| [Background]Listeria monocytogenes is a gram-positive, facultative intracellular bacterium that is responsible for causing the foodborne disease listeriosis in humans. It is reported that the incidence of Listeria monocytogenes is0.2～0.8/100000in Europe and US, but the mortality is as high as20～70%, so that the international health institutions have paid great attention to this bacterium. Listeria monocytogenes is widely present in the environment, which was infected mainly through contacting with Ready-to-Eat and frozen food. The clinical symptoms of listeriosis include septicemia, meningitis, mononucleosis and spontaneous abortion. High-risk groups include the elderly, pregnant women, newborns and immunocompromised individuals. As foodborne diseases resulted from Listeria monocytogenes were frequently reported worldwide with its high mortality, Listeria monocytogenes gradually became a threat for the public health. Massachusetts in1983,49people infected and14died as a result of consumption of contaminated milk. Consumption contaminated cheese caused142human cases, including29deaths in California in1985. In2002, contaminated turkeys led to46cases,7deaths and3miscarriages in a great many of states. In France, consumption of contaminated pork tongue led to279cases in1992. From1964to2003, there were150cases with39deaths in China. From the first Listeria monocytogenes resistant to tetracycline was reported in1988, the phenomenon that strains isolated from different environments, foods and clinicals resistant to various antibiotics was increasingly serious. With the risistance of Listeria monocytogenes is increasing, the pressure of clinical drug selection is gradually increased, which further increased the mortality of the diseases. Listeria monocytogenes has become the major public health problem in China. Recently, although many scholars had studied this bacterium, they largely confined to the active surveillance. Therefore, through analyzing Listeria monocytogenes in Shandong Province from2003to2010, respectively using serotyping, antibiotic resistance and PFGE to examine the genetic correlation between different strains and the association between different subtyping methods, this study aim to provide scientific basis to effectively control and prevent the foodborne diseases.[Objectives]1. To research the antibiotics sensitivity of Listeria monocytogenes from foods in Shandong Province in different strains sources, the resistance trends of the strains, in order to provide a theoretical basis for risk assessment and management of antibiotic resistance.2. To analyze the serological types of Listeria monocytogenes and the distribution of the advantage types in different foods types, collecting times and locations.3. To research the characteristics of PFGE types of Listeria monocytogenes and the genetic correlation between different strains. The establishment of database on Listeria monocytogenes of Shandong Province provide a platform for distribution, correlation and molecular epidemiology studies.4. Comparation the traditional typing methods (serotyping and antibiotic resistance) and molecular typing methods (PFGE) to analyze the association between the three methods.[Methods]1. Recommended by CLSI, broth microdilution susceptibility was used to antibiotic resistance.2. Using slide agglutination and tube agglutination methods for Listeria monocytogenes serotyping.3. PFGE was used to molecular typing according to standard methods of PulseNet.[Results]1.252Listeria monocytogenes were divided into21antibiotic resistance patterns.15.87%of the isolates were drug-resistant. Imipenem was the most prevalent (3.97%), followed by Tetracycline and Ciprofloxacin (both1.59%).There were no strains resistant to Gentamicin, Ampicillin and Penicillin. Multi-drug resistance rate was4.37%. Among different samples, years and locations, thehighest prevalent of antibiotic resistance were respectively raw pork (22.09%),2007(38.89%) and Linyi (29.41%)2.252Listeria monocytogenes were divided into6serotypes, mainly1/2c strains, including the most virulent strain4b-type. Among different samples, years and locations,1/2a(raw chicken,59.12%),1/2c(2005,40.54%),1/2c (Jinan,38.71%) were respectively the advantage serotypes.3. A total of252isolates were subtyped into73PFGE types with homology of50.40%to100.00%and the advantage type was type24(15.48%). The advantage types in different sources, years and locations respectively type33(23.94%), type24(22.97%), type24(15.48%)4. The Simpson index of the three methods were respectively:antibiotic resistance D=0.7048, serotyping D=0.7023, PFGE typing D=0.9371. PFGE typing has better ability to distinguish the strains.There was a clear-cut association of PFGE types with serotypes, but no correlation between PFGE patterns and antimicrobial resistance profiles.[Conclusions]1. There are various types of food contaminated by Listeria monocytogenes in Shandong Province, so the supervision of food hygiene should be strengthened.2. Listeria monocytogenes were subtyped by the combination of serotyping, antibiotic resistance and PFGE for the first time. In Shandong Province, different strains were resistant to some antibiotics, but there were no strains resistant to the first-line clinical antibiotics. The serotyps were distributed widely. It is necessary to strengthen the monitoring of virulent strains, especially4b-type. It should be alert to the spread of4b strains and the emergence of new resistance patterns. Listeria monocytogenes were from different clones, but a number of strains were closely related. There was no correlation between PFGE types and samples resources. PFGE types were closely linked with serotypes, but no correlation with antibiotic resistance.3. PFGE is the highest resolution typing methods. The establishment of database which is mainly PFGE combined with serotyping and antibiotic resistance can provide basis for grasping the trend of foodborne pathogens, investigating outbreaks of foodborne disease and tracking the infectious sources. |
PDF Full Text Request