辽宁省食品中产气荚膜梭菌的污染状况与基因特征

目的 了解辽宁省食品中产气荚膜梭菌污染状况、血清型及毒素基因携带特征。方法 在辽宁省6个市采集生畜肉和冷冻鱼糜制品样品260份,依据GB 4789.13—2012方法进行产气荚膜梭菌检测,同时采用生化和荧光定量聚合酶链式反应(PCR)方法进行菌种鉴定;提取菌体DNA,采用PCR方法进行毒素基因分型检测;并针对16S rRNA基因序列进行进化树分析。结果 260份不同食品样品中检出15株产气荚膜梭菌,总检出率为5.8%,其中生羊肉检出率最高,为29.0%(9/31)。所有菌株均检出α毒素,其中仅检出α毒素的菌株占66.7%(10/15),为A型产气荚膜梭菌;同时检出α毒素和β毒素菌株占33.3%(5/15),为C型菌株。总计6株菌检出β₂毒素,包括4株A型菌和2株C型菌;肠毒素CPE基因的检出率为6.7%(1/15);16S rRNA进化分析得出携带同一毒素基因的菌株遗传关系较近。结论 辽宁省生畜肉和冷冻鱼糜制品中均检出产气荚膜梭菌,其中生畜肉污染较严重,且主要为A型菌和C型菌,引起食物中毒风险高,对食品安全构成潜在的威胁,应加强监测与防控。     

产气荚膜梭菌TaqMan实时荧光定量PCR特异性引物设计和方法验证

目的 建立针对水样中产气荚膜梭菌检测的TaqMan实时荧光定量聚合酶链式反应(PCR)方法,并测试该方法在自来水样中的检测效果。方法 选择位于该菌拟核中高度保守的plc基因,设计特异性引物和TaqMan探针,经优化后建立了针对该菌的TaqMan实时荧光定量PCR检测方法,结合滤膜法处理含有plc基因的标准菌株的模拟污染水样,并对所建立的方法进行测试。结果 所建立的产气荚膜梭菌TaqMan实时荧光定量PCR检测方法具有高度的特异性,13株食源性致病菌、3株艰难梭菌及1株腐败梭菌的Ct值大于40;该方法的最低检出限为1×10 copies/μL,具有较高的灵敏性;对模拟污染水样的最低检测限为1.0×10² CFU/mL。应用该方法对4份人工模拟污染阳性水样与90份自来水样进行检测发现,2份1.0×10² CFU/mL的模拟污染水样可检出产气荚膜梭菌,2份1.0×10 CFU/mL的模拟污染水样与90份自来水样均未检出产气荚膜梭菌。结论 所建立的产气荚膜梭菌TaqMan实时荧光定量PCR检测方法具有特异性好、灵敏性高的优点,对水体中产气荚膜梭菌的检...     

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。     

新乡市生乳中菌落总数和金黄色葡萄球菌及β-内酰胺酶调查

目的了解新乡市规模化奶牛养殖场生乳中菌落总数、金黄色葡萄球菌和β-内酰胺酶的基线数据,为生乳安全性风险评估及国家标准更新提供资料。方法以新乡市3家规模化奶牛养殖场(A、B、C场)为观测基地,2016年5月—2017年4月每月采集2家生乳样品各29份和1份混合样品。分别按照GB 4789.2—2010《食品安全国家标准食品微生物学检验菌落总数测定》和GB 4789.10—2010《食品安全国家标准食品微生物学检验金黄色葡萄球菌检验》测定菌落总数和金黄色葡萄球菌,胶体金法测β-内酰胺酶残留。结果 3家奶牛养殖场单份样品菌落总数的中位数分别为13 000、4 450、130 000 CFU/ml,明显低于GB 19301—2010《食品安全国家标准生乳》中的限量(2×10~6CFU/ml),差异有统计学意义(P0.01),3家奶牛养殖场的菌落总数之间差异有统计学意义(P0.05)。各奶牛养殖场单份样品的菌落总数与混合样品比较,仅B场差异有统计学意义(P0.05)。7~8月菌落总数较高。3家奶牛养殖场样品中金黄色葡萄球菌检出率分别为1.1%(4/360)、16.7%(30/180)和0.0%(0/180),计数结果为50~42 000 CFU/ml。3家奶牛养殖场的所有样品中均检出β-内酰胺酶,检出率为6.1%~10.6%。结论 GB 19301—2010生乳菌落总数限量远高于新乡市实际情况,建议修订标准;个别奶牛养殖场生乳中存在一定程度的金黄色葡萄球菌污染,需加强监管;筛查出的β-内酰胺酶需进一步鉴定其来源,同时要加强对β-内酰胺酶检测方法的研究。     

火腿肠加工过程中微生物风险研究

目的开展火腿肠加工过程中微生物污染风险研究,掌握卫生指示菌、主要食源性致病菌的分布特征和污染途径,为火腿肠加工过程中微生物污染风险控制提供依据。方法 2015—2017年对4家企业的712份产品相关样品(原辅料、中间产品和终产品)和环境样品(包括生产用水、空气沉降菌、人员、工具等)进行监测,选择传统分离培养方法对卫生指示菌和主要食源性致病菌进行检验,并对沙门菌进行血清学鉴定。结果原辅料中菌落总数10~5 CFU/g和大肠菌群10~3 CFU/g的样品比例分别为33.00%(33/100)和29.00%(29/100);中间产品中菌落总数10~5 CFU/g和大肠菌群10~3 CFU/g的样品比例分别为62.86%(66/105)和36.19%(38/105);终产品未检出菌落总数10~4 CFU/g的样品,大肠菌群均10 CFU/g。结论火腿肠加工过程存在微生物污染风险,本研究对掌握火腿肠加工过程的污染分布,确定关键控制点,为制定相关生产质量管理规范、确保终产品的食品安全具有重要意义。     

环介导等温扩增技术快速检测产气荚膜梭菌的研究

目的:建立环介导等温扩增技术(LAMP)快速检测产气荚膜梭菌的方法。方法:以产气荚膜梭菌(ATCC13124)的α毒素全基因序列为保守序列,设计内、外、环引物,肉眼观察白色沉淀并判断检测结果。结果:LAMP检测产气荚膜梭菌的灵敏度为2.92×102CFU/mL,人工污染产气荚膜梭菌的全脂乳的检测限为15.7CFU/mL,耗时仅1h。对照PCR检测产气荚膜梭菌的灵敏度为2.92×105CFU/mL,人工污染产气荚膜梭菌的全脂乳的检出限1.57×105CFU/mL。采用同样的方法提取DNA,耗时3h。结论:建立LAMP快速、特异检测产气荚膜梭菌的方法,该方法灵敏度是PCR的1000倍,为食品中产气荚膜梭菌的检测构建了一个技术平台。     

2011—2016年广西壮族自治区市售肉及肉制品食源性致病菌污染状况分析

目的 了解广西壮族自治区市售肉及肉制品中食源性致病菌污染状况,为有效开展食源性疾病防控提供科学依据。方法 2011—2016年从广西壮族自治区14个市采集5类市售肉及肉制品共10 927份,按照国家标准方法进行9种食源性致病菌检验。结果 10 927份样品的食源性致病菌总检出率为5.0%(548/10 927),食源性致病菌检出率按样品种类依次为调理肉制品(33.3%,33/99)、生畜肉(24.5%,73/298)、生禽肉(24.2%,67/277)、冷冻肉糜制品(14.4%,14/97)、熟肉制品(3.6%,361/10 156)。检出的主要致病菌为沙门菌、金黄色葡萄球菌和单核细胞增生李斯特菌。生禽肉中未检出弯曲菌和致泻大肠埃希菌,调理肉制品中未检出致泻大肠埃希菌,熟肉制品中未检出志贺菌。熟肉制品各年度检出率范围为0.9%～4.9%。结论 广西壮族自治区市售肉及肉制品受到不同程度食源性致病菌污染,且污染持续多年存在。     

成都市进出口动物源食品安全风险监测及分析

目的 了解成都市进出口动物源性食品污染情况, 加强进出口动物源性食品安全监督管理。 方法 按照《进出境肉类产品检验检疫管理办法》对进出口动物源性食品样品进行采样检测, 并对检测数据进行分析。结果 2015~2016年共抽检动物源性食品样品5013份, 微生物指标合格率为94.92%(1570/1654), 卫生指示菌指标中超标率最高的为菌落总数, 食源性致病菌检出率最高的是霉菌与产气荚膜梭菌; 重金属中检出率、超标率以及平均暴露量最高的金属均为铬, 且个人平均年风险值大于国际辐射防护委员会(international radiation protection commission, ICRP)推荐的最大可接受风险值, 可能对人体健康造成危害; 兽药残留合格率为99. 76%(2511/2517), 多数样品中兽药残留均符合国家限量标准。结论 总体来看, 成都市进出口动物源性食品安全形势较好, 但食品中菌落总数和重金属中铬含量超标情况应该引起重视。     

婴幼儿辅食中细菌总数及蜡样芽孢杆菌污染情况分析

通过平板菌落计算法和最大近似值（MPN）法检测市售婴儿辅食中细菌总数和蜡样芽孢杆菌污染情况,并对MPN法得到的疑似蜡样芽胞杆菌进行基因间隔序列（ITS）插入性序列分析和形态鉴定。结果表明,101份样品中只有30份样品菌落总数达标,合格率仅为29.7%,部分超标产品的细菌总数达105CFU/g~106CFU/g。市售3种婴幼儿辅食-米粉、奶伴侣和面条中细菌总数及食源性致病菌蜡样芽孢杆菌检出情况不容乐观。     

北京市顺义区87名健康人中产气荚膜梭菌携带特征研究

目的调查北京市顺义区健康人群携带产气荚膜梭菌(Clostridium perfringens, Cp)的生物特征,研究分离菌株携带产气荚膜梭菌肠毒素(Clostridium perfringens enterotoxin,Cpe)、β2毒力基因情况以及Cp在人群中的分布特征,为Cp导致食源性疾病的判定提供健康对照组数据。方法对采集的87份健康体检者粪便开展Cp分离培养、平板计数和菌株cpe、β2毒力基因的聚合酶链式反应(PCR)检测,对检测结果进行统计分析。结果 87名健康人粪便中血平板分离培养后Cp检出率为64.37%(56/87);Cp的月份、性别、年龄分布差异无统计学意义(P0.05)。共有57份粪便标本平板计数结果大于最低检出限(10 CFU/g),最高定量值为4.12×10~6 CFU/g,均值为1.70×10~5 CFU/g,中位数为5.30×10~3 CFU/g,95%分位数为7.00×10~5 CFU/g。分离的56株Cp中,cpe毒力基因检出率为0.00%(0/56),β2毒力基因检出率为73.21%(41/56)。结论 87名健康人粪便中Cp检出率较高,且β2毒力基因携带率较高,Cp引起食源性疾病的原因需要更深度生物标志识别或定量数据分析进行研究。     

Effect of vacuum cooling followed by ozone repressurization on Clostridium perfringens germination and outgrowth in cooked pork meat under temperature-abuse conditions

The effect of combining vacuum cooling with an ozone-based inhibition process (InhVac) on Clostridium perfringens spore germination and outgrowth in cooked pork meat after exponential chilling (from 54.4 to 7.2 °C in 12, 15, 18, or 21 h) and isothermal storage (20, 25, 30, 36, or 45 °C) was evaluated. Ice cooling (IC) and vacuum cooling (VC) were used to compare the effects with InhVac. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain concentration of ca. 3 log₁₀ CFU/g. C. perfringens growth in samples treated by InhVac were 0.1, 0.37 and 0.9 log₁₀ CFU/g after 15, 18 and 21 h of cooling from 54.4 to 7.2 °C respectively, significantly lower (P<0.05) than those in samples subjected to IC (1.01, 2.10 and 2.8 log₁₀ CFU/g) and VC (0.56, 1.01 and 2.13 log₁₀ CFU/g). Compared to VC and IC, InhVac treatment increased the lag phase (λ), decreased the growth rates (μ_max), and extended the sample shelf-life (the time until a 1 log₁₀ CFU/g increase in C. perfringes from the initial concentration value) at all storage temperatures. InhVac-treated samples not only had a longer shelf-life than those treated by VC, but also exhibited almost two times longer shelf-life compared to those subjected to IC regardless of storage temperatures. Additionally, statistical indexes showed that a primary modified Gompertz model and a secondary Square Root model could fit the data well.Industrial relevanceIn this study, an innovative inhibition approach (InhVac) was found to show a better antimicrobial effect on C. perfringens germination and outgrowth in cooked pork meat compared to ice cooling and vacuum cooling under temperature-abuse conditions. A primary modified Gompertz model and a secondary Square Root model could be used to predict the C. perfringens growth in samples subjected to InhVac treatment.     

散装熟肉制品中单增李斯特菌污染状况分析

目的分析散装熟肉制品中单增李斯特菌污染状况。方法根据GB 4789.30-2016《单核细胞增生李斯特氏菌检验》规定的方法对散装熟肉制品的加工用原料、生产环境、各加工环节中产品以及不同销售环境下产品中的单增李斯特菌进行定性和定量检测。结果原料肉的总体带菌率达到21%;生产环境中第三区(远离食品接触面的区域)检出率为2%,其余区域未检出;各加工环节中产品单增李斯特菌检测结果均小于10CFU/g;不同销售环境下产品中单增李斯特菌检测结果小于10 CFU/g的比例为93%,处于10～50 CFU/g之间的样本占比6%,大于50 CFU/g的占比为1%。结论原料散装熟肉制品中单增李斯特菌污染的主要来源,蒸煮等加工环节能有效地杀灭单增李斯特菌。销售环境也关系到散装熟肉制品单增李斯特菌的污染程度,对于未包装的产品,专卖店优于农产品市场。     

ENTEROTOXIN FORMATION IN FOODS BY CLOSTRIDIUM PERFRINGENS TYPE A

Growth, sporulation and enterotoxin formation in various foods inoculated with a Clostridium perfringens type A enterotoxin-producing strain were studied. Good vegetative growth, 10⁷–10⁸ cells/g, was obtained after 4 hr of anaerobic growth and remained almost the same throughout the 20–24 hr observation in most of the foods. A gradual increase in spore count to the level of 10⁴–10⁵/g was observed with an increase in the incubation time. Enterotoxin was detected in moist cooked chuck roast, ground beef and turkey as well as in moist cooked and dry roasted chicken at levels up to 0.125μg/g. The earliest time at which enterotoxin was detected was after 10 hr of anaerobic growth in moist cooked turkey at 37°C. Although growth and some sporulation occurred, enterotoxin was not detected in dry roasted beef or turkey with or without gravy, or in moist cooked pork or lamb. Poor growth and sporulation also were obtained with chicken broth, chicken gravy and beef gravy. In moist cooked turkey that had been temperature abused for 6 hr at 37°C, held cold for 15 hr and reheated to 37°C, toxin could be detected after only 5 hr of holding at 37°C. The ability of certain foods to support sporulation and enterotoxin formation indicates that such preformed enterotoxin may contribute to early onset of symptoms in some cases of C. perfringens food poisoning.     

CONTROL OF CLOSTRIDIUM PERFRINGENS IN A MODEL ROAST BEEF BY SALTS OF ORGANIC ACIDS DURING CHILLING1

Control of Clostridium perfringens germination and outgrowth by the following salts of organic acids, sodium lactate [Purasal?S/SP (Purasal); 1.50, 3.00 and 4.80%], sodium lactate supplemented with sodium diacetate [Purasal? Opti.form? (Optiform), 1.50, 3.00 and 4.80%], buffered sodium citrate [Ional? (Ional), 0.75, 1.00 and 1.30]) and buffered sodium citrate supplemented with sodium diacetate [Ional Plus? (Ional Plus), 0.75, 1.00 and 1.30%] was evaluated during continuous chilling of a model roast beef product. Beef rounds were ground through an 1/8′’ plate and NaCl, potato starch and potassium tetra pyrophosphate were added to final concentrations of 0.85, 0.25 and 0.20%, respectively, and mixed. Portions (250 g) of the meat were mixed with either Purasal (1.5, 3.0 or 4.8%), Optiform (1.5, 3.0 or 4.8%), Ional (0.75, 1.0 or 1.3%) or Ional Plus (0.75, 1.0 or 1.3%) along with a control that did not have any added antimicrobials. Each product (10 g) inoculated with C. perfringens spores (ca. 2.2 log₁₀ spores/g) was packaged into vacuum bags (2 in. × 3 in.), vacuum sealed, heated to 60C within 1 h, and subsequently chilled from 54.4C to 7.2C in 18 or 21 h following exponential chilling rates. Products were sampled immediately after cooking to enumerate the C. perfringens populations (spores surviving heat treatment) and subsequent to chilling (total C. perfringens populations, including spores and vegetative cells resulting from germination and outgrowth of the spores). Chilling of cooked, model ground roast beef resulted in germination and outgrowth of C. perfringens spores; the population densities increased by 4.13 and 4.40 log₁₀ CFU/g, following 18 and 21 h chill rates, respectively. Incorporation of Purasal (1.5–4.8%), Optiform (1.5–4.8%), Ional and Ional Plus (0.75–1.3%) substantially (P ± 0.05) inhibited germination and outgrowth of C. perfringens spores. Incorporation of antimicrobial ingredients resulted in ± 1.0 log₁₀ CFU/g increase of the pathogen, except for model roast beef with Ional Plus at 0.75% concentration, following 18 h chilling rate. Similar results were obtained when 21 h chilling rate was followed, with roast beef containing ingredients (at all the concentrations) resulting in either reductions or ± 1.0 log₁₀ CFU/g growth in total C. perfringens populations, except for Purasal and Ional Plus at 1.5 and 0.75% concentrations, respectively. Use of sodium salts of organic acids in formulation of model roast beef can reduce the risk of C. perfringens spore germination and outgrowth during extended chilling rates.     

Impact of cooking,cooling, and subsequent refrigeration on the growth or survival of Clostridium perfringens in cooked meat and poultry products

In January 1999, the Food Safety and Inspection Service (FSIS) finalized performance standards for the cooking and chilling of meat and poultry products in federally inspected establishments. More restrictive chilling (stabilization) requirements were adopted despite the lack of strong evidence of a public health risk posed by industry practices employing the original May 1988 guidelines (U.S. Department of Agriculture FSIS Directive 7110.3). Baseline data led the FSIS to estimate a "worst case" of 10(4) Clostridium perfringens cells per g in raw meat products. The rationale for the FSIS performance standards was based on this estimate and the assumption that the numbers detected in the baseline study were spores that could survive cooking. The assumptions underlying the regulation stimulated work in our laboratory to help address why there have been so few documented outbreaks of C. perfringens illness associated with the consumption of commercially processed cooked meat and poultry products. Our research took into account the numbers of C. perfringens spores in both raw and cooked products. One hundred ninety-seven raw comminuted meat samples were cooked to 73.9 degrees C and analyzed for C. perfringens levels. All but two samples had undetectable levels (<3 spores per g). Two ground pork samples contained 3.3 and 66 spores per g. Research was also conducted to determine the effect of chilling on the outgrowth of C. perfringens spores in cured and uncured turkey. Raw meat blends inoculated with C. perfringens spores, cooked to 73.9 degrees C, and chilled according to current guidelines or under abuse conditions yielded increases of 2.25 and 2.44 log10 CFU/g for uncured turkey chilled for 6 h and an increase of 3.07 log10 CFU/g for cured turkey chilled for 24 h. No growth occurred in cured turkey during a 6-h cooling period. Furthermore, the fate of C. perfringens in cooked cured and uncured turkey held at refrigeration temperatures was investigated. C. perfringens levels decreased by 2.52, 2.54, and 2.75 log10 CFU/g in cured turkey held at 0.6, 4.4, and 10 degrees C, respectively, for 7 days. Finally, 48 production lots of ready-to-eat meat products that had deviated from FSIS guidelines were analyzed for C. perfringens levels. To date, 456 samples have been tested, and all but 25 (ranging from 100 to 710 CFU/g) of the samples contained C. perfringens at levels of <100 CFU/g. These results further support historical food safety data that suggest a very low public health risk associated with C. perfringens in commercially processed ready-to-eat meat and poultry products.     

Carvacrol, cinnamaldehyde, oregano oil, and thymol inhibit Clostridium perfringens spore germination and outgrowth in ground turkey during chilling

Inhibition of Clostridium perfringens by plant-derived carvacrol, cinnamaldehyde, thymol, and oregano oil was evaluated during abusive chilling of cooked ground turkey. Test substances were mixed into thawed turkey product at concentrations of 0.1, 0.5, 1.0, or 2.0% (wt/wt) along with a heat-activated three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.2 to 2.8 log CFU spores per g of turkey meat. Aliquots (5 g) of the ground turkey mixtures were vacuum packaged and then cooked in a water bath, where the temperature was raised to 60 degrees C in I h. The products were cooled from 54.4 to 7.2 degrees C in 12, 15, 18, or 21 h, resulting in 2.9-, 5.5-, 4.9-, and 4.2-log CFU/g increases, respectively, in C. perfringens populations in samples without antimicrobials. Incorporation of test compounds (0.1 to 0.5%) into the turkey completely inhibited C. perfringens spore germination and outgrowth (P < or = 0.05) during exponential cooling in 12 h. Longer chilling times (15, 18, and 21 h) required greater concentrations (0.5 to 2.0%) to inhibit spore germination and outgrowth. Cinnamaldehyde was significantly (P < 0.05) more effective (<1.0-log CFU/g growth) than the other compounds at a lower concentration (0.5%) at the most abusive chilling rate evaluated (21 h). These findings establish the value of the plant-derived antimicrobials for inhibiting C. perfringens in commercial ground turkey products.     

Market surveillance for contamination with thermotolerant campylobacters on various categories of chicken meat in Switzerland

From April 2009 to April 2010, 1,132 samples of different types of chicken meat were tested qualitatively and quantitatively for thermotolerant campylobacters. Samples were recovered at retail in shops from the entire territory of Switzerland and comprised imported meat and meat from domestic production. The meat categories covered by the study were refrigerated and frozen meat, meat with and without skin, and meat preparations. Overall, 38.4% of the samples were positive, and in 27.8%, Campylobacter bacteria could be quantified. Counts ranged from ≥10 to <10(4) CFU/g with a maximum value of 8 × 10(3) CFU/g in a sample of refrigerated chicken meat with skin. The contamination frequencies were 45.2% in meat with skin, 40.8% in meat without skin, and 27.4% in meat preparations. Refrigerated meat was contaminated with Campylobacter bacteria more often than frozen meat (53.9 versus 20.0%). The study also showed considerable differences between the contamination rates found for samples from different large retail chains. In 2010, a further study with 120 samples of refrigerated and sliced chicken meat and fresh chicken liver was carried out in order to test a possible seasonal variation of the occurrence of Campylobacter bacteria. The contamination frequency of sliced meat increased from 10.0% in the period from February to March to 36.7% during July to August. In both sampling periods, the counts remained in the range of ≥10 to <100 CFU/g with a maximum value of 30 CFU/g. For chicken liver, a 10.0% contamination rate was observed in the period from December to January, which rose to 100% in the period from August to October. Contrary to the results for sliced meat, not only did the frequency of contamination increase but so did the Campylobacter counts, with the highest recorded value being 2.2 × 10(4) CFU/g.     

Incidence of Clostridium perfringens in commercially produced cured raw meat product mixtures and behavior in cooked products during chilling and refrigerated storage

A total of 445 whole-muscle and ground or emulsified raw pork, beef, and chicken product mixtures acquired from industry sources were monitored over a 10-month period for vegetative and spore forms of Clostridium perfringens. Black colonies that formed on Shahidi-Ferguson perfringens (SFP) agar after 24 h at 37 degrees C were considered presumptive positive. Samples that were positive after a 15-min heat shock at 75 degrees C were considered presumptive positive for spores. Of 194 cured whole-muscle samples, 1.6% were positive; spores were not detected from those samples. Populations of vegetative cells did not exceed 1.70 log10 CFU/g and averaged 1.56 log10 CFU/g. Of 152 cured ground or emulsified samples, 48.7% were positive, and 5.3% were positive for spores. Populations of vegetative cells did not exceed 2.72 log10 CFU/g and averaged 1.98 log10 CFU/g; spores did not exceed 2.00 log10 CFU/g and averaged 1.56 log10 CFU/g. Raw bologna (70% chicken), chunked ham with emulsion, and whole-muscle ham product mixtures were inoculated with C. perfringens spores (ATCC 12916, ATCC 3624, FD1041, and two product isolates) to ca. 3.0 log10 CFU/g before being subjected either to thermal processes mimicking cooking and chilling regimes determined by in-plant temperature probing or to cooking and extended chilling regimes. Populations of C. perfringens were recovered on SFP from each product at the peak cook temperatures, at 54.4, 26.7, and 7.2 degrees C, and after up to 14 days of storage under vacuum at 4.4 degrees C. In each product, populations remained relatively unchanged during chilling from 54.4 to 7.2 degrees C and declined slightly during refrigerated storage. These findings indicate processed meat products cured with sodium nitrite are not at risk for the growth of C. perfringens during extended chilling and cold storage.