage, while resistant cells express genes associated with protein regulation in response to cabazitaxel. The patient-derived xenograft model specimens are from patients who have metastatic lethal castration-resistant prostate cancer, treated with androgen deprivation therapy, antiandrogens, and chemotherapy including second-line taxane chemotherapy, cabazitaxel. Immunohistochemistry revealed high expression of E-cadherin and low expression of vimentin resulting in redifferentiation toward an epithelial phenotype. Furthermore, the mitotic kinesin-related protein involved in microtubule binding and the SLCO1B3 transporter (implicated in cabazitaxel intracellular transport) are associated with resistance in these prostate tumors. Combinational targeting of kinesins (ispinesib) with cabazitaxel was more effective than single monotherapies in inducing cell death in resistant prostate tumors. Implications: Our findings are of translational significance in identifying kinesin as a novel target of cross-resistance toward enhancing therapeutic vulnerability and improved clinical outcomes in patients with advanced prostate cancer.

P450 gene CYP6a13 is responsible for cross-resistance of insecticides in field populations of Spodoptera frugiperda.

Continuous and long-term use of traditional and new pesticides can result in cross-resistance among pest populations in different fields. Study on the mechanism of cross-resistance and related genes will help resistance management and field pest control. In this study, the pesticide-resistance mechanism in Spodoptera frugiperda (FAW) was studied with field populations in 3 locations of South China. Field FAW populations were highly resistant to traditional insecticides, chlorpyrifos (organophosphate) and deltamethrin (pyrethroid), and had higher levels of cytochrome P450 activity than a non-resistant laboratory strain. Inhibition of P450 activity by piperonyl butoxide significantly increased the sensitivity of resistant FAW in 3 locations to chlorpyrifos, deltamethrin and chlorantraniliprole (amide), a new type of insecticide, suggesting that P450 detoxification is a critical factor for insecticide resistance in field FAW populations. Transcriptomic analysis indicated that 18 P450 genes were upregulated in the field FAW populations collected in 3 regions and in 2consecutive years, with CYP6a13, the most significantly upregulated one. Knockdown of CYP6a13 messenger RNA by RNA interference resulted in an increased sensitivity to the 3 tested insecticides in the field FAW. Enzyme activity and molecular docking analyses indicated that CYP6a13 enzyme was able to metabolize the 3 tested insecticides and interact with 8 other types of insecticides, confirming that CYP6a13 is a key cross-resistance gene with a wide range of substrates in the field FAW populations across the different regions and can be used as a biomarker and target for management of FAW insecticide resistance in fields.

Efficacy of the drug maribavir according to clinical studies

Modern medicine has a high demand for new drugs for the prevention and treatment of cytomegalovirus (CMV) infection. This review discusses maribavir — an oral antiviral drug with selective multimodal anti-CMV activity for the treatment of adults and children with post-transplant CMV infection resistant to traditional anti-CMV therapy. Despite numerous clinical trials of maribavir, the results of its effi cacy are ambiguous. Alongside successful studies indicating high effi cacy of the drug under review, there are data from statistically unsuccessful studies. The aim of this review is to examine the mechanism of its action on cytomegalovirus infection, viral sensitivity and cross-resistance mechanisms, as well as to summarize the results of clinical trials of the drug.

Abstract PO1-23-10: Multi-omics analysis identifies the mechanism in cross-resistance to endocrine therapy and CDK4/6 inhibitor in breast cancer

Abstract Background In advanced/metastatic breast cancer (MBC) or recurrent breast cancer on prior endocrine therapy (ET), selective estrogen receptor downregulator (SERD) of fulvestrant and CDK4/6i are the mainstream therapy regimen. In the clinical, fulvestrant combined with CDK4/6i is the second-line therapy for breast cancer (BC) that had progressed during previous endocrine therapy. The alternation of backbone from aromatase inhibitor or tamoxifen (endocrine sensitive) to fulvestrant (endocrine resistance) partially comes from the mechanism of ET resistance. Moreover, in the PALOMA-2 trial, approximately 30% of patients developed into recurrence after two years of CDK4/6i treatment, indicating that the ET backbone may affect CDK4/6i efficacy, bringing an emerging clinical issue of cross-resistance. However, whether the cross-resistance of ET would be more sensitive to CDK4/6i or impair the efficacy of CDK4/6i is still an ambiguous and heterogeneous issue. Also, in CDK4/6i resistance, whether the mechanism of ET resistance is associated with the dysregulation of the cell cycle or activation of other “bypass” signaling pathways is not fully understood. Methods We use a 3D and 2D culture of ET-sensitive cell S0.5, tamoxifen-resistant cell TAM, and fulvestrant-resistant cell 182R6 as our model. The 3D culture was performed by using the Tools 3d culture plus kit. Drug responses to fulvestrant and ribociclib were conducted by using CCK-8 assay. The potential target and pathway involved in the mechanisms of cross-resistance were analyzed by using multi-omics analysis of sequential window acquisition of all theoretical mass spectra (SWATH-MS), RNA-seq, micro-western array (MWA), traditional western blots, and open access database. Results In comparison with S0.5, the sensitivity to fulvestrant was indeed reduced in 182R6 cell; however, we found the sensitivity to ribociclib was also reduced in 182R6 cell, which was in contrast to the ribociclib-sensitive TAM cell. The different response to ribociclib between 182R6 and TAM, indicating that cross-resistance between fulvestrant and ribociclib existed in the model of 182R6 and TAM would be another control for 182R6 to find the target with or without cross-resistance. With multi-omics analysis of SWATH-MS, RNA-seq, MWA, western blots, and open access database, we found some unique or high expression of targets and pathways including EGFR, HER2, CDK6, CDK2, MAPK, and TNF-α pathways in cross-resistance R6 cell than in parental and TAM cell. We reconfirmed the above targets by 3D culture and found MAPK signaling pathway of p-ERK was not affected under ribociclib treatment, indicating the important role of the MAPK signaling pathway in ribociclib resistance. Conclusion To our knowledge, these results provide the first preliminary mechanism of cross-resistance between fulvestrant and ribociclib. We found fulvestrant resistant cell R6 exhibited the phenomenon of cross-resistance to ribociclib, which was in contrast to ribociclib-sensitive TAM cell. We also found some unique or high expression of target and pathway in cross-resistance R6 cells than in parental and TAM cells. In the future, with compound library screening and in vivo animal models, we expect to discover an FDA-approved drug or potential compound to overcome the cross-resistance between fulvestrant and ribociclib. Citation Format: Ming-Feng Hou, Chung-Liang Li, Chih-Po Chiang. Multi-omics analysis identifies the mechanism in cross-resistance to endocrine therapy and CDK4/6 inhibitor in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-23-10.

Investigation of lambda-cyhalothrin resistance in Spodoptera frugiperda: Heritability, cross-resistance, and mechanisms

Lambda-cyhalothrin, a representative pyrethroid insecticide widely used for Spodoptera frugiperda control in China, poses challenges due to the development of resistance. This study investigates the realized heritability, inheritance pattern, cross-resistance, and resistance mechanisms to lambda-cyhalothrin. After 21 generations of selection, the lambda-cyhalothrin-resistant strain (G21) developed a 171.11-fold resistance compared to a relatively susceptible strain (RS-G9), with a realized heritability (h2) of 0.11. Cross-resistance assays revealed that lambda-cyhalothrin-resistant strains showed no significant cross-resistance to the majority of tested insecticides. Genetic analysis indicated that lambda-cyhalothrin resistance in S. frugiperda was autosomal, incompletely dominant, and polygenic inheritance. The P450 enzyme inhibitor PBO significantly enhanced lambda-cyhalothrin toxicity in the resistant strains. Compared with the RS-G9 strain, the P450 enzyme activity was significantly increased and multiple P450 genes were significantly up-regulated in the lambda-cyhalothrin-resistant strains. RNAi targeting the most overexpressed P450 genes (CYP337B5 and CYP321B1) significantly increased the susceptibility of resistant S. frugiperda larvae to lambda-cyhalothrin. This study provides comprehensive insights into lambda-cyhalothrin resistance in S. frugiperda, and the results are helpful for developing effective resistance management strategies of this pest.

Heavy Metals as Catalysts in the Evolution of Antimicrobial Resistance and the Mechanisms Underpinning Co-selection.

The menace caused by antibiotic resistance in bacteria is acknowledged on a global scale. Concerns over the same are increasing because of the selection pressure exerted by a huge number of different antimicrobial agents, including heavy metals. Heavy metals are non-metabolizable and recalcitrant to degradation, therefore the bacteria can expel the pollutants out of the system and make it less harmful via different mechanisms. The selection of antibiotic-resistant bacteria may be influenced by heavy metals present in environmental reservoirs. Through co-resistance and cross-resistance processes, the presence of heavy metals in the environment can act as co-selecting agents, hence increasing resistance to both heavy metals and antibiotics. The horizontal gene transfer or mutation assists in the selection of mutant bacteria resistant to the polluted environment. Hence, bioremediation and biodegradation are sustainable methods for the natural clean-up of pollutants. This review sheds light on the occurrence of metal and antibiotic resistance in the environment via the co-resistance and cross-resistance mechanisms underpinning co-selection emphasizing the dearth of studies that specifically examine the method of co-selection in clinical settings. Furthermore, it is advised that future research incorporate both culture- and molecular-based methodologies to further our comprehension of the mechanisms underlying bacterial co- and cross-resistance to antibiotics and heavy metals.

Optimal Sequential Strategies for Antibody-Drug Conjugate in Metastatic Breast Cancer: Evaluating Efficacy and Cross-Resistance.

The optimal sequential strategy for antibody-drug conjugates (ADCs) in breast cancer remains uncertain. This study aimed to evaluate the efficacy and potential resistance of second ADC (ADC2) following the first ADC (ADC1) in human epidermal growth factor receptor 2 (HER2)-positive and HER2-low MBC. This retrospective, multicenter, real-world study enrolled patients with MBC who received at least 2 different types of ADCs in 3 hospitals in China between July 1, 2017 and May 1, 2023. Outcomes included the objective response rate (ORR) for ADC1 and ADC2, progression free survival 2 (PFS2), defined as the time from initiation of ADC2 to progression, and overall survival (OS). Seventy-nine female patients were included, 64 of whom had HER2-positive disease. The ORR for ADC2 with similar payload of ADC1 was found to be 5.3%. When switching to a different payload, the ORR of ADC2 increased to 22.6%. The PFS2 for ADC2 remained similar regardless of whether the payload was similar or different. Switching to different payload showed a higher ORR in patients with rapid progression and a durable response longer than 6 months (41.2% vs 15.0%). Specifically, significantly longer PFS2 and OS were seen in patients treated with trastuzumab deruxtecan (T-Dxd) compared to those treated with disitamab vedotin (RC48) after progression from trastuzumab emtansine (T-DM1; median PFS2 5.37 months vs 3.30 months, HR = 0.40, 95% CI 0.17-0.93, P = .034; median OS 50.6 months vs 20.2 months, HR = 0.27, 95% CI 0.08-0.91, P = .034). For patients who progressed after T-Dxd, the median PFS2 was 6.05 months for those treated with RC48 versus 0.93 months for those treated with T-DM1 (HR = 0.03, 95% CI 0.002-0.353, P = .0093). Genomic analysis revealed that alternation of retinoblastoma1 was significantly associated with superior PFS. The alternation of payload achieves different responses in different settings. T-Dxd followed by RC48 may be a potentially beneficial strategy in HER2-positive disease. Further research is needed to elucidate the mechanism of cross-resistance.

Adult mosquitoes of the sibling species Anopheles gambiae and Anopheles coluzzii exhibit contrasting patterns of susceptibility to four neonicotinoid insecticides along an urban-to-rural gradient in Yaoundé, Cameroon

BackgroundNeonicotinoids are potential alternatives for controlling pyrethroid-resistant mosquitoes, but their efficacy against malaria vector populations of sub-Saharan Africa has yet to be investigated. The aim of the present study was to test the efficacy of four neonicotinoids against adult populations of the sibling species Anopheles gambiae and Anopheles coluzzii sampled along an urban-to-rural gradient.MethodsThe lethal toxicity of three active ingredients for adults of two susceptible Anopheles strains was assessed using concentration–response assays, and their discriminating concentrations were calculated. The discriminating concentrations were then used to test the susceptibility of An. gambiae and An. coluzzii mosquitoes collected from urban, suburban and rural areas of Yaoundé, Cameroon, to acetamiprid, imidacloprid, clothianidin and thiamethoxam.ResultsLethal concentrations of neonicotinoids were relatively high suggesting that this class of insecticides has low toxicity against Anopheles mosquitoes. Reduced susceptibility to the four neonicotinoids tested was detected in An. gambiae populations collected from rural and suburban areas. By contrast, adults of An. coluzzii that occurred in urbanized settings were susceptible to neonicotinoids except acetamiprid for which 80% mortality was obtained within 72 h of insecticide exposure. The cytochrome inhibitor, piperonyl butoxide (PBO), significantly enhanced the activity of clothianidin and acetamiprid against An. gambiae mosquitoes.ConclusionsThese findings corroborate susceptibility profiles observed in larvae and highlight a significant variation in tolerance to neonicotinoids between An. gambiae and An. coluzzii populations from Yaoundé. Further studies are needed to disentangle the role of exposure to agricultural pesticides and of cross-resistance mechanisms in the development of neonicotinoid resistance in some Anopheles species.

A meta-analysis highlights the cross-resistance of plants to drought and salt stresses from physiological, biochemical, and growth levels.

In nature, drought and salt stresses often occur simultaneously and affect plant growth at multiple levels. However, the mechanisms underlying plant responses to drought and salt stresses and their interactions are still not fully understood. We performed a meta-analysis to compare the effects of drought, salt, and combined stresses on plant physiological, biochemical, morphological and growth traits, analyze the different responses of C3 and C4 plants, as well as halophytes and non-halophytes, and identify the interactive effects on plants. There were numerous similarities in plant responses to drought, salt, and combined stresses. C4 plants had a more effective antioxidant defense system, and could better maintain above-ground growth. Halophytes could better maintain photosynthetic rate (Pn) and relative water content (RWC), and reduce growth as an adaptation strategy. The responses of most traits (Pn, RWC, chlorophyll content, soluble sugar content, H2O2 content, plant dry weight, etc.) to combined stress were less-than-additive, indicating cross-resistance rather than cross-sensitivity of plants to drought and salt stresses. These results are important to improve our understanding of drought and salt cross-resistance mechanisms and further induce resistance or screen-resistant varieties under stress combination.

Anopheles gambiae larvae’s ability to grow and emerge in water containing lethal concentrations of clothianidin, acetamiprid, or imidacloprid is consistent with cross-resistance to neonicotinoids

BackgroundFor decades, various agrochemicals have been successfully repurposed for mosquito control. However, preexisting resistance caused in larval and adult populations by unintentional pesticide exposure or other cross-resistance mechanisms poses a challenge to the efficacy of this strategy. A better understanding of larval adaptation to the lethal and sublethal effects of residual pesticides in aquatic habitats would provide vital information for assessing the efficacy of repurposed agrochemicals against mosquitoes.MethodsWe reared field-collected mosquito larvae in water containing a concentration of agrochemical causing 100% mortality in susceptible mosquitoes after 24 h (lethal concentration). Using this experimental setup, we tested the effect of lethal concentrations of a pyrrole (chlorfenapyr, 0.10 mg/l), a pyrethroid (deltamethrin, 1.5 mg/l), and three neonicotinoids including imidacloprid (0.075 mg/l), acetamiprid (0.15 mg/l), and clothianidin (0.035 mg/l) on mortality rates, growth, and survival in third-instar larvae of the two sibling species Anopheles gambiae and Anopheles coluzzii collected from Yaoundé, Cameroon.ResultsWe found that An. gambiae and An. coluzzii larvae were susceptible to chlorfenapyr and were killed within 24 h by a nominal concentration of 0.10 mg/l. Consistent with strong resistance, deltamethrin induced low mortality in both species. Lethal concentrations of acetamiprid, imidacloprid, and clothianidin strongly inhibited survival, growth, and emergence in An. coluzzii larvae. By contrast, depending on the active ingredient and the population tested, 5–60% of immature stages of An. gambiae were able to grow and emerge in water containing a lethal concentration of neonicotinoids, suggesting cross-resistance to this class of insecticides.ConclusionsThese findings corroborate susceptibility profiles observed in adults and suggest that unintentional pesticide exposure or other cross-resistance processes could contribute to the development of resistance to neonicotinoids in some Anopheles populations.Graphical

Clothianidin-resistant Anopheles gambiae adult mosquitoes from Yaoundé, Cameroon, display reduced susceptibility to SumiShield® 50WG, a neonicotinoid formulation for indoor residual spraying

BackgroundChronic exposure of mosquito larvae to pesticide residues and cross-resistance mechanisms are major drivers of tolerance to insecticides used for vector control. This presents a concern for the efficacy of clothianidin, an agricultural neonicotinoid prequalified for Indoor Residual Spraying (IRS).MethodsUsing standard bioassays, we tested if reduced susceptibility to clothianidin can affect the efficacy of SumiShield® 50WG, one of four new IRS formulations containing clothianidin. We simultaneously monitored susceptibility to clothianidin and to SumiShield 50WG, testing adults of Anopheles gambiae, An. coluzzii and Culex sp sampled from urban, suburban and agricultural areas of Yaoundé, Cameroon.ResultsWe found that in this geographic area, the level of susceptibility to the active ingredient predicted the efficacy of SumiShield 50WG. This formulation was very potent against populations that reached 100% mortality within 72 h of exposure to a discriminating concentration of clothianidin. By contrast, mortality leveled off at 75.4 ± 3.5% within 7 days of exposure to SumiShield 50WG in An. gambiae adults collected from a farm where the spraying of the two neonicotinoids acetamiprid and imidacloprid for crop protection is likely driving resistance to clothianidin.ConclusionsDespite the relatively small geographic extend of the study, the findings suggest that cross-resistance may impact the efficacy of some new IRS formulations and that alternative compounds could be prioritized in areas where neonicotinoid resistance is emerging.

Metabolic Resistance Mechanisms Evident in Generations of Anopheles gambiae (Kisumu) Adults Exposed to Sub-lethal Concentrations of Permethrin Insecticide

Background: Anopheles gambiae mosquitoes are one of the best-known of the genus Anopheles because of their predominant role in transmitting the most dangerous malaria parasite species (to humans), Plasmodium falciparum. Unfortunately, An. gambiae mosquitoes have grown resistant to the most popular and widely used insecticides, particularly Permethrin, spreading across Africa. The current study sought to determine the lowest Permethrin concentrations that could be a selection pressure for metabolic resistance development in the renowned adult An. gambiae (Kisumu) mosquito population. Methods: Established, insectary-reared, and fully susceptible strains of Kisumu populations were reared, and exposed for mortality assay and Lowest Sub-lethal Concentrations (LSLCs) determination at the adult stage. Various exposure concentrations were achieved by slightly modifying the Centre for Disease Control (CDC) protocol. Adult Kisumu mosquitoes exposed to the same LSLC over generations were compared with unexposed control populations by way of resistance status and correlating levels of esterase, monooxygenase, and Glutathione-S -transferases (GST) metabolic enzymes. Information obtained was analysed using SPSS 16.0 and Analysis of Variance at P=0.05 with the aid of Graph-Pad prism 8. Results: The LSLCs of Permethrin with mortality rates not significantly (P> 0.05) different from control Kisumu strains (0.00) were 0.2μg (0.00) and 0.4μg (0.00) per CDC bottle, i.e., LSLC 1 and LSLC 2 respectively. The LSLC 1 exposure lasted five generations (f0-f4), during which resistance statuses were consistently below 1.00±0.82 (4.0%) after 1 hour. There was no significant difference (P>0.05) in the levels of esterase across generations, while monooxygenase and GST levels were significantly up-regulated (P<0.05) in subsequent generations of LSLC 1-treated mosquitoes. However, there was a consistent and progressive increase in GST level with advancing generations. Conclusion: It may be concluded that the P450 monooxygenase enzyme mechanism is a prelude to the overexpression of the GST enzyme. Hence, if the development of the GST resistance enzyme can be inhibited or stopped in An. gambiae mosquito vector populations, multiple resistance and cross-resistance mechanisms in malaria vectors could be effectively regulated.

Indoxacarb resistance in Iranian populations of Tuta absoluta (Lepidoptera: Gelechiidae): Cross-resistance, biochemical and molecular mechanisms

Tuta absoluta (Meyrick) is an invasive tomato pest that occurs worldwide, including Iran. This study investigates the occurrence of resistance to indoxacarb, an oxadiazine insecticide, and the underlying mechanisms in Iranian populations of T. absoluta. Bioassays were performed on second-instar larvae using indoxacarb alone and in combination with three synergists: Piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP). The activities of the main detoxification enzymes, including glutathione S-transferases (GST), general carboxylesterases (CarEs), and P450 monooxygenases (P450s), were evaluated. In addition, the presence of known amino acid substitutions in the IV segment 6 domain of the T. absoluta sodium channel was investigated. The results showed that resistance rates to indoxacarb in Iranian populations ranged from 2.37- to 14.45-fold. However, pretreatment with synergists did not significantly increase the toxicity of indoxacarb. Enzyme assays showed that Ardabil (Ar) and Kerman (Kr) populations had the highest CarEs activity, while Ar population showed the highest P450 activity. However, the observed increases in enzyme activities were <2-fold. Two indoxacarb resistance mutations, F1845Y and V1848I, were detected. Apart from a significant and positive correlation between LC50 values of indoxacarb and thiocyclam hydrogen oxalate, no cross-resistance between indoxacarb and other insecticides was detected. Overall, these results suggest that populations of T. absoluta in Iran have developed resistance to indoxacarb, primarily through changes at the target site.

Acaricide resistance in predatory mites of the genus Euseius (Acari: Phytoseiidae) and predation capacity on Brevipalpus yothersi (Acari: Tenuipalpidae)

One of the main citrus diseases in Brazil is citrus leprosis, transmitted by the mite Brevipalpus yothersi Baker (Acari: Tenuipalpidae). The predatory mites Euseius citrifolius Denmark & Muma and Euseius concordis (Chant) (Acari: Phytoseiidae) are important natural enemies for the pest mite. The objective of this work was to evaluate the susceptibility of different populations of E. concordis and E. citrifolius, from citrus groves in the state of São Paulo (SP), to the acaricides abamectin, fenpropathrin and chlorfenapyr; characterize the abamectin resistance in E. citrifolius, including studies on cross-resistance and biochemical mechanisms of resistance; and evaluate the predation capacity of an abamectin resistant population of E. citrifolius on B. yothersi. Significant differences in susceptibility to acaricides were observed among populations of E. citrifolius. Resistance ratios of 15.5 and 3.1 (times) were observed for abamectin and chlorfenapyr, respectively, comparing populations of E. citrifolius collected in the municipalities of Taquaral-SP and Bofete-SP. Studies with the synergist piperonyl butoxide indicated the involvement of cytochrome P450-dependent monooxygenases in the resistance of E. citrifolius to abamectin. Populations of E. concordis and E. citrifolius collected in Taquaral-SP showed low susceptibility to fenpropathrin, with LC50 values at least 95 times higher than the recommended concentration for the control of Brevipalpus mites in citrus in Brazil. The population of E. citrifolius from Taquaral showed a high capacity for predation of B. yothersi larvae, with consumption of up to 49.4 larvae per adult female per day.

A glimmer of hope - ash genotypes with increased resistance toash dieback pathogen show cross-resistance to emerald ash borer.

Plants rely on cross-resistance traits to defend against multiple, phylogenetically distinct enemies. These traits are often the result of long co-evolutionary histories. Biological invasions can force naïve plants to cope with novel, coincident pests, and pathogens. For example, European ash (Fraxinus excelsior) is substantially threatened by the emerald ash borer (EAB), Agrilus planipennis, a wood-boring beetle, and the ash dieback (ADB) pathogen, Hymenoscyphus fraxineus. Yet, plant cross-resistance traits against novel enemies are poorly explored and it is unknown whether naïve ash trees can defend against novel enemy complexes via cross-resistance mechanisms. To gain mechanistic insights, we quantified EAB performance on grafted replicates of ash genotypes varying in ADB resistance and characterized ash phloem chemistry with targeted and untargeted metabolomics. Emerald ash borer performed better on ADB-susceptible than on ADB-resistant genotypes. Moreover, changes in EAB performance aligned with differences in phloem chemical profiles between ADB-susceptible and ADB-resistant genotypes. We show that intraspecific variation in phloem chemistry in European ash can confer increased cross-resistance to invasive antagonists from different taxonomic kingdoms. Our study suggests that promotion of ADB-resistant ash genotypes may simultaneously help to control the ADB disease and reduce EAB-caused ash losses, which may be critical for the long-term stability of this keystone tree species.

Analysis of the binding modes and resistance mechanism of four methyl benzimidazole carbamates inhibitors fungicides with Monilinia fructicola β2-tubulin protein

Monilinia fructicola can infest plants during fruit flowering and during fruit storage and transportation, causing serious economic losses. The resistance problem of methyl benzimidazole carbamates inhibitors fungicide is becoming more and more prominent as the use time increases. By exploring the molecular binding mode, we studied the changes of the binding mode of the main amino acid residues between the four MBCs fungicides and the wild type and mutant Monilinia fructicoloa beta-tubulin protein constructed by homologous modeling. Constructing homology related models through sequence alignment based on sequence information from Monilinia fructicola beta-tubulin protein. Molecular docking and molecular dynamics simulations were then used to identify the optimum binding mode of benomyl, carbendazim, thiabendazole and thiophanate-methyl with Monilinia fructicola beta-tubulin protein. Furthermore, we calculated the binding free energy of four wild-type and mutant protein-ligand complexes using MM/PBSA. The result shows that when E198A was mutated, the hydrogen bonding force of thiophanate-methyl binding to the protein was reduced. The possible underlying cause of the resistance is the disappearance of the π-π stacking interaction with Phe200. When E198Q was mutated, all three fungicides, excluding carbendazim, interacted with Gln198 of the protein through hydrogen bonding. However, the binding pattern of carbendazim, thiophanate-methyl were least affected. When F200Y was mutated, the binding pocket of benomyl is slightly altered concerning the binding pattern between the wild-type protein and the fungicide concerning the amino acid residues. The resistance mechanism of M. fructicola beta-tubulin protein to MBCs fungicides and the mechanism of cross-resistance between MBCs fungicides were initially elucidated by computer simulation.

Overproduction of Efflux Pumps as a Mechanism of Metal and Antibiotic Cross-Resistance in the Natural Environment

Antibiotic and metal resistance can occur together in the environment and can be linked by the same detoxication mechanism (cross-resistance). The understanding of this linkage may be a key to further study of the spread of antibiotic resistance in the non-hospital environment worldwide. In our study, we examined the overproduction of efflux pumps as a possible mechanism of the cross-resistance of isolates originating from industrial and mine tailings. Resistance to metals (Cu, Ni, Zn and Pb) and antibiotics (ampicillin, chloramphenicol, tetracycline and kanamycin) was observed at all the sampling sites and ranged from 16 to 75%. Multiresistance (MAR index &gt; 0.38) was recorded in 26% of the isolates and was associated with the metal selective pressure duration. Overproduction of efflux pumps has mainly been observed in multiresistant isolates. Our results may indicate that the overproduction of efflux pumps could be the mechanism of cross-resistance between metals and therefore related to metal and antibiotic multiresistance. The results also show that the importance of sustainably storing metal-containing waste lies not only in its environmental impact but also in human health via antibiotic resistance proliferation.

Target and nontarget mechanisms of AHAS inhibitor cross-resistance patterns in Cyperus difformis

Weed resistance to acetohydroxyacid synthase (AHAS) inhibiting herbicides has been a critical issue for rice growers worldwide since the early 1990's. In California, resistance to bensulfuron-methyl was first detected in Cyperus difformis in 1993. Since then, populations of most major weeds of rice in California have been reported to show resistance to at least one AHAS inhibitor. We sought to describe the magnitude and mechanisms of AHAS inhibitor cross-resistance in California populations of C. difformis. Sixty-two populations were collected and screened for cross-resistance to bensulfuron-methyl (BEN), halosulfuron-methyl (HAL), bispyribac‑sodium (BIS), and penoxsulam (PEN), revealing six major patterns of cross-resistance. Representative C. difformis populations from each cross-resistance pattern were then subjected to dose-response, cytochrome P450 inhibition, AHAS gene sequencing, and metabolic studies with the same herbicides as in the screening. Dose-response confirmed the detected resistances in the representative populations, and suggested that the majority of observed resistance was dose-dependent. Cytochrome P450 inhibition via malathion revealed evidence of increased metabolic activity in resistant populations to BEN, BIS, and PEN. AHAS gene sequencing revealed amino acid substitutions in five of six populations: R3 (Pro197-Ser), R4 (Pro97-His), R10 (Asp376), R41 (Ala122-Asn), and R18 (Trp574-Leu). Metabolic studies confirmed evidence of increased activity of cytochrome P450s in all populations. Metabolic BEN and HAL analysis did not yield similar results to malathion inhibition, suggesting different P450's or other pathways. Taken together, the results of the studies confirm the complexity of AHAS inhibitor cross-resistance in C. difformis, and the presence of both target-site and metabolic resistance in most of the representative populations underscores the importance of proper herbicide selection, rotation, and scouting in fields.