Pulsed-field gel electrophoresis for Listeria monocytogenes

Pulsed-Field Gel Electrophoresis (PFGE) is a molecular subtyping method with high discriminatory power, reproducibility, and epidemiological concordance for the subtyping of Listeria monocytogenes and other bacteria. PFGE uses rare-cutting restriction enzymes (macrorestriction) that cut the genomic DNA, usually resulting in 6-25 DNA fragments ranging between 30 and 600 kb. Bacterial cells are immobilized in agarose plugs and subsequently lysed to release genomic DNA, which is then subjected to DNA digestion. AscI and ApaI restriction enzymes are typically used for L. monocytogenes. Electrophoresis using an alternating electric field direction results in a DNA banding pattern, or fingerprint, which is used to classify isolates into different pulsotypes. PFGE is currently the CDC's gold standard method for epidemiological studies in foodborne outbreaks.