Longitudinal Occurrence And Molecular Characteristics Of Listeria Monocytogenes In Meat Products From The Open Markets In A City Of Sichuan Province,2015

As an important foodborne pathogen,Listeria monocytogenes contamination in retailing meat products is a threat to both public health and food industry.A 12-month survey was conducted to investigate the longitudinal prevalence and epidemiological characteristics of L.monocytogenes from meat products in the open markets from a city in southern China.A total of 3622 raw meat and 873 cooked meat related samples(including meat pieces,environmental swabs,and water samples)were collected from 9 raw meat stalls types(pork,beef,frozen meat,mutton,dissection,chicken-duck,rabbit,fish and ell-loach stalls)and 2 cooked meat stalls types(cooked mutton restaurants and ready-to-eat stalls),with 443(12.2%)and 141(16.2%)samples being contaminated by L.monocytogenes,respectively.The prevalence ofL.monocytogenes was highest in frozen meat(46.9%),followed by cooked mutton and haggis(24.0%),raw mutton(20.7%),pork(16.5%)and fish viscera(13.0%),and was lowest in the viscera of rabbit(2.0%)and poultry(chickens and ducks)(2.0%).Seasonal variation for the occurrence of L.monocytogenes was observed in ready-to-eat food,pork,beef,mutton and meat in dissection stalls(rabbit,chicken and duck).But no seasonal variation was found in fish viscera and frozen meat(raw and cooked).By serotyping,the 584 strains of L.monocytogenes belonged to 6 serotypes with 1/2b(272,46.6%),1/2c(153,26.2%)and 1/2c(130,22.3%)being predominant.By multi-locus sequence typing(MLST),37 STs(sequence types)were found with ST9(130,22.3%),ST87(116,19.9%),ST8(98,16.8%)and ST3(78,13.4%)being most frequent.By pulsed-field gel electrophoresis(PFGE),73 PTs(pulsotypes)were found with PT30(115,19.7%),PT11(91,15.6%),PT4(87,14.9%)being most prevalent.The prevalence and predominantly contaminated subtypes differed among different open markets and sample types.Remarkably,there was no statistic difference in the distribution of predominant subtypes in ready-to-eat products and clinic listeriosis isolates.Among the 329 sampling stalls surveyed,32.2%(106/329)were contaminated by L.monocytogenes of the same subtypes for 2 to 10 times.Seven PTs(PT4,PT11,PT25,PT30,PT54,PT260 and PT309)in raw meat products were persisted from 6 to 12 months,being responsible for 31.8%(139/443)of all raw meatL.monocytogenes isolates.PT32 and PT310 might persist in the cooked mutton and haggis in mutton restaurants.The longitudinaloccurrence and persistence of L.monocytogeneswere systematically investigated in the open markets for 12 months,which would be helpful in developing preventive measures in food contamination and clinic infection.