EUROPE – Researchers at the University of Chemistry and Technology Prague have developed magnetic microrobots that can efficiently bind and isolate Staphylococcus aureus in milk.

Bovine mastitis produced by Staphylococcus aureus (S. aureus) can cause problems in milk quality and production due to the staphylococcal enterotoxins produced by this bacterium.

Given that S. aureus may withstand pasteurization and thermal sterilization techniques and that enterotoxins cannot be easily eliminated by routine sanitary measures after they have formed in dairy products, this may have an economic impact on the dairy industry.

A high concentration of S. aureus, defined by the FDA as having more than or equal to 104 colony-forming units per gram (CFU g1) in raw milk or other dairy products, suggests that the product was made in an unhygienic environment.

For this reason, efficient methods to isolate S. aureus bacteria from dairy products for removal or identification are in high demand and important for the dairy industry.

Designed to enter hard-to-reach places within a milk production plant and operate wirelessly, the microrobots (called MagRobots) are loaded with antibodies (IgG from rabbit serum) to bind and isolate S. aureus from milk.

In the past, light, chemicals, and even ultrasound have been used to push microscopic robots. But a unique magnetic field is used to propel these MagRobots.

The team decided that this kind of control was the best course to take since the robots can be remotely accessed for reconfiguring and reprogramming.

To create the MagRobots, paramagnetic microparticles are covered with a chemical compound that allows them to be coated with antibodies that match with proteins on the cell wall of S. aureus. This allows the MagRobot to find, bind, and retrieve the bacteria.

The bots are guided by a transversally rotating magnetic field with various frequencies. The MagRobots moved more quickly at higher frequencies.

Researchers preset the trajectory of the microrobots so that they would “walk” back and forth through a control solution and a container with milk in it in three rows and two columns. They are retrieved using a permanent magnet. 

The MagRobots were able to eradicate 3.42 104 CFU g1 of S. aureus in the proof-of-concept study. 2.8 micrometer-wide MagRobots were able to eliminate almost 60% of the S. aureus cells in an hour.

The outcomes show that the technology can effectively eliminate S. aureus that remains in milk after pasteurization.

According to the study that appeared in the journal Small, this fuel-free removal method based on magnetic robots is only effective against S. aureus bacteria and has no adverse effects on the normal milk microbiota or the addition of toxic compounds from fuel catalysis.

The MagRobots were able to bypass the E. coli and only target the S. aureus when they were introduced in milk containing both S. aureus and another bacteria, E. coli.

“This research brings microrobotics towards a new frontier: animal veterinary health and safe foods. Microrobots, due to their size, are able to solve challenges faster than traditional technologies,” said corresponding author Martin Pumera, Ph.D., of the University of Chemistry and Technology Prague.

As stated by the report, the system can be scaled up for industrial use in food production.

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