Susceptible Counterparts Research Articles

The level of ascorbate peroxidase is enhanced in benznidazole-resistant populations of Trypanosoma cruzi and its expression is modulated by stress generated by hydrogen peroxide

Ascorbate peroxidases (APX) are class I heme-containing enzymes that convert hydrogen peroxide into water molecules. The gene encoding APX has been characterized in 11 strains of Trypanosoma cruzi that are sensitive or resistant to benznidazole (BZ). Bioinformatic analysis revealed the presence of two complete copies of the T. cruzi APX (TcAPX) gene in the genome of the parasite, while karyotype analysis showed that the gene was present in the 2.000-kb chromosome of all of the strains analyzed. The sequence of TcAPX exhibited greater levels of similarity to those of orthologous enzymes from Leishmania spp than to APXs from the higher plant Arabidopsis thaliana. Northern blot and real-time reverse transcriptase polymerase chain reaction (RT-PCR) analyses revealed no significant differences in TcAPX mRNA levels between the T. cruzi strains analyzed. On the other hand, Western blots showed that the expression levels of TcAPX protein were, respectively, two and three-fold higher in T. cruzi populations with in vitro induced (17 LER) and in vivo selected (BZR) resistance to BZ, in comparison with their corresponding susceptible counterparts. Moreover, the two BZ-resistant populations exhibited higher tolerances to exogenous hydrogen peroxide than their susceptible counterparts and showed TcAPX levels that increased in a dose-dependent manner following exposure to 100 and 200 µM hydrogen peroxide.

Gene Expression Profiling in the Thiamethoxam Resistant and Susceptible B-biotype Sweetpotato Whitefly,Bemisia tabaci

Thiamethoxam has been used as a major insecticide to control the B-biotype sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Due to its excessive use, a high level of resistance to thiamethoxam has developed worldwide over the past several years. To better understand the molecular mechanisms underlying this resistance in B. tabaci, gene profiles between the thiamethoxam-resistant and thiamethoxam-susceptible strains were investigated using the suppression subtractive hybridization (SSH) library approach. A total of 72 and 52 upand down-regulated genes were obtained from the forward and reverse SSH libraries, respectively. These expressed sequence tags (ESTs) belong to several functional categories based on their gene ontology annotation. Some categories such as cell communication, response to abiotic stimulus, lipid particle, and nuclear envelope were identified only in the forward library of thiamethoxam-resistant strains. In contrast, categories such as behavior, cell proliferation, nutrient reservoir activity, sequence-specific DNA binding transcription factor activity, and signal transducer activity were identified solely in the reverse library.To study the validity of the SSH method, 16 differentially expressed genes from both forward and reverse SSH libraries were selected randomly for further analyses using quantitative realtime PCR (qRT-PCR). The qRT-PCR results were fairly consistent with the SSH results; however, only 50% of the genes showed significantly different expression profiles between the thiamethoxam-resistant and thiamethoxam-susceptible whiteflies. Among these genes, a putative NAD-dependent methanol dehydrogenase was substantially over-expressed in the thiamethoxamresistant adults compared to their susceptible counterparts. The distributed profiles show that it was highly expressed during the egg stage, and was most abundant in the abdomen of adult females.

Wolbachia Symbiont Infections Induce Strong Cytoplasmic Incompatibility in the Tsetse Fly Glossina morsitans

Tsetse flies are vectors of the protozoan parasite African trypanosomes, which cause sleeping sickness disease in humans and nagana in livestock. Although there are no effective vaccines and efficacious drugs against this parasite, vector reduction methods have been successful in curbing the disease, especially for nagana. Potential vector control methods that do not involve use of chemicals is a genetic modification approach where flies engineered to be parasite resistant are allowed to replace their susceptible natural counterparts, and Sterile Insect technique (SIT) where males sterilized by chemical means are released to suppress female fecundity. The success of genetic modification approaches requires identification of strong drive systems to spread the desirable traits and the efficacy of SIT can be enhanced by identification of natural mating incompatibility. One such drive mechanism results from the cytoplasmic incompatibility (CI) phenomenon induced by the symbiont Wolbachia. CI can also be used to induce natural mating incompatibility between release males and natural populations. Although Wolbachia infections have been reported in tsetse, it has been a challenge to understand their functional biology as attempts to cure tsetse of Wolbachia infections by antibiotic treatment damages the obligate mutualistic symbiont (Wigglesworthia), without which the flies are sterile. Here, we developed aposymbiotic (symbiont-free) and fertile tsetse lines by dietary provisioning of tetracycline supplemented blood meals with yeast extract, which rescues Wigglesworthia-induced sterility. Our results reveal that Wolbachia infections confer strong CI during embryogenesis in Wolbachia-free (GmmApo) females when mated with Wolbachia-infected (GmmWt) males. These results are the first demonstration of the biological significance of Wolbachia infections in tsetse. Furthermore, when incorporated into a mathematical model, our results confirm that Wolbachia can be used successfully as a gene driver. This lays the foundation for new disease control methods including a population replacement approach with parasite resistant flies. Alternatively, the availability of males that are reproductively incompatible with natural populations can enhance the efficacy of the ongoing sterile insect technique (SIT) applications by eliminating the need for chemical irradiation.

Multilevel population genetics in antibiotic resistance

Evolutionary approaches to antibiotic resistance have been mostly based on the consideration of the changes in frequency of resistant bacterial cells (organisms) in comparison with their susceptible counterparts. In this context, the term ‘population’ is frequently used to describe the ensemble of bacterial individuals within a species possessing or lacking a resistance trait (‘resistant population’ vs. ‘susceptible population’). Of course this ‘population’ concept is useful in epidemiology, but does not necessarily reflect real populational variation within a bacterial species (Camus & Lima, 2002; Waples & Gaggiotti, 2006; Balloux, 2010). A group of susceptible bacterial individuals might differ from a group of resistant individuals of the same species by only a single nucleotide, a difference that is not necessarily enough to consider them as different biological populations. Of course, the application of molecular techniques based on polymorphic changes in the bacterial genome to define the population structure of bacterial species, such as multilocus sequence typing, produces a much more faithful image of the population diversity of bacterial species. The term ‘susceptible’ or ‘resistant’ populations refers more to intraclonal ‘populations’, for which the term of intraclonal variants would be better. An emerging concept increasingly used in Public Health Microbiology and extensively treated in this Thematic Issue is reflected by the terms ‘high risk clones, or clonal complexes’, referring to highly specialized genetic populations or subpopulations with enhanced ability to colonize, spread and persist in particular niches after having acquired a diversity of adaptative traits that increase their …

African trypanosomiasis

African trypanosomiasis

Energetic Cost of Insecticide Resistance in Culex pipiens Mosquitoes

The extensive use of insecticides to control vector populations has lead to the widespread development of different mechanisms of insecticide resistance. Mutations that confer insecticide resistance are often associated to fitness costs that prevent them from spreading to fixation. In vectors, such fitness costs include reductions in preimaginal survival, adult size, longevity, and fecundity. The most commonly invoked explanation for the nature of such pleiotropic effects of insecticide resistance is the existence of resource-based trade-offs. According to this hypothesis, insecticide resistance would deplete the energetic stores of vectors, reducing the energy available for other biological functions and generating trade-offs between insecticide resistance and key life history traits. Here we test this hypothesis by quantifying the energetic resources (lipids, glycogen, and glucose) of larvae and adult females of the mosquito Culex pipiens L. resistant to insecticides through two different mechanisms: esterase overproduction and acetylcholinesterase modification. We find that, as expected from trade-off theory, insecticide resistant mosquitoes through the overproduction of esterases contain on average 30% less energetic reserves than their susceptible counterparts. Acetylcholinesterase-modified mosquitoes, however, also showed a significant reduction in energetic resources (20% less). We suggest that, in acetylcholinesterase-modified mosquitoes, resource depletion may not be the result of resource-based trade-offs but a consequence of the hyperactivation of the nervous system. We argue that these results not only provide a mechanistic explanation for the negative pleiotropic effects of insecticide resistance on mosquito life history traits but also can have a direct effect on the development of parasites that depend on the vector's energetic reserves to fulfil their own metabolic needs.

Backcrosses to Brassica napus of hybrids between B. juncea and B. napus as a source of herbicide-resistant volunteer-like feral populations

Introgression between genetically modified (GM) crops and wild relatives is considered to potentially modify the genetic background of the wild species. The emergence of volunteer-like feral populations through backcross of hybrids to the crop is also a concern. The progeny of spontaneous hybrids between mutant herbicide-resistant oilseed rape ( Brassica napus) and wild B. juncea was obtained. Parents, F 2 and BC 1 to B. napus were planted together in the field so as to study their performance. The chromosome number of BC 1 followed a Normal distribution. Mendelian ratio of the herbicide-resistance gene was found. The F 2 produced less seeds than B. napus, and BC 1 had intermediate production. Herbicide-resistant BC 1 were not different of their susceptible counterparts for plant weight, seed weight and seed number, but most of them exhibited B. napus morphology and larger flowers than the susceptible BC 1. They displayed an important genetic variability allowing further adaptation and propagation of the herbicide-resistance gene. Pollen flow to susceptible plants within the mixed stand was observed. As a consequence, the resistant BC 1 produced with B. napus pollen could frequently occur and easily establish as a false feral crop population within fields and along roadsides.

Cross‐resistance between the Mexican Rice Borer and the Sugarcane Borer (Lepidoptera: Crambidae): A Case Study Using Sugarcane Breeding Populations

The sugarcane borer (SCB) [Diatraea saccharalis (F.)] and Mexican rice borer (MRB) [Eoreuma loftini (Dyar)] are two economically important pests of sugarcane (Saccharum spp. hybrids) in the United States. Because of similarities in larval feeding behavior, selecting for resistance to one species could provide resistance to the other, a phenomenon we have termed “cross‐resistance”. The objective of this study was to determine if SCB‐resistance in sugarcane is correlated with resistance to MRB. Thirty genotypes from Louisiana previously identified as either resistant or susceptible to the SCB and 50 from Texas with unknown resistance status to either species were evaluated for percent borer‐damaged internodes. Data from the SCB‐resistant and‐susceptible genotypes were used to determine the SCB‐resistance status of all 80 genotypes. Similar (P = 0.578) levels of MRB damage were found between the Louisiana and Texas population, whereas, the Louisiana population suffered significantly (P < 0.05) less SCB damage compared to the Texas population. The SCB‐resistant genotypes suffered significantly (P < 0.01) less damage from the MRB compared to their susceptible counterparts. A significant (P < 0.001) association was found in percent SCB‐ and MRB‐damaged internodes among the Louisiana and the SCB‐resistant populations but not among the Texas or SCB‐susceptible populations. Furthermore, the SCB‐resistant genotypes were 40% less likely than susceptible ones to be bored by the MRB. Resources developed for SCB‐resistance could form the foundation material to breed for resistance to both pests.

Compensation of Fitness Costs and Reversibility of Antibiotic Resistance Mutations

Strains of bacterial pathogens that have acquired mutations conferring antibiotic resistance often have a lower growth rate and are less invasive or transmissible initially than their susceptible counterparts. However, fitness costs of resistance mutations can be ameliorated by secondary site mutations. These so-called compensatory mutations may restore fitness in the absence and/or presence of antimicrobials. We review literature data and show that the fitness gains in the absence and presence of antibiotic treatment need not be correlated. The aim of this study is to gain a better conceptual grasp of how compensatory mutations with different fitness gains affect evolutionary trajectories, in particular reversibility. To this end, we developed a theoretical model with which we consider both a resistance and a compensation locus. We propose an intuitively understandable parameterization for the fitness values of the four resulting genotypes (wild type, resistance mutation only, compensatory mutation only, and both mutations) in the absence and presence of treatment. The differential fitness gains, together with the turnover rate and the mutation rate, strongly affected the success of antibacterial treatment, reversibility, and long-term abundance of resistant strains. We therefore propose that experimental studies of compensatory mutations should include fitness measurements of all possible genotypes in both the absence and presence of an antibiotic.

Resistance to Fusarium Head Blight and Seedling Blight in Wheat Is Associated with Activation of a Cytochrome P450 Gene

ABSTRACT One plant genotype displays a resistance phenotype at one development stage but a susceptible reaction to the same pathogen at another stage, which is referred to here as resistance inversion. In wheat, Fusarium head blight (FHB)-resistant cv. Sumai3 showed a Fusarium seedling blight (FSB)-susceptible reaction whereas FHB-susceptible cv. Annong8455 exhibited FSB resistance when challenged with a Fusarium asiaticum strain that produces deoxynivalenol (DON). The resistance to FHB and FSB in wheat was closely associated with expression of a plant cytochrome P450 gene in response to FHB pathogens and mycotoxins. Quantitative real-time polymerase chain reaction analyses showed that expression of nine defense-related genes in spikes and seedlings was induced by the fungal infection, in which a massive accumulation of a plant cytochrome P450 gene, CYP709C1, was clearly associated with the resistance reaction in both seedling and spike. The FHB-resistant Sumai3 accumulated 7-fold more P450 transcripts than did the FHB-susceptible Annong8455, while 84-fold more P450 transcripts were accumulated in the FSB-resistant Annong8455 than the FSB-susceptible Sumai3. A Fusarium strain with a disrupted Tri5 gene, which is not able to produce the first enzyme essential for trichothecene mycotoxin biosynthesis, also induced more P450 transcripts in FHB- and FSB-resistant cultivars. The fungal activation of the P450 gene was more profound in the FSB-resistant reaction than the FHB-resistant reaction relative to their susceptible counterparts. DON triggered a differential expression of the P450 gene with comparable patterns in spikes and seedlings in a resistance-dependent manner. These results may provide a basis for dissecting mechanisms underlying FHB and FSB resistance reactions in wheat and revealing functions of the cytochrome P450 in plant detoxification and defense.

Costs of insensitive acetylcholinesterase insecticide resistance for the malaria vector Anopheles gambiae homozygous for the G119S mutation

BackgroundThe G119S mutation responsible for insensitive acetylcholinesterase resistance to organophosphate and carbamate insecticides has recently been reported from natural populations of Anopheles gambiae in West Africa. These reports suggest there are costs of resistance associated with this mutation for An. gambiae, especially for homozygous individuals, and these costs could be influential in determining the frequency of carbamate resistance in these populations.MethodsLife-history traits of the AcerKis and Kisumu strains of An. gambiae were compared following the manipulation of larval food availability in three separate experiments conducted in an insecticide-free laboratory environment. These two strains share the same genetic background, but differ in being homozygous for the presence or absence of the G119S mutation at the ace-1 locus, respectively.ResultsPupae of the resistant strain were significantly more likely to die during pupation than those of the susceptible strain. Ages at pupation were significantly earlier for the resistant strain and their dry starved weights were significantly lighter; this difference in weight remained when the two strains were matched for ages at pupation.ConclusionsThe main cost of resistance found for An. gambiae mosquitoes homozygous for the G119S mutation was that they were significantly more likely to die during pupation than their susceptible counterparts, and they did so across a range of larval food conditions. Comparing the frequency of G119S in fourth instar larvae and adults emerging from the same populations would provide a way to test whether this cost of resistance is being expressed in natural populations of An. gambiae and influencing the dynamics of this resistance mutation.

Putative Link between the Virulence-Associated fluA Gene and Fluoroquinolone Resistance in Uropathogenic Escherichia coli

Resistance to fluoroquinolones is a major problem in the treatment of various infectious diseases, including urinary tract infections (UTI) caused by Escherichia coli. It has been recognized that fluoroquinolone-resistant E. coli strains generally harbor fewer virulence genes than their susceptible counterparts (2, 4, 5, 7, 8). We observed an increased prevalence of the virulence-associated fluA gene, which encodes the autotransporter protein Ag43a (9), in E. coli isolated in 2006 to 2008 compared to that in isolates collected prior to fluoroquinolone use (1983 to 1986). This increase was seen only in E. coli isolated from patients with urosepticemia, displaying a fluoroquinolone resistance rate of 26%, but not among isolates from patients with UTI, all of which were sensitive to these agents. Interestingly, 11 of the 12 resistant isolates carried fluA. We therefore chose to study a set of resistant and sensitive strains from patients with urosepticemia for a possible association between fluA and fluoroquinolone resistance. A total of 34 sensitive and 57 resistant E. coli isolates collected from patients with urosepticemia between 2000 and 2009 at the Karolinska University Hospital Solna, Stockholm, Sweden, were investigated. Fluoroquinolone resistance was determined according to guidelines of the Swedish Reference Group for Antibiotics (www.srga.org). Isolates sensitive to ciprofloxacin but resistant to nalidixic acid were considered resistant after confirmation of target alteration by sequencing (10). The presence of fluA was determined by PCR (9), and isolates were assigned to phylogenetic group A, B1, B2, or D by multiplex PCR (1). Prevalence data were compared by using Fisher's exact test or the chi-square test, as appropriate. Differences with P values of <0.05 were considered statistically significant. The frequency of phylogenetic groups B2 and D differed significantly between the resistant and sensitive populations (Table ​(Table1).1). While the sensitive isolates mostly belonged to group B2, the resistant ones were associated with group D. This distribution is in line with previous studies (4, 5, 7, 8). TABLE 1. Distribution of phylogenetic groups and fluA in relation to susceptibility to fluoroquinolones As indicated by our initial observation, the prevalence of fluA was significantly higher in fluoroquinolone-resistant isolates than in fluoroquinolone-sensitive isolates (42 of 57 [74%] and 16 of 34 [47%], respectively; Table ​Table1).1). Also, the prevalence of fluA differed depending on the phylogenetic origin (P < 0.001), with fluA significantly associated with group D (83% versus 45% in the remaining groups, P = 0.0002). Further analysis revealed equal distribution of fluA in sensitive and resistant isolates belonging to group D (Table ​(Table1).1). In contrast, fluA was associated with resistance in isolates of group B2. This again is in agreement with other studies suggesting a relationship between the presence or absence of certain virulence genes and antimicrobial resistance only in group B2 (3, 7, 8) but not in group D (6). In conclusion, we report here that the virulence-associated fluA gene is positively linked to fluoroquinolone resistance, particularly in E. coli belonging to phylogenetic group B2. To our knowledge, fluA has not been previously described in this connection and might provide another factor to understand the complex relationship between fluoroquinolone resistance and virulence in E. coli.

The Quantity and Quality of African Children's IgG Responses to Merozoite Surface Antigens Reflect Protection against Plasmodium falciparum Malaria

BackgroundAntibodies, particularly cytophilic IgG subclasses, with specificity for asexual blood stage antigens of Plasmodium falciparum, are thought to play an important role in acquired immunity to malaria. Evaluating such responses in longitudinal sero-epidemiological field studies, allied to increasing knowledge of the immunological mechanisms associated with anti-malarial protection, will help in the development of malaria vaccines.Methods and FindingsWe conducted a 1-year follow-up study of 305 Senegalese children and identified those resistant or susceptible to malaria. In retrospective analyses we then compared post-follow-up IgG responses to six asexual-stage candidate malaria vaccine antigens in groups of individuals with clearly defined clinical and parasitological histories of infection with P. falciparum. In age-adjusted analyses, children resistant to malaria as well as to high-density parasitemia, had significantly higher IgG1 responses to GLURP and IgG3 responses to MSP2 than their susceptible counterparts. Among those resistant to malaria, high anti-MSP1 IgG1 levels were associated with protection against high-density parasitemia. To assess functional attributes, we used an in vitro parasite growth inhibition assay with purified IgG. Samples from individuals with high levels of IgG directed to MSP1, MSP2 and AMA1 gave the strongest parasite growth inhibition, but a marked age-related decline was observed in these effects.ConclusionOur data are consistent with the idea that protection against P. falciparum malaria in children depends on acquisition of a constellation of appropriate, functionally active IgG subclass responses directed to multiple asexual stage antigens. Our results suggest at least two distinct mechanisms via which antibodies may exert protective effects. Although declining with age, the growth inhibitory effects of purified IgG measurable in vitro reflected levels of anti-AMA1, -MSP1 and -MSP2, but not of anti-GLURP IgG. The latter could act on parasite growth via indirect parasiticidal pathways.

Attributable Hospital Cost and Length of Stay Associated with Health Care-Associated Infections Caused by Antibiotic-Resistant Gram-Negative Bacteria

Determination of the attributable hospital cost and length of stay (LOS) are of critical importance for patients, providers, and payers who must make rational and informed decisions about patient care and the allocation of resources. The objective of the present study was to determine the additional total hospital cost and LOS attributable to health care-associated infections (HAIs) caused by antibiotic-resistant, gram-negative (GN) pathogens. A single-center, retrospective, observational comparative cohort study was performed. The study involved 662 patients admitted from 2000 to 2008 who developed HAIs caused by one of following pathogens: Acinetobacter spp., Enterobacter spp., Escherichia coli, Klebsiella spp., or Pseudomonas spp. The attributable total hospital cost and LOS for HAIs caused by antibiotic-resistant GN pathogens were determined by comparison with the hospital costs and LOS for a control group with HAIs due to antibiotic-susceptible GN pathogens. Statistical analyses were conducted by using univariate and multivariate analyses. Twenty-nine percent of the HAIs were caused by resistant GN pathogens, and almost 16% involved a multidrug-resistant GN pathogen. The additional total hospital cost and LOS attributable to antibiotic-resistant HAIs caused by GN pathogens were 29.3% (P < 0.0001; 95% confidence interval, 16.23 to 42.35) and 23.8% (P = 0.0003; 95% confidence interval, 11.01 to 36.56) higher than those attributable to HAIs caused by antibiotic-susceptible GN pathogens, respectively. Significant covariates in the multivariate analysis were age >or=12 years, pneumonia, intensive care unit stay, and neutropenia. HAIs caused by antibiotic-resistant GN pathogens were associated with significantly higher total hospital costs and increased LOSs compared to those caused by their susceptible counterparts. This information should be used to assess the potential cost-efficacy of interventions aimed at the prevention of such infections.

Polymorphisms in the HSP90AA1 5′ flanking region are associated with scrapie incubation period in sheep

Susceptibility to scrapie is mainly controlled by point mutations at the PRNP locus. However, additional quantitative trait loci (QTL) have been identified across the genome including a region in OAR18. The gene which encodes the inducible form of the cytoplasmic Hsp90 chaperone (HSP90AA1) maps within this region and seems to be associated with the resistance/susceptibility to scrapie in sheep. Here, we have analyzed several polymorphisms which were previously described in the ovine HSP90AA1 5' flanking region and in intron 10 in two naturally scrapie infected Romanov sheep populations. First, we have studied 58 ARQ/VRQ animals pertaining to the sire family where the QTL influencing scrapie incubation period in OAR18 was detected. We have found a significant association between polymorphisms localized at -660 and -528 in the HSP90AA1 5' flanking region and the scrapie incubation period. These two polymorphisms have also been studied in a second sample constituted by 62 VRQ/VRQ sheep showing an extreme incubation period. Results are concordant with the first dataset. Finally, we have studied the HSP90AA1 expression in scrapie and control animals (N = 41) with different HSP90AA1 genotypes by real time PCR on blood samples. The HSP90AA1 expression rate was equivalent in CC(-600)AA(-528) and CG(-600)AG(-528) scrapie resistant animals (ARR/ARR) and was higher in their CC(-600)AA(-528) than in their CG(-600)AG(-528) scrapie susceptible counterparts (VRQ/VRQ). Our results support the hypothesis that the ovine HSP90AA1 gene acts as a modulator of scrapie susceptibility, contributing to the observed differences in the incubation period of scrapie infected animals with the same PRNP genotype.

Protective Response to Leishmania major in BALB/c Mice Requires Antigen Processing in the Absence of DM

Protection from the parasite Leishmania major is mediated by CD4 T cells. BALB/c mice are susceptible to L. major and show a nonprotective immunodominant CD4 T cell response to Leishmania homolog of activated receptor for c-kinase (LACK) 158-173. Host genes that underlie BALB/c susceptibility to L. major infections are poorly defined. DM, a nonclassical MHC class II molecule, due to its peptide editing properties has been shown to 1) edit the repertoire of peptides displayed by APC, and 2) focus the display of epitopes by APC to the immunodominant ones. We tested the hypothesis that deficiency of DM, by causing presentation of a different array of epitopes by infected APC than that presented by DM-sufficient APC, may change the course of L. major infection in the susceptible BALB/c mice. We show herein that unlike their susceptible wild-type counterparts, BALB/c mice deficient in DM are protected from infections with L. major. Furthermore, DM-deficient mice fail to display the immunodominant LACK 158-173 on infected APC. In its place, infected DM(-/-) hosts show elicitation of CD4 T cells specific for newer epitopes not presented by wild-type L. major-infected APC. Protection of BALB/c DM(-/-) mice is dependent on IFN-gamma. DM is thus a host susceptibility gene in BALB/c mice, and Ag processing in the absence of DM results in elicitation of a protective T cell response against L. major infections. This report suggests a novel mechanism to trigger host resistance against pathogens.

Occurrence of spvA Virulence Gene and Clinical Significance for Multidrug-Resistant Salmonella Strains

Nontyphoidal Salmonella strains are important reservoirs of antimicrobial resistance. An important issue that has not been investigated is whether the multiresistant Salmonella strains are more virulent than their susceptible counterparts. Salmonella isolates collected from clinical human (n=888) and porcine (n=2,120) cases at the same time period and geographic location were investigated. Antimicrobial susceptibility, PCR analysis for the spvA virulence gene, and pulsed-field gel electrophoresis (PFGE) genotyping were done. Carriage of spvA was associated with multidrug-resistant (MDR) type ACSSuT strains (odds ratio, 7.1; P<0.05), a type often implicated in bacteremic human cases. PFGE revealed that clinical isolates from pigs were more clonally related to those of human origin than the nonclinical porcine isolates. The findings suggest that MDR strains that also carry specific virulence factors are more likely to be of clinical significance.

Dissecting the insecticide‐resistance‐ associated cytochrome P450 gene Cyp6g1

The cytochrome P450 gene Cyp6g1 is overtranscribed in all field isolates of DDT-resistant Drosophila melanogaster (Meigen) and confers a fitness advantage when inherited via the female. Overtranscription is associated with the insertion of an Accord transposable element into the 5' end of the resistance allele. Here the authors attempt to dissect the transcription of the P450 gene in order to understand why resistance confers an advantage rather than the expected cost. Using a transgenic UAS:GAL4 reporter, the authors document the overexpression patterns of green fluorescent protein (GFP) in the fat body, midgut and Malpighian tubules driven by flies carrying the resistant 5' construct. Knockout of Cyp6g1 via RNAi decreases both the level of Cyp6g1 transcript and the metabolism of the artificial substrate MROD (methyl ether resorufin, Sigma M1544). RNAi does not, however, significantly increase the susceptibility of susceptible flies to DDT. Finally, quantification of Cyp6g1 RNA in embryos laid by resistant females indicates that they pass on more Cyp6g1 RNA to their progeny than their susceptible counterparts. These results help explain why the eggs and larvae of resistant females enjoy a fitness benefit rather than a cost, and suggest that the provisioning of Cyp6g1 RNA to embryos provides a direct, but uncharacterised, fitness benefit.

Virulence Factors in Urinary Escherichia coli Strains: Phylogenetic Background and Quinolone and Fluoroquinolone Resistance

Quinolone- and fluoroquinolone-resistant Escherichia coli strains harbor fewer virulence factors than susceptible strains. The reasons underlying this correlation are incompletely understood. We investigated the phylogenetic background, the presence of the papC, hlyA, and cnf1 (pathogenicity island II(J96)-associated), fimA, iss, and iutA genes, and the presence of type 1 fimbriae, P fimbriae, and hemolysin in 243 urinary E. coli isolates resistant only to quinolones (8%), resistant to both quinolones and fluoroquinolones (51%), or susceptible to both drugs (41%). Group B2 accounted for 56% of the isolates, showing a significantly higher prevalence among fluoroquinolone-susceptible strains than among resistant strains (65% versus 50% [P = 0.03]). hly and cnf1 were significantly more associated with susceptibility (P < 0.001) and with group B2 (P < 0.001 for group B2 versus groups A and D). However, within group B2, fluoroquinolone-resistant strains showed lower prevalences of papC, hlyA, and cnf1 than their susceptible counterparts (P < 0.001). In contrast, the incidence of iutA appeared higher for refractory isolates, including group B2, than for susceptible isolates (P < 0.001). Only in group B2 did fluoroquinolone-resistant strains reveal a lesser ability to agglutinate Saccharomyces cerevisiae (7%) than quinolone-resistant (87%) and susceptible (80%) isolates, despite uniform possession of fimA genes. No similar contrast emerged for expression of hemolysin and P fimbriae. Mutations conferring quinolone and fluoroquinolone resistance may thus require a particular genetic background, not strictly correlated with phylogenetic groups. More interestingly, the mutational event itself can affect the expression of type 1 fimbriae, at least in the prevalent and complex B2 strains.

Bloodstream Infections Among Transplant Recipients: Results of a Nationwide Surveillance in Spain1

Bloodstream infections (BSIs) are a major cause of morbidity and mortality in transplant recipients. The aim of this study is to describe the incidence, microbiology and outcomes of BSIs in transplant recipients in Spain. The Spanish Network for Research on Infection in Transplantation (RESITRA) is formed by 16 centers with transplant program in Spain. The incidence and characteristics of BSIs in transplant patients were obtained prospectively from the cohort. We included 3926 transplant recipients (2935 solid organ and 991 hematopoietic stem cell transplants). Overall, 730 episodes of BSIs were recorded with an incidence rate ranging from 3 episodes per 10 000 transplant days in kidney recipients to 44 episodes per 10 000 transplant days in allogeneic hematopoietic stem cell transplantation (HSCT). The most frequent sources were intravascular catheters and the most frequent microorganisms isolated were coagulase-negative staphylococci. Crude mortality of BSIs was 7.8%, being highest in liver recipients (16%). Multidrug resistant nonfermentative gram-negative BSIs had significantly worse prognosis than those caused by their susceptible counterparts (p = 0.015), but no differences were found between resistant and susceptible gram-negative enteric bacilli, S. aureus or Candida spp. BSIs are still a major concern in transplant recipients. The increasing isolations of multiresistant microorganisms represent a challenge for the next years.