Production and partial characterization of chitinase from a halotolerant Planococcus rifitoensis strain M2-26

peer reviewedThis paper is the first to investigate the production and partial characterization of the chitinase enzyme from a moderately halophilic bacterium Planococcus rifitoensis strain M2-26, earlier isolated from a shallow salt lake in Tunisia. The impact of salt, salinity concentration, pH, carbon and nitrogen sources on chitinase production and activity have been determined. This is the first report on a high salt-tolerant chitinase from P. rifitoensis, since it was active at high salinity (from 5 to 30% NaCl) as well as in the absence of salt. This enzyme showed optimal activity at 70 C and retained up to 82 and 66% of its original activity at 80 or 90 C, respectively. The activity of the enzyme was also shown over a wide pH range (from 5 to 11). For characterization of the enzyme activity, the chitinase secreted in the culture supernatant was partially purified. The preliminary study of the concentrated dialysed supernatant on native PAGE showed at least three chitinases produced by strain M2-26, with highest activity approximately at 65 kDa. Thus, the thermo-tolerant and high salt-tolerant chitinases produced by P. rifitoensis strain M2-26 could be useful for application in diverse areas such as biotechnology and agro-industry

Soil parameters drive the diversity of Citrus sinensis rhizosphere microbiota which exhibits a potential in plant drought stress alleviation

Plant associated microorganisms, particularly those exhibiting a plant growth promoting (PGP) effect, play an important role in plant nutrition and health and the adaptation to unfavorable climatic conditions, such as drought which threatens the productivity of agricultural crops. The selection of specific microbial populations in the soil habitats associated to plants depends upon the soil physico-chemical parameters besides the \u2018rhizosphere effect\u2019 played by each plant species through rhizodepositions. In this study, we investigated the community structure and PGP potential of the microbiota associated to Citrus sinensis plants located in different geographical regions of Tunisia. The bacteria community structure was correlated to soil physiochemical parameters and we identified potassium, carbon and organic matter content as drivers of the C. sinensis microbiota composition. The evaluation of the potential of selected bacteria as biofertilizer and bio-stimulator under drought stress was achieved through the phylogenetic and functional characterization of a large collection of bacterial strains isolated from the rhizosphere of C. sinensis. The strains were screened in vitro for putative plant growth promoting traits, and the six most promising isolates were tested in vivo on Solanum lycopersicum and Capsicum annuum model plants. The bacterized plants were cultivated under drought stress and compared with not bacterized and fully irrigated control plants. All the tested bacteria induced a significant increase in the number of leaves and in root biomass of both plant species compared to not inoculated plants. Our results highlighted that the strains Ensifer adhaerens S1B1.5 and Pseudomonas resinovorans S4R2.6 were, in particular, effective in promoting plant growth under water shortage, indicating them as promising strains for the development of sustainable biofertilizers suited for agriculture in arid and semi-arid regions characterized by water scarcity

Les fistules vesico-uterines a propos d'une nouvelle observation

No Abstract

Isolation and characterization of shiga toxin-producing Escherichia coli from meat and dairy products

This work was conducted in Laboratoire de Contrôle des Eaux et Denrées Alimentaires, Institut Pasteur de Tunis, Tunisia.International audienceShiga toxin-producing Escherichia coli (STEC) strains were detected among 250 E. coli strains isolated from 204 food samples (meat and dairy products) obtained from butcher shops and retail stores in BEN AROUS (a Tunisian State/south east of the Tunisian capital). These 250 E. coli strains were isolated by applying culture techniques using sorbitol MacConkey (SMAC) agar after preenrichment of the homogenized food samples in buffered peptone water for 6 and 24 h, and violet red bile lactose (VRBL) agar. The highest percentage of E. coli recovery was from SMAC/6h preenrichment time and VRBL agar for meat and dairy products, respectively. Serotype O55:B5 was found to be the most prevalent type among E. coli isolates. E. coli isolates were screened for virulence factors: Shiga toxin 1 [stx1 (130 bp)], Shiga toxin 2 [stx2 (346 bp)], and eae gene [494 bp] by colony blot hybridization using three radioactively labelled DNA probes. Results obtained were confirmed by PCR. The three STEC isolates: one isolate-produced stx2, another isolate-produced stx1 and stx2, and the third isolate-expressed stx1, stx2, as well as eae genes. All three isolates produced EAST1. All Shiga toxin positive by PCR were found positive in the verocytotoxin test. In conclusion, this study indicates the presence of a possible bovine reservoir for STEC strains in Tunisia, signaling a potential risk for humans

Multidrug-resistant enterococci in the hospital environment: Detection of novel vancomycin-resistant E. faecium clone ST910

Introduction: The role of the hospital environment as a reservoir of resistant bacteria in Tunisia has been poorly investigated; however, it could be responsible for the transmission of multidrug-resistant bacteria. The objective was to study the prevalence of Enterococcus in the environment of a Tunisian hospital and the antibiotic resistance phenotype/genotype in recovered isolates, with special reference to vancomycin resistance. Methodology: A total of 300 samples were taken (MarchJune, 2013) and inoculated in Slanetz-Bartley agar plates supplemented or not supplemented with 8 µg/mL of vancomycin. Antibiotic resistance genes were tested by polymerase chain reaction (PCR). The clonal relatedness of the vanA isolates was assessed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence testing (MLST). Results: Enterococci were recovered in 33.3% of tested samples inoculated in SB medium. E faecium was the most prevalent species, followed by E. faecalis and E. casseliflavus. Antimicrobial resistance genes detected were as follows (number of isolates): erm(B) (71), tet(M) (18), aph(3)-IIIa (27), ant(6)-Ia (15), cat(A) (4), and van(C2) (6). Vancomycin-resistant-enterococci (VRE) were recovered from 14 samples (4.7%), when tested in SB-VAN. The 14 VRE (one per positive sample) were identified as E. faecium and contained the van(A),erm(B), tet(M), ant(6)-Ia, and aph(3)-IIIa genes. Thirteen of the VRE strains were ascribed by PFGE and MLST to a novel clone (new ST910), and only one VRE strain was typed as ST80 included in CC17. Conclusions: The emergence and spread of new clones of VRE, especially in the hospital environment in this country, could become particularly problematic. © 2016 Dziri et al

Diversity of root endophytic bacteria associated with the date palm tree from the south of Tunisia

Endophytes are the microbes colonizing the internal tissues of plants. These microbes are able to establish different types of interaction with their host, such as mutualism, commensalism and symbiosis. The present work deals with the identification of entophytic bacteria from the palm date routs sampled in different oasis located in the south of Tunisia and the determination of the prevalent species adapted to such extreme conditions. The molecular characterization of isolates, based on the analysis of the intergenic-spacer amplification profiles, showed the differentiation of 16 different haplotypes. These groups reflect the diversity of isolates within the different samples and the spatial diversity inherent to the sampling region. The identification of these isolates by 16S rDNA sequen\ue7ing showed the prevalence of Proteobacteria, Actinobacteria and Bacteroidetes groups, including the species of Pseudomonas brassicacearum, Yersinia kristensenii, Ranella aquatilis, Pantoea ananatis, Microbacterium phyllosphareae and Buttiauxella noakiae. Screening of the strains for plant growth promoting properties showed that some of the strains were able to fix nitrogen, to produce high amounts of auxins and/or to express anti-fungal activity inhibiting the growth of Botrytis cineria and Aspergillus niger. This study showed the importance of these bacteria for potential application in the biocontrol of phytopathogenic fungi and in promoting the growth of plants

Caractérisation moléculaire et morphologique de deux espèces affines de

La description en 1998 de Phlebotomus riouxi a posé le problème de la diagnose différentielle délicate de la femelle avec celle d’une espèce affine : P. chabaudi. Le rôle suspecté de P. chabaudi dans la transmission de Leishmania killicki dans certains foyers tunisiens nous a amené, à partir de 37 spécimens algériens et tunisiens, à effectuer la caractérisation moléculaire de ces deux taxons. Les séquences du gène du cytochrome b (cyt b) de l’ADN mitochondrial individualisent clairement ces taxons et mettent en évidence une variabilité intraspécifique. L’analyse morphologique ne permet pas de différencier les femelles des deux espèces sur la base des caractères génitaux. Un caractère céphalique nouveau tenant à la présence de dents latérales antérieures sur l’armature pharyngienne de P. chabaudi, absentes chez P. riouxi, est proposé, mais un recours au typage moléculaire semble nécessaire pour une identification fiable

Caractérisation moléculaire et morphologique de deux espèces affines de Paraphlebotomus: Phlebotomus chabaudi Croset, Abonnenc & Rioux, 1970 et P. riouxi Depaquit, Killick-Kendrick & Léger, 1998 (Diptera : Psychodidae)

La description en 1998 de Phlebotomus riouxi a posé le problème de la diagnose différentielle délicate de la femelle avec celle d’une espèce affine : P. chabaudi. Le rôle suspecté de P. chabaudi dans la transmission de Leishmania killicki dans certains foyers tunisiens nous a amené, à partir de 37 spécimens algériens et tunisiens, à effectuer la caractérisation moléculaire de ces deux taxons. Les séquences du gène du cytochrome b (cyt b) de l’ADN mitochondrial individualisent clairement ces taxons et mettent en évidence une variabilité intraspécifique. L’analyse morphologique ne permet pas de différencier les femelles des deux espèces sur la base des caractères génitaux. Un caractère céphalique nouveau tenant à la présence de dents latérales antérieures sur l’armature pharyngienne de P. chabaudi, absentes chez P. riouxi, est proposé, mais un recours au typage moléculaire semble nécessaire pour une identification fiable

Prevalence, antimicrobial resistance and genetic lineages of Enterococcus spp. from vegetable food, soil and irrigation water in farm environments in Tunisia

BACKGROUND: The objective of this study was to determine the species, clonal diversity, antibiotic resistance and virulence of enterococci in different environments. Seventy-one samples of farm origin (34 of food vegetables, 27 of soil and ten of irrigation water) and 19 samples of vegetables from five markets, were inoculated in Slanetz-Bartley agar plates supplemented or not with gentamicin (SB-Gen and SB plates, respectively) for enterococci recovery. RESULTS: Enterococci were obtained from 72.2% of tested samples in SB media (food vegetables from farms, 88.2%; soil and irrigation water, 51%; food vegetables from markets, 84.2%), and 65 enterococcal isolates were obtained. Enterococcus faecium was the most prevalent species (52.3%), followed by E. hirae (35.4%), E. faecalis (6.15%), and E. casseliflavus (6.15%). Antibiotic resistance detected among these enterococci was as follows (percentage/detected gene): ciprofloxacin (60%), erythromycin (18.4%/erm(B)), tetracycline (15.4%/tet(M)-tet(L)), kanamycin (15.4%/aph(3)-III), chloramphenicol (7.7%), streptomycin (3%/ant(6)), vancomycin (6.15%/vanC2)), teicoplanin (0%) and ampicillin (0%). High-level gentamicin-resistant (HLR-G) enterococci were detected in SB-Gen plates in 14 of 90 tested samples (15.5%), and 15 isolates were characterized: ten E. faecalis, four E. faecium and one E. hirae. All HLR-G enterococci carried the aac(6)-aph(2), erm(B) and tet(M) genes, among other resistance genes. The HLR-G isolates showed high genetic diversity (ten different PFGE profiles), and were ascribed to the sequence types ST2, ST16, ST28 and new ST528 (in E. faecalis), and ST56, new ST885 and new ST886 (in E. faecium). CONCLUSION: Food vegetables in the farm or market settings are frequently contaminated by HLR-G enterococci, and these microorganisms could reach the human intestine through the food chain, if hygienic conditions are not followed. © 2015 Society of Chemical Industry