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Fresh-cut produces are often consumed uncooked, thus proper sanitation is essential for preventing cross contamination. The reduction and subsequent growth of Salmonella enterica sv Thompson were studied in pre-cut iceberg lettuce washed with simulated wash water (SWW), sodium hypochlorite (SH, free chlorine 25 mg/L), and peroxyacetic acid (PAA, 80 mg/L) and stored for 9 days under modified atmosphere at 9, 13, and 18 °C. Differences in reduction between SH and PAA were non-existent. Overall, visual quality, dehydration, leaf edge and superficial browning and aroma during storage at 9 °C were similar among treatments, but negative effects increased with temperature. These results demonstrated that PAA can be used as an effective alternative to chlorine for the disinfection of Salmonella spp. in fresh-cut lettuce. The growth of Salmonella enterica sv Thompson was successfully described with the Baranyi and Roberts growth model in the studied storage temperature range, and after treatment with SWW, chlorine, and PAA. Subsequently, predictive secondary models were used to describe the relationship between growth rates and temperature based on the models' family described by Belehrádek. Interestingly, the exposure to disinfectants biased growth kinetics of Salmonella during storage. Below 12 °C, growth rates in lettuce treated with disinfectant (0.010-0.011 log CFU/h at 9 °C) were lower than those in lettuce washed with water (0.016 log CFU/h at 9 °C); whereas at higher temperatures, the effect was the opposite. Thus, in this case, the growth rate values registered at 18 °C for lettuce treated with disinfectant were 0.048-0.054 log CFU/h compared to a value of 0.038 log CFU/h for lettuce treated with only water. The data and models developed in this study will be crucial to describing the wash-related dynamics of Salmonella in a risk assessment framework applied to fresh-cut produce, providing more complete and accurate risk estimates.

Assuntos

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Various strategies to accelerate the formation of biofilms on minerals have been studied, and one of them is the use of D-galactose as an inducer of EPS production in planktonic cells of biooxidant bacteria. With the aim to evaluate the influence on the attachment and the effect over the solubilization of a polymetallic mineral concentrate, the behavior of a microbial consortium formed by Acidithiobacillus thiooxidans DSM 14887T and Leptospirillum ferrooxidans DSM 2705T previously induced with D-galactose for the early formation of EPS was studied. These microorganisms were previously adapted to 0.15 and 0.25% of D-galactose, respectively; afterward, different proportions of both strains were put in contact with the particle surface of a concentrate of polymetallic mineral. Also, to evaluate the affinity of each bacterium to the mineral, attachment tests were carried out with one of these species acting as a pre-colonizer. The same consortia were used to evaluate the solubilization of the polymetallic mineral. The results obtained show that the induction by D-galactose increases the microbial attachment percentage to the mineral by at least 10% with respect to the control of non-adapted consortia. On the other hand, the tests carried out with pre-colonization show that the order of inoculation also affects the microbial attachment percentage. From the different proportions tested, it was determined that the use of a consortium with a proportion of 50% of each species previously adapted to D-galactose and inoculated simultaneously, present a microbial attachment percentage to the mineral greater than 95% and better solubilization of a polymetallic mineral, reaching values of 9.7 and 11.7mgL-1 h-1 of Fe3+ and SO4 2-, respectively. Therefore, the use of D-galactose in small concentrations as inducer of EPS in acidophilic cells and the selection of an adequate strategy of inoculation can be beneficial to improve biooxidation since it would allow this process to develop in a shorter time by achieving a greater number of attached cells in a shorter time accelerating the solubilization of a sulfide mineral. Graphical AbstractEPS production using D-galactose as inducer and its influence in the attachment of consortia formed by differents proportions of A. thiooxidans and L. ferrooxidans inoculated at the same time and when one of them acting as a pre-colonizer.

RESUMO

The estimation of growth or inactivation of bacterial population in fruits during preservation and storage provides useful information for the improvement of the safety of fresh-cut fruits and vegetables. This paper addressed the attachment to the surface and the growth in the flesh of apple fruits of four bacterial cultures (Escherichia coli, Bacillus cereus, Staphylococcus aureus and Pseudomonas aeruginosa). The growth of the bacterial cultures in apple flesh was monitored at particular time intervals, and Gompertz parameters, i.e. maximum number of bacteria (Pm), the maximum growth rate of bacteria rp,m, and lag time tl, were used to determine the growth kinetics. After the immersion, the highest number of P. aeruginosa and the lowest number of B. cereus adhered to the apples. After washing and swabbing, E. coli was reduced from the surface of apples to the highest extent (by 3.34 log cfu g-1), while the number of B. cereus was reduced to the lowest extent (1.66 log cfu g-1). Fitted curves of the Gompertz model corresponded quite well to the measured values of the number of microorganisms with R2 = 0.92-0.98. The values of the standard error (0.17-0.37) and extremely low p values of the Fischer test (p < 0.0001) indicated strict dependence between the model predicted and the maximum population density. The predicted values of the maximum number of microorganisms (Pm) correspond almost exactly to the actual values. A similar conclusion can be drawn for the maximum growth rate of microorganisms (rp,m), with the measured value being slightly higher than predicted values.

Assuntos

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The formation of biofilms capable of efficiently carrying out ureolysis is of fundamental importance in several biotechnological systems such as urinary tract infections, building materials and municipal wastewater treatment. This work proposes a straightforward method for the formation of a ureolytic biofilm attached to graphite. The proposed strategy reduced the time needed to complete ureolysis to 3 days instead of 16 days required in suspension culture. To confirm the formation of a ureolytic biofilm, scanning electron microscopy and confocal laser scanning microscopy studies were employed ex situ. However, it is imperative to analyse the biofilm by direct non-invasive techniques. Accordingly, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were used as in situ monitoring techniques. The reduction in OCP from - 0.01 to - 0.2 V vs. Ag/AgCl and the increase in capacitance from 200 to 260 µF cm-2 were related to biofilm attachment. To the best of our knowledge, this is the first time in which a ureolytic biofilm attachment has been analysed by EIS. The increase in the biomass from 0.04 to 2.81 µm3 µm-2 and in average thickness from 10.19 to 32.78 µm was related to biofilm maturation.

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BACKGROUND: Biofilm formation has been shown to be associated with damaged areas of endoscope channels. It was hypothesized that the passage of instruments and brushes through endoscope channels during procedures and cleaning contributes to channel damage, bacterial attachment and biofilm formation. AIM: To compare surface roughness and bacterial attachment in used and new endoscope channels in vivo and in vitro. METHODS: Surface roughness of 10 clinically used (retired) and seven new colonoscope biopsy channels was analysed by a surface profiler. For the in-vitro study, a flexible endoscope biopsy forceps was passed repeatedly through a curved 3.0-mm-diameter Teflon tube 100, 200 and 500 times. Atomic force microscopy was used to determine the degree of inner surface damage. The number of Escherichia coli or Enterococcus faecium attached to the inner surface of the new Teflon tube and the tube with 500 forceps passes in 1 h at 37oC was determined by culture. RESULTS: The average surface roughness of the used biopsy channels was found to be 1.5 times greater than that of the new biopsy channels (P=0.03). Surface roughness of Teflon tubes with 100, 200 and 500 forceps passes was 1.05-, 1.12- and 3.2-fold (P=0.025) greater than the roughness of the new Teflon tubes, respectively. The number of E. coli and E. faecium attached to Teflon tubes with 500 forceps passes was 2.9-fold (P=0.021) and 4.3-fold (P=0.004) higher compared with the number of E. coli and E. faecium attached to the new Teflon tubes, respectively. CONCLUSION: An association was found between endoscope usage with damage to the biopsy channel and increased bacterial attachment.

Assuntos