Fundamental Food Microbiology, Third Edition - Fuad Fathir

178 FUNDAMENTAL FOOD MICROBIOLOGY
make fermented sausages, such as phosphate or nitrite, and sanitizers from equipment.
These factors can prevent or reduce the growth of starters.
E. Bacteriophages of Lactic Acid Bacteria
The role of bacteriophages (or phages) in starter-culture failure in food fermentation
has been recognized for a long time. A short discussion on their life cycle that results
in starter failure, as well as some current practices used to overcome phage problems
in food fermentation, is presented here. 6–10
1. Morphology and Characteristics
Bacteriophages are filterable viruses of bacteria widely distributed in the environment,
especially in food fermentation environments. A phage contains several proteins
(that make the head, tail, tail fiber, and contractile sheath) and DNA, which
can be linear or circular, double stranded of ca. 20 to 55 kb in size. The doublestranded
DNA molecule is packed in the head, which can be round or hexagonal
(prolate or isometric, respectively).
Several schemes have been proposed at different times to classify the bacteriophages
of lactic acid bacteria. Currently, a scheme is used in which the family,
group, and morphotype are classified together. The three families Myoviridae,
Siphoviridae, and Podoviridae are included in three groups, A (with contractile
tails), B (with noncontractile long tails), and C (with noncontractile short tails),
respectively. They can have three morphotypes, namely 1 (with small isometric
heads), 2 (with small prolate heads), and 3 (with large prolate heads), respectively.
Lac. lactis ssp. lactis and ssp. cremoris appear to have many wide varieties of
phages. They have been divided into 12 species, of which 3 are in the Siphoviridae
family and are important because of their virulent nature. The 3 in the Siphoviridae
family are 936 species (all are virulent with small isometric head; e.g., sk1), c2
species (all are virulent with prolate head; e.g., c2), and P335 species (have both
virulent and temperate phages and small isometric heads; e.g., TP901-1). Genome
sequence analysis indicates that the species in the same family as well as those
in different families vary considerably. In contrast, the genome analysis of phages
of Streptococcus thermophilus (e.g., sfi 19, sfi 11) indicates a fairly good homology.
Phages of several species of Lactobacillus have been identified and genome
sequences of some species and strains are now available, namely for Lactobacillus
delbrueckii (LL-H), Lab. plantarum (phi-gle), Lactobacillus johnsonii (Lj 965),
Lab. gasseri (adh), and Lab. casei (a2). Very few phages of Leuconostoc and
Oenococcus have been isolated, and none have been isolated from Pediococcus. 6
2. Life Cycle
A phage cannot multiply by itself in food. Instead, it attaches (needs Ca 2+ for
adsorption) with its tail on the surface of a bacterial cell (specific host) and injects
its DNA inside the cell cytoplasm. If it is a lytic phage, the bacterial cell produces
a large number of copies of the phage DNA and phage proteins. Following