ABSTRACT
The Royal Veterinary and Agricultural University, Frederiksberg, Denmark
HORST NEVE
Federal Research Centre for Nutrition and Food, Kiel, Germany
I. INTRODUCTION
Food fermentations rely on actively growing lactic acid bacteria (LAB) which either are
added as starter cultures or grow spontaneously in the food matrix. The fermentation capa-
bilities of lactic acid bacteria can be severely inhibited by a panoply of nonviral inhibitors,
such as bacteriocins, nisin, residues from antibiotic or disinfectant treatments, or the lacto-
peroxidase-thiocyanate-hydrogen peroxide system present in raw milk. However, the
major commercial problem results from bacteriophage infections. These bacterial viruses
were identified as filter-transmissible agents by the work of Twort in 1915 and d’He´relle in
1917.[1] Their submicroscopic sperm-like morphology remained undetected until the first
electron microscopes became available during the 1940s. Phages attacking Lactococcus
lactis have been known since the 1930s, when Whitehead and Cox in New Zealand
observed that phages were responsible for the failure in the acid-producing activity of a
cheese starter culture.[2]
In the area of food fermentation, the permanent threat of phage infection is particu-
larly manifested in the dairy field. Here, phage attacks on lactic acid bacteria during the
fermentation process result in an unacceptably low production of lactic acid and flavor
compounds along with reduced proteolysis. Thus, starter activity is either severely
affected (“slow vats”) or, in extreme cases, a complete failure of starter growth may
occur (“dead vats”). Due to the constant risk of economic loss, phage control is a major
area of concern in handling lactic acid bacteria as starter cultures. Phages have also
been isolated from other fermentations, e.g., in the production of sauerkraut, coffee, and
wine, but most often these attacks are not as destructive as in milk fermentation. These
worldwide efforts focus on the understanding of the complex and dynamic mechanisms
of phage-host relationships, including (a) the characterization of the phage population
involved, including genomics analysis, (b) the analysis of “natural” and “intelligent” bac-
terial systems of phage defense, and (c) the identification of phage counterdefense
mechanisms.
