Lenka Vorlová

Detection of fluoroquinolone residues in milk using Yersinia spp. strains: towards better sensitivity for flumequine determination

Abstract Introduction: Plate diffusion methods play an important role in the monitoring system for antimicrobial agents in raw materials and foodstuffs of animal origin. The aim of this work was to select a Yersinia spp. strain for the plate diffusion method based on sensitivity to a fluoroquinolone, namely flumequine. Another aim was to determine the optimal conditions of the method with the selected strain of Yersinia ruckeri CCM 8467 and to determine the detection capability (CCβ) of this method for residues of selected fluoroquinolones in milk. Material and Methods: Optimum method conditions were set: cell concentration in the test agar at the level of 9.105–106 CFU/mL, discs with a diameter of 12.7 mm, Antimicrobial Inhibitor Test Agar with a pH of 6.0, and incubation at 30°C for at least 18 h and up to 24 h. Results: With respect to the maximum residue limit (MRL), the Y. ruckeri plate method demonstrated the lowest sensitivity to flumequine. The CCβ of the method for flumequine was in the concentration of 100 μg/L−1 (twice the MRL). The study also confirmed that the method exhibits very good sensitivity to the other tested fluoroquinolones, which were marbofloxacin (30 μg/L, 0.4 MRL), ciprofloxacin (10 μg/L, 0.1 MRL), and enrofloxacin (20 μg/L, 0.2 MRL), but lower sensitivity to danofloxacin (42 μg/L, 1.4 MRL). Conclusion: The method with the CCM 8467 strain of Y. ruckeri showed a higher sensitivity to flumequine than the method with the ATCC 11303 strain of E. coli.

Interspecies and seasonal differences of retinol in dairy ruminant´s milk

Milk is an essential source of macronutrients and among lipophilic vitamins is significant source of retinol. The contribution of milk to the reference daily intake for retinol varies from 11% to 16%, worldwide. The most consumed dairy products are fresh, dehydrated and condensed milk in which the amonuts of retinol are not modified to those of in whole milk. Retinol is essential to ensure a good functionality of the immune system and plays a critical role in vision, reproduction, cell differentiation as well as growth and development and is found only in animal tissues. The aim of our study was to evaluate the interspecies differences in the retinol concentration of whole raw bovine, caprine and ovine milk and to observe seasonal variation of retinol in bulk tank milk samples. Samples of raw milk were colleceted on different farms in the Czech Republic between 2013 and 2014. Retinol was measured by ultra high performance liquid chromatography with UV detection (325 nm) in isocratic mode after alkaline saponification with methanolic potassium hydroxide solution and liquid-liquid extraction into non polar organic solvent of whole raw milk. To avoid vitamin losses or degradation during the procedure, antioxidants were added to the sample extraction media. Our results indicate significant interspecies differences between bovine and ovine milk and caprine and ovine milk. Concentration of retinol is very similar in bovine and caprine milk 0.96 ±0.11 mg/L, 0.94 ±0.25 mg/L, respectively. The mean concentration in sheep´s milk is 1.75 ±0.24 mg/L. The seasonal variation of retinol in raw bovine milk was detected as high significant, with the highest concentration during winter. These results contribute to the nutrition evaluation of milk in the Czech Republic and indicate, that the sheep´s milk is the best source of retinol among the milks of ruminants kept in the Czech Republic, however it is not used in its fluid form for human consumption.