Serotypes of Listeria m onocytogenes strains isolated from
clinical and food samples
Trkov
1
M. ,
Rupel
1
T. ,
2
M. ,
Műller – Premru
Lorenčič Robnik
5
1
Fišer J. , Paragi M.
3
S. ,
Štrumbelj
4
I. ,
National Institute of Public Health of the Republic of Slovenia, Ljubljana, Slovenia; 2 University of Ljubljana, Medical Faculty, Institute of Microbiology and
Immunology, Ljubljana, Slovenia; 3 Institute of Public Health Maribor, Maribor, Slovenia; 4 Institute of Public Health Murska Sobota, Murska Sobota, Slovenia;
Hospital of “Dr. Franc Derganc” Nova Gorica, Nova Gorica, Slovenia
1
5
Introduction
Listeria m onocytogenes is the causative agent of listeriosis, a serious illness of humans that can be transmitted with contaminated food. The
disease primarily affects older adults, pregnant women, newborns, and immunocompromised patients. Listeriosis remains of great public
health concern due to its high mortality rate. L. m onocytogenes serotyping is commonly used at the first level of characterisation in the
long-term epidemiological surveillance of food and clinical isolates. For the species L. m onocytogenes 13 serotypes are described (1/2a,
1/2b. 1/2c, 3a, 3b, 3c, 4a, 4ab, 4b, 4c, 4d, 4e, 7).
Materials and methods
16
No. of L. monocytogenes isolates
78 L. m onocytogenes strains isolated from 11 clinical, 66 food and 1
environmental sample were serotyped. All clinical strains were isolated in the
year 2010 and environmental isolate in 2009. Food strains from different food
samples: various meat products (53 %), fishery products (28.8 %), fresh and
processed vegetables (4.6 %), ready-to-eat foods (13.6 %) were isolated in
the years 2007 (6 isolates), 2008 (32 isolates), 2009 (21 isolates) and 2010 (7
isolates) (Fig. 1). All strains were isolated and identified by standard
bacteriological methods. The species L. m onocytogenes was confirmed by
polymerase chain reaction (PCR) with primers described by Chen and Knabel
(2007). Serotyping was performed with commercial sera for somatic (O) and
flagellar (H) antigens according to the manufacturer’s protocol (Denka Seiken,
Tokyo, Japan) and with PCR method developed by Doumith et al. (2004). This
multiplex PCR do not distinguish, within L. m onocytogenes , serotype 1/2a from
3a, 1/2c from 3c, 1/2b from 3b and 7, or 4b from 4d and 4e.
14
12
10
8
6
4
2
0
2007
2008
2009
2010
Year
Meat products
Fishery products
Fresh and processed vegetables
Ready-to-eat foods
Figure 1: Number of L. monocytogenes strains isolated
from different food samples by years.
40
No. of L. monocytogenes isolates
35
30
4e
25
4b
4
4c
1/2
1/2a
20
15
10
1/2c
5
1/2b
0
Meat products
Fishery
products
1/2a
1/2b
Fresh and
processed
vegetables
1/2c
1/2
RTE
4b
4c
Human
4d
4e
Environmental
4
Figure 2: Serotypes / serogroups of L. monocytogenes isoleted from
different sources.
1/2a
1/2b
1/2c
1/2
4e
4b
4
4c
Figure 3: Serotype / serogroup distribution of food L. monocytogenes
isolates.
Results and conclusions
The results showed that 73 isolates belonged to the following serotypes 1/2a, 1/2b, 1/2c, 4b, 4e, 4c, 4d. For three and two food isolates
only serogroups 1/2 and 4 were detected (Fig. 2). Altogether 63 isolates (81%) belonged to the serogroup 1/2 and 15 isolates (19 %) to
serogroup 4, no isolate belonged to serogrups 3 and 7. Figure 3 shows serotype / serogroup distribution of L. m onocytogenes isolated from
food samples. The most prevalent serotype in foods was 1/2a (46.3 % of isolates), followed by serotype 1/2c (23.9 % of isolates).
Serotype 1/2b and serogroup 4 were represented equally (7.5 % each). Serotypes determined in clinical L. m onocytogenes isolates (1/2a,
1/2c and 4e) were represented also in food samples (Fig. 3). Serogroups 1/2 and 4 were determined in all groups of food. Serotype 4e was
not detected in meat products but was the most prevalent in RTE (ready-to-eat) food items. Pulsed-field gel electrophoresis (PFGE) typing
with two restriction enzymes enables further characterization and comparison of human and food L. m onocytogenes isolates.
Acknowledgment: The authors wish to thank Vesna Malus and Maja Klopčič for their diligent work on serotyping.
References: 1. Chen Y, Knabel S. Appl Environ Microbiol 2007:73, 6299-304. 2. Doumith M et al. J Clin Microbiol 2004:42, 3819-22.