Florfenicol [KLH]

Florfenicol belongs to a class of phenicol antimicrobials widely used as feed additives and for the treatment of respiratory infections. In recent years, increasing resistance to florfenicol has been reported in Campylobacter spp., the leading foodborne enteric pathogens causing diarrheal diseases worldwide. Here, we reported the identification of fexA, a novel mobile florfenicol resistance gene in Campylobacter. Of the 100 Campylobacter jejuni strains isolated from poultry in Zhejiang, China, 9 were shown to be fexA positive, and their whole-genome sequences were further determined by integration of Illumina short-read and MinION long-read sequencing. The fexA gene was found in the plasmid of one strain and chromosomes of eight strains, and its location was verified by S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) and Southern blotting. Based on comparative analysis, the fexA gene was located within a region with the tet(L)-fexA-catA-tet(O) gene arrangement, demonstrated to be successfully transferable among C. jejuni strains. Functional cloning indicated that acquisition of the single fexA gene significantly increased resistance to florfenicol, whereas its inactivation resulted in increased susceptibility to florfenicol in Campylobacter. Taken together, these results indicated that the emerging fexA resistance is horizontally transferable, which might greatly facilitate the adaptation of Campylobacter in food production environments where florfenicols are frequently used.

Pollutants such as n-TiO2 and tetracycline enter the marine environment through various sources starting from their production until disposal. Hence, it is vital to determine the interactive effect of one pollutant with the other when they coexist in the environment. In the present study, the effect of antibiotic - tetracycline (TC) on the toxicity of P25 n-TiO2 was studied with marine microalgae, Chlorella sp. The impact of TC (1 mg L-1) on five different concentrations of n-TiO2 (0.25, 0.5, 1, 2 and 4 mg L-1) under both visible and UV-A illuminations was evaluated. Effective diameter of n-TiO2 in ASW at 0th h increased from 690.69 +/- 19.55 nm (0.25 mg L-1) to 1183.04 +/- 37.10 nm (0.25 mg L-1 + 1 mg L-1) and 971.51 +/- 14.61 nm (4 mg L-1) to 1324.12 +/- 11.59 nm (4 mg L-1 + 1 mg L-1) in presence of TC. A significant increase in the toxicity of 4 mg L-1 n-TiO2 upon the addition of TC (68.16 +/- 0.37% under visible and 80.21 +/- 0.3% under UV-A condition) was observed. No significant difference in toxicity was observed between visible and UV-A illuminations. Further the toxicity data was corroborated through the measurement of oxidative stress and antioxidant enzyme activities. Independent action model showed antagonistic effect for lower concentrations of n-TiO2 and additive effect for higher concentrations of n-TiO2 when present in mixture with TC under both illuminations. For the higher mixture concentration of 4 mg L-1 n-TiO2 and 1 mg L-1 TC, the percentage TC removal was about 55.29% and 30% and the corresponding TOC removal was found to be 54.29% and 31.04% under visible and UV-A illuminations respectively. The site of ROS generation in Chlorella sp. was identified with electron transfer chain inhibitors. Both mitochondria and chloroplast acted as the site for the ROS generation in Chlorella sp. The SEM images of the algal cells upon exposure to n-TiO2 and mixture revealed the aggregation of cells and distortion of cell membrane.