| Listeria monocytogenes,a ubiquitous pathogenic saprophyte, has been recognized as an important foodborne pathogen, causing invasive infections inhumans and animals with a high fatality rate (20-30%). Groups at highest risk are neonates, pregnant women, person of advanced age, adults with underlying disease(AIDS, cancer, diabetes, transplant recipients, chronic hepatic disorder) and other immunocompromised individuals. Clinical manifestations of invasive listeriosis are usually severe and primarily comprise meningoencephalitis, spontaneous abortion,neonatal sepsis, central nervous system infections and febrile gastroenteritis syndrome.The organism is widely distributed in nature and various foods (meat,vegetables,milk, fish, chilled foods and dairy products), and has the ability to grow at refrigeration temperatures (2-4?), and tolerate high NaCl concentrations. Thus, food is considered to be the main vector of the pathogenic bacterium in sporadic and epidemic cases of systemic human listeriosis.To date, previous studies, which mainly focused on prevalence and molecular characteristics of foodborne L. monocytogenes isolates in various products, have been reported all over the world. However, there was a paucity of data regarding long-term fluctuation trend of L. monocytogenes from food samples for the food industries, public health agencies, and government bodies. Thus, in the present study,a 12-month-long surveillance on the occurrence of L.monocytogenes in different food items (raw meat and aquatic products) was conducted from a meat wholesale market in Beijing. Food samples, including poultry, aquatic animal, livestock products, were systematically collected from the markets from March 2014 to February 2015, and strain isolation and identification were performed according to the NMKL(Nordic Committee on Food Analysis) standard method. Our overall aim was to detect the occurrence of this pathogen in food samples, analyse the molecular characters of the isolates by serotyping, pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing(MLST).A total of 2147 food samples, comprised of livestock products (n=1082), poultry(n=406) and aquatic products (n=659), were obtained from the meat wholesale market.468 L. monocytogenes isolates were recovered, representing 21.80% of the total samples (n=2147), and the pathogen occurred among all kind of food samples and by category 33.64% (364/1082) of livestock products, 10.93% (72/659) of aquatic products and 7.78% (32/406) of poultry. Among livestock samples, the pathogen was detected among 55.18% (181/328) of ground pork products. The L. monocytogenes isolates (n=468) could be grouped into seven different serotypes (1/2a,1/2b,1/2c,3a,4a, 4c and 4b), the majority (318 isolates, 67.95%) were of serotype 1/2c, followed by serotype 1/2b (46 isolates, 9.83%) and serotype 3a (35strains, 7.48%). The PFGE typing was carried out by AscI for determination of genetic relatedness among all the 486 L. monocytogenes isolates, and those strains could be categorized into 43 pulse types (PTs) which were grouped into 6 clusters and GX6A16.CN0004 was the predominant PFGE type. Considering the genetic relatedness, lineage ?-related isolates were dominant in cluster ?/?/?/?, lineage ?-related isolates for cluster VI and lineage I-related isolates for cluster V. All of L. monocytogenes isolates could be grouped into 19 distinct sequence types (STs) by MLST analysis,and three novel STs were firstly presented. Among STs, the majority (312, 66.67%) were ST9 (312/468).Accordingly, the food sources contaminated by L. monocytogenes was confirmed in Beijing by our study, and the result of molecular subtypes indicated that common serotypes (1/2c),PTs (GX6A16.CN0004) and STs (ST9) in Beijing had the similar prevalent trends as in rest of China. Moreover,the presence of these epidemiologically important serotypes, STs and PTs among almost all kind of food samples indicates possible diverse sources of infection in Beijing of China and poses a potential public health risk.The current study illustrates a potential public health risk of L.monocytogenes in Beijing of China because of its continuous occurrence in various food items,particularly in pork products. Importantly, majority of isolates belonged to the serotypes (1/2c, 1/2b and 3a) capable of causing invasive illnesses and the combination of serotype detection along with PFGE and serotype analysis enabled us to distinguish differences among those isolates. Thus, strategy can be applied to trace the outbreak-causing L. monocytogenes strain to the source of contamination. To reduce the risk of L. monocytogenes infection, appropriate sanitation practices in food industries are required,and the control programs should be followed to minimize contamination from food processing or original sources. In addition, consumers should take proper care for prevention of the growth of the organism, and be very careful for high-risk foods. In order to understand L. monocytogenes contamination sources and prevention strategies, a large scale future research is extremely required in particular endemic regions with samples collected from the consumers, retail food shops, food processing plants as well as from other natural sources. |
PDF Full Text Request