Qx alignment marker 15 bp 1 kb

Isolates that were phenotypically resistant to tetracycline were tested for tetA and tetB genes. DNA extraction was performed by suspending a single colony from a blood agar plate in 500 μL of deionized water in 1.5 mL microcentrifuge tube, boiling for 10 min at 100°C, and centrifuging at 10,000 x g for 5 min. A duplex PCR assay for tetA and tetB was performed as described by Harvey et al. [25 (link)] with E. coli ATCC 47042 (positive for tetB) and XL1-Blue E. coli strain (positive for tetA) as positive controls. The DNA in 96-well plates were amplified using an Eppendorf Mastercycler gradient thermal cycler (USA Scientific, Inc., Ocala, FL), and PCR products were then transferred to the Automated QIAxcel System (QIAgen, Valencia, CA). Microcapillary electrophoresis was performed using a QIAxcel DNA screening cartridge (QIAgen), a QX alignment marker (15bp/1 kb; QIAgen), and a 50 to 800 bp QX size marker (QIAgen). The electrophoresis was documented and analyzed for the presence of specific bands.