Development and evaluation of DNA and RNA real-time assays for food analysis using the hilA gene of Salmonella enterica subspecies enterica

The objective of this study was the development of DNA and RNA real-time PCR methods for detection of food-borne Salmonella sp. as rapid alternatives to the traditional cultural method (ISO 6579, 2004) in fresh meat carcasses and processed meat samples. These PCR methods were based on the hilA sequence, with primers and hybridisation probes designed against this gene target. The primers and probes were evaluated for their efficiency and dynamic range and subsequently the specificity of the assay was tested using 106 Salmonella enterica subspecies enterica strains and 30 non-salmonellae strains. An internal amplification control (IAC) was also developed for incorporation. The optimum copy number of IAC was determined to be 500 copies per reaction. A complementary enrichment protocol was adapted from the existing standard ISO 6579:2004 and consisted of enrichment in Buffered Peptone Water (BPW) 22 ± 2 h and a second selective enrichment for 6 h in Rappaport Vassiliadis with Soya (RVS). The DNA and RNA-based real-time PCR protocols, were applied to meat samples inoculated with Salmonella enterica subspecies enterica strains, including swabs from meat carcasses and minced beef samples which were heat treated or frozen. The developed methods have the potential as useful alternatives to the standard ISO 6579:2004 method for the detection of Salmonella enterica subspecies enterica on carcass swabs and raw meat using hilA as a target. The DNA assay is a useful tool for the screening of meat samples in the abattoir within 3 days of slaughter or in a food production process and the RNA-based assay has the potential to detect viable Salmonella enterica subspecies enterica in ready-to-eat products.     

Survival of Escherichia coli O157:H7 and Salmonella on chill-stored vacuum or carbon dioxide packaged primal beef cuts

The ability of two Escherichia coli O157:H7 strains (E27, a cattle isolate, and B6-914 gfp-91, a fluorescent marker strain) and two Salmonella serotypes (S. typhimurium and S. brandenberg) to survive on chilled preservatively packaged primal beef cuts was examined. Each of the strains was inoculated separately at two dilution levels (10(3) and 10(5) cfu g(-1)) onto 500 g beef steaks, packaged under vacuum or 100% carbon dioxide, and stored, with uninoculated controls, for 6 weeks at - 1.5 degrees C, then for 2 weeks at 4 degrees C. Bacterial numbers were determined by dilution and incubation at 37 degrees C for 24 h on either Sorbitol McConkey Agar or Xylose Lysine Desoxycholate Agar for E. coli O157:H7 and Salmonella samples, respectively. Counts were corrected for background growth and their accuracy checked using immunological tests. Fluorescent E. coli O157:H7 B6-914 gfp-91 was also counted under ultra-violet light. No significant changes in numbers of the E. coli O157:H7 or Salmonella strains occurred during storage at either - 1.5 or 4 degrees C packaged under either vacuum or carbon dioxide. The ability of these pathogens to survive standard preservative packaging conditions is different from that reported from their generic counterparts and therefore a cause for public health concern.     

SURVIVAL OF THREE SALMONELLA SEROTYPES ON BEEF TRIMMINGS DURING SIMULATED COMMERCIAL FREEZING AND FROZEN STORAGE

This study investigated the survival of three Salmonella serotypes (S. Brandenberg, S. Dublin and S. Typhimurium) on beef trimmings during simulated commercial freezing, frozen storage for 9 months and subsequent abusive slow thawing and refreezing conditions. This was achieved by plating samples monthly and after thawing and refreezing on nonselective Tryptic Soy Agar (TSA) and selective Xylose Lysine Desoxycholate Agar (XLD) and incubating both at 37C for 24 h to determine Salmonella counts, aerobic counts and the presence, if any, of sublethal injury of this pathogen. Two freezing temperatures (−18C or −35C) to simulate slow or rapid freezing respectively, and two inoculation levels (10³ cfu g⁻¹ or 10⁵ cfu g⁻¹) were used. Aerobic counts and counts of all the Salmonella serotypes did not change significantly (p > 0.05) during frozen storage or for any of the other treatments applied in this study. This finding was attributed to the insulating nature of the subcutaneous fat layer in this manufacturing cut. These results are important with respect to food safety associated with ground beef processing.     

温州市食品中沙门菌污染状况及特征分析

目的了解温州市食品中沙门菌的污染状况,分析分离的沙门菌血清型分布、耐药性及脉冲场凝胶电泳(PFGE)分子分型特征。方法依据GB 4789.4—2016《食品安全国家标准食品微生物学检验沙门氏菌检验》进行菌株分离鉴定及血清学分型,采用微量肉汤稀释法进行药敏试验,PFGE法进行分子分型。结果 6类食品2 039份样品中,37份样品检出沙门菌,检出率为1.8%,其中生禽肉和生畜肉检出率较高,分别为6.9%(20/290)和3.4%(10/290)。37株沙门菌分属16种血清型,居前三位分别为鼠伤寒沙门菌、德尔卑沙门菌和肠炎沙门菌。81.1%(30/37)的菌株对17种抗生素产生不同程度的耐药,呈现24种耐药谱,多重耐药率为56.8%(21/37)。PFGE图谱分为31种PFGE带型,呈多态性。结论沙门菌在温州市食品中存在一定的污染率,耐药情况形式严峻,PFGE图谱的聚集性与沙门菌的血清型有一定的联系,与耐药谱之间的关联性并不明确。     

Thermal Inactivation of Salmonella spp., Salmonella typhimurium DT104, and Escherichia coli 0157:H7 in Ground Beef

ABSTRACT: In 19.1% fat ground beef, Escherichia coli 0157:H7 was less heat- resistant at ≥58°C than the Salmonella typhimurium DT104 and Salmonella senftenberg , but at 55°C the D value was similar to DT104 strains and higher than an eight-strain Salmonella cocktail. Inactivation of E. coli 0157:H7 was more temperature-dependent than the cocktail and DT104 strains. E. coli and DT104 strains were more heat-resistant in beef containing 19% fat than 4.8% fat. The cocktail was more thermally stable in stationary as compared to log phase. Freezing of inoculated raw meat decreased heat resistance of the cocktail. The pathogenic strain, growth phase of the organism, state of the meat (fresh or frozen) and meat composition must be considered when designing protocols to verify thermal processes.     

Occurrence and characterization of Salmonella from chicken nuggets, strips, and pelleted broiler feed

Raw, frozen chicken nuggets and strips have been identified as a significant risk factor in contracting foodborne salmonellosis. Cases of salmonellosis as a result of consuming partly cooked chicken nuggets may be due in part to Salmonella strains originating in broiler feed. This study was undertaken to determine the occurrence and characterize the strains of Salmonella contaminating chicken nuggets, strips, and pelleted feeds, in an attempt to demonstrate whether the same Salmonella strains present in broiler feed could be isolated from raw, frozen chicken nuggets and strips available for human consumption. Salmonellae were recovered using the Health Canada MFHPB-20 method for the isolation and identification of Salmonella from foods. Strains were characterized by serotyping, phage typing, antimicrobial resistance typing (R-typing), and by pulsed-field gel electrophoresis (PFGE). Salmonellae were isolated from 25-g samples in 27% (n=92) of nugget and strip samples, 95% (n=20) of chicken nugget meat samples, and from 9% (n=111) of pelleted feed samples. Salmonella Heidelberg, Salmonella Enteritidis, and Salmonella Orion were the most commonly isolated serovars from chicken nuggets and strips, nugget and strip meat, and pelleted broiler feeds, respectively. Salmonella Enteritidis phage type (PT) 13a with PFGE pattern SENXAI.0006 and R-type sensitive as well as Salmonella Enteritidis PT13a with PFGE pattern SENXAI.0068 and R-type sensitive were isolated from pelleted feed, and chicken nugget and strip meat in two separate instances. Data showed that Salmonella strains isolated from broiler feed were indistinguishable from strains isolated from packaged raw, frozen chicken nuggets and strips. However, results did not rule out the possibility that breeding stock or contamination during processing may have contributed to chicken meat contamination by Salmonella.     

Prevalence and characterization of Salmonella infantis isolates originating from different points of the broiler chicken-human food chain in Hungary

During the 10-month study period Salmonella contamination of broiler houses and the flocks reared in three farms (A, B and C), the slaughter houses where the flocks were slaughtered, as well as the carcass and retail raw meat products originating from them was investigated. In the broiler farm A five consecutive flocks, in the B and C farms one flock was sampled. Environmental samples were taken prior to the introductions. Environmental, drinking water, feed and faecal samples were collected regularly using standard methods. Before and during processing of the flocks, environmental and carcass samples were taken at the abattoirs. Salmonella contamination of the carcass, retail meat, as well as stool samples of farm and abattoir workers and from human illnesses registered in the same period and region were also examined. Isolation, sero-, phage- and antibiotic resistance typing, class 1 integron and plasmid profiling of the strains were performed; their genetic relationship was assessed by PFGE. Although the broiler house and the faecal samples of the 5 flocks of the farm A were negative for Salmonella, S. infantis was isolated from 20-100% of the abattoir carcass samples. The retail raw meat samples were 0-100% S. infantis positive. The environmental samples of farm B were Salmonella negative, but the examined flock was contaminated: S. infantis was identified from 43% of the faecal samples. This serotype was identified in 100% of the carcass and retail raw meat samples. From environmental samples taken before the arrival of the 1-day-old chicks in the broiler house C, S. infantis was cultured. S. infantis prevalence in the faecal samples was 35% and all the carcass and retail raw meat samples were S. infantis contaminated. Altogether 164 S. infantis strains were isolated out of which 145 were further characterized. The vast majority (142/145) of the strains belonged to phage types 217 and 213. All but one were characterized by the nalidixic acid-streptomycin-sulphonamide-tetracycline resistances, had an 885 bp class 1 integron and a large plasmid of >168 kb in size. The strains showed >/=88.7% genetic similarity. The results obtained shows that the same multi-drug resistant S. infantis clone was spread from the examined broiler farms contaminating the slaughter and the retail meat and appeared in the human illnesses of the examined region that was earlier detected as the dominant clone characteristic of the broiler and human population of the whole country.     

生牛肉中沙门菌的血清型鉴定与耐药性检测

目的了解新疆地区生牛肉中沙门菌的血清型和耐药状况。方法采用沙门菌诊断血清试剂盒检测血清型,微量肉汤稀释法检测分离菌株的耐药性。结果 28株牛肉源沙门菌共检出11种血清型,其5种优势血清型分别为伦敦沙门菌(17.9%)、德尔卑沙门菌(10.7%)、伤寒沙门氏菌(10.7%)、甲型副伤寒沙门菌(10.7%)和阿贡纳沙门菌(10.7%);沙门菌对10种抗菌药物耐药结果显示菌株对甲氧苄啶、氯霉素、四环素的耐药率最高,分别为100%、92.9%和75%,对氟苯尼考最为敏感,耐药率为7.1%。所有的菌株可耐2种或2种以上的抗生素。结论新疆地区牛肉源沙门菌存在一定的致病性,耐药状况比较严重。     

Incidence of Salmonella in minced meat produced in a European Union-approved cutting plant

Contamination of minced meat with Salmonella is still considered a major problem in food hygiene. Therefore, in this study the Salmonella incidence in minced meat produced in a European Union-approved slaughtering and cutting plant was investigated in detail. Throughout 21 months, 297 pool samples (1,485 individual samples) of mixed minced meat (beef and pork) were examined according to Council Directive 94/65/EC and to ISO 6579. Salmonellae were detected in 47 (15.8%) of the pool samples. After separation of the positive pools, 93 individual samples were determined to be Salmonella positive, representing 6.3% of the total 1,485 samples. Serotyping resulted in most isolates (69.6%) being identified as Salmonella Typhimurium. It was further shown that the incidence of Salmonella isolations varied during the year and that the isolation rate was higher on some days of the week compared with others.     

北京市售鸽肉中大肠杆菌和沙门氏菌分离鉴定及耐药性分析

目的对北京市售鸽肉中大肠杆菌和沙门氏菌进行分离鉴定,并对分离菌株进行抗生素耐药性分析。方法使用缓冲蛋白胨水增菌液淋洗肉鸽样品后,使用大肠杆菌(E.coli,EC)增菌肉汤和丹麦国家血清研究院(Statens Serum Institute, SSI)肠道细菌琼脂分离大肠杆菌,使用四硫磺酸盐(tetrasulfonate, TT)增菌肉汤和木糖赖氨酸脱氧胆盐(xyloselysinedeoxycholate,XLD)琼脂平板分离沙门氏菌,使用生化鉴定进行可疑菌确认。参照CLSI2016版推荐的肉汤稀释法,测定15种抗生素对所分离大肠杆菌和沙门氏菌的最低抑菌浓度(minimalinhibitory concentrations,MICs)。结果样品(n=200)中大肠杆菌(n=104)检出率为52.0%,沙门氏菌(n=41)检出率为21.0%。所分离的42株沙门氏菌菌株均对头孢他啶、氨曲南、厄他培南和替加环素敏感,对氨苄西林、萘啶酸、环丙沙星、四环素、复方新诺明和氯霉素的耐药率在30%以上,部分菌株对头孢噻肟(4.8%)和黏菌素(2.4%)耐药。所分离的104株大肠杆菌菌株均对替加环素敏感,对氨苄西林、头孢噻肟、氨曲南、萘啶酸、环丙沙星、四环素、复方新诺明、氯霉素和卡那霉素的耐药率在30%以上,部分菌株对头孢他啶(2.9%)、厄他培南和(1.0%)和黏菌素(9.6%)耐药。结论北京市售鸽肉是耐药大肠杆菌和沙门菌的重要储存库,相较于我国其他地区市售猪肉,鸡肉,牛肉等分离的耐药菌株,表现出不同的耐药谱,耐药率相对较低,但是北京市售鸽肉所携带的菌株已经累积了复杂的耐药特征,有必要对其中存在的耐药机制进行系统研究。     

南京市某食品厂酱卤熟肉制品生产加工过程微生物污染状况分析

目的了解南京市某食品厂酱卤熟肉制品加工过程中微生物污染状况及分布情况。方法 2016—2017年在南京市某食品厂采集生产加工过程中食品样品120份(原辅料60份、中间产品28份、成品24份、终产品8份)、环境样品204份、空气样品58份和生产用水14份,共396份,按照GB 4789食品微生物学检验系列标准和GB/T 16294—2010《医药工业洁净室(区)沉降菌的测试方法》对卫生指示菌和主要食源性致病菌进行检测,并对沙门菌进行血清型鉴定。结果在食品样品和环境样品中,李斯特菌检出率为7.4%(24/324),金黄色葡萄球菌检出率为2.6%(5/196),沙门菌检出率为1.9%(6/324);其中李斯特菌有2株单核细胞增生李斯特菌,其他以格氏李斯特菌和伊氏李斯特菌为主;沙门菌经血清学分型共4种血清型,分别为肠炎沙门菌(2株)、鼠伤寒沙门菌(2株)、依桑吉沙门菌(1株)和亚利桑那沙门菌(1株)。在原辅料、中间产品以及人员、仪器设备、清洁工具中均有致病菌检出,但成品和终产品中未检出致病菌。结论酱卤熟肉制品生产过程原辅料和环境中均存在多种致病菌污染。     

Campylobacter and Salmonella in raw red meats in the United Kingdom: prevalence, characterization and antimicrobial resistance pattern, 2003-2005

The prevalence of Campylobacter and Salmonella was assessed in 3959 raw red meats in the UK during 2003-2005. Meats were more frequently contaminated with Campylobacter (7.2%) than with Salmonella (2.4%). Lamb and other meats (e.g. mutton, rabbit) exhibited the highest contamination from Campylobacter (12.6% and 19.8%, respectively), compared with pork (6.3%) and beef (4.9%). Pork however had the highest contamination from Salmonella (3.9%), followed by lamb (2.0%), other meats (2.0%) and beef (1.3%). Offal samples (36.6%) were more frequently contaminated with Campylobacter or Salmonella than muscle tissue (7.0%). C. jejuni predominated in all meat types. C. coli isolates were more likely to exhibit antimicrobial drug resistance, including quinolones, than C. jejuni. Salmonella typhimurium was the most frequent Salmonella serotype isolated from meats; S. typhimurium DT104/104b isolates exhibited higher rates of multiple drug resistance than other serotypes. The findings reinforce the importance of adequate cooking of meat and good hygiene to avoid cross-contamination.     

Evaluation of the thermal resistance of different Salmonella serotypes in pork meat containing curing additives

The preliminary heat resistance evaluation of 94 Salmonella strains was carried out in culture medium (Trypticase soy broth, TSB). The heat resistance of three S. typhimurium strains (ATCC 14028, 133 and 1116), a strain each of S. derby B4373, S. potsdam 1133, S. menston 179. S. eppendorf 166, and S. kingston I124 was determined also in pork meat containing curing additives. As expected, the eight Salmonella strains showed greater heat resistance in pork meat than in TSB. At the lowest temperature (58 degrees C), the heat resistance increased 1.5-4 times, and it was most pronounced for the strains being most heat sensitive in TSB. S. potsdam 133 was the most resistant strain in pork meat, with D-values at 58 degrees C, 60 degrees C and 63 degrees C of 4.80, 1.57 and 0.30 min, respectively. The most sensitive strain turned out to be S. kingston 1124, with D-values of 2.79. 0.92 and 0.24 min, at the same temperatures. According to collected data, the heating processes, as applied to cured pork meat, providing an internal temperature of 60 degrees C for 9-10 min or of 63 degrees C for 3-4 min can be expected to provide a > or = 7 D kill of Salmonella belonging to the serotypes studied.     

Autoinducer-2 activity of gram-negative foodborne pathogenic bacteria and its influence on biofilm formation

ABSTRACT:  This study evaluated whether autoinducer-2 (AI-2) activity would be associated with biofilm formation by Salmonella and Escherichia coli O157:H7 strains on food contact surfaces. In study I, a Salmonella Typhimurium DT104 strain and an E . coli O157:H7 strain, both AI-2 positive, were individually inoculated into 50 mL of Luria–Bertani (LB) or LB + 0.5% glucose (LBG) broth, without or with stainless steel or polypropylene ( Salmonella ) coupons. At 0, 14 ( Salmonella ), 24, 48, and 72 h of storage (25 °C), cells in suspension and detached cells from the coupons, obtained by vortexing, were enumerated on tryptic soy agar. In study II, a Salmonella Thompson AI-2-positive strain and an AI-2-negative strain, and an E . coli O157:H7 AI-2-positive strain and an AI-2-negative strain were inoculated into LB broth with stainless steel coupons. Cells were enumerated as in study I. In both studies, AI-2 activity was determined in cell-free supernatants. Cell numbers of S . Typhimurium DT104 on biofilms were higher ( P < 0.05) in LB than those in LBG, while the E . coli O157:H7 strain showed no difference ( P ≥ 0.05) in biofilm cell counts between LB and LBG after storage for 72 h. Both S . Typhimurium DT104 and E . coli O157:H7 strains produced higher ( P < 0.05) AI-2 activity in LBG than LB cell suspensions. Cell counts of AI-2-positive and-negative S . Thompson and E . coli O157:H7 strains were not different ( P ≥ 0.05) within suspensions or coupons (study II). The results indicated that, under the conditions of this study, AI-2 activity of the pathogen strains tested may not have a major influence on biofilm formation on food contact surfaces, which was similar between AI-2-positive and -negative strains.     

Effect of gamma or beta radiation on Salmonella DT 104 in ground pork

Mixtures of six Salmonella Typhimurium DT 104 strains were inoculated into three ground pork products to determine the effect of fat content on the radiation resistance of Salmonella DT 104. The ground pork products were 90% lean, 50:50 fat:lean, and 100% fat. Inoculated products were irradiated using a gamma radiation source in a self-contained 137Cesium irradiator or a 10 MeV accelerator producing electrons (e-beam). The radiation D10-values (dose required for a 90% inactivation of viable CFU) for Salmonella DT 104 inoculated into 90% lean ground pork, 50:50 fat/lean ground pork, and 100% pork fat and subjected to beta radiation were 0.42 kGy, 0.43 kGy, and 0.43 kGy, respectively. The corresponding radiation D10-values for Salmonella DT 104 subject to gamma radiation were 0.56, 0.62, and 0.62 kGy, respectively. There was no statistical significant difference (P = 0.3) in radiation D10-values for Salmonella in the three products subject to either radiation treatment. Therefore, fat content had no effect. There was a significant difference (P = 0.001) between the radiation D10-values obtained with the two radiation sources. The radiation D10-values were within the reported range for irradiation destruction of Salmonella contaminated raw meat products.     

Salmonella enterica serotypes isolated from imported frozen chicken meat in the Canary islands

To determine the prevalence of Salmonella enterica serotypes in imported frozen chicken meat, 406 samples (whole chicken, legs, and breast meat) were analyzed for Salmonella according to ISO6579 rules, serotypes were assigned, and phage typing was conducted for Salmonella serotypes Enteritidis, Typhimurium, and Heidelberg. The overall frequency of Salmonella isolation was 16.5%. By country of origin, the highest percentage of cases was found among the samples from France followed by samples from Brazil. The differences between legs and breast meat were significant. The most frequently isolated serotype of Salmonella was Enteritidis, followed by Salmonella Heidelberg, Salmonella Typhimurium, and Salmonella Virchow. By country of origin, we identified a large percentage of serotype Salmonella Enteritidis in the samples imported from Brazil. There was a greater diversity of serotypes isolated from the French samples, and Salmonella Enteritidis was not the dominant strain. In the samples from the United States, the only serotype isolated was Salmonella Kentucky, although a smaller number of samples was analyzed. The Salmonella Enteritidis phage type that prevailed in both France and Brazil was 4. Phage types 204c and 204 were identified for Salmonella Typhimurium, and phage types 8, 31, and 37 were identified for Salmonella Virchow.     

Salmonella cross-contamination in swine abattoirs in Portugal: Carcasses, meat and meat handlers

In this study the occurrence of Salmonella in swine, pork meat and meat handlers along with their clonal relatedness is evaluated at abattoir level. Samples from the lymph nodes, carcass surface and meat of 100 pigs and 45 meat handlers were collected in eight abattoirs (July 2007-August 2008). Salmonella isolates were serotyped and genotyped by pulsed-field gel electrophoresis (PFGE). From the pigs tested, 42 produced at least one positive sample. A relatively high frequency of Salmonella occurrence was found in the ileoceacal lymph node samples (26.0%), followed by carcass (16.0%) and meat samples (14.0%). However, ileoceacal lymph nodes that test positive for Salmonella are not found to be a predictor of positive test results further on in the process. Besides the slaughterhouse environment, meat handlers were identified as a possible source of subsequent contamination, with 9.3% of the sample testing positive. Diverse Salmonella enterica serotypes were detected, mainly S. Typhimurium and the monophasic variant S. 4,[5],12:i:-, but also S. Derby, S. Rissen, S. Mbandaka, S. London, S. Give, S. Enteritidis and S. Sandiego, in total corresponding to 17 PFGE types. Our results demonstrate that besides a high level of Salmonella swine contamination at pre-harvest level, slaughtering, dressing, cutting and deboning operations are contributing to the occurrence of clinically relevant clones (e.g. S. Typhimurium DT104 and S. 4,[5],12:i:-) in pork products. This study also highlights the possibility of an ongoing Salmonella community being spread by abattoir workers.     

Improved detection of nontyphoid and typhoid Salmonellae with balanced agar formulations

A strategically balanced medium was developed for the improved detection of nontyphoid and typhoid salmonellae. Its balanced sugar (cellobiose, lactose, mannitol, and trehalose) and protein (beef extract and polypeptone peptone) formulation provided Salmonella with a selective growth advantage over non-Salmonella enteric organisms. The formulations promoted the production and detection of H2S production levels that otherwise might be missed with traditional agar formulations. In combination, these advantages contributed to increased sensitivity without the loss of specificity. In comparative studies using 86 samples of meat products (beef, pork, and chicken), the new media, Miller-Mallinson (MM) agar and xylose lysine tergitol (Niaproof) 4 agar, possessed significantly higher sensitivity (P < 0.001) and an improved specificity over bismuth sulfite, hektoen enteric, and xylose lysine desoxycholate agars. However, these samples did not contain nontyphoid salmonellae with weak to ultraweak H2S production characteristics. Modified formulations of MM agar were generally similar to bismuth sulfite and hektoen enteric agars in the identification of four of seven globally diverse strains of Salmonella serotype Typhi. Two of these seven strains were found to produce more readily identifiable black (H2S-positive) colonies on MM agar, whereas one of the seven was not readily detected by any of the media. The improved detection of nontyphoid and typhoid salmonellae attests to the sensitivity of MM agar and to its potentially broad utility in both clinical and food quality laboratories.     

Validation of a 1-Day Analytical Diagnostic Real-Time PCR for the Detection of Salmonella in Different Food Meat Categories

Foodborne disease caused by Salmonella represents a worldwide public health problem. In Europe, salmonellosis is still the second most commonly recorded zoonosis. Since the standard culture method for detecting Salmonella (ISO 6579:2002) requires up to 5 days to produce results, the need to develop rapid methods represents an important issue for the authorities and the producers. The aim of the present study was the in-house validation, according to ISO 16140, of an open-formula diagnostic real-time PCR for the detection of Salmonella in all the different meat categories reported in the EU Regulations relative to microbiological criteria for food safety. The assay employed specific primers and a probe target within the ttrRSBCA locus, which allows the tetrathionate respiration in Salmonella. Selectivity, relative accuracy, relative sensitivity and relative specificity were established by testing 110 bacterial strains and 175 various edible meat samples. Results showed 100 % selectivity, 100 % relative accuracy, 100 % relative sensitivity and 100 % relative specificity of the real-time PCR when compared to the standard culture method used as reference. In addition, in order to minimize the effect of the competitive micro-flora naturally present on meat samples, a highly nutritious and selective commercial medium (ONE Broth Salmonella, Oxoid) was evaluated in comparison with the classical non-selective pre-enrichment broth (buffered peptone water). Results demonstrated that the ONE Broth Salmonella medium increases the growth of Salmonella in the presence of competitive micro-flora.     

舟山市2006-2008年食源性致病菌污染状况分析

目的了解舟山市市售食品中食源性致病菌污染状况及分布和高危食品种类。方法参照国家食源性疾病监测网工作手册进行。结果检测生畜肉、生禽肉、非定型包装熟肉制品、动物性水产品、蔬菜、海水鱼、淡水鱼、冷菜、鲜榨果汁等共511件,检出沙门氏菌3株,检出单核细胞增生李斯特菌5株,检出空肠弯曲菌3株,副溶血性弧菌68株。结论舟山市居民主要消费食品存在食源性致病菌污染,其中水产品和熟肉制品污染较重,应引起有关部门重视,并加强监督、检查力度,加大对食品卫生安全的宣传教育工作。