Constitutive Resistance Research Articles

Detection of inducible and constitutive clindamycin resistance among Staphylococcus aureus isolates in a tertiary care hospital, Eastern India.

Introduction:Clindamycin is an excellent drug for skin and soft tissue Staphylococcus aureus infections, but resistance mediated by inducible macrolide-lincosamide-streptogramin B (iMLSB) phenotype leads to in vivo therapeutic failure even though they may be in vitro susceptible in Kirby–Bauer disk diffusion method.Objective:The study was aimed to detect the prevalence of iMLSB phenotype among S. aureus isolates by double disk approximation test (D-test) in a tertiary care hospital, Eastern India.Materials and Methods:A total of 209 consecutive S. aureus isolates were identified by conventional methods and subjected to antimicrobial susceptibility testing by Kirby–Bauer disk diffusion method. Erythromycin-resistant isolates were tested for D-test.Results:From 1282 clinical specimens, 209 nonrepeated S. aureus isolates were obtained. Majority of isolates 129 (61.7%) were methicillin-resistant S. aureus (MRSA). There was statistically significant difference between outpatients 60.1% and inpatients 39.9% (P < 0.0001). From 209 S. aureus isolates, 46 (22%) were D-test positive (iMLSB phenotype), 41 (19.6%) were D-test negative (methicillin sensitive [MS] phenotype), and 37 (17.7%) were constitutively resistant (constitutive macrolide-lincosamide-streptogramin B phenotype). The incidence of inducible, constitutive, and MS phenotype was higher in MRSA isolates compared to MS S. aureus (MSSA). The constitutive clindamycin resistance difference between MSSA and MRSA isolates were found to be statistically significant (P = 0.0086).Conclusion:The study revealed 22% of S. aureus isolates were inducible clindamycin resistant, which could be easily misidentified as clindamycin susceptible in Kirby–Bauer disk diffusion method. Therefore, clinical microbiology laboratory should routinely perform D-test in all clinically isolated S. aureus to guide clinicians for the appropriate use of clindamycin.

Antibiotic Resistance Patterns and Related Mobile Genetic Elements of Pneumococci and β-Hemolytic Streptococci in Thai Healthy Children.

Transmission of antibiotic resistance genes among Streptococcus pneumoniae and beta-hemolytic streptococcus (BHS) was generally associated with transmissible genetic elements. The objectives of this study were to investigate carriage rate, antibiotic resistance and related mobile genetic elements of pneumococci and BHS from school-children. The pneumococci and BHS were recovered from 220 Thai school-children, and then tested for antibiotic susceptibility pattern by disc diffusion. Antibiotic resistance genes and related genetic elements were detected by PCR with specific primers. A total of 77 pneumococcal isolates were resistant to erythromycin (42%), tetracycline (44%), clindamycin (8%), or penicillin (3%). Fifty-four BHS isolates were resistant to erythromycin (28%), tetracycline (52%), or clindamycin (13%). All isolates tested were 100% sensitive to penicillin and levofloxacin. Among erythromycin-resistant streptococcal isolates showed different phenotypes of clindamycin resistance. It was found that isolated pneumococci showed constitutive clindamycin resistance (19%), and inducible clindamycin resistance (12%). The BHS isolates exhibited constitutive clindamycin resistance (40%), and inducible resistance (20%) phenotypes. The predominant erythromycin resistance genes in pneumococci and BHS were mefE and ermB, while the most common tetracycline resistance gene in this population was tetM. Furthermore, almost all erythromycin- and tetracycline-resistant streptococci (97%) mainly contained various genetic elements, including mega elements and six different transposon types (Tn2009, Tn2017, Tn917, Tn3872, Tn6002 and Tn916). Therefore, carriages of pneumococci and BHS with multidrug resistance in children might be important reservoirs of antibiotic-resistance genes carried by transposons. Tn916-like elements could lead to dissemination of the antibiotic resistance genes among genus streptococcus in human oral cavity and nasopharynx.

Macrolones Are a Novel Class of Macrolide Antibiotics Active against Key Resistant Respiratory Pathogens In Vitro and In Vivo.

As we face an alarming increase in bacterial resistance to current antibacterial chemotherapeutics, expanding the available therapeutic arsenal in the fight against resistant bacterial pathogens causing respiratory tract infections is of high importance. The antibacterial potency of macrolones, a novel class of macrolide antibiotics, against key respiratory pathogens was evaluated in vitro and in vivo MIC values against Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and Haemophilus influenzae strains sensitive to macrolide antibiotics and with defined macrolide resistance mechanisms were determined. The propensity of macrolones to induce the expression of inducible erm genes was tested by the triple-disk method and incubation in the presence of subinhibitory concentrations of compounds. In vivo efficacy was assessed in a murine model of S. pneumoniae-induced pneumonia, and pharmacokinetic (PK) profiles in mice were determined. The in vitro antibacterial profiles of macrolones were superior to those of marketed macrolide antibiotics, including the ketolide telithromycin, and the compounds did not induce the expression of inducible erm genes. They acted as typical protein synthesis inhibitors in an Escherichia coli transcription/translation assay. Macrolones were characterized by low to moderate systemic clearance, a large volume of distribution, a long half-life, and low oral bioavailability. They were highly efficacious in a murine model of pneumonia after intraperitoneal application even against an S. pneumoniae strain with constitutive resistance to macrolide-lincosamide-streptogramin B antibiotics. Macrolones are the class of macrolide antibiotics with an outstanding antibacterial profile and reasonable PK parameters resulting in good in vivo efficacy.

Constitutive expression of pathogenesis-related proteins and antioxydant enzyme activities triggers maize resistance towards Fusarium verticillioides

Fusarium verticillioides is a fungal pathogen of maize that causes ear rot and contaminates the grains with fumonisin mycotoxins. Breeding for resistance to Fusarium emerged as the most economic and environmentally safe strategy; therefore the discovery of resistant sources and effective molecular markers are a priority. Ears of resistant (CO441 and CO433) and susceptible (CO354 and CO389) maize lines were inoculated with F. verticillioides and the expression of pathogenesis-related (PR) genes (PR1, PR5, PRm3, PRm6) and genes that protect from oxidative stress (peroxidase, catalase, superoxide dismutase and ascorbate peroxidase) were evaluated in the kernels at 72h post inoculation. In addition, the oxidation level and the enzymatic activity of ascorbate-glutathione cycle, catalase, superoxide dismutase and cytosolic and wall peroxidases were investigated. The uninoculated kernels of the resistant lines showed higher gene expression and enzymatic activities, highlighting the key role of constitutive resistance in limiting pathogen attack. In contrast, the susceptible lines activated defensive genes only after pathogen inoculation, resulting in increased levels of H2O2 and lipid peroxidation, as well as lower enzymatic activities. The constitutive defenses observed in this study from seed could be profitably exploited to develop markers to speed up conventional breeding programs in the selection of resistant genotypes.

The MisR Response Regulator Is Necessary for Intrinsic Cationic Antimicrobial Peptide and Aminoglycoside Resistance in Neisseria gonorrhoeae.

During infection, the sexually transmitted pathogen Neisseria gonorrhoeae (the gonococcus) encounters numerous host-derived antimicrobials, including cationic antimicrobial peptides (CAMPs) produced by epithelial and phagocytic cells. CAMPs have both direct and indirect killing mechanisms and help link the innate and adaptive immune responses during infection. Gonococcal CAMP resistance is likely important for avoidance of host nonoxidative killing systems expressed by polymorphonuclear granulocytes (e.g., neutrophils) and intracellular survival. Previously studied gonococcal CAMP resistance mechanisms include modification of lipid A with phosphoethanolamine by LptA and export of CAMPs by the MtrCDE efflux pump. In the related pathogen Neisseria meningitidis, a two-component regulatory system (2CRS) termed MisR-MisS has been shown to contribute to the capacity of the meningococcus to resist CAMP killing. We report that the gonococcal MisR response regulator but not the MisS sensor kinase is involved in constitutive and inducible CAMP resistance and is also required for intrinsic low-level resistance to aminoglycosides. The 4- to 8-fold increased susceptibility of misR-deficient gonococci to CAMPs and aminoglycosides was independent of phosphoethanolamine decoration of lipid A and the levels of the MtrCDE efflux pump and seemed to correlate with a general increase in membrane permeability. Transcriptional profiling and biochemical studies confirmed that expression of lptA and mtrCDE was not impacted by the loss of MisR. However, several genes encoding proteins involved in membrane integrity and redox control gave evidence of being MisR regulated. We propose that MisR modulates the levels of gonococcal susceptibility to antimicrobials by influencing the expression of genes involved in determining membrane integrity.

Constitutive and cold-induced resistance of rye and wheat seedlings to oxidative stress

The influence of cold hardening of rye (Secale cereale L.) and wheat (Triticum aestivum L.) seedlings on their resistance to the oxidative stress (OS) agents, namely, 50 mM hydrogen peroxide or 5 mM iron (II) sulfate was studied. Unhardened rye seedlings were more resistant to hydrogen peroxide than those of wheat, since their growth was less inhibited, and they accumulated lesser amounts of lipid peroxidation products after a treatment with H2O2. The interspecific differences in responses to FeSO4 were less significant. The unhardened seedlings of rye, in comparison with those of wheat, possessed more active guaiacol peroxidase (GPO) and more levels of anthocyanins and proline. In response to the OS agents, the unhardened rye seedlings enhanced activities of superoxide dismutase and catalase, whereas the wheat seedlings enhanced GPO activity and proline content. The cold hardening (6 days at 2°C) increased activities of antioxidant (AO) enzymes, contents of proline, sugars, and anthocyanins in seedlings of both species, and made the seedlings more resistant to the OS agents. After the cold hardening, rye seedlings were more resistant to OS than wheat seedlings. The hardened seedlings of both species activated the AO enzymes in response to H2O2 or FeSO4 greater than the unhardened ones. However, the hardened wheat seedlings, in contrast to the unhardened ones, did not augment the proline content in contact with the OS agents. The conclusion was drawn on different contributions of AO enzymes and low-molecular weight compounds to the basal and induced by the cold—hardening resistances of rye and wheat seedlings to OS.

NAD(P)H:Quinone Oxidoreductase-1 Expression Sensitizes Malignant Melanoma Cells to the HSP90 Inhibitor 17-AAG

The KEAP1-NRF2 pathway regulates cellular redox homeostasis by transcriptional induction of genes associated with antioxidant synthesis and detoxification in response to oxidative stress. Previously, we reported that KEAP1 mutation elicits constitutive NRF2 activation and resistance to cisplatin (CDDP) and dacarbazine (DTIC) in human melanomas. The present study was conducted to clarify whether an HSP90 inhibitor, 17-AAG, efficiently eliminates melanoma with KEAP1 mutation, as the NRF2 target gene, NQO1, is a key enzyme in 17-AAG bioactivation. In melanoma and non-small cell lung carcinoma cell lines with or without KEAP1 mutations, NQO1 expression and 17-AAG sensitivity are inversely correlated. NQO1 is highly expressed in normal melanocytes and in several melanoma cell lines despite the presence of wild-type KEAP1, and the NQO1 expression is dependent on NRF2 activation. Because either CDDP or DTIC produces reactive oxygen species that activate NRF2, we determined whether these agents would sensitize NQO1-low melanoma cells to 17-AAG. Synergistic cytotoxicity of the 17-AAG and CDDP combination was detected in four out of five NQO1-low cell lines, but not in the cell line with KEAP1 mutation. These data indicate that 17-AAG could be a potential chemotherapeutic agent for melanoma with KEAP1 mutation or NQO1 expression.

MOLEKÜLER İŞARETLEYİCİLERİN DAYANIKLILIK ISLAHINDA KULLANILMASI

Plants are attacked by viruses, bateria, fungi, nematodes and insects. Plants haven’t immune system to protect themselves against pathogens and pests. Howewer, they have carried mechanisms of antimicrobial defense which are either constitutive or inducible and resistance (R) genes. The purpose of resistance breeding is determined resistant genes, transfered to cultivar plants and cloned. Determination of resistance genes are time consuming and difficult in tradition breeding. These can be eliminated using molecular markers.

Clindamycin resistance among Staphylococcus aureus strains in Israel: implications for empirical treatment of skin and soft tissue infections.

The objectives of this study were to characterize isolates of Staphylococcus aureus obtained from skin and soft tissue infections in the community in Israel and to document the sensitivity patterns for commonly used antimicrobial agents. The susceptibilities of S. aureus isolates from skin and soft tissue infections in the community in Israel were reviewed to determine the appropriate empirical therapy for these infections. A total of 7221 isolates were collected during the period 2009-2012; 39% were from children (age 0-18 years). In children, S. aureus oxacillin resistance dropped from 8.4% to 3.8% (p=0.073). While inducible clindamycin resistance increased slightly from 20% to 25%, there was a prominent increase in constitutive clindamycin resistance from 0.1% to 26.8% (p=0.012). In adults, oxacillin resistance increased from 16% to 23% (p<0.001) and constitutive clindamycin resistance increased notably from 5% to 29% (p<0.001). These findings demonstrate a dramatic increase in clindamycin resistance among S. aureus isolates and suggest against the usage of clindamycin as empirical treatment for suspected S. aureus infections in Israel. Beta-lactam anti-staphylococcal agents may be given as empirical treatment for children, but should be considered according to risk factors for adults in Israel.

Abstract P3-05-09: Exploring bazedoxifene and palbociclib as potential therapeutic strategies for overcoming ESR1-mediated endocrine resistance

Abstract INTRODUCTION Despite effective endocrine treatments, endocrine resistance remains a major clinical challenge. We and other groups have recently detected ligand-binding domain ESR1 mutations in metastatic estrogen receptor positive ( ER+) breast cancers. Our preclinical studies showed that these mutations confer constitutive activity and relative resistance to tamoxifen and fulvestrant. In this study we sought to investigate therapeutic strategies to overcome resistance rendered by the ESR1 mutations. Since our previous studies showed relative resistance to tamoxifen or fulvestrant, we hypothesized that bazedoxifene, a high affinity third generation SERM/SERD could overcome resistance driven by the ER mutant resistance. Additionally, we hypothesized that inhibiting cyclin D1, a key ER transcriptional target gene and cell cycle regulator, is a second potential therapeutic strategy to circumvent resistance rendered by mutant ER. Therefore in this study we tested the effects of bazedoxifene, palbciclib and their combination on cell proliferation in the presence and absence of the ESR1 mutations. METHODS For this study we established doxycycline inducible MCF7 cell lines expressing the ER-LBD mutations (Y537S, Y537N and D538G) and WT-ER as control. Cell proliferation response to bazedoxifene, tamoxifen, fulvestrant, palbociclib and the bazedoxifene-palbociclib combination was evaluated. RESULTS Cells harboring mutant ER were relatively resistant to tamoxifen and fulvestrant, as expected, and remained sensitive to single agent bazedoxifene and palbociclib. The combination of bazedoxifene and palbociclib was found to be superior to the single agents and exhibits synergistic activity. CONCLUSION The combination of bazedoxifene and palbociclib inhibits mutant ER cell growth and other cell models of endocrine resistance and is a potential therapeutic combination. Citation Format: Nguyen M, Buchwalter G, Luo F, Garraway L, Brown M, Jeselsohn R. Exploring bazedoxifene and palbociclib as potential therapeutic strategies for overcoming ESR1-mediated endocrine resistance. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-05-09.

Downy mildew intensity in tolerant grapes varieties in highlands of southern Brazil

The aim of this study was to evaluate the different degrees of tolerance to infection by P. viticola among three genotypes with constitutive resistance in comparison to susceptible varieties Vitis vinifera . For this purpose two experiments was conducted at EPAGRI Experimental Station, located in the city of Sao Joaquim, Santa Catarina State, at 2015/16 cycle. In the first experiment on the field, were quantified the incidence and severity and downy mildew intensity was compared by epidemiological variables, on the tolerant varieties Bronner, Regent, Cabernet Cortis and the susceptible Sangiovese. On the second experiment forty leaf discs for the same tolerant genotypes and the susceptible variety Chardonnay were artificially infected with P. viticola sporangia suspension and after seven days of incubation the discs were examined and the degree of infection was estimated based on the intensity of sporangiophore formation. Sangiovese showed highest downy mildew intensity in comparison to the tolerant varieties Cabernet Carbon, Regent and Bronner. Under controlled conditions, the susceptible variety Chardonnay showed higher sporangiophore formation on discs leafs in comparison to the tolerant varieties. All the downy mildew tolerant varieties evaluated showed lower disease development in comparison with V. vinifera varieties.

Inducible clindamycin resistance among the clinical isolates of Staphylococcus aureus in a tertiary care hospital

Introduction: Clindamycin is commonly used to treat skin and soft tissue infections caused by Staphylococcus aureus particularly in methicillin-resistant S. aureus (MRSA) infections. Inducible clindamycin resistance (inducible macrolide–lincosamide–streptogramin B resistance [MLSB]) is a critical factor in antimicrobial susceptibility testing. This study was aimed to detect MLSB phenotypes and inducible clindamycin resistant phenotypes among S. aureus. Materials and Methods: A total of 649 S. aureus isolates from different clinical samples were evaluated, and methicillin-resistance was determined using the cefoxitin (30 μg) disc. Inducible resistance to clindamycin was detected by D-zone test as per Clinical and Laboratory Standards Institute guidelines. Results: Of the 649 isolates, 404 (62.2%) were methicillin-sensitive S. aureus (MSSA) and 245 (37.8%) were MRSA. Ninety-six (14.8%) isolates showed inducible clindamycin resistance, 175 (27%) showed constitutive resistance, and 55 (8.5%) isolates showed MS phenotype. Inducible and constitutive resistance phenotypes were found to be higher in MRSA (25% and 64.8%) as compared to MSSA (8.7% and 4.7%), respectively. Conclusions: Considering the higher prevalence of clindamycin resistance in MRSA isolates as compared MSSA isolates, routine D-test of MRSA isolates is strongly recommended to prevent treatment failure. Therefore, inducible clindamycin detection should be the part of S. aureus sensitivity testing in all the microbiology laboratories.

Clindamycin microbial resistance in clinical isolates of Staphylococcus sp. derived from blood cultures of hospitalized patients

Introduction: Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) strains have become common in hospitals, and this resistance has limited patients' treatment with beta-lactam antibiotics. Clindamycin is an important therapeutic agent for MRSA infections; however, inducible macrolide-lincosamide-streptogramin B (MLSB) resistance (iMLSB) has resulted in therapeutic failures with the use of this antimicrobial, with a consequent increase in patient mortality and length of stay. Objective: This study was carried out in order to detect phenotypes of inducible and constitutive resistance to clindamycin in blood culture samples of Staphylococcus sp. from hospitalized patients. Material and methods: A hundred bacterial samples from blood cultures of adult patients were evaluated, identified by conventional phenotypic tests, and subject to determination of susceptibility and resistance profiles with cefoxitin, erythromycin, and clindamycin discs; and to phenotypic evaluation of iMLSB resistance using the D-test. The results were interpreted in accordance with the recommendations of the Clinical and Laboratory Standards Institute (CLSI) 2014. Results: In this study, 65% of 60 bacterial strains were susceptible to cefoxitin and 35%, resistant. The constitutive MLSB (cMLSB) resistance phenotype was observed in 15.56% of the methicillin-sensitive Staphylococcus aureus (MSSA) samples, 33.33% of methicillin-sensitive coagulase-negative Staphylococcus (MSCONS), 26.67% of MRSA and 20% of methicillin-resistant coagulase-negative Staphylococcus (MRCONS), while iMLSB resistance was observed only in strains susceptible to cefoxitin, corresponding to 80% in MSSA and 20% in MSCONS. Conclusion: The D-test is a key test for the constant monitoring of the inducible resistance phenotype (which may impair the effectiveness of treatment with clindamycin), minimizing potential medication errors and adverse clinical outcomes.

Inducible-Clindamycin Resistance in &amp;lt;i&amp;gt;Staphylococcus aureus &amp;lt;/i&amp;gt; Isolates in Rivers State, Nigeria

Clindamycin is indicated in the treatment of skin and soft-tissue infections caused by Staphylococcal species. Treatment of an infection caused by a strain carrying inducible erm gene using clindamycin or any non-inducer macrolide can lead to clinical failure. The present study was aimed to detect inducible-clindamycin resistance (MLSBi) among S. aureus isolates in Port Harcourt, Nigeriaand to study the relationship between clindamycin and methicillin-resistant <i S. aureus (MRSA).Two hundred and five (205) non-duplicate Staphylococcus aureus previously isolated from human sources were randomly collected from three health facilities- University of Port Harcourt Teaching Hospital, Braithwaite Memorial Specialist Hospital and De-Integrated Laboratories-all located in Port Harcourt, Nigeria, for this study from August, 2012 to July, 2013. Isolates were grouped as hospital in-patient (termed hospital- acquired – Nosocomial; n = 76) and out- patient cases (community-acquired; n = 129) Staphylococcus aureus . The isolates collected were reconfirmed following standard laboratory protocols. All confirmed isolates were stored in glycerol at +4°C (later sub-cultured for various phenotypic analyses). Using the disk diffusion method, detection of MRSA was carried out with 1μg of oxacillin (OXOID) placed on Mueller-Hinton agar with 4% NaCl supplementation).Antimicrobial susceptibility testing was performed using Erythromycin (15μg) and Clindamycin (2μg) both obtained from OXOID, UK. All clindamycin-sensitive isolates that were also erythromycin-resistant were subjected to D-Test phenotype (Inducible-clindamycin resistance). Among the 205 S. aureus isolates studied, Forty-four (21.5%) showed resistance to erythromycin, while 38 of these erythromycin-resistant isolates were simultaneously sensitive to clindamycin. Overall, out of 205 isolates, inducible-clindamycin resistance was detected in 23 (11.2%) of the isolates. These 23 (inducible MLSB phenotype) are among 38 erythromycin-resistant S. aureus that were simultaneously sensitive (phenotypically) to clindamycin. Ten (4.9%) of the total (205) study isolates expressed constitutive resistance to clindamycin. Oxacillin Resistance (MRSA) was detected in 25 (12.2%) of the 205 isolates. Among the 38 erythromycin-resistant S. aureus, four were MRSA while 3 (75%) of the 4 erythromycin-resistant MRSA expressed inducible resistance to clindamycin. 20 (58.8%) of 34 erythromycin-resistant MSSA expressed inducible resistance to clindamycin. MRSA phenotype was not significantly correlated (p=0.9430) to inducible-clindamycin resistance. Inducible clindamycin-resistance often leads to treatment failure. The clinical microbiology laboratories in Nigeria should consider routine testing and reporting of inducible clindamycin resistance in S. aureus . There is also the need for sustained surveillance of antimicrobial susceptibilities of S. aureus in this region.

Transcriptional Analysis of Maize Resistance against Fusarium graminearum

Gibberella stalk rot, caused by Fusarium graminearum (teleomorph, Gibberella zeae), is one of the most devastating soil-borne diseases in maize. It seriously decreases maize yield and quality. Molecular mapping led to the identification of two QTLs, qRfg1 and qRfg2, on chromosomes 10 and 1 respectively, conferring resistance to Gibberella stalk rot. In order to characterize the defense mechanism of maize against F. graminearum, NIL-R with resistant alleles at both QTLs and NIL-S with the susceptible alleles at both QTLs were generated and used in transcriptome analysis. After inoculation of young seedling roots of both NILs with the F. graminearum spores, the inoculated roots were sampled at 0, 6, and 18 hours after inoculation (hai) for transcriptome analysis using RNAseq. The basal difference was achieved by the comparison between control samples. In total, 2958 genes were differentially expressed between control samples of NIL-R and NIL-S, among which 1170 genes were more abundant in NIL-R. GO analysis revealed that genes involved in biological processes related to JA/ET and SA biosynthesis, JA/ET mediated signaling pathway and SA mediated signaling pathway were significantly enriched. Phenylpropanoid biosynthesis process was enriched in the genes more abundant in NIL-R and genes encoding enzymes involved in phenylpropanoid biosynthesis like PAL, 4CL2, CAD, and HCT were more abundant in NIL-R. There were 431 genes differentially expressed between NIL-R and NIL-S at 6 hai, among which 83 genes were more abundant in NIL-R. Genes encoding pathogenesis-related (PR) proteins like lipid-transfer protein and germin-like protein were more abundant in NIL-R. Among the 1292 genes differentially expressed between NIL-R and NIL-S. At 18 hai, 291 genes were more abundant in NIL-R. Genes involved in ET biosynthesis like ACO and JA biosynthesis like LOX were more abundant in NIL-R. Genes involved in DON detoxification like PDR1 and MDR2 were more abundant in NIL-R. After inoculation with F. graminearum, 428 genes were exclusively up-regulated in NIL-R at 6 hai compared with control. Genes involved in ET biosynthesis and ET-mediated signaling pathway like ACO, ERF, EBF1, and EIL1 and pathogenesis-related genes like PR1, OSM34, and germin-like protein were exclusively up-regulated in NIL-R. At 18 hai, 359 genes were exclusively up-regulated in NIL-R compared with control. Pathogenesis-related genes like PR1, PR4, and genes encoding 第 8期 刘永杰等: 玉米抗禾谷镰刀菌的转录组分析 1123 the transporters of DON out of cytoplasm like ABC transport family protein, heavy metal transport protein and MATE efflux family protein were exclusively up-regulated in NIL-R. All these results indicate that NIL-R can increase the resistance of maize to F. graminearum by the constitutive resistance characterized by the higher expression of genes related to defense responses. Genes involved in defense responses exclusively up-regulated in NIL-R and higher expression level of disease resistance genes in NIL-R at 6 and 18 hai may restrict the pathogen invasion after infection. The phenylpropanoid biosynthesis pathway and DON-detoxification proteins identified in this study are important for the resistance against F. graminearum infection.

Inducible clindamycin resistance among clinical isolates of Staphylococcus aureus

Objective: The aim of the study was to detect the presence of inducible clindamycin resistance among clinical isolates of Staphylococcus aureus. Background: The resistance to antimicrobial agents among staphylococci is an increasing problem. This has led to renewed interest in the usage of macrolide–lincosamide–streptogramin B (MLSB) antibiotics to treat S. aureus infections. The resistance to macrolide can be mediated by the msrA gene coding for efflux mechanism or by the erm gene encoding for enzymes that confer inducible or constitutive resistance to MLSB antibiotics. Materials and methods: Ninety staphylococcal isolates were collected and were tested for antibiotic susceptibility using the disk diffusion method. Inducible resistance to clindamycin in S. aureus was tested by using the double disk diffusion test as per CLSI guidelines. Results: Inducible MLSBresistance (EryRClinInd) was seen in 7/90 (7.7%) isolates, the constitutive phenotype of MLSBresistance (EryRClinR) was detected in 6/90 (6.6%) isolates, and the MSBphenotype (EryRClinS) was seen in 34 (37.7%) isolates. In these isolates, inducible clindamycin resistance was detected in 4.3% (3/70) of S. aureus and 20% (4/20) of coagulase-negative staphylococci. Conclusion: This study showed that the double disk diffusion test should be used as a mandatory method in routine disk diffusion testing to detect inducible clindamycin resistance in staphylococci for the optimum treatment of patients.

In Vivo Characterization of the Activation and Interaction of the VanR-VanS Two-Component Regulatory System Controlling Glycopeptide Antibiotic Resistance in Two Related Streptomyces Species.

The VanR-VanS two-component system is responsible for inducing resistance to glycopeptide antibiotics in various bacteria. We have performed a comparative study of the VanR-VanS systems from two streptomyces strains, Streptomyces coelicolor and Streptomyces toyocaensis, to characterize how the two proteins cooperate to signal the presence of antibiotics and to define the functional nature of each protein in each strain background. The results indicate that the glycopeptide antibiotic inducer specificity is determined solely by the differences between the amino acid sequences of the VanR-VanS two-component systems present in each strain rather than by any inherent differences in general cell properties, including cell wall structure and biosynthesis. VanR of S. coelicolor (VanRsc) functioned with either sensor kinase partner, while VanR of S. toyocaensis (VanRst) functioned only with its cognate partner, S. toyocaensis VanS (VanSst). In contrast to VanRsc, which is known to be capable of phosphorylation by acetylphosphate, VanRst could not be activated in vivo independently of a VanS sensor kinase. A series of amino acid sequence modifications changing residues in the N-terminal receiver (REC) domain of VanRst to the corresponding residues present in VanRsc failed to create a protein capable of being activated by VanS of S. coelicolor (VanSsc), which suggests that interaction of the response regulator with its cognate sensor kinase may require a region more extended than the REC domain. A T69S amino acid substitution in the REC domain of VanRst produced a strain exhibiting weak constitutive resistance, indicating that this particular amino acid may play a key role for VanS-independent phosphorylation in the response regulator protein.

Doble terapia antiagregante en el postoperatorio de cirugía coronaria: revisión bibliográfica

IntroductionExtensive and early use of acetyl-salicylic acid (ASA) is widely accepted in the post-operative period after coronary artery bypass grafting surgery (CABG), however, its combination in double antiplatelet therapy (DAT) is still controversial. DAT may improve coronary graft patency due to a lower vulnerability against constitutive and/or transient antiplatelet therapy resistance, and due to potential pleiotropic effects against intimal hyperplasia. Nevertheless, dosage and duration of the treatment are not completely established. MethodsSystematic bibliographic review in Medline combining 3 clusters of key words and stepwise selection of articles obtained. ResultsOut of a total of 56 preliminary studies found, 19 were chosen for analysis, of which 7 were randomised controlled trials, 2 meta-analyses, 1 literature review, 3 clinical guidelines, and 6 non-randomised studies. All of them were individually analysed and classified as favourable or not to DAT. ConclusionsThere is not enough evidence to warrant extensive use of DAT after CABG. However, DAT could show a benefit in certain clinical scenarios, such as CABG after prior coronary acute syndrome, extensive use of venous grafts, or CABG off-pump. The benefits shown in studies favourable to DAT on the improvement of coronary graft patency in the short-midterm did not lead to differences in the incidence of major cardiovascular events. Neither of the groups showed differences in terms of safety related to haemorrhagic events, nor in the immediate postoperative or follow-up period

Comparative erythromycin and tylosin susceptibility testing of streptococci from bovine mastitis

Tylosin, a 16-membered macrolide, is – besides other indications – used for the treatment of bovine mastitis. So far, there is only limited information available on the tylosin susceptibility of streptococci isolated from mastitis. The aim of the present study was to comparatively investigate 303 streptococci from bovine mastitis, including 101 Streptococcus agalactiae, 100 Streptococcus dysgalactiae and 102 Streptococcus uberis, for their tylosin and erythromycin susceptibility by broth microdilution and agar disk diffusion. Both tests followed the recommendations of the Clinical and Laboratory Standards Institute (CLSI). For erythromycin, the results were interpreted using the CLSI-approved clinical breakpoints. Moreover, erythromycin-resistant isolates were tested for the presence of macrolide resistance genes and for inducible macrolide resistance. In general, both testing methods showed a good correlation for the three streptococcal species, although for the erythromycin susceptibility testing 11 S. uberis isolates fell into the very major error category. All but one of the erythromycin-resistant isolates harbored at least one macrolide resistance gene, with the erm(B) gene being most common. Moreover, single isolates of S. agalactiae and S. dysgalactiae proved to be inducibly macrolide-resistant. Since inducible macrolide resistance can easily switch to constitutive resistance, tylosin should not be used for the treatment of infections caused by inducibly resistant streptococci.

Differential Costs of Two Distinct Resistance Mechanisms Induced by Different Herbivore Species in Arabidopsis

Plants respond to herbivory with the induction of resistance, mediated by distinct phytohormonal signaling pathways and their interactions. Phloem feeders are known to induce plant resistance via the salicylic acid pathway, whereas biting-chewing herbivores induce plant resistance mainly via the jasmonate pathway. Here, we show that a specialist caterpillar (biting-chewing herbivore) and a specialist aphid (phloem feeder) differentially induce resistance against Pieris brassicae caterpillars in Arabidopsis (Arabidopsis thaliana) plants. Caterpillar feeding induces resistance through the jasmonate signaling pathway that is associated with the induction of kaempferol 3,7-dirhamnoside, whereas aphid feeding induces resistance via a novel mechanism involving sinapoyl malate. The role of sinapoyl malate is confirmed through the use of a mutant compromised in the biosynthesis of this compound. Caterpillar-induced resistance is associated with a lower cost in terms of plant growth reduction than aphid-induced resistance. A strong constitutive resistance against P. brassicae caterpillars in combination with a strong growth attenuation in plants of a transfer DNA (T-DNA) insertion mutant of WRKY70 (wrky70) suggest that the WRKY70 transcription factor, a regulator of downstream responses mediated by jasmonate-salicylic acid signaling cross talk, is involved in the negative regulation of caterpillar resistance and in the tradeoff between growth and defense. In conclusion, different mechanisms of herbivore-induced resistance come with different costs, and a functional WRKY70 transcription factor is required for the induction of low-cost resistance.