264 Modern Food Microbiology
epidemiologic value. Listeria phages contain dsDNA and belong to two groups: Siphoviridae (noncontractile tails) and Myoviridae (contractile tails). The phage receptors on Listeria monocytogenes
cells are N-acetylglucosamine and rhamnose substituents of teichoic acids, or the peptidoglycan
itself.
58,221 A phage-resistant strain of L. monocytogenes lacked glucosamine in its wall structure.
221
In a study of 823 strains of L. monocytogenes collected in France over the period 1958–1978, 69.4%
were serotype 4, and a phage typing system was defined using 12 principal and 3 secondary phages.
5
Six phages could be used to differentiate serotype 1, nine phages for serotype 4, and only two phages
for serotype 2 strains. By employing a set of 20 phages, these investigators were able to type 78.4%
of the 823 strains, with 88% of serotype 4 and 57% of serotype 1 being typable. For 552 of the
645 typable strains, 8 principal phage patterns could be established.
5 When a set of 29 phages was
employed in a multicenter study, 77% and 54% of serotypes 4 and 1/2, respectively, were typable.
173
The typing set of Audurier and co-workers is divided into three groups: 12 phages for 1/2 strains, 16
for 4b strains, and 7 for other strains.
4 Typability of 826 serovar 4b strains isolated in France in the
period 1985–1987 was 84% compared with 49% of 1,644 serovar 1 strains employing the 35 phages.
By use of this scheme, L. monocytogenes isolates involved in three outbreaks of human listeriosis
were shown to be of the same phage type, whether recovered from victims or foods.
The phage typing of 80 cultures of L. monocytogenes was compared by six laboratories in Europe
using an international phage set in five laboratories and phage sets unique to two laboratories. A high
level of agreement among the laboratories was found, and suggestions for the possible improvement
of the international set were presented.
110,139
In a study that employed 127 isolates of L. monocytogenes,
203 lytic patterns allowed eight phage
groups to be established, but findings suggested that the lytic agents were monocins—defective phages
with tails that lack head region.
153 Although monocin susceptibility appeared to be associated with
serotypes, no relationship was found relative to animal source or geographic origin of L. monocytogenes
strains.
203 Monocins of the listeriae are cryptic prophages that are closely related to intact phages,
suggesting that they are incompletely assembled phage particles.
231 Monocin proteins are highly
similar to the major protein of phage tails, and 75% of listerial phage DNA hybridize to DNA of
monocin-producing strains.
231 The tails contain a lytic principle on their base plate region, which can
lead to cell lysis if/when sufficient numbers of tails attach to cells. L. monocytogenes monocins do not
attach to other bacteria.
231
In a study of 807 L. monocytogenes cultures collected in Britain from human cases over the period
1967–1984, phage typing was shown to be an effective tool for common source cases of listeriosis
involving more than one patient or for recurrent episodes in the same patient.
140 The 807 cultures
belonged to serotypes 1/2, 3, and 4. In another study that employed a set of 16 phages recovered
from lysogenic and environmental sources, 464 strains representing five species were placed in four
groups.
132 Although the results were highly reproducible, species and serovar specificities did not
conform to any lytic patterns. The phage susceptibility of L. monocytogenes was highest for serotype
4 (98%) followed by serotype 1 (90%) and serotype 3 (10%). No phages were restricted to either
one species or serovar in lytic patterns. L. grayi was not lysed by any of the selected phages.
132 A
reversed typing procedure that employs ready-to-use plates containing phage suspensions on tryptose
agar plates was developed by Loessner.
131 With a set of 21 genus-specific phages, the overall typability
rate was 89.5% on 1,087 listerial strains.
The phage typing of 105 strains of toxigenic E. coli 0157:H7 recovered from humans in Finland
between 1990 and 1999 revealed that 56% belonged to PT2 and 11% to PT54.
176 Seventy percent of
the PT2 strains contained the stx 2 gene alone and in combinations. In a study of 166 strains of Bacillus
cereus from food-poisoning cases, 97% were phage typable using a set of 12 phages.
2 Interestingly,
most B. thuringiensis strains were also typable by the same set of phages.
epidemiologic value. Listeria phages contain dsDNA and belong to two groups: Siphoviridae (noncontractile tails) and Myoviridae (contractile tails). The phage receptors on Listeria monocytogenes
cells are N-acetylglucosamine and rhamnose substituents of teichoic acids, or the peptidoglycan
itself.
58,221 A phage-resistant strain of L. monocytogenes lacked glucosamine in its wall structure.
221
In a study of 823 strains of L. monocytogenes collected in France over the period 1958–1978, 69.4%
were serotype 4, and a phage typing system was defined using 12 principal and 3 secondary phages.
5
Six phages could be used to differentiate serotype 1, nine phages for serotype 4, and only two phages
for serotype 2 strains. By employing a set of 20 phages, these investigators were able to type 78.4%
of the 823 strains, with 88% of serotype 4 and 57% of serotype 1 being typable. For 552 of the
645 typable strains, 8 principal phage patterns could be established.
5 When a set of 29 phages was
employed in a multicenter study, 77% and 54% of serotypes 4 and 1/2, respectively, were typable.
173
The typing set of Audurier and co-workers is divided into three groups: 12 phages for 1/2 strains, 16
for 4b strains, and 7 for other strains.
4 Typability of 826 serovar 4b strains isolated in France in the
period 1985–1987 was 84% compared with 49% of 1,644 serovar 1 strains employing the 35 phages.
By use of this scheme, L. monocytogenes isolates involved in three outbreaks of human listeriosis
were shown to be of the same phage type, whether recovered from victims or foods.
The phage typing of 80 cultures of L. monocytogenes was compared by six laboratories in Europe
using an international phage set in five laboratories and phage sets unique to two laboratories. A high
level of agreement among the laboratories was found, and suggestions for the possible improvement
of the international set were presented.
110,139
In a study that employed 127 isolates of L. monocytogenes,
203 lytic patterns allowed eight phage
groups to be established, but findings suggested that the lytic agents were monocins—defective phages
with tails that lack head region.
153 Although monocin susceptibility appeared to be associated with
serotypes, no relationship was found relative to animal source or geographic origin of L. monocytogenes
strains.
203 Monocins of the listeriae are cryptic prophages that are closely related to intact phages,
suggesting that they are incompletely assembled phage particles.
231 Monocin proteins are highly
similar to the major protein of phage tails, and 75% of listerial phage DNA hybridize to DNA of
monocin-producing strains.
231 The tails contain a lytic principle on their base plate region, which can
lead to cell lysis if/when sufficient numbers of tails attach to cells. L. monocytogenes monocins do not
attach to other bacteria.
231
In a study of 807 L. monocytogenes cultures collected in Britain from human cases over the period
1967–1984, phage typing was shown to be an effective tool for common source cases of listeriosis
involving more than one patient or for recurrent episodes in the same patient.
140 The 807 cultures
belonged to serotypes 1/2, 3, and 4. In another study that employed a set of 16 phages recovered
from lysogenic and environmental sources, 464 strains representing five species were placed in four
groups.
132 Although the results were highly reproducible, species and serovar specificities did not
conform to any lytic patterns. The phage susceptibility of L. monocytogenes was highest for serotype
4 (98%) followed by serotype 1 (90%) and serotype 3 (10%). No phages were restricted to either
one species or serovar in lytic patterns. L. grayi was not lysed by any of the selected phages.
132 A
reversed typing procedure that employs ready-to-use plates containing phage suspensions on tryptose
agar plates was developed by Loessner.
131 With a set of 21 genus-specific phages, the overall typability
rate was 89.5% on 1,087 listerial strains.
The phage typing of 105 strains of toxigenic E. coli 0157:H7 recovered from humans in Finland
between 1990 and 1999 revealed that 56% belonged to PT2 and 11% to PT54.
176 Seventy percent of
the PT2 strains contained the stx 2 gene alone and in combinations. In a study of 166 strains of Bacillus
cereus from food-poisoning cases, 97% were phage typable using a set of 12 phages.
2 Interestingly,
most B. thuringiensis strains were also typable by the same set of phages.