Previous Article | Next Article 
Applied and Environmental Microbiology, April 2001, p. 1793-1799, Vol. 67, No. 4
Food Microbiology Laboratory, Food
Department, Istituto Superiore di Sanità, 00161 Rome, Italy
Received 5 June 2000/Accepted 22 January 2001
A total of 32 Listeria monocytogenes strains (16 from a
recent outbreak of invasive listeriosis and 16 from two outbreaks of
noninvasive listeriosis, all three occurring in Italy) were characterized by PCR-ribotyping, arbitrarily primed PCR (AP-PCR), and
the recently developed infrequent-restriction-site PCR (IRS-PCR). The
discriminatory ability of the techniques, first evaluated on 29 unrelated L. monocytogenes food isolates using Simpson's index of diversity, was 0.714 for PCR-ribotyping, 0.690 for AP-PCR, and
0.919 for IRS-PCR. IRS-PCR was also more capable of distinguishing among strains from the invasive listeriosis outbreak: three
different clusters were identified by IRS-PCR compared to two clusters
identified by both PCR-ribotyping and AP-PCR. Within each of the two
outbreaks of noninvasive listeriosis, the patterns were practically
identical, as demonstrated by all three techniques. Only IRS-PCR
succeeded in clearly discriminating the strains related to noninvasive
listeriosis from all of the other strains included in this study,
including those from the outbreak of invasive listeriosis. This finding may suggest the presence of unique differences in their DNA sequences.
Listeria monocytogenes
has been recognized as a foodborne pathogen causing listeriosis in
humans since the 1980s, when a number of listeriosis outbreaks were
found to be associated with the consumption of contaminated foodstuffs.
Until recently, food-borne listeriosis was commonly regarded as an
invasive disease that affected only susceptible population groups
(e.g., immunocompromised persons, newborn children, and pregnant
women); it was considered to be associated with bacteremia only in
certain target organs and was only rarely associated with
gastrointestinal symptoms (24). However, recent reports of
a new noninvasive form of listeriosis that causes febrile
gastroenteritis clearly indicate that persons with no predisposing
conditions may be affected. This finding increases the public health
significance of L. monocytogenes (2, 3, 12, 19,
22), in that the emergence of this new form of food-borne
listeriosis could affect the epidemiology of the disease both in terms
of a higher attack rate and in terms of a wider range of potential
vehicles. However, the factors that influence the infectious dose and
the occurrence and course of infection still need to be clarified. It
is possible that the clonal variants of the pathogen each interact with
the host in a different way (6, 26). Of the
high-resolution molecular typing methods for assessing genetic
heterogeneity, fingerprinting techniques based on PCR have proven to be
among the most effective (27). They are generally based on
enzymatic amplification through PCR of DNA segments flanking either
undetermined sequences (e.g., randomly amplified polymorphic DNA
[RAPD] and arbitrarily primed PCR [AP-PCR] [15, 16])
or defined and conserved sequences (e.g., rRNA genes [PCR-ribotyping]
[25] and the repetitive-element families [ERIC- and
REP-PCR] [14, 23]).
A new PCR-based fingerprinting technique, known as
infrequent-restriction-site PCR (IRS-PCR), based on the selective
amplification of DNA restriction fragments, has recently been
developed and used to type several bacterial species (17,
21, 30). We applied this technique to related and
unrelated L. monocytogenes isolates and compared the
results to those obtained by PCR-ribotyping and AP-PCR. The
related strains were those isolated during the investigations of
an outbreak of invasive listeriosis and two outbreaks of noninvasive
listeriosis that recently occurred in Italy. The outbreak of invasive
listeriosis occurred in 1998: six hospitalized patients, three of whom
were heart transplanted, while the others, affected with Woldenstrom's
syndrome, hepatic cirrhosis, and chronic hepatitis, respectively, had
developed mild to severe (meningoencephalitis) symptoms of listeriosis
while in the same hospital (P. Aureli and G. Franciosa, unpublished data). The two outbreaks of noninvasive listeriosis occurred in 1994 and 1997 (2, 22); both involved a large number of
immunocompetent persons, and L. monocytogenes was detected
from the clinical specimens and from the environmental samples
collected where the suspected food sources had been prepared. However,
whereas in the 1994 outbreak the implicated food remained uncertain
(22), in the 1997 outbreak it was clearly identified as a
cold salad of corn and tuna fish (2).
The main objective of the present study was to verify the causal
relationships among the L. monocytogenes strains isolated from each outbreak and to compare the epidemic clones to isolates recovered from different types of foods.
Bacterial isolates and culture conditions.
A total of 61 L. monocytogenes isolates were used in this study (Table
1). A total of 29 of them were unrelated
strains and, of these, 25 were from different types of food recovered
over a period of 2 years (i.e., 1997 and 1998) and were randomly
selected from the culture collection at the Food Microbiology
Laboratory of the Istituto Superiore di Sanità. L. monocytogenes ScottA (a clinical isolate of serotype 4b
[7]), kindly provided by M. P. Doyle, University of
Georgia, Griffin, was included in the experiments as a reference
strain. Strains 26 through 28 were clinical isolates of serotype 4b
obtained, respectively, from two elderly people (strains 26 and 27) and
a newborn (strain 28). These strains were sent to our laboratory by
some local health units of southern and northern Italy.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1793-1799.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of Listeria
monocytogenes Strains Involved in Invasive and Noninvasive
Listeriosis Outbreaks by PCR-Based Fingerprinting
Techniques
ABSTRACT
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
INTRODUCTION
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
MATERIALS AND METHODS
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
TABLE 1.
L. monocytogenes isolates analyzed by
PCR-fingerprinting techniques
Serotyping. All of the strains were serotyped on the basis of somatic (O) and flagellar (H) antigens by a commercial kit (Listeria O Antisera; Denka Seiken, Tokyo, Japan) according to the manufacturer's instructions.
Preparation of template DNA. Either purified DNA or DNA from listeria cell lysates was used directly as the template in all PCR amplification assays except for the IRS-PCR assay, which requires the pretreatment of DNA, performed as described below.
Genomic DNA was extracted and purified as reported elsewhere (8). The DNA from each strain was dissolved in 150 µl of 1× TE buffer (10 mM Tris, 1 mM EDTA; pH 8.0). Yields were estimated by using a UV spectrophotometer (GeneQuant II; Pharmacia Biotech, Cambridge, England), and DNA samples were stored at
20°C
until use.
Listeria cell lysates were obtained by centrifuging 1 ml of 24-h TSB
cultures; the pellets were washed twice with 1× TE buffer, suspended
in 1 ml of sterile distilled water, and subjected to ultrasound
treatment (model T460; Trans-Sonic, Singen, Germany) for 10 min to
facilitate lysis. Lysates were freshly prepared for each experiment.
To obtain the appropriate template for the IRS-PCR experiments, we
adopted the procedure of Riffard et al. (21), with some modifications. Bacterial DNA (either pure [2 µg] or from the crude lysates [18 µl], without further purification) was first cleaved with 40 U of XbaI and 40 U of PstI (Boehringer,
Mannheim, Germany) in a total reaction volume of 25 µl overnight at
37°C. The resulting restriction fragments were stored at 20°C
until subsequent ligation to double-stranded restriction
halfsite-specific adapters (AX and PS) (17, 21).
Specifically, the adapters were the partially complementary
oligonucleotides AX1 (5'-CTA GTA CTG GCA GAC TCT-3') and AX2
(5'-GCCAGT A-3') (for XbaI) and PS1 (5'-GAC
TCG ACT CGC ATG CA-3') and PS2 (5'-TGC GAG T-3') (for
PstI) (Biogen, Rome, Italy). Equal molar amounts of AX1
(previously phosphorylated at the 5' end by T4 Polynucleotide Kinase
3'-Phosphatase Free [Boehringer], as recommended by the manufacturer)
and AX2 and of PS1 and PS2 were mixed in 1× PCR buffer (Perkin-Elmer
Cetus, Branchburg, N.J.): annealing was performed with a thermal cycler (Model PTC-150 Minicycler; M. J. Research, Inc., Watertown, Mass.) programmed to decrease the temperature from 80 to 4°C over 1 h. The restriction fragments were ligated to the adapters in accordance with the procedures of Riffard et al. (21). Finally, the
ligation products were redigested with 10 U of XbaI and 10 U
of PstI at 37°C for 30 min.
XbaI-PstI restriction fragments tagged with
specific adapters were kept at 20°C until their use as templates in
the IRS-PCR experiments.
PCR conditions. All reaction mixtures contained, in a total volume of 50 µl, 1× PCR buffer II (10 mM Tris-HCl, 50 mM KCl [pH 8.3]; Perkin-Elmer Cetus), 200 µM concentrations of each deoxynucleoside triphosphate (Pharmacia), and 1.25 U of Taq polymerase (Perkin-Elmer Cetus). The final concentrations of MgCl2 (Perkin-Elmer Cetus) were adjusted to 1.5 mM in the IRS-PCR experiments and to 3 mM in the PCR-ribotyping and AP-PCR experiments.
The PCR-ribotyping and AP-PCR experiments were performed with both purified DNA (2 ng) and crude lysates (2.5 µl); when crude lysates were used, PCR mixtures were heated in a thermal cycler at 99°C for 10 min prior to the addition of the polymerase for a better release of the DNA. The IRS-PCR experiments were performed using as templates for amplification 5 µl of the ligation products obtained after restriction either of purified DNA or of the genetic material released from the lysed bacteria. We used different oligonucleotide primers (Biogen) and amplification parameters for each technique, as follows. (i) PCR-ribotyping was carried out according to the method of Sontakke and Farber (25). The primers for the amplification of the DNA spacer regions between the 16S and 5S rRNA genes were P (5'-TTG TAC ACA CCG CCC GTC A-3') and M (5'-GCTTAA CTT CCG TGT TCG GTA TGG G-3'). Amplification was achieved after initial denaturation of the template at 94°C for 2 min, followed by 35 cycles at 94°C for 1 min, 35°C for 1 min, and 72°C for 2.5 min, with a ramp time of 2 min between 35 and 72°C; a final extension phase was performed at 72°C for 5 min. (ii) For AP-PCR, the primer M13 (5'-GTT GTA AAA CGA CGG CCA GT-3'), derived from the core sequence of the bacteriophage M13 genome, was used at a final concentration of 0.5 µM. This primer was selected from among 10 different 20-mer oligonucleotides, previously tested with different serotypes of L. monocytogenes, for its higher discriminatory power. The use of primers selected from the bacteriophage M13 sequence has been recommended for detecting DNA polymorphisms in virtually all species (4). The temperature profile consisted of two cycles at 94°C for 5 min, 40°C for 5 min, and 72°C for 5 min, followed by 40 high-stringency cycles at 94°C for 1 min, 60°C for 1 min, and 72°C for 2 min. Both the primer sequence and the temperature profile were adapted from the method of Vila et al. (28). (iii) For IRS-PCR, primers PS1 and PX-G (5'-AGA GTC TGC CAG TAC TAG AG-3') (17) for the selective amplification of the XbaI-PstI restriction fragments were used at a final concentration of 1 µM. The cycling conditions were the same as those described by Mazurek et al. (17). After initial denaturation at 94°C for 5 min, the PCR mixtures were subjected to 30 cycles at 94°C for 30 s, 60°C for 30 s, and 72°C for 90 s; a final extension was performed at 72°C for 5 min. The amplification experiments were performed in duplicate with a thermal cycler (model PT100; M. J. Research) to assess the reproducibility of the patterns.Analysis of the amplification products.
The PCR products (35 µl) were separated by electrophoresis on a 1.5 or 2% agarose gel
containing ethidium bromide (0.5 µg/ml) at 60 V for 4 h in 1×
TAE (Tris-acetate-EDTA) buffer. Gel images were digitized through a
UV-gel image acquisition camera (Gel Doc 1000; Bio-Rad Laboratories,
Hercules, Calif.). Intergel comparison was performed with the GelCompar
3.1 system (Applied Maths, Kortrijk, Belgium) (9).
Following normalization and background subtraction with mathematical
algorithms, three separate lists were created for the reconstructed
patterns of PCR-ribotyping, AP-PCR, and IRS-PCR. Finally, the
similarities between profiles within each list were calculated by
applying the Pearson product-moment correlation coefficient
(r), and clustering was performed by the unweighted pair-group method using arithmetic averages (UPGMA). An intralinkage homology level of 
80% between patterns was assumed as the cutoff for
defining a close genetic relationship between strains and was used to
define the clusters.
| |
RESULTS AND DISCUSSION |
|---|
|
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
|
|---|
Unrelated isolates.
Based on the results of serotyping, the 25 unrelated L. monocytogenes food strains were divided into
eight different serovars, distributed as follows: 1/2a (n = 9), 4b (n = 6), 1/2b (n = 4), 3a
(n = 2), 1/2c (n = 1), 3c (n = 1), 4ab (n = 1), and 4d (n = 1)
(Table 1). Hence, serovars 1/2a, 1/2b, and 4b, which commonly cause the
clinical disease, were the most frequently detected. In no case was the
prevalence of a serovar associated with a specific food. The clinical
isolates were confirmed as serotype 4b. The number of bands varied
according to the specific PCR-based fingerprinting technique:
PCR-ribotyping showed from 4 to 11 bands, AP-PCR showed from 5 to 13 bands, and the amplification of the XbaI-PstI
restriction fragments by IRS-PCR showed from 6 to 11 bands. All bands
were evenly distributed along the tracks and shorter than 2,036 bp (Fig. 1). PCR-ribotyping, AP-PCR, and
IRS-PCR revealed percentages of similarity greater than 83, 87, and
90%, respectively, when comparing the analysis using purified DNA to
that using crude cell lysates. Since these differences did not affect
the final clustering of the genetic profiles, we used the patterns
obtained with cell lysates to construct the UPGMA dendrograms.
Computer analysis showed that PCR-ribotyping and AP-PCR produced,
respectively, 7 and 6 clusters of strains and that neither technique
was capable of distinguishing among serotypes (Fig. 2a and
b), whereas IRS-PCR produced 13 clusters and was generally able to distinguish among serotypes.
Specifically, the degree of differentiation was greatest among the most
common serovars (i.e., 1/2a, 1/2b, and 4b), whereas the single
representatives of the rarer serovars was not distinguished (i.e., 1/2c
and 3a clustered with a 1/2a strain, 4d clustered with a 1/2b strain,
and 4ab clustered with a 4b strain) (Fig. 2c). These results are
consistent with the divisions of L. monocytogenes strains
obtained with other techniques, specifically, restriction fragment
length polymorphism analysis (29), multilocus enzyme electrophoresis (MEE) (11), ribotyping (11),
pulsed-field gel electrophoresis (PFGE) (20), and the
recently developed amplified fragment length polymorphism (AFLP)
technique (1). AFLP is conceptually similar to IRS-PCR, in
that both methods are based on the selective amplification by PCR of
double-digested genomic DNA. However, AFLP has a number of drawbacks,
all of which can be overcome with IRS-PCR; specifically, in AFLP, the
two adapters are of equal length, neither is phosphorylated (hence,
they are not prevented from acting as primers), one of the primers is
radioactively or fluorescently labeled, denaturing polyacrylamide gel
electrophoresis is required to resolve the large number of products
generated, and sophisticated detection systems must be employed to
detect the fingerprints. All replications with IRS-PCR showed identical profiles, demonstrating this technique's high level of
reproducibility.
|
|
Isolates from the outbreak of invasive listeriosis (outbreak 1). One clinical L. monocytogenes isolate and all of the isolates recovered from the frozen foods (Table 1) were identified as serotype 1/2a, whereas the remaining isolates, including those from the environment, were serotype 1/2b. The dendrograms of the profiles obtained with PCR-ribotyping and AP-PCR also consisted of two clusters. However, whereas the grouping obtained with PCR-ribotyping was identical to that of serotyping, when using AP-PCR, the clinical isolate of serotype 1/2a clustered with the 1/2b isolates. In contrast to the other techniques, IRS-PCR revealed three different clusters. Specifically, five clinical isolates and all of the isolates from the cooked foods and the environment, all serotype 1/2b, were in the same cluster (89% intralinkage homology level), suggesting that this outbreak was likely due to cross-contamination. A second cluster consisted of all of the isolates from frozen foods, all serotype 1/2a, which were strictly interrelated (87% homology level). The third cluster consisted of the one clinical isolate of serotype 1/2a, which showed a homology level of <70% with the second cluster and could therefore be discriminated. These results can be considered as plausible, since the frozen foods were boiled before being served and thus probably did not account for any cases of listeriosis. The clinical isolate of serotype 1/2a may have originated from a different unidentified source of infection. Figure 1 shows representative IRS-PCR, AP-PCR, and PCR-ribotyping profiles of the outbreak-related L. monocytogenes strains.
Isolates from the outbreaks of noninvasive listeriosis (outbreaks 2 and 3). The clinical, food, and environmental isolates from outbreaks 2 and 3 were confirmed as belonging to serotypes 1/2b and 4b, respectively (Table 1). Highly homologous PCR-based fingerprints were obtained for all of the isolates associated with outbreak 2, except for isolate 52 (isolated from a mixer), which had a homology level of <20% according to IRS-PCR and of <50% according to both PCR-ribotyping and AP-PCR. These findings are consistent with the previous subtyping of the same strains by MEE, PFGE, and RAPD, and they substantiate the lack of causal relationship for the isolate from the mixer (8, 22).
All of the strains from outbreak 3 showed nearly identical profiles with all PCR-based typing techniques, resulting in homology levels among isolates of >90, 97, and 93% when IRS-PCR, AP-PCR, and PCR-ribotyping, respectively, were used. Previous analysis of the same strains, using PFGE and RAPD, also showed indistinguishable patterns (2). These results strongly support the hypothesis of extensive cross-contamination as the primary cause of infection in both outbreaks (2, 22); indeed, some environmental isolates showed the same profiles as those of the food and clinical isolates.Comparison between related and unrelated strains.
The
comparison between the IRS-PCR patterns of the related and unrelated
isolates revealed the following: (i) the strains from outbreak 1 (invasive listeriosis) were divided into three clusters, all of which
included some unrelated food isolates of similar serotypes (i.e., 1/2a
and 1/2b); (ii) all but one of the related strains of outbreak 2 (noninvasive listeriosis) clustered apart from all of the other
isolates tested in this study, whereas the isolate from the mixer,
which was not apparently implicated in the outbreak, clustered with a
strain of serotype 3a; and (iii) the strains from outbreak 3 (noninvasive listeriosis) clustered apart from all other strains
tested, although the homology level was approximately 75% with respect
to some strains of serotype 1/2b, including those involved in outbreak
1 (Fig. 3). The strains from outbreak 3 were also distinguished from L. monocytogenes ScottA and the
other clinical isolates of serotype 4b, the relative genetic similarity
level between them being <50% (Fig. 3).
|
| |
ACKNOWLEDGMENTS |
|---|
This work was supported by a grant from the National Research Program of the Ministry of Health.
We thank Peter Ben Embarek of the Fisheries Department, Food and Agriculture Organization of the United Nations (FAO), Rome, Italy, for revision of the manuscript and Mark Kanjeff, Laboratorio Epidemiologia e Biostatistica, ISS, for English editing.
| |
FOOTNOTES |
|---|
* Corresponding author. Mailing address: Laboratorio Alimenti, Istituto Superiore della Sanità, Viale Regina Elena 299, I-00161 Rome, Italy. Phone: 39-6-49902254. Fax: 39-6-49387101. E-mail: p.aureli{at}iss.it.
| |
REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
|
|---|
| 1. | Aarts, H. J. M., L. E. Hakemulder, and A. M. A. Van Hoef. 1999. Genomic typing of Listeria monocytogenes strains by automated laser fluorescence analysis of amplified fragment length polymorphism fingerprint patterns. Int. J. Food Microbiol. 49:95-102[CrossRef][Medline]. |
| 2. |
Aureli, P.,
G. C. Fiorucci,
D. Caroli,
G. Marchiaro,
O. Novara,
L. Leone, and S. Salmaso.
2000.
An outbreak of febrile gastroenteritis associated with corn contaminated by Listeria monocytogenes.
N. Engl. J. Med.
342:1236-1241 |
| 3. |
Dalton, C.,
C. Austin,
J. Sobel,
P. S. Hayes,
W. F. Bibb,
L. M. Graves,
B. Swaminathan,
M. E. Proctor, and P. M. Griffin.
1997.
An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk.
N. Engl. J. Med.
336:100-105 |
| 4. |
Desmarais, E.,
I. Lanneluc, and J. Lagnel.
1998.
Direct amplification of length polymorphisms (DALP), or how to get and characterize new genetic markers in many species.
Nucleic Acids Res.
26:1458-1465 |
| 5. | Donnelly, C. W. 1999. Conventional methods to detect and isolate Listeria monocytogenes, p. 225-260. In E. T. Ryser, and E. H. Marth (ed.), Listeria, listeriosis, and food safety, 2nd ed. Marcel Dekker, Inc, New York, N.Y. |
| 6. | Farber, J. M. 1996. An introduction to the hows and whys of molecular typing. J. Food Prot. 59:1091-1101. |
| 7. |
Fleming, D. W.,
S. L. Cochi,
K. L. MacDonald,
J. Brondum,
P. S. Hayes,
B. D. Plikaytis,
M. B. Holmes,
A. Audurier,
C. V. Broome, and A. L. Reingold.
1985.
Pasteurized milk as a vehicle of infection in an outbreak of listeriosis.
N. Engl. J. Med.
312:404-407 |
| 8. | Franciosa, G., M. Pourshaban, M. Gianfranceschi, and P. Aureli. 1998. Genetic typing of human and food isolates of Listeria monocytogenes from episodes of listeriosis. Eur. J. Epidemiol. 14:205-210[CrossRef][Medline]. |
| 9. |
Gerner-Smidt, P.,
L. M. Graves,
S. Hunter, and B. Swaminathan.
1998.
Computerized analysis of restriction fragment length polymorphism patterns: comparative evaluation of two commercial software packages.
J. Clin. Microbiol.
36:1318-1323 |
| 10. | Gianfranceschi, M., G. Franciosa, A. Gattuso, and P. Aureli. 1998. Detection of two phospholipases C by means of plate tests for the rapid identification of pathogenic Listeria monocytogenes. Arch. Lebensmittelhyg. 49:54-57. |
| 11. |
Graves, L. M.,
B. Swaminathan,
M. W. Reeves,
S. B. Hunter,
R. E. Weaver,
B. D. Plikaytis, and A. Schuchat.
1994.
Comparison of ribotyping and multilocus enzyme electrophoresis for subtyping of Listeria monocytogenes isolates.
J. Clin. Microbiol.
32:2936-2943 |
| 12. | Heitmann, M., P. Gerner-Smidt, and O. Heltberg. 1997. Gastroenteritis caused by Listeria monocytogenes in a private day-care facility. Pediatr. Infect. Dis. J. 16:827-828[CrossRef][Medline]. |
| 13. |
Hunter, P. A., and M. A. Gaston.
1988.
Numerical index of the discriminatory ability of typing systems: an application of Simpson's index of diversity.
J. Clin. Microbiol.
26:2465-2466 |
| 14. |
Jers k, B.,
P. Gilot,
M. Gubina,
N. Klun,
J. Mehle,
E. Tcherneva,
N. Rijpens, and L. Herman.
1999.
Typing of Listeria monocytogenes strains by repetitive element sequence-based PCR.
J. Clin. Microbiol.
37:103-109 |
| 15. |
Lawrence, L. M.,
J. Harvey, and A. Gilmour.
1993.
Development of a random amplification of polymorphic DNA typing method for Listeria monocytogenes.
Appl. Environ. Microbiol.
59:3117-3119 |
| 16. | Louie, M., P. Jayaratne, I. Luchsinger, J. Devenish, J. Yao, W. Schlech, and A. Simor. 1996. Comparison of ribotyping, arbitrarily primed PCR, and pulsed-field gel electrophoresis for molecular typing of Listeria monocytogenes. J. Clin. Microbiol. 34:15-19[Abstract]. |
| 17. | Mazurek, G. H., V. Reddy, B. J. Marston, W. H. Haas, and J. T. Crawford. 1996. DNA fingerprinting by infrequent-restriction-site amplification. J. Clin. Microbiol. 34:2386-2390[Abstract]. |
| 18. | Meng, J., and M. P. Doyle. 1997. Emerging issues in microbiological food safety. Annu. Rev. Nutr. 17:255-275[CrossRef][Medline]. |
| 19. |
Miettinen, M. K.,
A. Siitonen,
P. Heiskanen,
H. Haajanen,
K. J. Björkroth, and H. J. Korkeala.
1999.
Molecular epidemiology of an outbreak of febrile gastroenteritis caused by Listeria monocytogenes in cold-smoked rainbow trout.
J. Clin. Microbiol.
37:2358-2360 |
| 20. | Moore, M. A., and A. R. Datta. 1994. DNA fingerprinting of Listeria monocytogenes strains by pulsed-field gel electrophoresis. Food Microbiol. 11:31-38. |
| 21. |
Riffard, S.,
F. Lo Presti,
F. Vandenesch,
F. Forey,
M. Reyrolle, and J. Etienne.
1998.
Comparative analysis of infrequent-restriction-site PCR and pulsed-field gel electrophoresis for epidemiological typing of Legionella pneumophila serogroup 1 strains.
J. Clin. Microbiol.
36:161-167 |
| 22. | Salamina, G., E. Dalle Donne, A. Niccolini, G. Poda, D. Cesaroni, M. Bucci, R. Fini, M. Maldini, A. Schuchat, B. Swaminathan, W. Bibb, J. Rocourt, N. Binkin, and S. Salmaso. 1996. A foodborne outbreak of gastroenteritis involving Listeria monocytogenes. Epidemiol. Infect. 117:429-436[Medline]. |
| 23. |
Sciacchitano, C. J.
1998.
DNA fingerprinting of Listeria monocytogenes using enterobacterial repetitive intergenic consensus (ERIC) motifs polymerase chain reaction/capillary electrophoresis.
Electrophoresis
19:66-70[CrossRef][Medline].
|
| 24. | Slutsker, L., and A. Schuchat. 1999. Listeriosis in humans, p. 75-95. In E. T. Ryser, and E. H. Marth (ed.), Listeria, listeriosis, and food safety, 2nd ed. Marcel Dekker, Inc, New York, N.Y. |
| 25. | Sontakke, S., and J. M. Farber. 1995. The use of PCR ribotyping for typing strains of Listeria spp. Eur. J. Epidemiol. 11:665-673[CrossRef][Medline]. |
| 26. | Struelens, M. J., Y. De Gheldre, and A. Deplano. 1998. Comparative and library epidemiological typing systems: outbreak investigations versus surveillance systems. Infect. Control Hosp. Epidemiol. 19:565-569[Medline]. |
| 27. |
van Belkum, A.
1994.
DNA fingerprinting of medically important microorganisms by use of PCR.
Clin. Microbiol. Rev.
7:174-184 |
| 28. |
Vila, J.,
A. Marcos,
T. Llovet,
P. Coll, and T. Jimenez De Anta.
1994.
A comparative study of ribotyping and arbitrarily primed polymerase chain reaction or investigation of hospital outbreaks of Acinetobacter baumannii infection.
J. Med. Microbiol.
41:244-249 |
| 29. | Vines, A., M. W. Reeves, S. Hunter, and B. Swaminathan. 1992. Restriction fragment length polymorphism in four virulence-associated genes of Listeria monocytogenes. Res. Microbiol. 143:281-294[Medline]. |
| 30. |
Yoo, J. H.,
J. H. Choi,
W. S. Shin,
D. H. Huh,
Y. K. Cho,
K. M. Kim,
M. Y. Kim, and M. W. Kang.
1999.
Application of infrequent-restriction-site PCR to clinical isolates of Acinetobacter baumannii and Serratia marcescens.
J. Clin. Microbiol.
37:3108-3112 |
Applied and Environmental Microbiology, April 2001, p. 1793-1799, Vol. 67, No. 4
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1793-1799.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Liu, D.
(2006). Identification, subtyping and virulence determination of Listeria monocytogenes, an important foodborne pathogen. J Med Microbiol
55: 645-659
[Abstract] [Full Text] -
Somer, L., Danin-Poleg, Y., Diamant, E., Gur-Arie, R., Palti, Y., Kashi, Y.
(2005). Amplified Intergenic Locus Polymorphism as a Basis for Bacterial Typing of Listeria spp. and Escherichia coli. Appl. Environ. Microbiol.
71: 3144-3152
[Abstract] [Full Text]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»