Distribution, Detection And Tracing Of Three Types Of Food-borne Pathogens From Kiwifruit Chain In Shaanxi Province

Kiwifruit, originated in China, is a kind of highly nutrient fruit, and spreads aroud China. Due to its highly nutrient, kiwifruit has a good propect of market. However, there is rare about the study on the safety of food-borne pathogens from kiwifruit. So, this study made an investigation of the contamination of food-borne pathogens on kiwifruits in Shaanxi province, one of the most producer. This study sampled from orchards in Zhouzhi and Meixian in Shaanxi as well as plants in Zhouzhi and Baoji, then by a combination of National Standard and Polymerase Chain Reaction, this study made an investigation of the contamination of food-borne pathogens. And a further study on virulence, serotype, and antibiotic resistance were made. Meanwhile, to find a sufficient way to guarantee the safety of kiwifruit, this study traced the source of isolates by Pulsed Field Gel Electrophoresis and Multiple Locus Sequence Typing. At the same time, considering the possibility of the existence of foodborne pathogens in kiwifruit juice, which is highly commercialized, this study applied a method that could detect three ktypes of food-borne pathogens in kiwifruit juice by real-time PCR. The main research results are as follows:(1)A totle of 348 samples from kiwifruit orchards and 59 samples from plants were collected from Meixian and Zhouzhi. In kiwifruit orchards, the positive rates of Escherichia coli from fresh fruits, fallen fruits, soil, air, and irrigation water were 18.3%, 35.0%, 69.2%, 0.0%, and 25.0%, respectively; the positive rates of Escherichia coli from plants in Zhouzhi and Meixian were 23.3% and 6.9%, respectively. In kiwifruit orchards, the positive rates of Staphylococcus aureus from fresh fruits and fallen fruits were 3.9% and 1.0%, respectively; the positive rates of Staphylococcus aureus from plants in Zhouzhi and Baoji were 23.3% and 6.9%, respectively. The positive rate of Salmonella from all samples was 0.0%.(2)According to the detection of virulence genes in 160 isolates of Escherichia coli and 14 isolates of Staphylococcus aureus: three isolates of Escherichia coli from orchards contains Shiga toxin-producing gene type 2; two isolates of Staphylococcus aureus contains enterotoxin type b and enterotoxin type h.(3)The serotypes of three isolates of Shiga toxin-producing Escherichia coli were O86a:MH, O158:H21, O158:H2, respectively. One hundred and sixty isolates of Escherichia coli and 14 isolates of Staphylococcus aureus showed some difference in antibiotic resistance. Among the 160 isolates of Escherichia coli, the rates of antibiotic resistance were 25.6% to trimethoprim-sulfamethoxazole, 20.6% to cefoxitin, 19.4% to ceftriaxone, 16.9% to nalidixic acid, 15.0% to tetracycline, and less than 10.0% to the other antibiotic. Among the 14 isolates of Staphylococcus aureus, the rates of antibiotic resistance were 21.4% to erythromycin, 7.1% to oxacillin, 7.1% to cefoxitin, 7.1% to amoxicillin, and 7.1% to ampicillin. Among them, 15.6% of Escherichia coli and 78.6% of Staphylococcus aureus were susceptible to the antibiotics.( 4) The result of Pulsed Field Gel Electrophoresis indicated that there was cross-contamination between the water used for processing and the blides. In orchards, irrigation water maybe the source of contamination in kiwifruit.(5)This study established a system to detect more than 101 CFU/mL of Shiga toxin-producing Escherichia coli, Salmonella, and Listeria monocytogenes efficiently, applying real-time Polymerase Chain Reaction and distinguishing the differences in melting curve of the amplification.