Abstract Polygalacturonases (PGs), enzymes that hydrolyze the homogalacturonan of the plant cell wall, are virulence factors of several phytopathogenic fungi and bacteria. On the other hand, PGs may activate defense responses by releasing oligogalacturonides (OGs) perceived by the plant cell as host-associated molecular patterns. Tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana) plants expressing a fungal PG (PG plants) have a reduced content of homogalacturonan. Here, we show that PG plants are more resistant to microbial pathogens and have constitutively activated defense responses. Interestingly, either in tobacco PG or wild-type plants treated with OGs, resistance to fungal infection is suppressed by exogenous auxin, whereas sensitivity to auxin of PG plants is reduced in different bioassays. The altered plant defense responses and auxin sensitivity in PG plants may reflect an increased accumulation of OGs and subsequent antagonism of auxin action. Alternatively, it may be a consequence of perturbations of cellular physiology and elevated defense status as a result of altered cell wall architecture.
Abstract The ongoing research carried out in our laboratory to elucidate the roles of polygalacturonase, PGIP and oligogalacturonides is reviewed. Keywords: Polygalacturonasespolygalacturonase-inhibiting proteinsplant defenceoligogalacturonidespectinelicitors
Pectins are a highly complex family of cell wall polysaccharides comprised of homogalacturonan (HGA), rhamnogalacturonan I and rhamnogalacturonan II. We have specifically modified HGA in both tobacco (Nicotiana tabacum) and Arabidopsis by expressing the endopolygalacturonase II of Aspergillus niger (AnPGII). Cell walls of transgenic tobacco plants showed a 25% reduction in GalUA content as compared with the wild type and a reduced content of deesterified HGA as detected by antibody labeling. Neutral sugars remained unchanged apart from a slight increase of Rha, Ara, and Gal. Both transgenic tobacco and Arabidopsis were dwarfed, indicating that unesterified HGA is a critical factor for plant cell growth. The dwarf phenotypes were associated with AnPGII activity as demonstrated by the observation that the mutant phenotype of tobacco was completely reverted by crossing the dwarfed plants with plants expressing PGIP2, a strong inhibitor of AnPGII. The mutant phenotype in Arabidopsis did not appear when transformation was performed with a gene encoding AnPGII inactivated by site directed mutagenesis.
Epstein Barr Virus (EBV), also classified as Human Herpes Virus 4, infects the vast majority of adults worldwide and establishes both non-productive (latent) and productive (lytic) infection. Classical EBV diagnosis includes quantitative determination of viral DNA and serological analysis, based on the determination of IgG and IgM responses against the viral capsid antigen (VCA) and the IgG response against the EBV nuclear antigen-1 (EBNA-1). EBV-serology can be misleading in some cases, such as acute infections with low or undetectable VCA IgM, convalescent patients with persistent or reactivated VCA IgM and negative anti- EBNA-1 IgG, due to a loss of this marker during immunosuppression. In all these cases avidity determination of IgG is helpful to prevent false diagnosis. Avidity represents the stability of the antigen-antibody interaction. Its value increases during the infection, so high avidity never associates with a primary acute infection. We studied the importance of avidity determination of p18 (VCA)-IgG to achieve unequivocal interpretation of serological results. The amount of IgG and IgM is determined by Chemiluminescent Immune Assay (CLIA), a rapid and highly sensitive method suitable for automation. The intensity of luminous signal produced by antibody-antigen recognition is expressed as Relative Light Unit (RLU). p-18 IgG is determined using a recombinant p18 antigen expressed in E. coli. Avidity index is determined in CLIA by the ratio between denaturated and not denaturated IgG specific antibodies expressed in RLU. These results demonstrate that avidity determination represents an important additional marker particularly in cases with aberrant serological profile.
Introduzione.Una appropriata diagnostica microbiologica nella gestione di pazienti ricoverati in Terapia Intensiva (T.I.), ha ricadute positive non solo per una terapia antibiotica mirata, ma anche per la sorveglianza dell'epidemiologia delle infezioni.Metodi.Sono stati analizzati i risultati relativi agli esami microbiologici eseguiti nell'anno 2006 presso la T.I. periferica e polivalente dell'Ospedale S. Biagio di Domodossola (VB).Nell'anno 2006 sono stati ammessi in T.I. 205 pazienti, sui quali sono stati eseguiti esami microbiologici di routine ( broncoaspirato, urinocoltura) una volta alla settimana, oppure al bisogno, in relazione alle condizioni cliniche del paziente.Nel periodo preso in esame sono state inviate in laboratorio 149 urinocolture e 29 emocolture.Gli esami colturali di aspirato tracheale esaminati nel 2006 sono 208, risultati positivi in 56 pazienti (27%).Risultati.I referti microbiologici inerenti le colture di aspirato bronchiale, evidenziano una colonizzazione da cocchi gram positivi nel 30% dei campioni ( in prevalenza Staphylococcus aureus), e nel 69% da batteri gram negativi (Pseudomonas aeruginosa, Escherichia coli ed Enterobacter aerogenes, i più frequenti).Lo studio della farmaco sensibilità ha evidenziato che il 50% di Staphylococcus aureus presenta il fenotipo MRSA.Pseudomomas aeruginosa risulta sensibile ad aminoglicosidi e carbapenemi rispettivamente nel 100% e nel 90% dei casi.Tutti i ceppi di Pseudomaonas aeruginaosa isolati, risultano essere probabili produttori di beta lattamasi verso piperacillina e ceftazidime.Lo studio del consumo di antibiotici espresso in DDD% per l'anno 2006, rileva che gli antibiotici più usati nel reparto sono: amoxicillina -acido clavulanico e ampicicillina -sulbactam in ragione di una DDD% di 36, i chinolonici e piperacillina -tazobactam, con DDD% rispettivamente di 24 e di 20.Conclusioni.L'esame microbiologico eseguito con costanza permette di raccogliere dati, tali da poter attivare protocolli di terapia antibiotica empirica, il più possibile aderenti all'epidemiologia di reparto.
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