One Coli Collins Mp3 Download
Mathilda Allhands
The potential role of rock pigeons (Columba livia) in the epidemiology of shiga toxin-producing Escherichia coli (STEC) and Salmonella enterica is unclear. Our objective was to determine the prevalence of STEC and S. enterica in pigeons at urban and dairy settings as a function of season. Prevalence of STEC and S. enterica was estimated by bacteriologic culture of cloacal swabs collected from pigeons trapped at urban and dairy locations in and around Fort Collins, Colorado from January to November 2003. Presumptive E. coli isolates were tested for the presence of virulence genes SLT-1, SLT-2, eae, hlyA, K1, CNF-1, CNF-2, and LT using polymerase chain reaction. Shiga toxins were not isolated from any of 406 samples from pigeons, but virulence genes typically associated with disease in humans were identified in isolates from 7.9% (95% CI: 5.5% to 10.9%) of captured pigeons. S. enterica were detected in 3.2% of 277 samples from pigeons, with all positive samples originating from dairy locations (nine of 106 [8.5%]; 95% CI: 4.0-15.5%). The results suggest that although pigeons may acquire S. enterica from cattle and play a role in recirculation and persistence of the microorganism at dairies, pigeons are not important carriers of STEC.
Enterokinase (EK) is a heterodimeric serine protease which plays a key role in initiating the proteolytic digestion cascade in the mammalian duodenum. The enzyme acts by converting trypsinogen to trypsin via a highly specific cleavage following the pentapeptide recognition sequence (Asp)4-Lys. This stringent site specificity gives EK great potential as a fusion protein cleavage reagent. Recently, a cDNA encoding the catalytic (light) chain of bovine enterokinase (EKL) was identified, characterized, and transiently expressed in mammalian COS cells. We report here the production of EKL in Escherichia coli by a novel secretory expression system that utilizes E. coli DsbA protein as an N-terminal fusion partner. The EKL cDNA was fused in-frame to the 3'-end of the coding sequence for DsbA, with the two domains of the fusion protein separated by a linker sequence encoding an enterokinase recognition site. Active, processed recombinant EKL (rEKL) was generated from this fusion protein via an autocatalytic cleavage reaction. The enzymatic properties of the bacterially produced rEKL were indistinguishable from the previously described COS-derived enzyme. Both forms of rEKL were capable of cleaving peptides, polypeptides and trypsinogen with the same specificity exhibited by the native heterodimeric enzyme purified from bovine duodena. Interestingly, rEKL activated trypsinogen poorly relative to the native heterodimeric enzyme, but was superior in its ability to cleave artificial fusion proteins containing the (Asp)4-Lys recognition sequence.
Chris Collins, right, rests at his Lake Oswego, Ore., home with his wife, Kellie, Wednesday, Nov. 4, 2015. Collins was one of at least 39 people in Oregon and Washington state to be sickened with E. coli in the outbreak associated with the popular Mexican food chain, Chipotle.
Be a good neighbor and help keep it off streets and out of local parks, natural areas, streams, rivers and lakes. When you pick up your pet's waste, you prevent giardia, E-coli and other bacteria from reaching our waterways. Do your duty for a healthier river.
In this case, the researchers designed their model to look for chemical features that make molecules effective at killing E. coli. To do so, they trained the model on about 2,500 molecules, including about 1,700 FDA-approved drugs and a set of 800 natural products with diverse structures and a wide range of bioactivities.
In this study, the researchers found that E. coli did not develop any resistance to halicin during a 30-day treatment period. In contrast, the bacteria started to develop resistance to the antibiotic ciprofloxacin within one to three days, and after 30 days, the bacteria were about 200 times more resistant to ciprofloxacin than they were at the beginning of the experiment.
Silk-elastin-like proteins (SELPs) combining the physicochemical and biological properties of silk and elastin have a high potential for use in the pharmaceutical, regenerative medicine and materials fields. Their development for use is however restrained by their production levels. Here we describe the batch production optimisation for a novel recently described SELP in the pET-E. coli BL21(DE3) expression system. Both a comprehensive empirical approach examining all process variables (media, induction time and period, temperature, pH, aeration and agitation) and a detailed characterisation of the bioprocess were carried out in an attempt to maximise production with this system.
We have identified the optimal conditions for the shake flask production of a novel SELP with the final production levels obtained being the highest reported to date. While this study is focused on SELPs, we believe that it could also be of general interest to any study where the pET (ampicillin selective marker)-E. coli BL21(DE3) expression system is used. In particular, we show that induction time is critical in this system with, in contrast to that which is generally believed, optimal production being obtained by induction at the beginning of the stationary phase. Furthermore, we believe that we are at or near the maximum productivity for the system used, with rapid degradation of the selective agent by plasmid encoded β-lactamase, plasmid instability on induction and high acetate production levels being the principal limiting factors for further improved production.
In an attempt to further improve the production in TB and SB we investigated these media further, initially investigating the effect of varying the sugar supplements used. Glycerol, glucose and fructose were examined at concentrations from 0 to 20 g/L but no significant increases in biomass or SELP yields were detected under the conditions used. Indeed, at the higher concentrations of these carbon sources, a drop in pH to below pH 6.0 was accompanied by a reduced cellular density and drastically reduced SELP production (> 90% loss). Interestingly, differences in final cell density and recombinant protein production might have been expected with the different carbon sources tested as these have dissimilar uptake rates and lead to different byproducts in E.coli[23, 31]. However, with the complex rich media used in this study, the sugar supplements do not constitute the only source of carbon present [23] and hence these have a reduced effect. In fact, we even found that TB without a sugar supplement led to a final cell density of as much as 75% of that in sugar supplemented media. The effects of varying the concentrations of yeast extract and bacto tryptone in TB were also investigated, but again no increases in SELP production levels were noted. Ammonium and amino acid additives were then examined as previous studies have indicated the positive effects of ammonium as a nitrogen source, even in the presence of excess organic nitrogen [32]. Furthermore, due to the highly repetitive nature of the amino acid sequences of PBPs, the potential benefits of exogenously added amino acids can be easily understood and has been previously shown. Chow et al. [26] documented increased PBP production in rich media supplemented with proline and alanine, while Tuite et al. [33] showed the beneficial effects of methionine and isoleucine supplementation on E coli growth in minimal media due to reduced acetate toxicity. In contrast, in our study, addition of ammonium or various amino acids (V, P, A, G, S, M, I), or of supplements such as NaCl or magnesium, did not have any significant effect on production levels under the conditions used. These ingredients are most probably already present in sufficiently high concentrations in the rich media used here. In fact, this inability to further improve SELP production by media composition manipulation, under the conditions used, points to effects other than media composition being limiting to further recombinant protein production.
E. coli is a facultative anaerobe with an optimal growth temperature of 37C and optimal pH range of between 6.0 and 7.5. It is generally grown under aerobic conditions as anaerobic growth yields less energy for metabolic processes such as protein synthesis [34].
Aeration, or oxygen availability, and mixing efficiency are critical parameters for the growth and metabolism of E. coli. In shake flask productions, the flask volume to liquid volume ratio and the agitation rate are the modifiable parameters which influence the culture mixing and aeration and hence were optimised in our study (Figures 4 and 5). Increases in the values of these parameters, which lead to an improved aeration and oxygen transfer efficiency, were found to allow increased host cell growth. However, this increase was counterbalanced by a reduced productivity of the cells and resulted in a maximum SELP volumetric production being observed at a flask volume to culture volume ratio of 10:1 and an agitation rate of 200 to 250 rotations per minute (rpm). This saturating effect on SELP productivity at the higher volume:volume ratios and agitation rates tested indicates the presence of other limiting factors under the conditions used, including possibly a greater production of toxic byproducts at the higher growth rates achieved.
Effect of acetic acid on growth of E. coli BL21 DE3(+)/ pET25b/ SELP- 59- A. Effect of acetic acid, added at an elapsed fermentation time of 0 hours, on growth of E. coli BL21 DE3(+)/pET25b/SELP-59-A cultivated under the optimised shake flask conditions of the present study. The variation in the initial growth rates (measured over the initial 30 minutes of incubation) as a function of the amount of acetic acid added (top), and biomass levels (as measured by g/L DCW) over the course of the bioprocess (bottom) are shown.
9738318194