Klebsiella pneumoniae OmpA confers resistance to antimicrobial peptides

A Klebsiella pneumoniae ompA mutant was more susceptible to antimicrobial peptides (APs) than the wild type. Susceptibility did not result from surface changes other than the absence of OmpA. Our data suggest that OmpA is implicated in the activation of yet-unknown systems dedicated to ameliorating AP cytotoxicity.

Capsule polysaccharide mediates bacterial resistance to antimicrobial peptides

The innate immune system plays a critical role in the defense of areas exposed to microorganisms. There is an increasing body of evidence indicating that antimicrobial peptides and proteins (APs) are one of the most important weapons of this system and that they make up the protective front for the respiratory tract. On the other hand, it is known that pathogenic organisms have developed countermeasures to resist these agents such as reducing the net negative charge of the bacterial membranes. Here we report the characterization of a novel mechanism of resistance to APs that is dependent on the bacterial capsule polysaccharide (CPS). Klebsiella pneumoniae CPS mutant was more sensitive than the wild type to human neutrophil defensin 1, beta-defensin 1, lactoferrin, protamine sulfate, and polymyxin B. K. pneumoniae lipopolysaccharide O antigen did not play an important role in AP resistance, and CPS was the only factor conferring protection against polymyxin B in strains lacking O antigen. In addition, we found a significant correlation between the amount of CPS expressed by a given strain and the resistance to polymyxin B. We also showed that K. pneumoniae CPS mutant bound more polymyxin B than the wild-type strain with a concomitant increased in the self-promoted pathway. Taken together, our results suggest that CPS protects bacteria by limiting the interaction of APs with the surface. Finally, we report that K. pneumoniae increased the amount of CPS and upregulated cps transcription when grown in the presence of polymyxin B and lactoferrin.

Temperature-regulated efflux pump/potassium antiporter system mediates resistance to cationic antimicrobial peptides in Yersinia

Most bacterial pathogens are resistant to cationic antimicrobial peptides (CAMPs) that are key components of the innate immunity of both vertebrates and invertebrates. In Gram-negative bacteria, the known CAMPs resistance mechanisms involve outer membrane (OM) modifications and specifically those in the lipopolysaccharide (LPS) molecule. Here we report, the characterization of a novel CAMPs resistance mechanism present in Yersinia that is dependent on an efflux pump/potassium antiporter system formed by the RosA and RosB proteins. The RosA/RosB system is activated by a temperature shift to 37 degrees C, but is also induced by the presence of the CAMPs, such as polymyxin B. This is the first report of a CAMPs resistance system that is induced by the presence of CAMPs. It is proposed that the RosA/RosB system protects the bacteria by both acidifying the cytoplasm to prevent the CAMPs action and pumping the CAMPs out of the cell.

Alteration of beta-tubulin in Nicotiana plumbaginifolia confers resistance to amiprophos-methyl

A Nicotiana plumbaginifolia plant (apm5(r)) resistant to amiprophos-methyl (APM), a phosphoroamide herbicide, was isolated from protoplasts prepared from leaves of haploid plants. Genetic analysis revealed that the resistance is coded for by a dominant nuclear mutation and is associated with the increased stability of cortical microtubules. Two-dimensional polyacrylamide-gel electrophoresis, combined with immunoblotting using anti-tubulin monoclonal antibodies, showed that part of the beta-tubulin in the resistant plant possessed lower isoelectric points than the beta-tubulin of susceptible wild-type plants. These results provide evidence that the resistance to APM is associated with a mutation in a beta-tubulin gene. The APM-resistant line showed cross-resistance to trifluralin, a dinitroaniline herbicide, suggesting a common mechanism of resistance between these two classes of herbicides.

Efficacy of Biocides Used in the Modern Food Industry To Control Salmonella enterica, and Links between Biocide Tolerance and Resistance to Clinically Relevant Antimicrobial Compounds

Biocides play an essential role in limiting the spread of infectious disease. The food industry is dependent on these agents, and their increasing use is a matter for concern. Specifically, the emergence of bacteria demonstrating increased tolerance to biocides, coupled with the potential for the development of a phenotype of cross-resistance to clinically important antimicrobial compounds, needs to be assessed. In this study, we investigated the tolerance of a collection of susceptible and multidrug-resistant (MDR) Salmonella enterica strains to a panel of seven commercially available food-grade biocide formulations. We explored their abilities to adapt to these formulations and their active biocidal agents, i.e., triclosan, chlorhexidine, hydrogen peroxide, and benzalkonium chloride, after sequential rounds of in vitro selection. Finally, cross-tolerance of different categories of biocidal formulations, their active agents, and the potential for coselection of resistance to clinically important antibiotics were investigated. Six of seven food-grade biocide formulations were bactericidal at their recommended working concentrations. All showed a reduced activity against both surface-dried and biofilm cultures. A stable phenotype of tolerance to biocide formulations could not be selected. Upon exposure of Salmonella strains to an active biocidal compound, a high-level of tolerance was selected for a number of Salmonella serotypes. No cross-tolerance to the different biocidal agents or food-grade biocide formulations was observed. Most tolerant isolates displayed changes in their patterns of susceptibility to antimicrobial compounds. Food industry biocides are effective against planktonic Salmonella. When exposed to sublethal concentrations of individual active biocidal agents, tolerant isolates may emerge. This emergence was associated with changes in antimicrobial susceptibilities.

Fasciola hepatica in the rat:immune responses associated with the development of resistance to infection

F. hepatica infections were established in rats and immune responses were monitored during primary and challenge infections. Antibody levels peaked at 3 weeks post-primary infection and at 6 days post-challenge infection. No significant correlation was found between antibody titre and number of flukes recovered at autopsy. Immunoblotting revealed a limited number of immunogenic polypeptides. When antibodies from these reactive bands were eluted and tested by IFA they all gave identical binding patterns: on juvenile fluke sections tegumental syncytium, tegumental cells and gut cells were labelled, while on adult sections the same antibodies labelled gut cells, reproductive tissue, excretory ducts and flame cells. This suggested that these tissues shared a common epitope or range of epitopes. A pronounced eosinophilia was observed throughout the infection period studied and infected liver sections showed massive cellular infiltration. Histochemical and immunocytochemical investigation of infected liver revealed the presence of large numbers of eosinophils, neutrophils, lymphocytes and phagocytes. The implications of these findings, to an understanding of concomitant immunity in the rat are discussed.

Associations between repetitive questioning, resistance to change, temper outbursts and anxiety in Prader-Willi and Fragile-X syndromes

The behavioural phenotypes of Prader-Willi (PWS) and Fragile-X (FraX) syndromes both comprise repetitive behaviours with differences between the profiles. In this study we investigated the context and antecedents to the repetitive behaviours and the association with other behavioural phenotypic characteristics in order to generate testable hypotheses regarding the cause of the behaviours.

The parents or carers of 46 children with PWS (mean age 14.1 years; 20 girls), and 33 boys with FraX (mean age 13.11 years) were interviewed about their children's repetitive behaviour in a semi-structured format.

Children showed negative emotional behaviour (PWS: 87.0%; FraX: 79.4%) and repetitive questions (PWS: 78.3%; FraX: 73.5%) following changes in routine or expectations. Significantly more temper outbursts were reported to follow changes in children with PWS (89.1%) compared with boys with FraX (41.2%) (chi(2) = 20.93; P <0.001). Anxiety that was frequently associated with repetitive and self-injurious behaviours in boys with FraX, followed changes in significantly more boys with FraX (76.5%) compared with children with PWS (6.5%) (chi(2) = 43.19, P <0.001).

On the basis of these reports and existing literature, we hypothesise that decreases in predictability are aversive to children with PWS and FraX. We also hypothesise that these children have a propensity to show a syndrome-related pattern of behaviour (temper outbursts in PWS and displays of anxiety in FraX) when an event in the environment has this aversive property. We hypothesise that questions may be reinforcing to children in their own right by increasing the predictability of the environment. We outline how a specific cognitive deficit in the endophenotypes associated with both PWS and FraX could be investigated as a potential explanation for the hypothesised aversive properties of decreased predictability.

ADAM17-Dependent c-MET-STAT3 Signaling Mediates Resistance to MEK Inhibitors in KRAS Mutant Colorectal Cancer

There are currently no approved targeted therapies for advanced KRAS mutant (KRASMT) colorectal cancer (CRC). Using a unique systems biology approach, we identified JAK1/2-dependent activation of STAT3 as the key mediator of resistance to MEK inhibitors in KRASMT CRC in vitro and in vivo. Further analyses identified acute increases in c-MET activity following treatment with MEK inhibitors in KRASMT CRC models, which was demonstrated to promote JAK1/2-STAT3-mediated resistance. Furthermore, activation of c-MET following MEK inhibition was found to be due to inhibition of the ERK-dependent metalloprotease ADAM17, which normally inhibits c-MET signaling by promoting shedding of its endogenous antagonist, soluble "decoy" MET. Most importantly, pharmacological blockade of this resistance pathway with either c-MET or JAK1/2 inhibitors synergistically increased MEK-inhibitor-induced apoptosis and growth inhibition in vitro and in vivo in KRASMT models, providing clear rationales for the clinical assessment of these combinations in KRASMT CRC patients.

Genome-wide association study identifies novel loci associated with resistance to bovine tuberculosis

Tuberculosis (TB) caused by Mycobacterium bovis is a re-emerging disease of livestock that is of major economic importance worldwide, as well as being a zoonotic risk there is significant heritability for host resistance to bovine TB (bTB) in dairy cattle. To identify resistance loci for bTB, we undertook a genome-wide association study in female Holstein-Friesian cattle with 592 cases and 559 age-matched controls from case herds. Cases and controls were categorised into distinct phenotypes: skin test and lesion positive vs skin test negative on multiple occasions, respectively these animals were genotyped with the Illumina BovineHD 700K BeadChip. Genome-wide rapid association using linear and logistic mixed models and regression (GRAMMAR), regional heritability mapping (RHM) and haplotype-sharing analysis identified two novel resistance loci that attained chromosome-wise significance, protein tyrosine phosphatase receptor T (PTPRT; P=4.8 × 10 -7) and myosin IIIB (MYO3B; P=5.4 × 10 -6). We estimated that 21% of the phenotypic variance in TB resistance could be explained by all of the informative single-nucleotide polymorphisms, of which the region encompassing the PTPRT gene accounted for 6.2% of the variance and a further 3.6% was associated with a putative copy number variant in MYO3B the results from this study add to our understanding of variation in host control of infection and suggest that genetic marker-based selection for resistance to bTB has the potential to make a significant contribution to bTB control.

Down-regulation of PERK enhances resistance to ionizing radiation

Although, ionizing radiation (IR) has been implicated to cause stress in endoplasmic reticulum (ER), how ER stress signaling and major ER stress sensors modulate cellular response to IR is unclear. Protein kinase RNA-like endoplasmic reticulum kinase (PERK) is an ER transmembrane protein which initiates unfolded protein response (UPR) or ER stress signaling when ER homeostasis is disturbed. Here, we report that down-regulation of PERK resulted in increased clonogenic survival, enhanced DNA repair and reduced apoptosis in irradiated cancer cells. Our study demonstrated that PERK has a role in sensitizing cancer cells to IR.