Alteration of virulence factors and rearrangement of pAsa5 plasmid caused by the growth of Aeromonas salmonicida in stressful conditions

Aeromonas salmonicida, a fish pathogen, is the causative agent of furunculosis. It was already shown that growing this bacterium in stressful conditions such as temperature above 22°C might lead to virulence attenuation. Unfortunately, many veterinary microbiology services and reference centers still routinely cultivate A. salmonicida at 25°C. Here we tested the presence of virulence factors by growth on specific medium as well as the integrity of the pAsa5 plasmid, which bears an important virulence factor, the type III secretion system (TTSS), by PCR analysis in twenty strains, most of which were grown at 25°C in their laboratory of origin. The analysis revealed that strains, which encountered the more stressful growth conditions displayed the most frequent absence of A-layer protein and secreted proteolytic activity. Moreover, many strains had lost parts of the pAsa5 plasmid in which the TTSS region was almost always affected. To confirm the effect of stressful growth conditions on the plasmid, three strains with an intact pAsa5 were cultured at 25°C for two weeks. A low but significant fraction of the tested colonies displayed pAsa5 rearrangements. The rearrangement always affected the TTSS region and led to a loss of virulence in the Dictyostelium discoideum co-culture assay. These results demonstrate that the instability of pAsa5 did not lead to its complete loss as previously proposed but to a more complex rearrangement phenomenon and emphasizes the necessity to grow A. salmonicida in appropriate conditions to preserve the complete virulence of the bacterium

Pregnant and non-pregnant women and low back pain-related differences on postural control measures during different balance tasks

Introduction: Low back pain (LBP) is the most common musculoskeletal complaint in pregnancy, being responsible for many negative impacts. Objective: To evaluate the effect of LBP on static and dynamic balance in pregnant women and whether pregnancy mediates the results compared to non-pregnant women. Methods: 44 women (mean age 30 yrs) participated voluntarily in this study: 16 pregnant women with LBP starting in pregnancy, 14 pregnant women without LBP and 14 non-pregnant women as a group control. Participants were assessed for static postural balance using a force platform and dynamic mobility balance using the Timed Up and Go (TUG) test. Results: The pregnant women with LBP showed significant (P < 0.04, for mean, d= 1,2) poor postural balance in static tests (force platform), in the area of COP eyes open. In dynamic balance (TUG test), statistical difference was found between the groups (P 0.038) and the effect size were moderate to strong in the comparison between the three groups. The most sensitive differences were reported mainly between pregnant women with LBP versus non-pregnant control group in balance measures from force platform. Conclusion: The findings indicate that LBP associated to pregnant clinical status can decrease the balance capacity in women. These results have implication for balance evaluation and retraining in pregnant women with and without LBP from rehabilitation or prevention programs

An Insertion Sequence-Dependent Plasmid Rearrangement in Aeromonas salmonicida Causes the Loss of the Type Three Secretion System

Aeromonas salmonicida, a bacterial fish pathogen, possesses a functional Type Three Secretion System (TTSS), which is essential for its virulence. The genes for this system are mainly located in a single region of the large pAsa5 plasmid. Bacteria lose the TTSS region from this plasmid through rearrangements when grown in stressful growth conditions. The A. salmonicida genome is rich in insertion sequences (ISs), which are mobile DNA elements that can cause DNA rearrangements in other bacterial species. pAsa5 possesses numerous ISs. Three IS11s from the IS256 family encircle the rearranged regions. To confirm that these IS11s are involved in pAsa5 rearrangements, 26 strains derived from strain A449 and two Canadian isolates (01-B526 and 01-B516) with a pAsa5 rearrangement were tested using a PCR approach to determine whether the rearrangements were the result of an IS11-dependent process. Nine out of the 26 strains had a positive PCR result, suggesting that the rearrangement in these strains were IS-dependent. The PCR analysis showed that all the rearrangements in the A449-derived strains were IS11-dependent process while the rearrangements in 01-B526 and 01-B516 could only be partially coupled to the action of IS11. Unidentified elements that affect IS-dependent rearrangements may be present in 01-B526 and 01-B516. Our results suggested that pAsa5 rearrangements involve IS11. This is the first study showing that ISs are involved in plasmid instability in A. salmonicida

Étude de la fonction d'Ati2, un effecteur du système de sécrétion de type trois chez Aeromonas salmonicida

La bactérie Aeromonas salmonicida utilise le système de sécrétion de type trois (SSTT) pour injecter des effecteurs à l'intérieur des cellules de l'hôte lors de l'infection. L'étude du génome d'A. salmonicida a révélé l'existence d'Ati2, un nouvel effecteur du SSTT. Ce projet avait pour but d'étudier la relation structure-fonction d'Ati2 afin de déterminer son rôle dans la virulence d'A. salmonicida. Des analyses biochimiques et en modélisation moléculaire ont permis de démontrer qu'Ati2 est une inositol polyphosphate 5-phosphatase qui hydrolyse les PtdIns(4,5)P₂ et les PtdIns(3,4,5)P₃. Divers mutants d'Ati2 ont été produits et clones dans des vecteurs d'expression chez l'amibe Dictyostelium discoideum. Les tests d'expression ont démontré qu'Ati2 est toxique pour l'amibe et que cela est lié à son activité catalytique. Ce projet de recherche a ainsi permis de démontrer l'existence d'un nouvel effecteur du SSTT et d'en spécifier la fonction dans la pathogénicité d'A. salmonicida

École Cherrier, 811, rue Cherrier, Montréal, 1931

Connue aussi sous le nom d'École Espace-Jeunesse; Architecte du bâtiment d'origine: Eugène Larose; Firme responsable des travaux d'agrandissement: Dufresne & Dallaire; Date de construction: 1931; Date d'agrandissement: 1967; Photographie: J.-P. Gariépy, commandée par Pierre-Richard Bisson, 1978.0

École Cherrier, 811, rue Cherrier, Montréal, 1931

Connue aussi sous le nom d'École Espace-Jeunesse; Architecte du bâtiment d'origine: Eugène Larose; Firme responsable des travaux d'agrandissement: Dufresne & Dallaire; Date de construction: 1931; Date d'agrandissement: 1967; Photographie: J.-P. Gariépy, commandée par Pierre-Richard Bisson, 1978.0

École Cherrier, 811, rue Cherrier, Montréal, 1931

Connue aussi sous le nom d'École Espace-Jeunesse; Architecte du bâtiment d'origine: Eugène Larose; Firme responsable des travaux d'agrandissement: Dufresne & Dallaire; Date de construction: 1931; Date d'agrandissement: 1967; Photographie: J.-P. Gariépy, commandée par Pierre-Richard Bisson, 1978.03À gauche: Petite façade latérale ouest donnant sur la rue Saint-Hubert; À droite: Longue façade principale donnant sur la rue Cherrie