MLEE of the Bacillus cereus group

MultiLocus Enzyme Electrophoresis (MLEE) (Selander et al. 1986) is a tool that has been widely used for phylogenetic typing of bacteria, but that has recently been supplanted by MultiLocus Sequence Typing (MLST), which is less ambiguous and electronically portable. MLEE is based on the relative electrophoretic mobilities of a large number (usually 10 to 20) of water-soluble cellular enzymes, whose genetic loci are spread around the bacterial chromosome. Protein extracts are prepared from cell lysates and subjected to one-dimensional starch-gel electrophoresis. Selected proteins are specifically stained, and their relative mobilities are used to defined MLEE profiles, or electrophoretic types (ETs). Genetic relatedness among isolates is then determined by comparison of the ETs (see figure below). MLEE schemes have been used in large-scale studies to estimate the genetic diversity and structure in natural populations of a variety of bacterial species, including important pathogens such as Neisseria, Legionella, Bordetella, Escherichia coli, and Hæmophilus influenzæ.

Our research group, led by Prof. Anne-Brit Kolstø at the Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, has been the first and main laboratory to apply MLEE for phylogenetic analysis of B. cereus group bacteria (Carlson et al. 1994, Helgason et al. 1998, Helgason et al. 2000a, Helgason et al. 2000b), leading to the identification of clonal lineages comprising strains associated with human infections, and further demonstrating that B. anthracis, B. cereus, and B. thuringiensis are genetically very closely related within the B. cereus group. In total, we have typed 316 B. cereus group isolates by MLEE. Another large-scale MLEE study of the B. cereus group has been conducted by Vilas−Boas et al. 2002. We have recently combined MLEE data with MLST and Amplified Fragment Length Polymorphism (AFLP) typing data using a supertree approach to build a comprehensive phylogenetic view of the B. cereus group population, available in the HyperCAT database containing 3193 B. cereus group isolates.

Below is an overview of the MLEE procedure (for details see Selander et al. 1986):

MLEE summary picture