Concentration of Low-Density Microorganisms in Sterile Body Fluids Using Magnetic Nanoparticles

The diagnosis of acute bacterial meningitis is typically made by analyzing sterile body fluids such as cerebrospinal fluid (CSF), pleural, peritoneal and pericardial fluids, and joint fluid. The detection of infectious microorganisms in sterile body fluids is performed using direct examination and culture methods. Even a single colony of a microorganism detected in the culture of a sterile body fluid is considered an infection. However, the presence of very low amounts of microorganisms in sterile body fluids poses a significant problem for disease diagnosis. Therefore, it is often necessary to use concentration and/or enrichment methods to detect microorganisms in CSF and other samples that should be sterile under normal conditions.

The aim of this study is to concentrate infection-causing microorganisms in cerebrospinal fluid by binding them to magnetic nanoparticles and separating them from the supernatant using a magnetic separation method. Magnetic nanoparticles were synthesized using the co-precipitation method. Techniques such as SEM, TEM, FT-IR, zeta potential, and zeta-sizer were used for characterization. Stability studies of the magnetic nanoparticles were conducted.

The detection of infectious microorganisms was performed using the direct culture method. The concentration method using magnetic nanoparticles was compared with the centrifuge concentration method, which is frequently used in microbiology laboratories. A total of 500 CSF samples were studied. The concentration method with magnetic nanoparticles was tested on culture-negative CSF samples taken from suspected bacterial meningitis cases. Each sample was divided into two 1 mL portions. One portion was concentrated using centrifugation and the other using magnetic nanoparticles. After centrifugation and magnetic separation, the supernatants were cultured. No microorganism growth was observed in the supernatant concentrated with magnetic nanoparticles, while microorganism growth was observed in the supernatant concentrated using centrifugation. While centrifugation could not precipitate all microorganisms, magnetic nanoparticles captured and concentrated all microorganisms. After concentration with centrifugation and magnetic nanoparticles, the solid part remaining after separating the supernatant was cultured. No microorganism growth was observed in the culture medium with centrifugation, while microorganism growth was observed with magnetic nanoparticles. Incorrect results from low-density samples concentrated using centrifugation can hinder treatment. Therefore, the concentration method using magnetic nanoparticles is an easy, inexpensive, and simple method to apply for suspected meningitis patients, as it can concentrate samples less than 1 mL and trace levels of microorganisms.