Current Research on Listeria monocytogenes in Foods: an Overview

Abstract

Listeria monocytogenes is well-recognized as a foodborne pathogen. Two aspects of its control in foods are improvement in analytical methods and, secondly, the development of new methods to control its growth in foods. Much progress has been made since 1985 in developing both conventional and rapid methods for detecting L. monocytogenes in foods. When using conventional methodology it is readily acknowledged that the use of two methods, rather than one, will increase the recovery rates of the organism from naturally contaminated foods. Some of the newer rapid methods will be specifically targeting L. monocytogenes and not the entire Listeria genus as with previous kits. In the future many additional rapid test kits will come onto the market, as is the case now for Salmonella testing. The problem lies in proper evaluation of all of the kits. Advances have also been made in identification kits with at least two new tests showing great promise, the API™ Listeria, which can identify all species in the genus, and the Listeria ACCUPROBE™, which will specifically identify L. monocytogenes. Secondly, a lot of work has been done recently to develop new ways of controlling the growth of L. monocytogenes through the application of the “hurdle” concept. Research is concentrated in the area of biological controls by using starter cultures. Many different organisms along with their respective bacteriocins, have been found to have either bacteriostatic or bactericidal effects on the organism. Future work may concentrate on the use of genetically modified organisms that produce at least two different bacteriocins and on increasing the stability of pure bacteriocins in foods. The “hurdle” that still remains, however, is regulatory acceptance of the use of genetically modified organisms or pure bacteriocins in foods. We are still not much closer than we were 8 years ago to knowing the minimum infectious dose of the organism, and various countries have adopted different policies regarding the presence of L. monocytogenes in foods. It appears that more countries may be moving towards establishing tolerance levels for the presence of the organism in foods, especially for those low-risk foods which do not support growth of the organism and for those foods with a very short shelf life.