Optimization of electrically active magnetic nanoparticles as accurate and efficient microbial extraction tools.

Barbara Cloutier,Evangelyn Alocilja,Ashley Cloutier

doi:10.3390/bios5010069

Abstract

Food defense requires the means to efficiently screen large volumes of food for microbial pathogens. Even rapid detection methods often require lengthy enrichment steps, making them impractical for this application. There is a great need for rapid, sensitive, specific, and inexpensive methods for extracting and concentrating microbial pathogens from food. In this study, an immuno-magnetic separation (IMS) methodology was developed for Escherichia coli O157:H7, using electrically active magnetic nanoparticles (EAMNPs). The analytical specificity of the IMS method was evaluated against Escherichia coli O55:H7 and Shigella boydii, and was improved over previous protocols by the addition of sodium chloride during the conjugation of antibodies onto MNPs. The analytical sensitivity of the IMS method was greatest when a high concentration of antibodies (1.0 mg/mL) was present during conjugation. EAMNP concentrations of 1.0 and 0.5 mg/mL provided optimal analytical sensitivity and analytical specificity. The entire IMS procedure requires only 35 min, and antibody-conjugated MNPs show no decline in performance up to 149 days after conjugation. This analytically sensitive and specific extraction protocol has excellent longevity and shows promise as an effective extraction for multiple electrochemical biosensor applications.

Highlights

Food-borne microbial pathogens comprise one of the single largest threats to maintaining a safe food supply
Immuno-magnetic capture of E. coli O157:H7 cells were quantified by plate counts, but capture was visually confirmed by scanning electron microscopy (SEM)
Two-tailed independent T-tests performed on the mean concentrations of captured cells for all three bacteria in the initial study showed that the addition of sodium chloride causes a significant decrease in capture of the negative control S. boydii (n = 178; p = 0.029), with no significant effect on the capture of the target E. coli O157:H7 or the other negative control E. coli O55:H7

Summary

Introduction

Food-borne microbial pathogens comprise one of the single largest threats to maintaining a safe food supply. The food defense (securing food sources against malicious biological attack) and food safety (identifying and eradicating contamination from natural sources) are growing increasingly relevant, as foods are processed and shipped further and faster than ever before [1,2]. Standard overnight culture methods for identifying microbial pathogens are no longer adequate, as the speed and breadth of food movement demands rapid, sensitive, specific, and economical means of extracting and detecting pathogens from food sources. Even with the new Food Safety Modernization Act (FSMA), the highest risk plants will only be inspected every three years by the FDA [4,5]. The FDA in the United States inspects less than 1% of the imported food supply before consumption and less than

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