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Grupo CoopAustralis

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Anthony Wilson
Anthony Wilson

Selenite F Broth Pdf Download UPDATED

Selenite F Broth is the medium used for the selective enrichment of Salmonella spp from both clinical and food samples. It is a buffered Lactose Peptone Broth to which Sodium Biselenite is added as the selective agent.

Selenite F Broth Pdf Download

These particular SeNPs display special physical characteristics such as photoelectric, semiconducting and X-ray-sensing properties [22] which make them attractive for possible nano-technological applications. They also possess adsorptive ability, antioxidant functions and due to their high surface area-to-volume ratio, a marked biological reactivity [23]; including anti-hydroxyl radical efficacy, a protective effect against DNA oxidation [24] and anti-microbial activity. Indeed, SeNPs have been found to strongly inhibit growth of Staphylococcus aureus, a key bacterial pathogen commonly occurring in human infections [25]. However, concern is now growing for the environmental impact of nanoparticle synthesis based on physico-chemical methods that require for high pressures and temperatures, are energy consuming, use toxic chemicals, and generate hazardous by-products. Consequently, applications using biological systems such as microbial cultures for the production of metal nanoparticles, including SeNPs, are becoming increasingly a realistic perspective. In the present paper the reduction of selenite by a strain of Bacillus sp. (previously classified as Bacillus mycoides SeITE01 [26]) has been investigated. This strain has been shown to be highly resistant to selenite (up to 25 mM) and able to transform this oxyanion into elemental SeNPs. In particular, a detailed comparison is given between the dynamics of disappearance of selenite from the growth medium and the appearance of SeNPs. Evidence is also provided for the SeNPs formation to be mainly in the extracellular environment. Based on the findings of microscopic analyses, coupled with biochemical and metabolic assays, hypotheses are advanced about possible mechanisms of reduction of selenite by B. mycoides SeITE01, compatible with the appearance of Se0 nanoparticles both inside or outside the bacterial cell.

The bacterial strain SeITE01 was isolated from the rhizosphere of the Se-hyperaccumulator plant Astragalus bisulcatus grown on a Se-polluted soil through enrichment cultures spiked with 2.0 mM sodium selenite, as described previously [26]. It was originally hypothesized that strain SeITE01 belonged to the Bacillus mycoides species on the basis of partial 16S rRNA gene sequence. In the present work, a combined approach using both gene sequencing analysis and evaluation of morphological traits has provided strain SeITE01 with a definitive taxonomic position.

The capability of SeITE01 to transform selenite to elemental selenium was tested in liquid rich medium (Nutrient Broth) at 0.5 and 2.0 mM concentration of Na2SeO3 (Figure 4). Selenite concentration in the growth medium, elemental selenium content, and bacterial growth were all measured.

Again, Sarret and colleagues demonstrated that selenite addition into cultures of Ralstonia metallidurans CH34 was followed by a lag of slow uptake, during which the bacteria contained Se0 and alkyl selenide in equivalent proportions [40]. Subsequently, selenite uptake strongly increased and Se0 resulted as the predominant transformation product, suggesting an activation of selenite transport and reduction systems after several hours of contact. The authors indicated that two reactions took place in R. metallidurans CH34: an assimilatory pathway leading to alkyl selenide and a detoxification pathway leading to Se0. The identification of a SAM dependent methyltransferase (SefB) in an operon adjacent to the SeNP assembly protein SefA in T. selenatis has also suggested a link between both reductive and alkyl-selenide dependent selenite detoxification [14]. Moreover, Kessi and Hanselmann, while investigating the possible involvement of the Painter type reaction in selenite reduction to elemental selenium in Rhodospirillum rubrum and Escherichia coli, hypothesized at first a quick formation of a selenium-digluthathione intermediate followed by elemental selenium production [21].

Results in agreement with those here presented have been described for other bacterial strains able to induce the formation of Se0 nanoparticles by selenite reduction. Bacillus subtilis, Pantoea agglomerans UC-32 and Shewanella sp. HN-41 all have shown to produce SeNPs of size and shape depending on time of incubation [38, 41, 42]. Further characterization of the selenium nanospheres formed by strain SeITE01 was also carried out using UV-Visible absorption spectroscopy (Figure 7). SeNPs were analyzed at three different incubation times, 6, 24 and 48 hours. All spectra presented a recurrent absorption peak at 280 nm probably due to the presence of aromatic amino acids, thus indicating possible adhesion of proteinaceous material on the surface of SeNPs. These data are consistent with the previously recognized occurrence of peptides and proteins associated to SeNPs of bacterial origin [14, 43, 44]. In particular, Lenz and co-workers showed that selenium nanoparticles can be coupled with a variety of high-affinity proteins. For instance, they demonstrated that a protein (RarA) next to a metalloid reductase was associated with Se-nanoparticles formed by Sulfurospirillum barnesii SES-3 [44]. The work of Debieux et al., [14] has also identified a secreted protein (SefA) from T. selenatis that has been demonstrated to stabilize the formation of SeNPs during selenate respiration.

Efficiency of selenite reduction was determined for SeITE01 in rich growth medium (Nutrient Broth). All microbiological tests were carried out in 250-ml Erlenmeyer flasks containing 100 ml of growth medium incubated at 28C on an orbital shaker (200 rpm). Each flask was inoculated with aliquots from stationary-phase cultures of the strain SeITE01 to reach a final optical density of 0.01. Assays were performed in the presence of two different Na2SeO3 concentrations, namely 0.5 or 2.0 mM. Culture samples collected at different times during different tests were analyzed for bacterial growth, residual selenite in the medium, and formation of elemental Se.

To check the selenite reduction activity by SeITE01 bacterial cultures reduction activity assays were carried out starting from different cell protein components (i.e. cytosolic and membrane-associated) as well as exopolysaccharide (EPS) fraction, and supernatant of SeITE01 liquid culture.

The collected samples were cultured on 1% peptone broth then 1 ml selenite F. broth and incubated aerobically at 37 C for 18 h then were subcultured to MacConkey, Salmonella shigella agar and/or XLD media. The cultured plates were incubated at 37 C for 24 h. Suspected colonies were picked up, preserved into semi solid agar as stock medium and into slant agar for further biochemical and serological identification.

Biochemical tests performed to characterize the enteric gram-negative bacteria include gram stain morphology, pigment production, motility, urease, citrate, hydrogen sulfide utilization, oxidase, indole, lysine, and sugar fermentation. The media used were nutrient broth (CONDA, Spain), lysine iron agar (LIA) (OXIOD, England), MRVP, Simmons citrate agar (HIMEDIA, India), Kligler iron agar (KIA) (SRL, India), Sulfide-Indole-Motility (SIM), urea broth base (OXIOD, England), Motility Indole Ornithine Medium (MIO) (OXIOD, England). The 3% H2O2 was used to identify Salmonella, Shigella species, and other enteric bacteria as adopted from the Basic laboratory Procedures in Clinical bacteriology WHO (Vandepitteet al., 2nd ed. 2003).

Background : Salmonella is a short rod shape, gram-negative, non-encapsulated, aerobic and anaerobic options that cause food poisoning in humans. Raw food of animal origin, particularly meat and eggs of birds have important role in the transfer of this disease. Since duck and turkey eggs are very important in the transmission of Salmonellosis and consuming of local and non-industrial eggs of ducks and turkeys in this area is common, the present study was performed to clarify the prevalence of salmonella contamination. Materials and Methods: In the present study, 300 native duck and turkey eggs were collected and transferred to the lab. In laboratory after sampling from surface of the eggs shell were disinfected with 80% ethanol and contents of 5 duck and turkey eggs, sparately mixed in special dishes. After 24 hr incubation at 37C with a swab in selenite - F broth were inoculated. Samples were transferred to Salmonella - Shigella agar from selenite-f environment. After incubation in 37C, colonies suspected to Salmonella were evaluated. Suspicious colonies in the TSI and lysine decarboxylase environments were inoculated. And bacteria that had reactions related to Salmonella, were studied by PCR with specific primers for Salmonella and serotypes of Salmonella Enteritidis and Salmonella Typhimurium. Results: A total of 300 eggs of ducks and turkeys ,7 cases (2.3%) were contaminated with Salmonella, and from 7 unclean egg s shell , 1 case of turkey egg shell (0.66%) was infected with Salmonella Typhimurium. And 6 duck eggs shell (4%) were infected, that all of the serotypes were Salmonella Typhimurium. Conclusion: Regarding the present study, and other researches, it can be concluded that the Salmonella infection in the duck and turkey eggs were less than poultry eggs and it seems that vertical transmission of Salmonella in the turkeys and ducks was less than poultry. 350c69d7ab

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