Oxidized halogen antimicrobials, such as hypochlorous and hypobromous acids, have been used extensively for microbial control in industrial systems. Recent discoveries have shown that acylated homoserine lactone cell-to-cell signaling molecules are important for biofilm formation in Pseudomonas aeruginosa, suggesting that biofouling can be controlled by interfering with bacterial cell-to-cell communication. This study was conducted to investigate the potential for oxidized halogens to react with acylated homoserine lactone-based signaling molecules. Acylated homoserine lactones containing a 3-oxo group were found to rapidly react with oxidized halogens, while acylated homoserine lactones lacking the 3-oxo functionality did not react. The Chromobacterium violaceum CV026 bioassay was used to determine the effects of such reactions on acylated homoserine lactone activity. The results demonstrated that 3-oxo acyl homoserine lactone activity was rapidly lost upon exposure to oxidized halogens; however, acylated homoserine lactones lacking the 3-oxo group retained activity. Experiments with the marine alga Laminaria digitata demonstrated that natural haloperoxidase systems are capable of mediating the deactivation of acylated homoserine lactones. This may illustrate a natural defense mechanism to prevent biofouling on the surface of this marine alga. The Chromobacterium violaceum activity assay illustrates that reactions between 3-oxo acylated homoserine lactone molecules and oxidized halogens do occur despite the presence of biofilm components at much greater concentrations. This work suggests that oxidized halogens may control biofilm not only via a cidal mechanism, but also by possibly interfering with 3-oxo acylated homoserine lactone-based cell signaling.
The clinical and economic importance of fasciolosis has been recognised for centuries, yet diagnostic tests available for cattle are far from perfect. Test evaluation has mainly been carried out using gold standard approaches or under experimental settings, the limitations of which are well known. In this study, a Bayesian no gold standard approach was used to estimate the diagnostic sensitivity and specificity of five tests for fasciolosis in cattle. These included detailed liver necropsy including gall bladder egg count, faecal egg counting, a commercially available copro-antigen ELISA, an in-house serum excretory/secretory antibody ELISA and routine abattoir liver inspection. In total 619 cattle slaughtered at one of Scotland’s biggest abattoirs were sampled, during three sampling periods spanning summer 2013, winter 2014 and autumn 2014. Test sensitivities and specificities were estimated using an extension of the Hui Walter no gold standard model, where estimates were allowed to vary between seasons if tests were a priori believed to perform differently for any reason. The results of this analysis provide novel information on the performance of these tests in a naturally infected cattle population and at different times of the year where different levels of acute or chronic infection are expected. Accurate estimates of sensitivity and specificity will allow for routine abattoir liver inspection to be used as a tool for monitoring the epidemiology of F. hepatica as well as evaluating herd health planning. Furthermore, the results provide evidence to suggest that the copro-antigen ELISA does not cross-react with Calicophoron daubneyi rumen fluke parasites, while the serum antibody ELISA does.
The O-polysaccharide fraction of the lipopolysaccharide from Klebsiella pneumoniae serotype O8 was found to comprise two galactose-containing homopolymers. Structural analysis, using chemical and high-field nuclear magnetic resonance (NMR) techniques, established that the K. pneumoniae O8 polysaccharides are composed of the linear, disaccharide repeating units [formula: see text] K. pneumoniae O8 mutant RFK-1 was isolated by resistance to phage KO1-2; strain RFK-1 expressed only D-galactan I-OAc. The 1H- and 13C-NMR resonances from this O-polysaccharide indicate that all of the O-acetyl groups within the K. pneumoniae O8 polysaccharide are carried on D-galactan I and O-acetylation occurs only on the beta-D-galactofuranose residues; 60% of the available beta-D-galactofuranose residues are non-acetylated. The O-acetylation of the remaining residues is equally distributed between the O-2 and O-6 positions. The carbohydrate backbone structures in the O8 polysaccharide are identical to D-galactan I and II expressed by K. pneumoniae O1, accounting for the antigenic cross-reaction between strains belonging to serotypes O1 and O8. However, the O1 polysaccharides are not acetylated and the O-acetyl groups present in the K. pneumoniae serotype O8 polysaccharides provide a structural basis for their recognition as distinct serotypes. The rfb (O-polysaccharide biosynthesis) gene cluster of K. pneumoniae serotype O1 determines the synthesis of D-galactan I. rfbKpO1-specific gene probes were used to examine conservation in the rfb gene clusters of other K. pneumoniae serotypes which produce D-galactan I. Six O1 strains were examined and all showed hybridization with rfbKpO1 probes under conditions of high stringency. Three serotype O2 strains produce D-galactan I and these strains also contained DNA sequences recognized by rfbKpO1 probes under high stringency. The physical maps of these homologous rfb chromosomal regions showed some polymorphism. Surprisingly, the rfbKpO8 region from K. pneumoniae serotype O8 was only recognized by rfbKpO1 probes under low-stringency hybridization conditions, providing evidence for two substantially different clonal groups of rfb genes from K. pneumoniae strains with structurally related O-antigens.
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