Submitted to: Journal of Applied & Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/1997
Publication Date: N/A
Interpretive Summary: Listeria monocytogenes is a microorganism which can contaminate food products and can be involved in illness caused by infection from these tainted foods. This microorganism presents a problem in that it can grow at refrigerator temperatures, which is not the case with most bacteria which cause food poisoning or food infections. It is proposed that the cell membranes or envelope that surround bacteria must be in a fluid state for them to grow, and cold temperatures will generally cause this envelope to become less fluid or solidify and stop growth. The composition of the cell membrane of Listeria monocytogenes grown at different temperature was studied and showed that this microorganism is able to change the chemical composition of the envelope as the temperature drops to keep the cell envelope in a fluid state, but the change observed is not the same as is typical of most other bacteria that grow at low temperatures.
Technical Abstract: Listeria monocytogenes is a foodborne pathogen capable of growth at refrigeration temperatures. Membrane lipid fatty acid composition is a major determinant of a membrane state sufficiently fluid to permit growth at low temperatures. The fatty acid profile of L. monocytogenes is dominated to an unusual extent by branched chain fatty acids (greater than 95%), with the major fatty acids being anteiso C15:0, anteiso C17:0, and iso C15:0 in cultures grown in either complex or defined media at 37 deg C. Determination of the fatty acid composition of L. monocytogenes strains 10403S and SLCC53 grown over the temperature range of 5-45 deg C revealed two modes of adaptation of fatty acid composition to lower growth temperature: shortening of fatty acid chain length and alteration of branching from iso to anteiso. Two cold sensitive mutant strains exhibited low levels of isoC15:0, anteiso C15:0 and anteiso C17:0 and high levels of iC14:0, C14:0, iC16:0, and C16:0. The levels of aC15:0 and aC17:0 and the ability to grow at low temperatures were increased by supplementing media with 2-methylbutyrate. No evidence was found for a role of fatty acid unsaturation in adaptation of L. monocytogenes in adaptation to growth in cold temperature. The switch to a fatty acid profile dominated by aC15:0 at low temperatures and the association of cold sensitivity with a deficiency of this fatty acid indicate a critical role in the growth of L. monocytogenes in the cold.