Pathogen testing of ready-to-eat meat and poultry products collected at federally inspected establishments in the United States, 1990 to 1999

The Food Safety and Inspection Service (FSIS) conducted microbiological testing programs for ready-to-eat (RTE) meat and poultry products produced at approximately 1,800 federally inspected establishments. All samples were collected at production facilities and not at retail. We report results here for the years 1990 through 1999. Prevalence data for Salmonella, Listeria monocytogenes, Escherichia coli O157:H7, or staphylococcal enterotoxins in nine different categories of RTE meat and poultry products are presented and discussed. The prevalence data have certain limitations that restrict statistical inferences, because these RTE product-testing programs are strictly regulatory in nature and not statistically designed. The cumulative 10-year Salmonella prevalences were as follows: jerky, 0.31%; cooked, uncured poultry products, 0.10%; large-diameter cooked sausages, 0.07%; small-diameter cooked sausages, 0.20%; cooked beef, roast beef, and cooked corned beef, 0.22%; salads, spreads, and patés, 0.05%; and sliced ham and luncheon meat, 0.22%. The cumulative 3-year Salmonella prevalence for dry and semidry fermented sausages was 1.43%. The cumulative 10-year L. monocytogenes prevalences were as follows: jerky, 0.52%; cooked, uncured poultry products, 2.12%; large-diameter cooked sausages, 1.31%; small-diameter cooked sausages, 3.56%; cooked beef, roast beef, and cooked corned beef, 3.09%; salads, spreads, and patés, 3.03%; and sliced ham and luncheon meat, 5.16%. The cumulative 3-year L. monocytogenes prevalence for dry and semidry fermented sausages was 3.25%. None of the RTE products tested for E. coli O157:H7 or staphylococcal enterotoxins was positive. Although FSIS and the industry have made progress in reducing pathogens in these products, additional efforts are ongoing to continually improve the safety of all RTE meat and poultry products manufactured in federally inspected establishments in the United States.     

重庆市即食食品中单核细胞增生李斯特菌污染监测及初步风险评估

目的 了解重庆市市售即食食品中单核细胞增生李斯特菌(以下简称单增李斯特菌)的污染情况,进行初步风险评估,为预防食源性疾病提供科学依据。方法 2016—2019年对全市39个区县的市售即食食品中的单增李斯特菌进行监测,并用半定量微生物风险评估方法,初步评估重庆市即食食品中单增李斯特菌的风险。结果 重庆市2 680份即食食品中单增李斯特菌的检出率为1.77%;中式凉拌菜的单增李斯特菌检出率显著高于熟肉制品、生食水产品和即食豆制品(非发酵)(P＜0.05);超市、餐饮单位、农贸市场、便利店的即食食品中单增李斯特菌检出率大致相当(P＞0.05);第四季度单增李斯特菌检出率最高(P＞0.05);包装形式上,散装食品污染率最高(P＜0.05)。重庆市每年预计因食用熟肉制品、中式凉拌菜、生食水产品、即食豆制品(非发酵)引起每百万人口的李斯特菌病的发病例数分别为633.7例、126.1例、2.4例、31.5例。结论 重庆市即食食品中存在单增李斯特菌污染,其中熟肉制品致病风险最大。建议对即食食品加工后期采取有效的控制和监测措施,优先开展熟肉制品和中式凉拌菜中单增李斯特菌的定量风险评估研究,以降低潜在危害。     

Technologies and Mechanisms for Safety Control of Ready-to-eat Muscle Foods: An Updated Review

Ready-to-eat (RTE) muscle foods refer to a general category of meat and poultry products that are fully cooked and consumable without reheating. These products, including whole and sliced pork, beef, turkey, chicken, and variety of meats, in the forms of ham, roast, rolls, sausage, and frankfurter, are widely available in the delicatessen section of retail stores or various food service outlets. However, difficulties in avoidance of contamination by foodborne pathogens, notably Listeria monocytogenes, during product postlethality repackaging render RTE meats labile to outbreaks. Accordingly, the USDA-FSIS has established processing guidelines and regulations, which are constantly updated, to minimize foodborne pathogens in RTE products. Technologies that complement good manufacturing practice have been developed to control RTE meat safety. Among them, various antimicrobial product formulations, postpackaging pasteurization (thermal and nonthermal), and antimicrobial packaging are being used. Through these efforts, outbreaks linked to RTE meat consumption have substantially reduced in recent years. However, the pervasive and virulent nature of L. monocytogenes and the possible presence of other cold-tolerant pathogens entail continuing developments of new intervention technologies. This review updates existing and emerging physical and chemical methods and their mode of action to inactivate or inhibit threatening microorganisms in RTE muscle foods.     

Random amplified polymorphic DNA typing applied to the study of cross-contamination by Listeria monocytogenes in processed food products

The presence of Listeria spp. was investigated in 369 samples of cooked meat products and 52 of smoked salmon. Incidences of 17.6% for cooked meat and 38.5% for smoked salmon samples were found. All Listeria monocytogenes isolates (34 from meat products and 16 from smoked salmon) were typed serologically and by random amplified polymorphic DNA (RAPD) typing using primers HLWL74 (5'-ACGTATCTGC-3'), HLWL85 (5'-ACAACTGCTC-3'), and OMP-01 (5'-GTI'GGTGGCT-3'). Strains from cooked meat products were characterized and compared in relation to their origin. The detection of identical strains in products of different type and brand packed on the same date suggested cross-contamination, probably during the slicing process. All L monocytogenes isolates from smoked salmon were indistinguishable by serotyping and RAPD, suggesting that this strain was highly disseminated and adapted to the treatment used for the preservation of this food. RAPD subtypes were analyzed using GelCompar version 4.1 software and the unweighted pair method using arithmetic averages, and six groups with at least 78% similarity were established. Serotyping and RAPD results were in concordance, although RAPD showed a higher discriminatory power with L. monocytogenes isolates from meat products. RAPD is an easy method that could be useful to detect cross-contamination occurring during postprocessing manipulations.     

Incidence of Listeria monocytogenes in different types of meat products on the Belgian retail market

A survey was undertaken to determine the incidence and numbers of L. monocytogenes in a variety of meat products (cooked meat products, raw cured meat products (dried or not), mayonnaise based salads and prepared meals). As expected, raw cured meat products were significantly higher contaminated with L. monocytogenes than cooked meat products, 13.71% (113/824) and 4.90% (167/3405), respectively. Also a larger proportion of raw cured meat product samples contained a high initial level of the pathogen ( > 10 cfu/g). Higher incidence rates were obtained for whole cooked meat products (e.g. cooked ham, bacon) after slicing than before slicing, 6.65 and 1.56%, respectively, indicating cross-contamination. Due to multiple handling and processing steps, the incidence rate of the pathogen was higher for cooked minced meat products than for whole cooked meat products, 6.14 and 3.96%, respectively. No significant differences were obtained in the incidence of L. monocytogenes in whole cured meat products (e.g., raw ham) and minced cured meat products (e.g., dry fermented sausage), 14.92 and 11.69%, respectively. Lower incidence rates of L. monocytogenes were obtained for raw, cured meat products using beef or horse meat, 4.65 and 5.88%, respectively, A high incidence rate of L. monocytogenes was noted for the mayonnaise based salads (21.28% (186/874)) as well as for prepared meals (11.70% (92/786)), the latter especially due to contamination of vegetarian meals.     

延边地区2011~2015年食品中食源性致病菌的监测

【目的】 了解食品中主要食源性致病菌的污染状况,确定高危食品,为预防和控制食源性疾病提供科学依据。 【方法】 按照《全国食源性致病菌监测工作手册》 的检测技术要求,2011 － 2015 年在延边地区的几个监测点采集食品样品1069份,对沙门氏菌、单核细胞增生李斯特菌（定量）、金黄色葡萄球菌（定量）、铜绿假单胞菌、蜡样芽孢杆菌的污染情况进行监测。 【结果】 1069份样品中,共检出致病菌115株,总检出率为10.76%.熟肉制品、生食动物性水产品、凉拌菜、熟制米面制品、婴幼儿食品、乳及乳制品、速冻米面品、特殊膳食用食品、饮用水、三明治以及流动早餐样品的致病菌检出率分别为17.65%（3/17)、15.79%（3/19)、11.76%(4/34)、34.48%(10/29)、33.80%（24/71）、40.00%(12/30)、6.67%(1/15)、42.86%(6/14)、58.33%（7/12）、10.00%（1/10）和71.43%（10/14）;2011-2015年食源性致病菌检出率分别为0.94% 、1.87% 、6.83% 、0.65%、0.19%。 【结论】 乳及乳制品、特殊膳食用食品、饮用水和流动早餐是延边地区食品的主要污染品种,作为直接入口食品的熟肉制品、凉拌菜、熟制米面制品和婴幼儿食品可能导致较高的食源性疾病风险。     

9274份肉及肉制品食源性致病菌监测结果分析

目的 了解吉林省9274份肉及肉制品食源性致病菌污染情况,为防控食源性疾病提供科学依据。方法从吉林省9个地市级行政区采集市售6类肉及肉制品样品共9274份,包括生畜肉、生禽肉、熟肉制品、调理肉制品、冷冻肉糜制品和动物血液及制品。按照国家标准方法检测10种食源性致病菌。结果 全部9274份样本食源性致病菌总阳性检出率为3.9%(366/9274)。检出率最高为调理肉制品 (13.0%,63/483),其次是生禽肉(5.6%,107/1900)和生畜肉(5.0%,71/1428)。检出的主要致病菌为单核细胞增生李斯特菌、金黄色葡萄球菌和沙门菌。生禽肉中弯曲菌检出率(7.5%,31/411)和产气荚膜梭菌检出率(3.9%,7/180)均高于沙门菌检出率(3.5%,8/231)。生禽肉、生畜肉中未检出小肠结肠炎耶尔森菌。动物血液及制品未检出单细胞增生李斯特菌、弯曲菌和小肠结肠炎耶尔森菌。冷冻肉糜制品未检出沙门菌。熟肉制品未检出大肠埃希氏菌O157、志贺菌和蜡样芽胞杆菌。熟肉制品各年度检出率范围为1.3%-4.4%。结论 吉林省市售的肉及肉制品较长时间受到不同程度的食源性致病菌污染,存在食源性疾病发生的风险。     

Investigation for possible source(s) of contamination of ready-to-eat meat products with Listeria spp. and other pathogens in a meat processing plant in Trinidad

In 2003, there was a recall of three processed (chicken franks, spice ham and turkey ham ready-to-eat (RTE) meat products by a large processing plant in Trinidad as a result of contamination by Listeria monocytogenes. The study was conducted to investigate the possible source(s) of Listeria contamination of recalled RTE meat products and to determine the prevalence of Listeria spp., Salmonella spp., Escherichia coli and Campylobacter spp. in the products and air within the plant. Raw and processed meat products, as well as food contact surfaces were also tested for Salmonella spp., Listeria spp. and Campylobacter spp. initially after thorough clean-up and close-down of the plant. Faecal and effluent samples from the piggery, in close proximity to the plant, were tested for the presence of Salmonella spp., Listeria spp. and Campylobacter spp. Air samples and food contact surfaces were negative for the tested organisms. Ten (58.8%) of the 17 effluent samples and 4 (11.8%) of the 34 faecal samples were positive for Campylobacter coli. Of the 11 raw meat products tested, 10 (90.9%) were positive for E. coli and Listeria spp. either singly or in combination. Of the 32 processed RTE products tested, 11 (34.4%) were positive for E. coli, Salmonella spp., Listeria spp. and Campylobacter spp. in combination or singly. Eleven (61.1%) of 18 processed products contained unacceptable levels of aerobic bacteria using international standards. Four months later, following the implementation of recommended cleaning, sanitizing and hygienic practices at the plant, pre- and post-processed products were sampled and Listeria spp. were identified in 4 (80.0%) of the 5 raw products and in 1 of the 5 (20.0%) finished products. Two (40.0%) of the finished products contained unacceptable microbial levels. It was concluded that the close proximity of the piggery to the processing plant was not the probable source of Listeria contamination of the recalled meat products. The data suggested that improved sanitary practices on food contact surfaces and during handling of products, reduced the risk of Listeria spp. and other pathogens studied. The problem at the plant can therefore, be inferred to be due to lapses in good sanitary practices, inadequate heat treatments or the presence of pathogens particularly Listeria in biofilms on different surfaces continuously or occasionally contaminating finished products.     

我国市售冷冻肉糜制品中常见食源性致病菌污染状况研究

目的研究分析我国市售冷冻肉糜制品中常见食源性致病菌污染状况。方法运用随机抽样原则,在具有代表性的流通和餐饮环节随机抽样采集冷冻肉糜制品样品共计3 905份,采用国标方法检测单核细胞增生李斯特菌、金黄色葡萄球菌和沙门菌。结果在3 905份冷冻肉糜制品中,共检出阳性样品536份,三种致病菌的总检出率为13.73%,其中单核细胞增生李斯特菌检出率为5.71%(223/3 905),金黄色葡萄球菌检出率为8.32%(325/3 905),沙门菌为0.72%(28/3 905)。不同种类样品中,猪肉肉糜沙门菌检出率最高。散装冷冻肉糜制品沙门菌检出率高于预包装制品。经过统计分析,造成污染的主要原因:一是食品原材料污染;二是冷冻肉糜制品加工过程中污染,如加工步骤较多而质控不严格;三是冷冻肉糜制品运输过程污染,主要是难以保证冷链。结论我国市售冷冻肉糜制品存在致病菌污染,卫生状况有待提高。     

熟食肉鱼制品氧化安全性评价

对市售火腿肠、肉片、肉松、腊肠和鱼片5类19种熟食肉鱼制品的氧化产物丙二醛(MDA)和亚硝酸盐(NO2)这2种致癌物的含量进行了测定和分析。结果表明,只有1种鸡肉卷火腿肠的NO2残留量(36mg/kg)超标,其余熟食制品的NO2含量均在允许安全范围。猪肉和牛肉火腿肠的MDA值均低于05mg/kg,未出现任何异味,表现出很高的安全性,但是脂肪和蛋白质含量普遍偏低,影响了口感和应有的品质。鸡肉火腿肠的MDA值在05～10mg/kg范围内,出现氧化异味。肉片、鱼片、肉松及腊肠制品的MDA值在抽样时多数都超过10mg/kg,氧化安全期与标签保质期相差42～177d,对这类熟食肉鱼制品在标签保质期内所存在的氧化安全隐患,应引起足够的重视。     

Occurrence and distribution of listeria species in facilities producing ready-to-eat foods in British Columbia, Canada

In British Columbia (BC), Canada, food processing facilities licensed under provincial authority are not required to sample for Listeria monocytogenes in food products or processing environments. In 2009, we conducted a survey of dairy, fish, and meat facilities under BC authority to estimate the prevalence of Listeria spp. and L. monocytogenes in ready-to-eat (RTE) foods and production environments. From August to October, 250 RTE food samples and 258 swabs from the food processing environments of 43 facilities were collected. Standard culture methods were applied to both food samples and swabs. Of swabs collected from all 258 environmental surfaces, 15% were positive for Listeria spp. Significantly (P, 0.001) more fish facilities than dairy and meat facilities had food contact surfaces contaminated with Listeria spp. L. monocytogenes was found in RTE foods from fish facilities alone (5 of 12); in all five of the fish facilities with contaminated product, one or more environmental swabs were also positive for L. monocytogenes. The results suggest that while control of L. monocytogenes in BC-inspected dairy and meat facilities is effective in limiting food contamination, there is a need for provincial inspectors to initiate improved monitoring and management of contamination by L. monocytogenes in RTE fish processing facilities.     

2010年山西省食品中食源性致病菌监测分析

目的 了解山西省食源性致病菌的污染现状.方法 按照2010年度《全国食源性致病菌监测工作手册》进行.结果 1 576份样品中共检出阳性菌株149株,检出率为9.45％,其中单核细胞增生李斯特氏菌、副溶血性弧菌污染比较严重,总检出率为9.50％和8.22％,金黄色葡萄球菌、阪崎肠杆菌和沙门氏菌的总检出率分别为3.02％、1.11％和0.87％.不同类别食品中致病菌的检出率差异较大,生肉中致病菌的检出率高居榜首为49.33％,主要污染菌为沙门氏菌、单核细胞增生李斯特氏菌;沙拉中致病菌的检出率为17.39％,主要污染菌为单核细胞增生李斯特氏菌、金黄色葡萄球菌;生食水产品中致病菌的检出率为16.94％,主要污染菌为单核细胞增生李斯特氏菌、副溶血性孤菌;熟肉制品中致病菌的检出率为9.84％,主要污染菌为单核细胞增生李斯特氏菌、金黄色葡萄球菌、沙门氏菌;中式凉拌菜中致病菌的检出率为8.89％,主要污染菌为金黄色葡萄球菌;鲜榨果汁中致病菌的检出率为6.67％,主要污染菌为金黄色葡萄球菌;鲜冻水产品中致病菌的检出率为5.00％,主要污染菌为副溶血性弧菌;婴幼儿配方粉/米粉/谷粉/豆奶粉中阪崎杆菌的检出率为1.11％.结论 山西省多种食品均存在食源性致病菌不同程度的污染,应加大对散装食品、即食食品和生食水产品的监管.     

Protective cultures inhibit growth of Listeria monocytogenes and Escherichia coli O157:H7 in cooked, sliced, vacuum- and gas-packaged meat

Contamination of cooked meat products with Listeria monocytogenes poses a constant threat to the meat industry. The aim of this study was therefore to investigate the use of indigenous lactic acid bacteria (LAB) as protective cultures in cooked meat products. Cooked, sliced, vacuum- or gas-packaged ham and servelat sausage from nine meat factories in Norway were inoculated with 10(3) cfu/g of a mixture of three rifampicin resistant (rif-mutant) strains of L. monocytogenes and stored at 8 degrees C for four weeks. Growth of L. monocytogenes and indigenous lactic acid flora was followed throughout the storage period. LAB were isolated from samples where L. monocytogenes failed to grow. Five different strains growing well at 3 degrees C. pH 6.2, with 3% NaCl, and producing moderate amounts of acid were selected for challenge experiments with the rif-resistant strains of L. monocytogenes. a nalidixic acid/streptomycin sulphate-resistant strain of Escherichia coli O157:H7 and a mixture of three rif-resistant strains of Yersinia enterocolitica O:3. All five LAB strains inhibited growth of both L. monocytogenes and E. coli O157:H7. No inhibition of Y. enterocolitica O:3 was observed. A professional taste panel evaluated cooked, sliced, vacuum-packaged ham inoculated with each of the five test strains after storage for 21 days at 8 degrees C. All samples had acceptable sensory properties. The five LAB strains hybridised to a 23S rRNA oligonucleotide probe specific for Lactobacillus sakei. These indigenous LAB may be used as protective cultures to inhibit growth of L. monocytogenes and E. coli O157:H7 in cooked meat products.     

2012—2017年广西壮族自治区市售食品中沙门菌监测数据分析

目的 了解广西市售食品中沙门菌污染状况和特征,为减少污染和防控食源性疾病提供科学依据。方法 2012—2017年从广西14个市采集14类市售食品共60 174份,其中生鲜类食品5 712份,即食食品54 462份,按照GB 4789.4—2010《食品安全国家标准 食品微生物学检验 沙门氏菌检验》方法进行沙门菌检验。结果 生鲜类食品中生肉及生肉制品、生水产品及其制品、速冻米面制品、鲜蛋类沙门菌检出率分别为10.3%(399/3 883)、6.2%(50/806)、0.5%(2/440)、0.0%(0/583),即食食品中熟肉制品、餐饮食品、生食蔬菜及其制品沙门菌检出率分别为0.6%(58/10 175)、0.3%(39/14 721)、1.0%(5/489),焙烤及油炸类食品、饮料、水果及其制品均为0.1%,熟蛋制品、豆制品、冷冻饮品、调味品均未检出。生肉及生肉制品共检出51种血清型,德尔卑沙门菌为优势血清型(16.2%,70/432),主要在生猪肉中检出。即食食品共检出32种血清型,德尔卑沙门菌为优势血清型(14.5%,11/76),主要在熟肉制品中检出。结论 生鲜类受沙门菌污染最严重的食品是生畜肉和生禽肉,即食食品受沙门菌污染较严重食品是凉拌类食品。应加强从农场到餐桌的食品安全防控,减少食源性疾病的发生。     

中国肉制品分类

根据我国肉制品最终产品的特征和产品的加工工艺,可以将肉制品分为以下十大类:香肠制品、火腿制品、腌腊制品、酱卤制品、熏烧烤制品、干制品、油炸制品、调理肉制品、罐藏制品、其他类制品。     

Impact of nitrite on detection of Listeria monocytogenes in selected ready-to-eat (RTE) meat and seafood products

ABSTRACT:  The impact of sodium nitrite (NaNO₂) on detection and recovery of Listeria monocytogenes from select ready-to-eat (RTE) foods including smoked salmon, smoked ham, beef frankfurters, and beef bologna was assessed. Nitrite-containing (NC; 100 to 200 ppm NaNO₂) or nitrite-free (NF) foods were inoculated with a 5-strain cocktail of L. monocytogenes by immersion into Butterfield's buffer solution containing 5.4 to 7.4 × 10³ L. monocytogenes per milliliter. Inoculated products were vacuum-packaged and stored at 5 °C. A weekly comparative analysis was performed for presence of L. monocytogenes using 5 detection methods on products held at 5 °C for up to 8 wk. L. monocytogenes initially present at <100 CFU/g during the first 2 wk of storage increased throughout the study, attaining final populations of approximately 1 × 10⁴ to 1 × 10⁵ CFU/g. Lactic acid bacteria predominated throughout the study in all products. Exposure to NaNO₂ (100 to 200 ppm) resulted in 83% to 99% injury to the L. monocytogenes strains tested. The genetic-based BAX^® System (DuPont™ Qualicon, Wilmington, Del., U.S.A.) and modified USDA/FSIS methods detected 98% to 100% of Listeria -positive food samples and were consistently superior to and significantly different ( P < 0.05) from conventional cultural methods in recovering Listeria from NC samples. Data show that nitrite-induced injury adversely affects detection and recovery of L. monocytogenes from NC food, confirming earlier findings that nitrite-induced injury masks L. monocytogenes detection in NC RTE food products. Nitrite-injured Listeria can subsequently repair upon nitrite depletion and grow to high levels over extended refrigerated storage.     

Industrial application of an antilisterial strain of Lactobacillus sakei as a protective culture and its effect on the sensory acceptability of cooked, sliced, vacuum-packaged meats.

The application of a protective lactic acid bacterium (LAB) during the commercial production of cooked meat products is described. The LAB, a strain of Lactobacillus sakei, was previously isolated from cooked ham and inhibited growth of Listeria monocytogenes and Escherichia coli O157:H7 in this product. L. sakei was applied to the cooked products at a concentration of 10(5)-10(6) cfu/g immediately before slicing and vacuum-packaging using a hand-operated spraying bottle. The LAB strain inhibited growth of 10(3) cfu/g of a cocktail of three rifampicin resistant mutant L. monocytogenes strains both at 8 degrees C and 4 degrees C. Consumer acceptance tests of cooked ham and of servelat sausage, a Norwegian non-fermented cooked meat sausage, showed that control and inoculated products were equally acceptable. The products were still acceptable after storage for 28 days at 4 degrees C and, after opening the packages, for a further 5 days at 4 degrees C. The findings presented here confirm that the L. sakei strain is suitable for use as a protective culture and may technically easily be implemented in the commercial production of cooked meat products.     

Listeria monocytogenes in foods in Norway

Three-hundred-and-eighty-two samples of different retail food items in Norway (imported soft cheese, raw chicken, minced meat, fermented sausages, vacuum-packed processed meat products, smoked salmon, peeled shrimps, raw minced fish) and 78 carcass samples (sheep, pig, cattle), were screened for Listeria monocytogenes. Of the 460 samples investigated, 78 were found to contain L. monocytogenes. Five of these contained greater than 10(3) cfu/g, four greater than 10(2) cfu/g, while the remainder were shown to contain L. monocytogenes only after enrichment. L. monocytogenes was isolated most frequently from raw chicken, sporadically from soft cheese, shrimps, processed meat products and smoked salmon, and not at all from carcasses and fermented sausages.     

Prevalence and concentration of Listeria monocytogenes in sliced ready-to-eat meat products in the Hellenic retail market

The aim of this work was to estimate the prevalence and concentration of Listeria monocytogenes in packaged precut (slices or cubes) ready-to-eat (RTE) meat products available in the Hellenic retail market. Samples of these RTE meat products (n = 209) were taken from local supermarkets during a 3-month period and analyzed for the presence of L. monocytogenes with an automated enzymatic qualitative immunoassay followed by biochemical confirmation of positive results. The concentration of the pathogen in the positive samples was also determined. Seventeen samples (8.1%) were positive for L. monocytogenes. Eight (47.1%) of these 17 samples were from the same manufacturer; 36.4% of the products tested from this manufacturer were positive for L. monocytogenes. When bacon samples were not considered, the estimated prevalence of L. monocytogenes in sliced RTE meat products was much lower (3.1%). The L. monocytogenes populations in all positive samples were low, < or = 10 CFU/g. In 64.7% of the L. monocytogenes-positive samples, other Listeria species, including L. innocua and L. welshimeri, were also present at <10 to 690 CFU/g. These results indicate that L. monocytogenes is present in low numbers but is in a considerable proportion of the packaged precut RTE meat products that are sold in the Hellenic retail market. Cooked ham and bacon cut in cubes were the sample types most often contaminated with L. monocytogenes. The higher level of handling (e.g., cutting) associated with these products may further increase the risk of contamination with L. monocytogenes.     

Occurrence of Listeria monocytogenes in fresh and processed foods in Navarra (Spain)

The presence of Listeria spp. was investigated in a total of 3685 food samples obtained from different industries and markets of Northern Spain in the last 4 years. The samples analyzed include fresh raw products (meat, milk and poultry) and treated products (cooked and cured meats, frozen vegetables and smoked salmon). Occurrence of Listeria spp. varied from 8.1% in soft cheese to 76.3% in raw poultry samples. The highest incidence of L. monocytogenes also occurred in raw poultry (36.1% positive samples). Despite this high incidence of contamination, these kinds of products carry a low risk of listeriosis transmission because of the heat treatment prior to consumption. On the other hand, the ready-to-eat products (RTE) tested in this study showed incidences that could pose serious health problems, taking into account that the storage conditions may allow for rapid growth of the pathogen. It was also found that up to 75.5% of the L. monocytogenes strains isolated in this study belonged to serogroup 1, mainly serotype 1/2a, while the clinical cases observed in Navarra in the same period of time belonged mainly to serotype 4b/4bx.