Screening On Isolation And Antimicrobial Susceptibilities Of Listeria Monocytogenes In Pork

Listeria monocytogenes was a common foodborne pathogen, which could cause seriouszoonotic disease. L.monocytogenes, E.coli O157:H7, Salmonella, Staphylococcus aureus weredefined as four major foodborne pathogens by World Health Organization. It is aGram-positive pathogen that are widely distributed in the environment, such as factoryequipment, waste water, food, and the feces of human and animals. The pathogen can causelisteriosis such as meningitis and sepsis. The susceptible population is the elderly, children,and pregnant women, with a death rate more than40%. Since the first L.monocytogenes hasbeen reported as a multi-resistant strain from a meningitis patient in France in1988, othersisolates resisting to more than one antibiotic have been constantly detect from food,environment, human and animals.With the improvement of people’s living quality, pork and meat products becomeindispensable on the table because of their rich nutrient. However, pork and meat products areeasy to be contaminated by bacteria during transportation and sales. People can be infectedand sicken by the pathogenic bacteria through direct contact with contaminated pork.Strains in this study were isolated from pork and meat products isolating fromsupermarkets and retail markets of Guangzhou and farms of Xiamen, using traditionalbiochemical identification methods (GB4789.30~2010) and PCR. PCR was used to study theserotypes, virulence genes, and mechanisms of tetracycline resistance of L.monocytogenes.K-B disc diffusion assay was used to identify the antibiotic resistant profile of the isolates.Among a total of273pork samples examined,52(19.02%) were positive for L.monocytogenes,with78distinct isolates being obtained at last. Of all isolates,33(42.31%),24(30.71%),16(20.51%),3(3.85%), and2(2.56%) were identified as serotypes1/2a (or3a),1/2b (or3b or7),1/2c (or3c),4a (or4c) and4b (or4d or4e), respectively. Each strain contains at least onevirulence gene. The78strains are divided into13groups of genotype. According to K-B discdiffusion assay, all strains were susceptible to the ampicillin, ampicillin-sulbactam, imipenem,ciprofloxacin, levofloxacin, and vancomycin. Resistance to tetracycline (20.51%) were mostserious among detected antibiotics.11.54%isolates were resistant to penicillin, gentamicin,erythromycin which are commonly used in the treatment of human listeriosis. The harboring of tet(M) gene is one of the major mechanisms of L.monocytogenes resistant to tetracycline inthis study. Conjugative transposon Tn916is an important determinant in spreading tet(M)gene.Tn916mediated tetracycline resistance mechanism accelerates the spread ofdrug-resistant genes among strains, making the clinical treatment of listeria difficult.The main purpose of this study was to detect prevalence of L.monocytogenes in pork andmeat products, evaluate the susceptibility of L.monocytogenes strains, and identify theunderlying mechanisms of tetracycline resistance in L.monoctogenes. It could provide ascientific basis for the prevention and control of food-borne illness.