Structure-based drug design studies of the interactions of ent-kaurane diterpenes derived from Wedelia paludosa with the Plasmodium falciparum sarco/endoplasmic reticulum Ca2+-ATPase PfATP6

Malaria is responsible for more deaths around the world than any other parasitic disease. Due to the emergence of strains that are resistant to the current chemotherapeutic antimalarial arsenal, the search for new antimalarial drugs remains urgent though hampered by a lack of knowledge regarding the molecular mechanisms of artemisinin resistance. Semisynthetic compounds derived from diterpenes from the medicinal plant Wedelia paludosa were tested in silico against the Plasmodium falciparum Ca²⁺-ATPase, PfATP6. This protein was constructed by comparative modelling using the three-dimensional structure of a homologous protein, 1IWO, as a scaffold. Compound 21 showed the best docking scores, indicating a better interaction with PfATP6 than that of thapsigargin, the natural inhibitor. Inhibition of PfATP6 by diterpene compounds could promote a change in calcium homeostasis, leading to parasite death. These data suggest PfATP6 as a potential target for the antimalarial ent-kaurane diterpenes.     

Resistome analysis of Mycobacterium tuberculosis: Identification of aminoglycoside 2'-Nacetyltransferase (AAC) as co-target for drug desigining

The emergence of multidrug resistant tuberculosis (MDRTB) highlights the urgent need to understand the mechanisms of resistance to the drugs and to develop a new arena of therapeutics to treat the disease. Ethambutol, isonazid, pyrazinamide, rifampicin are first line of drugs against TB, whereas aminoglycoside, polypeptides, fluoroquinolone, ethionamide are important second line of bactericidal drugs used to treat MDRTB, and resistance to one or both of these drugs are defining characteristic of extensively drug resistant TB. We retrieved 1,221 resistant genes from Antibiotic Resistance Gene Database (ARDB), which are responsible for resistance against first and second line antibiotics used in treatment of Mycobacterium tuberculosis infection. From network analysis of these resistance genes, 53 genes were found to be common. Phylogenetic analysis shows that more than 60% of these genes code for acetyltransferase. Acetyltransferases detoxify antibiotics by acetylation, this mechanism plays central role in antibiotic resistance. Seven acetyltransferase (AT-1 to AT-7) were selected from phylogenetic analysis. Structural alignment shows that these acetyltransferases share common ancestral core, which can be used as a template for structure based drug designing. From STRING analysis it is found that acetyltransferase interact with 10 different proteins and it shows that, all these interaction were specific to M. tuberculosis. These results have important implications in designing new therapeutic strategies with acetyltransferase as lead co-target to combat against MDR as well as Extreme drug resistant (XDR) tuberculosis.

Abbreviations

AA - amino acid, AT - Acetyltransferase, AAC - Aminoglycoside 2''-N-acetyltransferase, XDR - Extreme drug-resistant, MDR - Multidrug-resistant, Mtb - Mycobacterium tuberculosis, TB - Tuberculosis.     

An Epigenetic Antimalarial Resistance Mechanism Involving Parasite Genes Linked to Nutrient Uptake

Acquired antimalarial drug resistance produces treatment failures and has led to periods of global disease resurgence. In Plasmodium falciparum, resistance is known to arise through genome-level changes such as mutations and gene duplications. We now report an epigenetic resistance mechanism involving genes responsible for the plasmodial surface anion channel, a nutrient channel that also transports ions and antimalarial compounds at the host erythrocyte membrane. Two blasticidin S-resistant lines exhibited markedly reduced expression of clag genes linked to channel activity, but had no genome-level changes. Silencing aborted production of the channel protein and was directly responsible for reduced uptake. Silencing affected clag paralogs on two chromosomes and was mediated by specific histone modifications, allowing a rapidly reversible drug resistance phenotype advantageous to the parasite. These findings implicate a novel epigenetic resistance mechanism that involves reduced host cell uptake and is a worrisome liability for water-soluble antimalarial drugs.     

Bacterial recombination promotes the evolution of multi-drug-resistance in functionally diverse populations

Bacterial recombination is believed to be a major factor explaining the prevalence of multi-drug-resistance (MDR) among pathogenic bacteria. Despite extensive evidence for exchange of resistance genes from retrospective sequence analyses, experimental evidence for the evolutionary benefits of bacterial recombination is scarce. We compared the evolution of MDR between populations of Acinetobacter baylyi in which we manipulated both the recombination rate and the initial diversity of strains with resistance to single drugs. In populations lacking recombination, the initial presence of multiple strains resistant to different antibiotics inhibits the evolution of MDR. However, in populations with recombination, the inhibitory effect of standing diversity is alleviated and MDR evolves rapidly. Moreover, only the presence of DNA harbouring resistance genes promotes the evolution of resistance, ruling out other proposed benefits for recombination. Together, these results provide direct evidence for the fitness benefits of bacterial recombination and show that this occurs by mitigation of functional interference between genotypes resistant to single antibiotics. Although analogous to previously described mechanisms of clonal interference among alternative beneficial mutations, our results actually highlight a different mechanism by which interactions among co-occurring strains determine the benefits of recombination for bacterial evolution.     

Evidence for a substrate specific and inhibitable drug efflux system in chloroquine resistant Plasmodium falciparum strains

The mechanism underpinning chloroquine drug resistance in the human malarial parasite Plasmodium falciparum remains controversial. By investigating the kinetics of chloroquine accumulation under varying-trans conditions, we recently presented evidence for a saturable and energy-dependent chloroquine efflux system present in chloroquine resistant P. falciparum strains. Here, we further characterize the putative chloroquine efflux system by investigating its substrate specificity using a broad range of different antimalarial drugs. Our data show that preloading cells with amodiaquine, primaquine, quinacrine, quinine, and quinidine stimulates labeled chloroquine accumulation under varying-trans conditions, while mefloquine, halofantrine, artemisinin, and pyrimethamine do not induce this effect. In the reverse of the varying-trans procedure, we show that preloaded cold chloroquine can stimulate quinine accumulation. On the basis of these findings, we propose that the putative chloroquine efflux system is capable of transporting, in addition to chloroquine, structurally related quinoline and methoxyacridine antimalarial drugs. Verapamil and the calcium/calmodulin antagonist W7 abrogate stimulated chloroquine accumulation and energy-dependent chloroquine extrusion. Our data are consistent with a substrate specific and inhibitible drug efflux system being present in chloroquine resistant P. falciparum strains.     

Investigating the activity of quinine analogues versus chloroquine resistant Plasmodium falciparum

Plasmodium falciparum, the deadliest malarial parasite species, has developed resistance against nearly all man-made antimalarial drugs within the past century. However, quinine (QN), the first antimalarial drug, remains efficacious worldwide. Some chloroquine resistant (CQR) P. falciparum strains or isolates show mild cross resistance to QN, but many do not. Further optimization of QN may provide a well-tolerated therapy with improved activity versus CQR malaria. Thus, using the Heck reaction, we have pursued a structure-activity relationship study, including vinyl group modifications of QN. Certain derivatives show good antiplasmodial activity in QN-resistant and QN-sensitive strains, with lower IC(50) values relative to QN.     

Use of Arabidopsis thaliana and Pseudomonas syringae in the Study of Plant Disease Resistance and Tolerance

The interaction between Arabidopsis thaliana and the bacterium Pseudomonas syringae is being developed as a model experimental system for plant pathology research. Race-specific ("gene-for-gene") resistance has been demonstrated for this interaction, and pathogen genes that determine avirulence have been isolated and characterized. Because certain lines of both Arabidopsis and soybean are resistant to bacteria carrying the avirulence genes avrRpt2 and avrB, extremely similar pathogen recognition mechanisms are apparently present in these two plant species. Isogenic bacterial strains that differ by the presence of single avirulence genes are being used to analyze plant resistance. Plant resistance genes have been identified in crosses between resistant and susceptible lines. The extensive map-based cloning tools available in Arabidopsis are being used to isolate these resistance genes. In a related project, ethylene-insensitive Arabidopsis mutants are being used to examine the role of ethylene in disease development. Ethylene apparently mediates symptom formation in susceptible plants and is not required for resistance, suggesting possible strategies for enhancement of disease tolerance in crops.     

Reproduction of Meloidogyne spp. on Resistant Peanut Genotypes from Three Breeding Programs

Three described species of root-knot nematode parasitize peanut (Arachis hypogaea): Meloidogyne arenaria race 1 (Ma), M. hapla (Mh), and M. javanica (Mj). Peanut cultivars with broad resistance to Meloidogyne spp. will be useful regardless of the species present in the field. The objective of this study was to determine whether peanut genotypes with resistance to M. arenaria originating from three different breeding programs were also resistant to M. hapla and M. javanica. The experiment used a factorial arrangement (completely randomized) with peanut genotype and nematode population as the factors. The five peanut genotypes were ''COAN'' and AT 0812 (highly resistant to Ma), C209-6-13 (moderately resistant to Ma), and ''Southern Runner'' and ''Georgia Green'' (susceptible to Ma). The four nematode populations were two isolates of Ma (Gibbs and Gop) and one isolate each of Mh and Mj. On COAN or AT 0812, both Ma and Mj produced <10% of the eggs produced on Georgia Green. On the peanut genotype C209-6-13, Ma and Mj produced about 50% of the eggs produced on Georgia Green. None of the resistant genotypes exhibited a high level of resistance to Mh. The lack of resistance to Mh in any cultivars or advanced germplasm is a concern because the identity of a Meloidogyne sp. in a particular peanut field is generally not known. Breeding efforts should focus on moving genes for resistance to M. hapla into advanced peanut germplasm, and combining genes for resistance to the major Meloidogyne spp. in a single cultivar.     

Mutations upstream of fabI in triclosan resistant Staphylococcus aureus strains are associated with elevated fabI gene expression

Background

The enoyl-acyl carrier protein (ACP) reductase enzyme (FabI) is the target for a series of antimicrobial agents including novel compounds in clinical trial and the biocide triclosan. Mutations in fabI and heterodiploidy for fabI have been shown to confer resistance in S. aureus strains in a previous study. Here we further determined the fabI upstream sequence of a selection of these strains and the gene expression levels in strains with promoter region mutations.

Results

Mutations in the fabI promoter were found in 18% of triclosan resistant clinical isolates, regardless the previously identified molecular mechanism conferring resistance. Although not significant, a higher rate of promoter mutations were found in strains without previously described mechanisms of resistance. Some of the mutations identified in the clinical isolates were also detected in a series of laboratory mutants. Microarray analysis of selected laboratory mutants with fabI promoter region mutations, grown in the absence of triclosan, revealed increased fabI expression in three out of four tested strains. In two of these strains, only few genes other than fabI were upregulated. Consistently with these data, whole genome sequencing of in vitro selected mutants identified only few mutations except the upstream and coding regions of fabI, with the promoter mutation as the most probable cause of fabI overexpression. Importantly the gene expression profiling of clinical isolates containing similar mutations in the fabI promoter also showed, when compared to unrelated non-mutated isolates, a significant up-regulation of fabI.

Conclusions

In conclusion, we have demonstrated the presence of C34T, T109G, and A101C mutations in the fabI promoter region of strains with fabI up-regulation, both in clinical isolates and/or laboratory mutants. These data provide further observations linking mutations upstream fabI with up-regulated expression of the fabI gene.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1544-y) contains supplementary material, which is available to authorized users.     

Herbicide resistance-endowing ACCase gene mutations in hexaploid wild oat (Avena fatua): insights into resistance evolution in a hexaploid species

Many herbicide-resistant weed species are polyploids, but far too little about the evolution of resistance mutations in polyploids is understood. Hexaploid wild oat (Avena fatua) is a global crop weed and many populations have evolved herbicide resistance. We studied plastidic acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicide resistance in hexaploid wild oat and revealed that resistant individuals can express one, two or three different plastidic ACCase gene resistance mutations (Ile-1781-Leu, Asp-2078-Gly and Cys-2088-Arg). Using ACCase resistance mutations as molecular markers, combined with genetic, molecular and biochemical approaches, we found in individual resistant wild-oat plants that (1) up to three unlinked ACCase gene loci assort independently following Mendelian laws for disomic inheritance, (2) all three of these homoeologous ACCase genes were transcribed, with each able to carry its own mutation and (3) in a hexaploid background, each individual ACCase resistance mutation confers relatively low-level herbicide resistance, in contrast to high-level resistance conferred by the same mutations in unrelated diploid weed species of the Poaceae (grass) family. Low resistance conferred by individual ACCase resistance mutations is likely due to a dilution effect by susceptible ACCase expressed by homoeologs in hexaploid wild oat and/or differential expression of homoeologous ACCase gene copies. Thus, polyploidy in hexaploid wild oat may slow resistance evolution. Evidence of coexisting non-target-site resistance mechanisms among wild-oat populations was also revealed. In all, these results demonstrate that herbicide resistance and its evolution can be more complex in hexaploid wild oat than in unrelated diploid grass weeds. Our data provide a starting point for the daunting task of understanding resistance evolution in polyploids.     

Prevalence of Drug Resistance-Associated Gene Mutations in Plasmodium vivax in Central China

Resistance of Plasmodium spp. to anti-malarial drugs is the primary obstacle in the fight against malaria, and molecular markers for the drug resistance have been applied as an adjunct in the surveillance of the resistance. In this study, we investigated the prevalence of mutations in pvmdr1, pvcrt-o, pvdhfr, and pvdhps genes in temperate-zone P. vivax parasites from central China. A total of 26 isolates were selected, including 8 which were previously shown to have a lower susceptibility to chloroquine in vitro. For pvmdr1, pvcrt-o, and pvdhps genes, no resistance-conferring mutations were discovered. However, a highly prevalent (69.2%), single-point mutation (S117N) was found in pvdhfr gene. In addition, tandem repeat polymorphisms existed in pvdhfr and pvdhps genes, which warranted further studies in relation to the parasite resistance to antifolate drugs. The study further suggests that P. vivax populations in central China may still be relatively susceptible to chloroquine and sulfadoxine-pyrimethamine.     

Double-drug development against antioxidant enzymes from Plasmodium falciparum

New drugs against malaria are urgently and continuously needed. Plasmodium parasites are exposed to higher fluxes of reactive oxygen species and need high activities of intracellular antioxidant systems. A most important antioxidative system consists of (di)thiols which are recycled by disulfide reductases (DR), namely both glutathione reductases (GR) of the malarial parasite Plasmodium falciparum and man, and the thioredoxin reductase (TrxR) of P. falciparum. The aim of our interdisciplinary research is to substantiate DR inhibitors as antimalarial agents. Such compounds are active per se but, in addition, they can reverse thiol-based resistance against other drugs in parasites. Reversal of drug resistance by DR inhibitors is currently investigated for the commonly used antimalarial drug chloroquine (CQ). Our recent strategy is based on the synthesis of inhibitors of the glutathione reductases from parasite and host erythrocyte. With the expectation of a synergistic or additive effect, double-headed prodrugs were designed to be directed against two different and essential functions of the malarial parasite P. falciparum, namely glutathione regeneration and heme detoxification. The prodrugs were prepared by linking bioreversibly a GR inhibitor to a 4-aminoquinoline moiety which is known to concentrate in the acidic food vacuole of parasites. Drug-enzyme interaction was correlated with antiparasitic action in vitro on strains resistant towards CQ and in vivo in Plasmodium berghei-infected mice as well as absence of cytotoxicity towards human cells. Because TrxR of P. falciparum was recently shown to be responsible for the residual glutathione disulfide-reducing capacity observed after GR inhibition in P. falciparum, future development of antimalarial drug-candidates that act by perturbing the redox equilibrium of parasites is based on the design of new double-drugs based on TrxR inhibitors as potential antimalarial drug candidates.     

Retention of Resistance to Meloidogyne incognita in Lycopersicon Genotypes at High Soil Temperature

Lycopersicon glandulosum and L. peruvianum clones and L. esculentum cultivars ''VFN8'' (resistant) and ''Rutgers'' (susceptible) were tested for their resistance to Meloidogyne incognita (race l) at soil temperatures of 25 and 32 C. L. esculentum cv. VFN8 and L. peruvianum Acc. No. 128657, both of which possess the Mi gene, were resistant at 25 C but were susceptible at 32 C. L. glandulosum Acc. No. 126443 and L. peruvianum Acc. No. 270435, with combined resistance to M. hapla and M. incognita, and L. peruvianum Acc. Nos. 129152 and LA2157, with resistance to M. incognita, were highly resistant at both temperatures. In a second experiment three of these accessions under heat stress simulated by 32 C ambient and soil temperature retained a high level of resistance. Two clones of L. glandulosum Acc. No. 126440, with resistance to M. hapla, were moderately susceptible to M. incognita at 25 and highly susceptible at 32 C. M. incognita produced significantly (P = 0.01) more eggs on L. esculentum cv. Rutgers at 32 than at 25 C. This study supports the existence of genes other than the Mi gene that confer resistance to M. incognita and are functional at high soil temperatures.     

Drug-resistant malaria: molecular mechanisms and implications for public health

Resistance to antimalarial drugs has often threatened malaria elimination efforts and historically has led to the short-term resurgence of malaria incidences and deaths. With concentrated malaria eradication efforts currently underway, monitoring drug resistance in clinical settings complemented by in vitro drug susceptibility assays and analysis of resistance markers, becomes critical to the implementation of an effective antimalarial drug policy. Understanding of the factors, which lead to the development and spread of drug resistance, is necessary to design optimal prevention and treatment strategies. This review attempts to summarize the unique factors presented by malarial parasites that lead to the emergence and spread of drug resistance, and gives an overview of known resistance mechanisms to currently used antimalarial drugs.     

Genetics of Soybean-Heterodera glycines Interactions

The soybean cyst nematode, Heterodera glycines, is one of the most economically important pathogens of soybean. Effective management of the nematode is often dependent on the planting of resistant soybean cultivars. During the past 40 years, more than 60 soybean genotypes and plant introductions (PI) have been reported as resistant to H. glycines. About 130 modern soybean cultivars registered in the United States are resistant to certain races of H. glycines. Several resistance genes have been identified and genetically mapped; however, resistance levels in many soybean cultivars are not durable. Some older cultivars are no longer resistant to certain H. glycines populations in many production areas, especially if a soybean monoculture has been practiced. Past soybean registration reports show that all resistant cultivars developed in public institutions from the mid-1960s to the present have been derived from five PIs. This narrow genetic background is fragile. To further complicate the issue, soybean-H. glycines genetic interactions are complex and poorly understood. Studies to identify soybean resistance genes sometimes have overlapped, and the same genes may have been reported several times and designated by different names. Nevertheless, many potential resistance genes in existing germplasm resources have not yet been characterized. Clearly, it is necessary to identify new resistance genes, develop more precise selection methods, and integrate these resistance genes into new cultivars. Rational deployment of resistant cultivars is critical to future sustained soybean production.     

Behavioral and electrophysiological analysis of general anesthesia in 3 background strains of Drosophila melanogaster

General anesthetics achieve behavioral unresponsiveness via a mechanism that is incompletely understood. The study of genetic model systems such as the fruit fly Drosophila melanogaster is crucial to advancing our understanding of how anesthetic drugs render animals unresponsive. Previous studies have shown that wild-type control strains differ significantly in their sensitivity to general anesthetics, which potentially introduces confounding factors for comparing genetic mutations placed on these wild-type backgrounds. Here, we examined a variety of behavioral and electrophysiological endpoints in Drosophila, in both adult and larval animals. We characterized these endpoints in 3 commonly used fly strains: wild-type Canton Special (CS), and 2 commonly used white-eyed strains, isoCJ1 and w¹¹¹⁸. We found that CS and isoCJ1 show remarkably similar sensitivity to isoflurane across a variety of behavioral and electrophysiological endpoints. In contrast, w¹¹¹⁸ is resistant to isoflurane compared to the other 2 strains at both the adult and larval stages. This resistance is however not reflected at the level of neurotransmitter release at the larval neuromuscular junction (NMJ). This suggests that the w¹¹¹⁸ strain harbors another mutation that produces isoflurane resistance, by acting on an arousal pathway that is most likely preserved between larval and adult brains. This mutation probably also affects sleep, as marked differences between isoCJ1 and w¹¹¹⁸ have also recently been found for behavioral responsiveness and sleep intensity measures.     

Using Aspergillus nidulans To Identify Antifungal Drug Resistance Mutations

Systemic fungal infections contribute to at least 10% of deaths in hospital settings. Most antifungal drugs target ergosterol (polyenes) or its biosynthetic pathway (azoles and allylamines), or beta-glucan synthesis (echinocandins). Antifungal drugs that target proteins are prone to the emergence of resistant strains. Identification of genes whose mutations lead to targeted resistance can provide new information on those pathways. We used Aspergillus nidulans as a model system to exploit its tractable sexual cycle and calcofluor white as a model antifungal agent to cross-reference our results with other studies. Within 2 weeks from inoculation on sublethal doses of calcofluor white, we isolated 24 A. nidulans adaptive strains from sectoring colonies. Meiotic analysis showed that these strains had single-gene mutations. In each case, the resistance was specific to calcofluor white, since there was no cross-resistance to caspofungin (echinocandin). Mutation sites were identified in two mutants by next-generation sequencing. These were confirmed by reengineering the mutation in a wild-type strain using a gene replacement strategy. One of these mutated genes was related to cell wall synthesis, and the other one was related to drug metabolism. Our strategy has wide application for many fungal species, for antifungal compounds used in agriculture as well as health care, and potentially during protracted drug therapy once drug resistance arises. We suggest that our strategy will be useful for keeping ahead in the drug resistance arms race.     

Double-drug development against antioxidant enzymes from Plasmodium falciparum

Abstract

New drugs against malaria are urgently and continuously needed. Plasmodium parasites are exposed to higher fluxes of reactive oxygen species and need high activities of intracellular antioxidant systems. A most important antioxidative system consists of (di)thiols which are recycled by disulfide reductases (DR), namely both glutathione reductases (GR) of the malarial parasite Plasmodium falciparum and man, and the thioredoxin reductase (TrxR) of P. falciparum. The aim of our interdisciplinary research is to substantiate DR inhibitors as antimalarial agents. Such compounds are active per se but, in addition, they can reverse thiol-based resistance against other drugs in parasites. Reversal of drug resistance by DR inhibitors is currently investigated for the commonly used antimalarial drug chloroquine (CQ). Our recent strategy is based on the synthesis of inhibitors of the glutathione reductases from parasite and host erythrocyte. With the expectation of a synergistic or additive effect, double-headed prodrugs were designed to be directed against two different and essential functions of the malarial parasite P. falciparum, namely glutathione regeneration and heme detoxification. The prodrugs were prepared by linking bioreversibly a GR inhibitor to a 4-aminoquinoline moiety which is known to concentrate in the acidic food vacuole of parasites. Drug-enzyme interaction was correlated with antiparasitic action in vitro on strains resistant towards CQ and in vivo in Plasmodium berghei-infected mice as well as absence of cytotoxicity towards human cells. Because TrxR of P. falciparum was recently shown to be responsible for the residual glutathione disulfide-reducing capacity observed after GR inhibition in P. falciparum, future development of antimalarial drug-candidates that act by perturbing the redox equilibrium of parasites is based on the design of new double-drugs based on TrxR inhibitors as potential antimalarial drug candidates.     

Single-molecule sequencing reveals the molecular basis of multidrug-resistance in ST772 methicillin-resistant Staphylococcus aureus

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-associated infection, but there is growing awareness of the emergence of multidrug-resistant lineages in community settings around the world. One such lineage is ST772-MRSA-V, which has disseminated globally and is increasingly prevalent in India. Here, we present the complete genome sequence of DAR4145, a strain of the ST772-MRSA-V lineage from India, and investigate its genomic characteristics in regards to antibiotic resistance and virulence factors.

Results

Sequencing using single-molecule real-time technology resulted in the assembly of a single continuous chromosomal sequence, which was error-corrected, annotated and compared to nine draft genome assemblies of ST772-MRSA-V from Australia, Malaysia and India. We discovered numerous and redundant resistance genes associated with mobile genetic elements (MGEs) and known core genome mutations that explain the highly antibiotic resistant phenotype of DAR4145. Staphylococcal toxins and superantigens, including the leukotoxin Panton-Valentinin Leukocidin, were predominantly associated with genomic islands and the phage φ-IND772PVL. Some of these mobile resistance and virulence factors were variably present in other strains of the ST772-MRSA-V lineage.

Conclusions

The genomic characteristics presented here emphasize the contribution of MGEs to the emergence of multidrug-resistant and highly virulent strains of community-associated MRSA. Antibiotic resistance was further augmented by chromosomal mutations and redundancy of resistance genes. The complete genome of DAR4145 provides a valuable resource for future investigations into the global dissemination and phylogeography of ST772-MRSA-V.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1599-9) contains supplementary material, which is available to authorized users.