Development of a magnetic separation method for rapid isolation and enrichment of bacteria in raw pork using chitosan functionalized magnetic Fe3O4@MIL-100(Fe) composites.

In this study, a pretreatment method based on a magnetic capture probe for the rapid isolation and enrichment of bacteria from raw pork was developed. The chitosan immobilized Fe3O4@MIL-100(Fe) was prepared as a capture probe for total bacterial counts through the electrostatic interaction of positively charged chitosan and the negatively charged substances on the surface of bacteria. The interference of matrix in pork samples on this method was studied and removed by differential centrifugation. The results showed the capture probe had a great selectivity binding and magnetic separation properties for the tested six common bacteria in pork. Under the optimal conditions, the capture efficiency of the bacteria (105 CFU mL-1) from pork surface samples was all above 90%. The capture efficiency of the bacteria in a homogenate system was greatly decreased due to the interference of sarcoplasmic protein and myofibrillar protein in pork. The matrix effect was mitigated by a differential centrifugation method, and the capture efficiency of all six bacteria was >80%. The developed magnetic separation method took 40 min and showed good isolation and enrichment properties of bacteria. Thus, the proposed method is expected to provide a simple, convenient, and time-saving pretreatment method for the detection of total bacterial counts in pork.

Colorimetric aptasensor for Listeria monocytogenes detection using dual functional Fe3O4@MIL-100(Fe) with magnetic separation and oxidase-like activities in food samples.

A novel colorimetric aptasensor assay based on the excellent magnetic responsiveness and oxidase-like activity of Fe3O4@MIL-100(Fe) was developed. Fe3O4@MIL-100(Fe) absorbed with aptamer and blocked by BSA served as capture probe for selective isolation and enrichment of Listeria monocytogenes one of the most common and dangerous foodborne pathogenic bacteria. The aptamer absorbed on Fe3O4@MIL-100(Fe) was further used as signal probe that specifically binds with target bacteria conjugation of capture probe for colorimetric detection of Listeria monocytogenes, taking advantages of its oxidase-like activity. The linear range of the detection of Listeria monocytogenes was from 102 to 107 CFU mL-1, with the limit of detection as low as 14 CFU mL-1. The approach also showed good feasibility for detection of Listeria monocytogenes in milk and meat samples. The spiked recoveries were in the range 81-114% with relative standard deviations ranging from 1.28 to 5.19%. Thus, this work provides an efficient, convenient, and practical tool for selective isolation and colorimetric detection of Listeria monocytogenes in food.

[Influence of different ultrasonic irrigation solutions after root canal preparation with ProTaper by machine on micro-hardness of root canal dentin].

PURPOSE: To develope the influence of different ultrasonic irrigations after root canal preparation with nickel titanium ProTaper on micro-hardness of root canal dentin. METHODS: Sixty of maxillary anterior teeth with single-canal were collected and randomly divided into 6 groups. Group A was control group, group B was prepared to F3 with nickel titanium ProTaper by machine, group C was ultrasonic irrigated with 3% hydrogen peroxide solution for 1 minute after preparation, group D was ultrasonic irrigated with koutai mouthwash for 1 minute after preparation, group E was ultrasonic irrigated with 17% EDTA solution for 1 minute after preparation, group F was ultrasonic irrigated with distilled water for 1 minute after preparation. The roots were then sectioned horizontally into 3 parts, split longitudinally into halves and examined under a micro Vickers hardness test machine. The data was analyzed by one-way ANOVA and t test with SPSS 17.0 software package. RESULTS: The micro-hardness of group A was (52.66 ± 1.64) HV,(52.08 ± 1.53) HV and (51.47 ± 2.53) HV. There was no significant difference in all parts of the root canal in group A (P>0.05). The micro-hardness of the apical third of root canal was lower than that of the cervical and middle of root canal in the other groups (P<0.05). In the cervical and middle third of the root canals, the micro-hardness of group E was (44.65 ± 1.33) HV and(42.55 ± 1.12) HV, and there were statistical significances between group E and the other groups (P<0.05). In the apical third of root canal,the micro-hardness of group E was (37.82 ± 1.60) HV, and group C was (44.14±1.73) HV, both of the comparative differences with other groups were statistically significant (P<0.05). There was no significant difference among group B, group D and group F (P>0.05). CONCLUSIONS: Root canal preparation to F3 with nickel titanium ProTaper by machine can make the micro-hardness of the apical third of root canal decrease. Ultrasonic irrigation with 17% EDTA solution for 1 minute can make the micro-hardness of the root canal decrease ultrasonic irrigation with. Ultrasonic irrigation with 3% hydrogen peroxide can make the micro-hardness of the apical third of root canal decrease. Ultrasonic irrigation with Koutai mouthwash and distilled water for 1 minute have no influence on the micro-hardness of root canal.