Antibiotic Resistances of Clostridioides difficile

The rapid evolution of antibiotic resistance in Clostridioides difficile and the consequent effects on prevention and treatment of C. difficile infections (CDIs) are a matter of concern for public health. Antibiotic resistance plays an important role in driving C. difficile epidemiology. Emergence of new types is often associated with the emergence of new resistances, and most of the epidemic C. difficile clinical isolates is currently resistant to multiple antibiotics. In particular, it is to worth to note the recent identification of strains with reduced susceptibility to the first-line antibiotics for CDI treatment and/or for relapsing infections. Antibiotic resistance in C. difficile has a multifactorial nature. Acquisition of genetic elements and alterations of the antibiotic target sites, as well as other factors, such as variations in the metabolic pathways or biofilm production, contribute to the survival of this pathogen in the presence of antibiotics. Different transfer mechanisms facilitate the spread of mobile elements among C. difficile strains and between C. difficile and other species. Furthermore, data indicate that both genetic elements and alterations in the antibiotic targets can be maintained in C. difficile regardless of the burden imposed on fitness, and therefore resistances may persist in C. difficile population in absence of antibiotic selective pressure.

Molecular Biomarkers of Disease Outcomes and Mechanisms of Acquired Resistance to First-Line Osimertinib in Advanced EGFR-Mutant Lung Cancers

INTRODUCTION

Preferred first-line treatment for patients with metastatic EGFR-mutant lung cancer is osimertinib, yet it is not known whether patient outcomes may be improved by identifying and intervening on molecular markers associated with therapeutic resistance.

METHODS

All patients with metastatic EGFR-mutant lung cancer treated with first-line osimertinib at the Memorial Sloan Kettering Cancer Center (n = 327) were identified. Available pretreatment and postprogression tumor samples underwent targeted gene panel sequencing and mutational signature analysis using SigMA algorithm. Progression-free survival (PFS) and overall survival were estimated using the Kaplan-Meier method.

RESULTS

Using multivariate analysis, baseline atypical EGFR (median PFS = 5.8 mo, p < 0.001) and concurrent TP53/RB1 alterations (median PFS = 10.5 mo, p = 0.015) were associated with shorter PFS on first-line osimertinib. Of 95 patients with postprogression biopsies, acquired resistance mechanisms were identified in 52% (off-target, n = 24; histologic transformation, n = 14; on-target, n = 12), with MET amplification (n = 9), small cell lung transformation (n = 7), and acquired EGFR amplification (n = 7), the most frequently identified mechanisms. Although there was no difference in postprogression survival on the basis of identified resistance (p = 0.07), patients with subsequent second-line therapy tailored to postprogression biopsy results had improved postprogression survival (hazard ratio = 0.09, p = 0.006). The paired postprogression tumors had higher tumor mutational burden (p = 0.008) and further dominant APOBEC mutational signatures (p = 0.07) compared with the pretreatment samples.

CONCLUSIONS

Patients with EGFR-mutant lung cancer treated with first-line osimertinib have improved survival with treatment adaptation on the basis of identified mechanisms of resistance at time of progression using tissue-based genomic analysis. Further survival gains may be achieved using risk-based treatment adaptation of pretreatment genomic alterations.

Transmission of Staphylococcus aureus in the anaesthesia work area has greater risk of association with development of surgical site infection when resistant to the prophylactic antibiotic administered for surgery

BACKGROUND

The extent to which the transmission of prophylactic-antibiotic-resistant bacteria from the anaesthesia work area increases the risk of surgical site infection (SSI) is unknown. It was hypothesized that the risk of SSI would increase progressively from no transmission to transmission of prophylactic-antibiotic-resistant isolates.

METHODS

This was a retrospective analysis of archival samples collected in two previously published studies with similar inclusion criteria and sample collection methodology (observational study 2009-2010 and randomized trial 2018-2019). Archival isolates were linked by barcode to all patient demographic and procedural information, including the prophylactic antibiotic administered, transmission and development of SSI. For this study, all archival isolates underwent prophylactic antibiotic susceptibility testing, and the ordered association of transmission of Staphylococcus aureus (no transmission, transmission of prophylactic-antibiotic-susceptible isolates and transmission of prophylactic-antibiotic-resistant isolates) with SSI was assessed.

RESULTS

The risk of development of SSI was 2% (8/406) without S. aureus transmission, 11% (9/84) with transmission of S. aureus isolates that were susceptible to the prophylactic antibiotic used, and 18% (4/22) with transmission of prophylactic-antibiotic-resistant S. aureus isolates. The Cochrane-Armitage two-sided test for ordered association was P<0.0001. Treating these three groups as 0, 1 and 2, by exact logistic regression, the odds of SSI increased by 3.59 with each unit increase (95% confidence interval 1.92-6.64; P<0.0001).

CONCLUSIONS

Transmission of S. aureus in the anaesthesia work area reliably increases the risk of SSI, especially when the isolates are resistant to the prophylactic antibiotic administered.

Cluster of resistance-inducing genes in MCF-7 cells by estrogen, insulin, methotrexate and tamoxifen extracted via NMF

Breast cancer has become a leading cause of death for women as the economy has grown and the number of women in the labor force has increased. Several biomarkers with diagnostic, prognostic, and therapeutic implications for breast cancer have been identified in studies, leading to therapeutic advances. Resistance, on the other hand, is one of clinical practice's limitations. In this paper, we use Nonnegative Matrix Factorization to automatically extract two gene signatures from gene expression profiles of wild-type and resistance MCF-7 cells, which were then investigated further using pathways analysis and proved useful in relating resistance pathways to breast cancer regardless of the stimulus that caused it. A few extracted genes (including MAOA, IL4I1, RRM2, DUT, NME4, and SUMO3) represent new elements in the functional network for resistance in MCF-7 ER+ breast cancer. As a result of this research, a better understanding of how resistance occurs or the pathways that contribute to it may allow more effective therapies to be developed.

Scaffold-based three-dimensional cell model of pancreatic cancer is more suitable than scaffold-free three-dimensional cell model of pancreatic cancer for drug discovery

Pancreatic cancer is one of the deadliest malignancies. Three-dimensional (3D) pancreatic cancer cell models for drug screening have been established to improve treatment for pancreatic cancer. However, few studies focus on different drug responses and drug-related molecular mechanisms in various types of 3D cell models. In this study, we constructed 3D scaffold-free cell models and 3D scaffold-based cell models of pancreatic cancer, evaluated chemotherapeutic drug responses in different 3D models, assessed clinical relevance of the models, and investigated molecular mechanisms of chemoresistance and drug pathways in different 3D models. Both types of 3D models showed resistance to chemotherapeutic drugs, and scaffold-based pancreatic cancer models could better reflect in vivo drug efficacy than 2D and scaffold-free pancreatic cancer models did. Increased cell adhesion, extracellular matrix (ECM) synthesis and drug transport were essential for drug resistance in 3D models, and anti-apoptosis might contribute to extreme chemoresistance in scaffold-free models. Moreover, scaffold-based pancreatic cancer models were more suitable than scaffold-free models for drug pathway research.

Conversion from Positive to Negative EGFR Mutation due to Clonal Selection during Long-Term Treatment with Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitors: A Case Report

A 77-year-old woman with postoperative recurrent non-small cell lung adenocarcinoma, which exhibited an epidermal growth factor receptor (EGFR) L858R mutation, was treated with gefitinib and erlotinib. Seven years after the start of treatment, the patient experienced a recurrence of malignant pleural effusion. However, 3 different genetic tests revealed that the lung adenocarcinoma cells in the pleural effusion had lost EGFR L858R mutation, suggesting that long-term treatment with EGFR-tyrosine kinase inhibitors (TKIs) converted EGFR mutation from positive to negative. The negative conversion of EGFR mutation as a mechanism of acquired resistance to EGFR-TKIs is considered rare and needs to be further investigated.

Resistance response to Arenicin derivatives in Escherichia coli

The rising prevalence of antibiotic resistance poses the greatest health threats. Antimicrobial peptides (AMPs) are regarded as the potentially effective therapy. To avoid current crisis of antibiotic resistance, a comprehensive understanding of AMP resistance is necessary before clinical application. In this study, the development of resistance to the anti-Gram-negative bacteria peptide N6NH₂ (21 residues, β-sheet) was characterized in E. coli ATCC25922. Three N6NH₂-resistant E. coli mutants with 32-fold increase in MIC were isolated by serially passaging bacterial lineages in progressively increasing concentrations of N6NH₂ and we mainly focus on the phenotype of N6NH₂-resistant bacteria different from sensitive bacteria. The results showed that the resistance mechanism was attributed to synergy effect of multiple mechanisms: (i) increase biofilm formation capacity (3 ~ 4-fold); (ii) weaken the affinity of lipopolysaccharide (LPS) with N6NH₂ (3 ~ 8-fold); and (iii) change the cell membrane permeability and potential. Interestingly, a chimeric peptide-G6, also a N6NH₂ analog, which keep the same antibacterial activity to both wild-type and resistant clones (MIC value: 16 μg/mL), could curb N6NH₂-resistant mutants by stronger inhibition of biofilm formation, stronger affinity with LPS, and stronger membrane permeability and depolarization than that of N6NH₂.

Endocrine resistance in breast cancer: from molecular mechanisms to therapeutic strategies

Estrogen receptor-positive (ER +) breast cancer accounts for approximately 75% of all breast cancers. Endocrine therapies, including selective ER modulators (SERMs), aromatase inhibitors (AIs), and selective ER down-regulators (SERDs) provide substantial clinical benefit by reducing the risk of disease recurrence and mortality. However, resistance to endocrine therapies represents a major challenge, limiting the success of ER + breast cancer treatment. Mechanisms of endocrine resistance involve alterations in ER signaling via modulation of ER (e.g., ER downregulation, ESR1 mutations or fusions); alterations in ER coactivators/corepressors, transcription factors (TFs), nuclear receptors and epigenetic modulators; regulation of signaling pathways; modulation of cell cycle regulators; stress signaling; and alterations in tumor microenvironment, nutrient stress, and metabolic regulation. Current therapeutic strategies to improve outcome of endocrine-resistant patients in clinics include inhibitors against mechanistic target of rapamycin (mTOR), cyclin-dependent kinase (CDK) 4/6, and the phosphoinositide 3-kinase (PI3K) subunit, p110α. Preclinical studies reveal novel therapeutic targets, some of which are currently tested in clinical trials as single agents or in combination with endocrine therapies, such as ER partial agonists, ER proteolysis targeting chimeras (PROTACs), next-generation SERDs, AKT inhibitors, epidermal growth factor receptor 1 and 2 (EGFR/HER2) dual inhibitors, HER2 targeting antibody-drug conjugates (ADCs) and histone deacetylase (HDAC) inhibitors. In this review, we summarize the established and emerging mechanisms of endocrine resistance, alterations during metastatic recurrence, and discuss the approved therapies and ongoing clinical trials testing the combination of novel targeted therapies with endocrine therapy in endocrine-resistant ER + breast cancer patients.

Molecular Pathology of Breast Tumors: Diagnostic and Actionable Genetic Alterations

Breast cancer is a heterogenous disease with various histologic subtypes, molecular profiles, behaviors, and response to therapy. After the histologic assessment and diagnosis of an invasive breast carcinoma, the use of biomarkers, multigene expression assays and mutation profiling may be used. With improved molecular assays, the identification of somatic genetic alterations in key oncogenes and tumor suppressor genes are playing an increasingly important role in many areas of breast cancer care. This review summarizes the most clinically significant somatic alterations in breast tumors and how this information is used to facilitate diagnosis, provide potential treatment options, and identify mechanisms of resistance.

Current Status of CAR T Cell Therapy for Leukemias

OPINION STATEMENT

Chimeric antigen receptor (CAR) T-cell therapy has become the standard of care for children and young adults with relapsed and refractory B-cell acute lymphoblastic leukemia (B-ALL), and it is a highly promising therapy under investigation for adults with relapsed disease. Despite having potentially life-threatening toxicities, such as cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome, the benefits of CAR T-cell therapy far outweigh these risks, particularly as increased experience and improved supportive care measures are mitigating these toxicities. CAR T cells can result in complete remission for significant proportion of patients with relapsed and refractory B-ALL and permit them to proceed to potentially curative allogeneic hematopoietic stem cell transplantation (allo-HSCT). CAR T cells may also be curative by themselves. Herein lie the greatest challenges and questions for clinical investigators, specifically, how are CAR T cells best employed and how do we overcome mechanisms of resistance to them? The primary clinical question is the timing and even the necessity of allo-HSCT. Relative to resistance, we know that target antigen loss, specifically CD19, is a major contributor to resistance. However, current investigations of alternative targets, such CD22, and CAR T cells expressing dual targeting antigen receptors have demonstrated encouraging initial results and provide a high degree of optimism that the efficacy and the broader application of CAR T-cell therapy will gradually increase in B-ALL. That optimism is not as high and the challenges are increased for the application of CAR T cells in T-cell leukemias and acute myeloid leukemia due to the relative lack of suitable leukemia surface targets that are not also expressed on normal hematopoietic progenitors. Despite these significant challenges, considerable research is being conducted into the development of CAR T cells for these diseases utilizing unique technologies, which may be applicable to other diseases.

Treatment of Chronic Lymphocytic Leukemia After Discontinuation of Bruton's Tyrosine Kinase Inhibitors

The Bruton's tyrosine kinase inhibitors (BTKis) ibrutinib and acalabrutinib have led to durable responses for patients with both treatment-naïve and relapsed/refractory chronic lymphocytic leukemia (CLL). Many patients, however, ultimately discontinue BTKis due to toxicity or progressive CLL. This article reviews the two most common reasons for ibrutinib and acalabrutinib discontinuation, including adverse events as well as CLL progression. The data for specific CLL-directed therapies following BTKi discontinuation, including venetoclax, phosphatidylinositol 3-kinase inhibitors, cellular therapies, and ongoing clinical trials, are reviewed. An evidence-based sequencing algorithm for treatment of CLL following BTKi discontinuation is proposed.

Multiple insecticide resistance in Aedes aegypti (Diptera: Culicidae) from Boyeros municipality, Cuba and associated mechanisms

In this study, insecticide resistance and the mechanisms responsible were characterized in Ae. aegypti of Boyeros municipality from Havana, Cuba. Boyeros represents a high epidemiological risk because it is located near the Havana International Airport, it is highly urbanized, and it has a large influx of people from endemic countries so that it qualifies as a sentinel site for surveillance. The larvae collected from five areas of this municipality showed resistance to temephos associated with metabolic enzymes. The adult mosquitoes displayed a deltamethrin resistance and less distinctly to other pyrethroids associated with a high frequency of sodium channel gene mutations (F1534C and V1016I), detected for the first time in a field population from Cuba. The presence in the field populations of two insecticide resistance mechanisms represents a limiting factor in the success of the control operations of this vector, so other strategies should be considered to preserve the effectiveness of the insecticides available in public health for vector control in Cuba.

Resistance in Vancomycin-Resistant Enterococci

Serious infections owing to vancomycin-resistant enterococci have historically proven to be difficult clinical cases, requiring combination therapy and management of treatment-related toxicity. Despite the introduction of new antibiotics with activity against vancomycin-resistant enterococci to the therapeutic armamentarium, significant challenges remain. An understanding of the factors driving the emergence of resistance in vancomycin-resistant enterococci, the dynamics of gastrointestinal colonization and microbiota-mediated colonization resistance, and the mechanisms of resistance to the currently available therapeutics will permit clinicians to be better prepared to tackle these challenging hospital-associated pathogens.

[Immunotherapy of metastatic non-small cell lung cancer from first line to resistance and its management]

Immunotherapy alone or in combination with chemotherapy is now an integral part of the treatment of metastatic NSCLC. This treatment is transforming the management of these cancers, with 20-30% of patients achieving long survival. However, disease progression under treatment is still the rule for the majority of patients, raising problems both in understanding its mechanisms and in subsequent appropriate management. This study examines current therapeutic options and proposes solutions to circumvent resistance to immunotherapy. The mechanisms of resistance to these treatments is also analysed.

Drug resistance in liver flukes

Liver flukes include Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis spp., Fascioloides magna, Gigantocotyle explanatum and Dicrocoelium spp. The two main species, F. hepatica and F. gigantica, are major parasites of livestock and infections result in huge economic losses. As with C. sinensis, Opisthorchis spp. and Dicrocoelium spp., they affect millions of people worldwide, causing severe health problems. Collectively, the group is referred to as the Food-Borne Trematodes and their true significance is now being more widely recognised. However, reports of resistance to triclabendazole (TCBZ), the most widely used anti-Fasciola drug, and to other current drugs are increasing. This is a worrying scenario. In this review, progress in understanding the mechanism(s) of resistance to TCBZ is discussed, focusing on tubulin mutations, altered drug uptake and changes in drug metabolism. There is much interest in the development of new drugs and drug combinations, the re-purposing of non-flukicidal drugs, and the development of new drug formulations and delivery systems; all this work will be reviewed. Sound farm management practices also need to be put in place, with effective treatment programmes, so that drugs can be used wisely and their efficacy conserved as much as is possible. This depends on reliable advice being given by veterinarians and other advisors. Accurate diagnosis and identification of drug-resistant fluke populations is central to effective control: to determine the actual extent of the problem and to determine how well or otherwise a treatment has worked; for research on establishing the mechanism of resistance (and identifying molecular markers of resistance); for informing treatment options; and for testing the efficacy of new drug candidates. Several diagnostic methods are available, but there are no recommended guidelines or standardised protocols in place and this is an issue that needs to be addressed.

Mechanisms of resistance to mTOR inhibitors

In several tumors the PI3K/AKT/mTOR pathway is frequently disrupted, an event that results in uncontrolled cell proliferation and tumor growth. Through the years, several compounds have been developed to inhibit the pathway at different steps: the mammalian target of rapamycin (mTOR) seemed to be the most qualified target. However, this kinase has such a key role in cell survival that mechanisms of resistance are rapidly developed. Nevertheless, clinical results obtained with mTOR inhibitors in breast cancer, renal cell carcinoma, neuroendocrine tumors and mantle cell lymphoma push oncologists to actively further develop these drugs, maybe by better selecting the population to which they are offered, through the research of predictive factors of responsiveness. In this review, we aim to describe mechanisms of resistance to mTOR inhibitors, from preclinical and clinical perspectives.

Drug resistance of BRAF-mutant melanoma: Review of up-to-date mechanisms of action and promising targeted agents

Melanoma onset and progression are associated with a high variety of activating mutations in the MAPK-pathway, most frequently involving BRAF (35-45%) and NRAS (15-25%) genes, but also c-KIT and PTEN. Targeted therapies with BRAF and MEK inhibitors showed promising results over the past years, but it is known that most responses are temporary, and almost all of patients develop a tumor relapse within one year. Different drug-resistance mechanisms underlie the progression of disease and activation of both MAPK and PI3K/AKT/mTOR pathways. Therefore, in this article we reviewed the main studies about clinical effects of several target inhibitors, describing properly the most prominent mechanisms of both intrinsic and acquired resistance. Furthermore, suggestive strategies for overcoming drug resistance and the most recent alternative combination therapies to optimize the use of MAPK pathway inhibitors were also discussed.

Treg-mediated acquired resistance to immune checkpoint inhibitors

T Regulatory cells (Tregs) act as a double-edged sword by regulating immune homeostasis (protective role) and inhibiting immune responses in different disease settings (pathological role). They contribute to cancer development and progression by suppressing T effector cell (Teff) functions. Decreased ratios of intratumoral CD8⁺ T cells to Tregs have been associated with poor prognosis in most cancer types. Targeting immune checkpoints (ICs), such as cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and programmed cell death-1 (PD-1), by immune checkpoint inhibitors (ICIs) in cancer patients has been beneficial in inducing anti-tumor immune responses and improving clinical outcomes. However, response rates remain relatively low, ranging from 15 to 40% depending on cancer type. Additionally, a significant proportion of patients who initially demonstrates a clinical response can acquire resistance overtime. This acquired resistance could occur due to the emergence of compensatory mechanisms within the tumor microenvironment (TME) to evade the anti-tumor effects of ICIs. In this review, we describe the immunosuppressive role of Tregs in the TME, the effects of currently approved ICIs on Treg phenotype and function, and the mechanisms of acquired resistance to ICIs mediated by Tregs within the TME, such as the over-expression of ICs, the up-regulation of immunosuppressive molecules, and apoptotic Treg-induced immunosuppression. We also describe potential therapeutic strategies to target Tregs in combination with ICIs aiming to overcome such resistance and improve clinical outcomes. Elucidating the Treg-mediated acquired resistance mechanisms should benefit the designing of well-targeted therapeutic strategies to overcome resistance and maximize the therapeutic efficacy in cancer patients.

Treg-mediated acquired resistance to immune checkpoint inhibitors

T Regulatory cells (Tregs) act as a double-edged sword by regulating immune homeostasis (protective role) and inhibiting immune responses in different disease settings (pathological role). They contribute to cancer development and progression by suppressing T effector cell (Teff) functions. Decreased ratios of intratumoral CD8⁺ T cells to Tregs have been associated with poor prognosis in most cancer types. Targeting immune checkpoints (ICs), such as cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and programmed cell death-1 (PD-1), by immune checkpoint inhibitors (ICIs) in cancer patients has been beneficial in inducing anti-tumor immune responses and improving clinical outcomes. However, response rates remain relatively low, ranging from 15 to 40% depending on cancer type. Additionally, a significant proportion of patients who initially demonstrates a clinical response can acquire resistance overtime. This acquired resistance could occur due to the emergence of compensatory mechanisms within the tumor microenvironment (TME) to evade the anti-tumor effects of ICIs. In this review, we describe the immunosuppressive role of Tregs in the TME, the effects of currently approved ICIs on Treg phenotype and function, and the mechanisms of acquired resistance to ICIs mediated by Tregs within the TME, such as the over-expression of ICs, the up-regulation of immunosuppressive molecules, and apoptotic Treg-induced immunosuppression. We also describe potential therapeutic strategies to target Tregs in combination with ICIs aiming to overcome such resistance and improve clinical outcomes. Elucidating the Treg-mediated acquired resistance mechanisms should benefit the designing of well-targeted therapeutic strategies to overcome resistance and maximize the therapeutic efficacy in cancer patients.

An interim report on the investigator-initiated phase 2 study of pembrolizumab immunological response evaluation (INSPIRE)

Background

Immune checkpoint inhibitors (ICIs) demonstrate unprecedented efficacy in multiple malignancies; however, the mechanisms of sensitivity and resistance are poorly understood and predictive biomarkers are scarce. INSPIRE is a phase 2 basket study to evaluate the genomic and immune landscapes of peripheral blood and tumors following pembrolizumab treatment.

Methods

Patients with incurable, locally advanced or metastatic solid tumors that have progressed on standard therapy, or for whom no standard therapy exists or standard therapy was not deemed appropriate, received 200 mg pembrolizumab intravenously every three weeks. Blood and tissue samples were collected at baseline, during treatment, and at progression. One core biopsy was used for immunohistochemistry and the remaining cores were pooled and divided for genomic and immune analyses. Univariable analysis of clinical, genomic, and immunophenotyping parameters was conducted to evaluate associations with treatment response in this exploratory analysis.

Results

Eighty patients were enrolled from March 21, 2016 to June 1, 2017, and 129 tumor and 382 blood samples were collected. Immune biomarkers were significantly different between the blood and tissue. T cell PD-1 was blocked (≥98%) in the blood of all patients by the third week of treatment. In the tumor, 5/11 (45%) and 11/14 (79%) patients had T cell surface PD-1 occupance at weeks six and nine, respectively. The proportion of genome copy number alterations and abundance of intratumoral 4-1BB+ PD-1+ CD8 T cells at baseline (P < 0.05), and fold-expansion of intratumoral CD8 T cells from baseline to cycle 2–3 (P < 0.05) were associated with treatment response.

Conclusion

This study provides technical feasibility data for correlative studies. Tissue biopsies provide distinct data from the blood and may predict response to pembrolizumab.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0541-0) contains supplementary material, which is available to authorized users.

Antibiotic Resistances of Clostridium difficile

The rapid evolution of antibiotic resistance in Clostridium difficile and the consequent effects on prevention and treatment of C. difficile infections (CDIs) are matter of concern for public health. Antibiotic resistance plays an important role in driving C. difficile epidemiology. Emergence of new types is often associated with the emergence of new resistances and most of epidemic C. difficile clinical isolates is currently resistant to multiple antibiotics. In particular, it is to worth to note the recent identification of strains with reduced susceptibility to the first-line antibiotics for CDI treatment and/or for relapsing infections. Antibiotic resistance in C. difficile has a multifactorial nature. Acquisition of genetic elements and alterations of the antibiotic target sites, as well as other factors, such as variations in the metabolic pathways and biofilm production, contribute to the survival of this pathogen in the presence of antibiotics. Different transfer mechanisms facilitate the spread of mobile elements among C. difficile strains and between C. difficile and other species. Furthermore, recent data indicate that both genetic elements and alterations in the antibiotic targets can be maintained in C. difficile regardless of the burden imposed on fitness, and therefore resistances may persist in C. difficile population in absence of antibiotic selective pressure.

Two novel house fly Vssc mutations, D600N and T929I, give rise to new insecticide resistance alleles

The house fly, Musca domestica, is a serious pest because it transmits a large diversity of human and veterinary diseases. Insecticides, particularly pyrethroids, are commonly used to control house flies. However, the evolution of pyrethroid resistance has reduced the effectiveness of these insecticides. A major mechanism of resistance to pyrethroids is target site insensitivity caused by the mutations in the voltage-sensitive sodium channel (Vssc) gene (e.g. kdr [L1014F] and super-kdr [M918T+L1014F]). Recently, two novel Vssc alleles, super-kdr+D600N and kdr+T929I were detected in a field collected resistant house fly population in Kansas, USA in 2013. To determine the levels of resistance that these new alleles confer to pyrethroids, we isolated strains having the unique Vssc alleles, but being otherwise congenic to the susceptible strain, aabys. We compared levels of resistance conferred to 14 pyrethroids and determined the inheritance of resistance to 8 pyrethroids. Our results revealed that super-kdr+D600N conferred higher levels of resistance to seven pyrethroids relative to super-kdr, and kdr+T929I showed super-kdr-like levels of resistance in house flies. Our results are compared with previous studies and reveal that addition of T929I to the kdr mutation (L1014F) increased resistance to all pyrethroids (except etofenprox), and enhanced resistance by ~1000-fold to acrinathrin and flumethrin. The implications of these results on the evolution of resistance are discussed.

Virulence factors, antifungal susceptibility and molecular mechanisms of azole resistance among Candida parapsilosis complex isolates recovered from clinical specimens

Background

The aim of this study was to determine the biofilm formation, the extracellular enzymatic activities of 182 clinical isolates of the Candida parapsilosis complex.

Methods

Molecular identification of the C. parapsilosis species complex was performed using PCR RFLP of SADH gene and PCR sequencing of ITS region. The susceptibility of ours isolates to antifungal agents and molecular mechanisms underlying azole resistance were evaluated.

Results

63.5% of C. parapsilosis were phospholipase positive with moderate activity for the majority of strains. None of the C. metapsilosis or C. orthopsilosis isolates was able to produce phospholipase. Higher caseinase activities were detected in C. parapsilosis (Pz = 0.5 ± 0.18) and C. orthopsilosis (Pz = 0.49 ± 0.07) than in C. metapsilosis isolates (Pz = 0.72 ± 0.1). 96.5% of C. parapsilosis strains and all isolates of C. metapsilosis and C. orthopsilosis produced gelatinase. All the strains possessed the ability to show haemolysis on blood agar. C. metapsilosis exhibited the low haemolysin production with statistical significant differences compared to C. parapsilosis and C. orthopsilosis. The biofilm forming ability of C. parapsilosis was highly strain dependent with important heterogeneity, which was less evident with both C. orthopsilosis and C. metapsilosis.

Some C. parapsilosis isolates met the criterion for susceptible dose dependent to fluconazole (10.91%), itraconazole (16.36%) and voriconazole (7.27%). Moreover, 5.45% and 1.82% of C. parapsilosis isolates were respectively resistant to fluconazole and voriconazole. All strains of C. metapsilosis and C. orthopsilosis were susceptible to azoles; and isolates of all three species exhibited 100% of susceptibility to caspofungin, amphotericin B and 5-flucytosine.

Conclusions

A combination of molecular mechanisms, including the overexpression of ERG11, and genes encoding efflux pumps (CDR1, MDR1, and MRR1) were involved in azole resistance in C. parapsilosis.

Genetic markers associated with resistance to beta-lactam and quinolone antimicrobials in non-typhoidal Salmonella isolates from humans and animals in central Ethiopia

Background

Beta-lactam and quinolone antimicrobials are commonly used for treatment of infections caused by non-typhoidal Salmonella (NTS) and other pathogens. Resistance to these classes of antimicrobials has increased significantly in the recent years. However, little is known on the genetic basis of resistance to these drugs in Salmonella isolates from Ethiopia.

Methods

Salmonella isolates with reduced susceptibility to beta-lactams (n = 43) were tested for genes encoding for beta-lactamase enzymes, and those resistant to quinolones (n = 29) for mutations in the quinolone resistance determining region (QRDR) as well as plasmid mediated quinolone resistance (PMQR) genes using PCR and sequencing.

Results

Beta-lactamase genes (bla) were detected in 34 (79.1%) of the isolates. The dominant bla gene was blaTEM, recovered from 33 (76.7%) of the isolates, majority being TEM-1 (24, 72.7%) followed by TEM-57, (10, 30.3%). The blaOXA-10 and blaCTX-M-15 were detected only in a single S. Concord human isolate. Double substitutions in gyrA (Ser83-Phe + Asp87-Gly) as well as parC (Thr57-Ser + Ser80-Ile) subunits of the quinolone resistance determining region (QRDR) were detected in all S. Kentucky isolates with high level resistance to both nalidixic acid and ciprofloxacin. Single amino acid substitutions, Ser83-Phe (n = 4) and Ser83-Tyr (n = 1) were also detected in the gyrA gene. An isolate of S. Miami susceptible to nalidixic acid but intermediately resistant to ciprofloxacin had Thr57-Ser and an additional novel mutation (Tyr83-Phe) in the parC gene. Plasmid mediated quinolone resistance (PMQR) genes investigated were not detected in any of the isolates. In some isolates with decreased susceptibility to ciprofloxacin and/or nalidixic acid, no mutations in QRDR or PMQR genes were detected. Over half of the quinolone resistant isolates in the current study 17 (58.6%) were also resistant to at least one of the beta-lactam antimicrobials.

Conclusion

Acquisition of blaTEM was the principal beta-lactamase resistance mechanism and mutations within QRDR of gyrA and parC were the primary mechanism for resistance to quinolones. Further study on extended spectrum beta-lactamase and quinolone resistance mechanisms in other gram negative pathogens is recommended.

Raoultella spp.-clinical significance, infections and susceptibility to antibiotics

The genus Raoultella belongs to the family of Enterobacteriaceae. Raoultella spp. are Gram-negative, aerobic, non-motile rods. This genus can be distinguished from the genus Klebsiella, in that genus use histamine as the only source of carbon in the medium. Also, Raoultella grow at 4 °C and do not produce gas from lactose at 44.5 °C. Raoultella sp. is known to inhabit natural environments (water, soil, plants). The reservoir of Raoultella is the gastrointestinal tract and upper respiratory tract. Raoultella spp. are opportunistic bacteria, which usually cause infections of the biliary tract, pneumonia and bacteraemia in oncologic and with lower immunity patients. Raoultella planticola and Raoultella ornithinolytica are the most frequently encountered human pathogens among the genus Raoultella. In this review, the current knowledge on Raoultella infections is summarized.

Understanding and overcoming the mechanisms of primary and acquired resistance to abiraterone and enzalutamide in castration resistant prostate cancer

In recent years, in castration resistant prostate cancer (CRPC), several new drugs have been approved that prolong overall survival, including enzalutamide and abiraterone, two new-generation hormonal therapies. Despite the demonstrated benefit of these agents, not all patients with CRPC are responsive to treatment, the gain in median progression-free survival with these therapies compared to standard of care is, rather disappointingly, still less than six months and the appearance of acquired resistance is almost universal. Approximately one third of patients treated with abiraterone and 25% of those treated with enzalutamide show primary resistance to these agents. Even if the mechanisms of resistance to these agents are not fully defined, many hypotheses are emerging, including systemic and intratumoral androgen biosynthesis up-regulation, androgen receptor (AR) gene mutations and amplifications, alteration of pathways involved in cross-talk with AR signaling, glucocorticoid receptor overexpression, neuroendocrine differentiation, immune system deregulation and others. The aim of this paper is to review currently available data about mechanisms of resistance to abiraterone and enzalutamide, and to discuss how these mechanisms could be potentially overcome through novel therapeutic agents.

Pyrethroid resistance in Culex pipiens mosquitoes

Mosquitoes within the Culex pipiens complex are widely distributed and important in the transmission of many human diseases. Insecticides, pyrethroids in particular, remain a mainstay for control of these important vectors. In this paper we review what is known about the levels, mechanisms and fitness costs of pyrethroid resistance in Cx. pipiens. Pyrethroid resistance in Cx. pipiens is a global problem, and resistance ratios of up to 7000-fold have been found in larvae of field collected mosquitoes. However, there is considerable variation between populations, indicating significant geographic heterogeneity of the resistance. The two major mechanisms of resistance to pyrethroids in Culex are mutations in Vssc (target site insensitivity) and overexpression of cytochrome P450(s) (increased detoxification). The most frequently reported Vssc mutation is L1014F (i.e. kdr), which has been found throughout the world. The L1014S mutation has been found in Cx. p. pallens from Japan and China, and in Cx. p. pipiens from China. The L1014C mutation has only been reported for Cx. p. pipens molestus from China and the V1016G mutation has only been reported from Saudi Arabia. Studies on the P450s of Cx. pipiens have identified several that are overexpressed (measured as transcript levels) in pyrethroid resistant strains. CYP9M10 is consistently overexpressed in pyrethroid resistant Cx. pipiens from at least seven countries, suggesting this P450 might be of global importance in resistance. Both CYP9M10-mediated pyrethroid resistance and kdr have fitness costs in the absence of insecticides under certain environmental conditions. Research needs and future directions are discussed.

Antimicrobial susceptibility of Salmonella isolates from healthy pigs and chickens (2008-2011)

Using the agar dilution method, antimicrobial susceptibility to human-use antibiotics was determined among Belgian faecal Salmonella isolates from healthy pigs and broiler chickens. Both epidemiological cut-off values and clinical breakpoints were applied for interpretation of the results. Cephalosporin-resistant isolates were examined for the presence of genes encoding CTX-M, SHV, TEM and CMY β-lactamases. All isolates with decreased quinolone susceptibility were screened for plasmid-borne genes qnr, qepA and aac(6')-Ib-cr. In all, 368 Salmonella isolates were recovered from pigs and 452 from chickens. Clinical resistance to ciprofloxacin was absent in isolates of both host species, and was 1.9 and 13.1% to cefotaxime in pig and poultry isolates, respectively. Decreased susceptibility to cefotaxime amounted to 2.2 and 0.7%, whereas for ciprofloxacin this was 3.0 and 23.0% in pig and poultry isolates, respectively. Ciprofloxacin decreased susceptibility was limited to few serovars, mainly Paratyphi B. Multidrug resistance was markedly higher for pig isolates (39.7%) than for chicken isolates (17.3%). Sixty-six cefotaxime-resistant isolates, 59 from chickens and 7 from pigs, were phenotypically determined as ESBL/AmpC producers; predominantly Paratyphi B and Typhimurium serovars. BlaCTX-M (mostly blaCTXM-1, but also blaCTXM-2 and blaCTXM-9) and blaTEM-52 were the predominant ESBL genes. Only few isolates expressed SHV-12 or an AmpC enzyme (CMY-2). Isolates of four serovars carried qnr genes: Brandenburg and Llandof from pigs, both qnrS; Indiana and Paratyphi B from chickens with qnrB and qnrA. The latter isolate carried blaCTX-M-9 and was the only strain with a plasmid-borne quinolone resistance gene among the ESBL/AmpC producers. This Salmonella survey confirms that the ESBL/AmpC producers are particularly prevalent in chickens (12.8%), and much less in pigs (1.9%). A link between plasmid-borne quinolone resistance genes and ESBLs/AmpC was uncommon.