Riboflavin (vitamin B2) sensitized photooxidation of ascorbic acid (vitamin C): A kinetic study.

Ascorbic acid (AH2) photoxidation sensitized by riboflavin (RF) has been studied between pH 2.0 and 12.0 in ambient air and anaerobic environment using UV and visible irradiation sources. The kinetics of AH2 degradation in aqueous medium along with RF is found to be first-order for its photodegradation. AH2 photolysis rate constants in aerobic and anaerobic conditions with RF (1.0-5.0 × 10-5 M) are 0.14-3.89 × 10-2 and 0.026-0.740 × 10-2 min-1, respectively. The rate constants (k2) of second-order kinetics for AH2 and RF photochemical interaction in aerobic and anaerobic conditions are in the range of 0.24-3.70 to 0.05-0.70 × 10-3 M-1 min-1, respectively, which manifests that increasing the RF concentration also increases the rate of photodegradation (photooxidation) of AH2. The k2 versus pH graph is bell-shaped which indicates that increasing the pH increases photolytic degradation rate of AH2 with RF. Increasing the pH results in the increased ionization of AH2 (ascorbyl anion, AH-) and redox potential which leads to the higher rates of photodegradation of AH2. Two-component spectrophotometric (243 and 266 nm, AH2 and RF, respectively) and high-performance liquid chromatography (HPLC) methods have been used to determine the concentration of AH2 and RF in pure and degraded solutions. The results obtained from these two methods are compared using a student t-test which showed no noteworthy difference between them.

Investigating the Role of Antibiotics on Induction, Inhibition and Eradication of Biofilms of Poultry Associated Escherichia coli Isolated from Retail Chicken Meat.

Background: Widespread use of antibiotics as growth promoters and prophylactic agents has dramatic consequences for the development of antibiotic resistance. In this study, we investigated effects of selected antibiotics on bacterial biofilms and performed extensive antibiotic and VF profiling of poultry-meat associated E. coli strains. Methods: Antibiotic susceptibility was performed by a disc diffusion method, followed by molecular screening of resistance and virulence determinants. Further biofilm formation assays, MIC-p, MIC-b, MBIC and MBEC, were performed using standard tissue culture plate method. Results: In total, 83 (75%) samples were confirmed as E. coli from poultry sources, 26 different antibiotics were tested, and maximum numbers of the isolates were resistant to lincomycin (100%), while the least resistance was seen against cefotaxime (1%) and polymyxin B (1%). Overall, 48% of the isolates were ESBL producers and 40% showed carbapenemase activity; important virulence genes were detected in following percentages: fimH32 (39%), papC21 (25%), iutA34 (41%), kpsMT-II23 (28%), papEF9 (11%), papGII22 (27%) and fyuA13 (16%). Colistin showed remarkable anti-biofilm activity, while at sub-MIC levels, gentamicin, ceftriaxone and enrofloxin significantly (p < 0.01) inhibited the biofilms. A strong induction of bacterial biofilm, after exposure to sub-minimal levels of colistin clearly indicates risk of bacterial overgrowth in a farm environment, while use of colistin aggravates the risk of emergence of colistin resistant Enterobacteriaceae, a highly undesirable public health scenario.