A new automated magnetic bead based nucleic acid sample preparation directly from nasal swabs for MRSA diagnostics

Abstract number: 1733_399

Kolpus T.E., Høidal Berthelsen H.K., Lorentzen M., Refseth U.H.

Objectives: The term MRSA (methicillin resistant Staphylococcus aureus) is used to describe Staphylococcus aureus that is resistant to commonly used antibiotics. The bacterium is known to mainly colonise the nostrils, but the respiratory tract, open wounds, catheters and urinary tract are also potential sites of infection. It is believed that as many as 53 million people carry MRSA. The traditional method of testing for MRSA is both cumbersome and time consuming, and can take several days before a result can be reported.

We have developed a unique principle for bacterial DNA extraction directly from nasal swabs. Collection and transport systems from alternative manufacturers have been successfully tested, such as rayon and nylon swabs in Liquid Stuart or Amies (liquid and gel) Transport Medium. The dimensions of many types of transport tubes limits full automation because they are unsuitable for insertion into the automation instruments, which necessitates manual transfer of sample into sample preparation tubes. In this study we present results of a fully automated BUGS' n BEADS system for bacterial DNA isolation, using swab and transport devices manufactured by Copan, Brescia, Italy.

Methods: The specimen is collected from the patient using a flocked nylon swab that is submerged into a polypropylene screw-cap tube containing 1 ml of Liquid Amies Transport Medium following transport to the test laboratory, the tube is vortexed, the swab removed and the tube is placed straight into the automation instrument to serve as the primary tube for automated transfer of sample into the sample preparation tube.

Microbial contents remaining in the primary tube after withdrawal of sample for BUGS' n BEADS may be used for cultivation.

Results: Automated BUGS' n BEADS extraction of MRSA DNA directly from swab was achieved using automation instrument compatible polypropylene screw-cap tubes containing Liquid Amies Transport Medium, in combination with flocked nylon swabs (Copan, Brescia, Italy). The obtained sensitivity was 150 cfu MRSA per swab.

Conclusions: MRSA is detected directly from swab without prior cultivation, at a sensitivity of about 150 cfu per swab, using Copan swab and transport tubes in fully automated BUGS' n BEADS sample preparation.