Fitness Costs of Tigecycline Resistance in Acinetobacter baumannii and the Resistance Mechanism Revealed by a Transposon Mutation Library.

Acinetobacter baumannii is one of the main pathogens causing nosocomial and community-acquired infections. Tigecycline is an important antibiotic for the treatment of multidrug-resistant A. baumannii infections, but strains resistant to tigecycline have also emerged. There are still many unclear questions concerning the mechanism of tigecycline resistance in A. baumannii. In this study, tigecycline-susceptible and tigecycline-intermediate strains were gradually cultured with sub-minimum inhibitory concentrations of tigecycline to select for tigecycline-resistant mutants, and a tigecycline-resistant strain was cultured under 42 °C to select for tigecycline-susceptible mutants. We found that the acquisition of tigecycline resistance affected the susceptibility of the strains to other antibiotics. Resistance to ampicillin-sulbactam is negatively correlated with tigecycline resistance. The strains will experience fitness costs along with the acquisition of tigecycline resistance. Tigecycline resistance in the strains was not related to 16S rRNA target variation or outer membrane integrity alteration. By constructing a transposon mutation library, we found that transposon insertion of the adeL gene reduced the sensitivity of A. baumannii to tigecycline. This study provides important clues for understanding the mechanism of tigecycline resistance in A. baumannii.

[Contamination and dietary exposure assessment of fatty acid esters of chloropropanediols in vegetable oil and fat-rich food in Shaanxi Province].

OBJECTIVE: To investigate the contamination of chloropropanediols in fat-rich food in Shaanxi Province, and to assess the dietary chloropropanediols exposure and the health risk of intaking chloropropanediols from fat-rich food for Shaanxi residents. METHODS: In 2015-2016, three kinds of food including vegetable oil, fried food and baked food were collected randomly from ten cities of Shaanxi Province, and determined by gas chromatography. Dietary intake assessment of human exposure to 3-monochloropropane-1, 2-diol ester(3-MCPD ester) was carried out in combination of food consumption data with concentration of chloropropanediols. RESULTS: A total of 203 samples were detected, the total detection rates of 3-MCPD ester and 2-monochloropropane-1, 3-diol ester(2-MCPD ester) were 31.53% and 12.30%, respectively, with the mean values of 0.22 and 0.02 mg/kg.Among all food samples, baked food were more seriously polluted than other kinds of foods with 3-MCPD ester, its detection rate was 47.06%. The highest detection rate of 2-MCPD ester was fried food with 20.00% detection rate. Getting rid of rapeseed oil, olive oil, pastries and biscuits, and 2-MCPD esters were detected in the rest. The ratio of the average exposure and high-end exposure to the maximum daily tolerance of 3-MCPD ester in the three fatty foods were less than 100%. CONCLUSION: The overall level of 3-MCPD esters contamination in fat-rich food is common in Shaanxi Province. The risk assessment result suggests that the current dietary intake of 3-MCPD esters from fried food in Shaanxi Province has acceptable effect on health.

Visual chiral recognition of tryptophan enantiomers using unmodified gold nanoparticles as colorimetric probes.

A simple protocol to distinguish enantiomers is extremely intriguing and useful. In this study, we propose a low-cost, facile, sensitive method for visual chiral recognition of enantimers. It is based on the inherent chirality of gold nanoparticles (AuNPs), and the unmodified AuNPs are used as chiral selector for D- and L-Tryptophan (Trp). In the presence of D-Trp, an appreciable red-to-blue color change of AuNPs solution can be observed, whereas no color change is found in the presence of L-Trp. The method can be used to detect D-Trp in the range of 0.2-10 µM, and the limit of detection is 0.1 µM. The chiral assay described in this work is easily readout with the naked eye or using a UV-vis spectrometer. Furthermore, the AuNPs can selectively adsorb D-Trp, and simple centrifugation can allow the precipitation of D-Trp with AuNPs and leave a net excess of the other enantiomer in solution, thus resulting in enantioseparation. In this method, AuNPs do not need any labeling or modifying with chiral molecules. The method is more attractive because of its high sensitivity, low cost, ready availability and simple manipulation.