Doctor of Philosophy / Food Science / Daniel Y.C. Fung / James L. Marsden / The ubiquitous nature and continued presence in food processing environments makes Listeria monocytogenes a significant threat in ready-to-eat (RTE) food products. This study was performed in two phases; Phase 1 studied lauric arginate (LAE) as an antimicrobial on food contact surfaces and shredded mozzarella cheese, and use of glucose oxidase (GOX), sodium lactate (SL), and acidified calcium sulfate (ACS) as preservatives in mozzarella cheese; Phase 2 evaluated efficacy of Photohydroionization (PHI) technology to control L. monocytogenes on food contact surfaces, sliced American cheese, and ready-to-eat turkey. Stainless steel coupons, mozzarella cheese, American cheese, and turkey were surface inoculated with a three- or five-strain cocktail of L. monocytogenes. Coupons were treated with 100 and 200 ppm solution of lauric arginate for 5 and 15 min. Mozzarella cheese was treated with different combinations of treatments comprising LAE, GOX, SL, ACS, dextrose, and anticaking agents (free flow 1031 and cellulose). Results indicated up to 2.5 log CFU/coupon reductions and it was concluded that LAE was effective in controlling low levels of contamination of L. monocytogenes on food contact surfaces. In mozzarella cheese, results indicated that lauric arginate provided no additional antimicrobial effect (P > 0.05) as compared to GOX + dextrose. The antimicrobial blends with GOX, SL, and ACS were different (P < 0.05) from the controls but showed no differences (P > 0.05) in their effect in controlling bacterial populations. Results from treatment with PHI unit showed significant (P < 0.05) reduction in bacterial populations. L. monocytogenes populations reduced by 4.37 log CFU/coupon on stainless steel surfaces after 15 min of treatment; 2.16 and 2.52 log CFU/sample reduction on American cheese and ready-to-eat turkey, respectively, after short treatment time of 5 min. Lipid oxidation analyses performed on cheese and turkey samples indicated that the PHI treatment did not affect (P > 0.05) TBAR values. These studies suggest that LAE and GOX as antimicrobials and PHI treatment can be used as intervention strategies in an integrated process to ensure safe production of food. Further research is needed to evaluate applicability of SL and ACS in mozzarella cheese.

Dissertation submitted in fulfilment of the requirements for the degree Master of Technology: Environmental Health in the Faculty of Applied Sciences at the Cape Peninsula University of Technology, 2011 / The retail sector in South Africa is increasingly evolving into a dynamic industry, driven by changes in technology, saturating markets and globalisation. A major phenomenon in South Africa has been the evolution of hypermarkets, which sell large quantities of almost all consumer goods on a self-service basis. The South African consumers are becoming increasingly health conscious and, as such, the demand for wellness foods, health and convenience food has escalated. Convenience foods are expected to remain popular with consumers and supermarkets and will therefore increase the amount of ready-to-eat food items offered. As the retail industry has changed over the last two decades, so has the epidemiology of foodborne illnesses, with an increase in the incidence of bacterial infections caused by emerging organisms. In addition, there are certain food safety issues specifically associated with ready-to-eat foods. In recent years, incidences of enteric diseases associated with meat consumption have risen. The emergence of several new foodborne diseases has led to an increased focus attention on the issue of food safety by consumers and the industry. The most commonly implicated foods in these disease outbreaks have been meat and dairy products. The microbial load of eight convenience food manufacturing plants was determined by firstly sampling stainless steel food contact surfaces after they had been cleaned and sanitised at the end of a day‘s shift. The samples were analysed for Total Plate Count (TPC), Escherichia coli, Salmonella species and Staphylococcus aureus and Listeria. The results showed that 59 % of the total areas sampled for TPC failed to comply with the legal requirements for food surfaces specified in the South African Health Act (< 100 cfu.cm-2). Listeria was detected in 23 % of the samples taken and E.coli was found in 1.3 % of the samples, while S. aureus was not detected in any of the samples. Fifty percent of the plants applied conventional cleaning methods for cleaning and sanitation and the remaining 50 % used the low-pressure foam (LPF) method. The bacterial results of the two cleaning methods were statistically compared and a statistically significant difference (P ≤ 0.05) was found between the TPC means of the cleaning methods after cleaning. No statistically significant difference (P > 0.05) was found in terms of the Listeria species counts after both cleaning processes. The LPF method proved to be the superior cleaning option for reducing TPC counts. Secondly surface samples were collected from washed and sanitised dominant hands of food handlers and analysed for the presence of total plate counts, S. aureus and E. coli. The study aimed to evaluate the efficacy of hand washing practices and sanitation before commencing work. A total of 230 samples were collected, involving 100 % of the food handlers in selected convenience food outlets. The highest bacterial count taken from handswas 7.4 x 10-3 cfu.cm-2 and the lowest showed no detectable growth. Forty percent of the TPC analysed complied with the legal limit of < 100 cfu.cm-2 and only 18 % of the food handlers had no detectable bacteria present on their hands. One hand sample tested positive for E. coli, which is generally viewed as an indication of faecal contamination. S. aureus could not be detected on the hands of any of the food handlers. The results of this study indicated that hand hygiene is unsatisfactory and underlined the importance of further training to improve food handlers‘ knowledge of good hand washing practices. The study also aimed to present data on the food hygiene knowledge and practices of food handlers based on a representative sample from convenience food outlets in the Gauteng area. The management, as well as food handlers, were interviewed without prior announcement and managers were interviewed prior to starting their shifts, followed by food handlers, after they had passed through the change room and hand wash facilities. Although the majority of food handlers adhered to basic hygiene principles, the results highlighted a need for proper and continuous training in hygiene practices, not only for food handlers, but also for management. Furthermore, all food handlers should adhere to a formal cleaning schedule and specific courses should be planned for food handlers. Most training is done away from the workplace and the workers might find it difficult to translate theory into practice. Although food safety training programmes are essential, behavioural changes will not occur merely as a result of having received training but rather continuous development of food handlers. In conclusion, the popularity of convenience food is bound to increase with the growing appeal for modern foods. Consumers in South Africa nowadays demand good quality and safe products at a reasonable cost. Due to continuous time constraints, convenience food is the food of the future for the working mother. It is clear that managing foodborne disease is a challenge and an economic problem subject to various constraints. Food safety has too often become a hit-or-miss gamble, with parents obliged to roll the dice when it comes to the safety of their children‘s food and consumers in general. The food industry therefore needs to improve food safety processes to prevent the contamination of foods and use methods to ensure safe food for consumers. Better training, more testing and better methods of tracking food must be utilised to verify that the processes are working. This study endeavoured to add to the understanding and improvement of hygiene processes as well as food handlers‘ practices in the convenience food industry in the Gauteng Province.

Control of the pathogen Listeria monocytogenes in ready-to-eat (RTE) meats is a major concern in the food industry. The objective of this study was to compare the growth of L. monocytogenes on refrigerated RTE meats containing sodium levulinate (4-oxopentanoic acid, a five carbon organic acid with GRAS status), sodium lactate, or a combination of sodium lactate and sodium diacetate. Turkey roll and bologna were prepared to contain (wt/wt) sodium lactate (2%); sodium lactate in combination with sodium diacetate (1.875% sodium lactate, 0.125% sodium diacetate); sodium levulinate (1, 2, or 3%); or no antilisterial additive. Samples were sliced, inoculated with a 5-strain cocktail (102 to 103 CFU/cm2) of L. monocytogenes, vacuum packaged, and stored at 2°C for 0-12 weeks. Triplicate packages of each treatment were analyzed bi-weekly for growth of the pathogen. Bacterial counts exceeded 105 CFU/cm2 in controls after 4 weeks in turkey and over 106 CFU/cm2 after 8 weeks in bologna. In turkey, L. monocytogenes showed significant growth in samples containing sodium lactate after 6 weeks(>104 CFU/cm2) and after 8 weeks when used in combination with diacetate. Further, samples containing 1% sodium Jevulinate did not show significant growth of the pathogen for 10 weeks (~104 CFU/cm2), while those containing 2% and 3% levulinate inhibited growth for 12 weeks. In bologna, adding any antimicrobial inhibited growth for 12 weeks. Finally, Listeria-free samples of turkey roll and bologna, containing the various organic acid salts, were evaluated by members of consumer taste panels. Statistical analysis (ANOV A) showed that there were no differences in overall liking of samples of turkey roll (p = 0.19) or bologna (p = 0.42). In turkey, sodium levulinate was more effective at preventing growth of L. monocytogenes, while in bologna it was as effective as the current industry standards lactate and diacetate. Addition of levulinate did not alter the sensory acceptability of either product

Listeriosis has the highest fatality and hospitalization rate among foodborne illnesses. Listeria monocytogenes causes listeriosis and is a difficult bacterium for ready-to-eat food processors to eliminate because of its ability to grow in the absence of oxygen and under refrigeration. Recently, milk and its proteins have gained recognition as the largest source of biologically active peptides, and, it stands reason that several antimicrobial peptides (AMP) can be released from casein as it is the most abundant milk protein. AMPs are commonly obtained by cutting the whole protein into peptide fragments using enzymes or by acidification. The objective of this study was to predict potential AMPs through computer aided tools, improve hydrolysate preparation, and determine trypsin and pepsin-casein hydrolysate antimicrobial activity in growth media and on frankfurters against two strains of Listeria monocytogenes (Scott A and 310) and Escherichia coli O157:H7 (Salami strain). The prediction study procedure was to identify the most common variants of primary peptide sequences. The sequences were analyzed for greatest possible enzyme cuts on the protein, peptide masses, isoelectric point, net charge and percent hydrophilic residues using online proteomics programs. The fragments were explored for AMP commonalities: fragment length of 3 to 50 amino acids, positive (cationic) net charge, and hydrophilic residues between 25 and 50%. This technique identified 16 potential AMPs which proved that it is possible to screen for AMPs. The method used to determine the trypsin-casein hydrolysate (TCH) and pepsin-casein hydrolysate (PCH) antimicrobial activity was to hydrolyze sodium caseinate with pepsin or trypsin. L. monocytogenes (strains Scott A and 310) were incubated in 0, 10, 20, and 40% PCH and 0 and 50% TCH concentrations over a 24 hour period. PCH suppressed growth of L. monocytogenes Scott A by 1.76 log CFU/mL and reduced initial populations of L. monocytogenes 310 and E. coli O157:H7 by 0.52 and 0.62 log CFU/ml, respectively. TCH had little or no effect on growth suppression of any of the three test organisms. The frankfurter study was conducted by spot inoculating frankfurters with L. monocytogenes Scott A and then dipping frankfurters into one of five treatments (deionized water, pH 2.7 buffer, pH 5.1 buffer, pH 2.7 PCH, and pH 5.1 PCH) for 30 seconds; inoculated frankfurters that were not dipped served as controls. Frankfurters were incubated at 32°C for seven days. The results showed that there was no significant difference (p>0.05) in antimicrobial effectiveness among the treatments and control. This study demonstrated that enzymatically derived casein hydrolysates somewhat inhibit growth of L. monocytogenes and E. coli O157:H7 in culture media, but were ineffective when applied to frankfurters. Casein hydrolysate solutions can be easily made in a processing facility for application in fluid systems such as an antimicrobial spray on beef carcasses and in milk, juice, sports drinks, soda, soups, and yogurt. It also could be used in solid systems such as frankfurters, cheese, ground beef, and processed or RTE foods.

Background: Listeria monocytogenes and ready-to-eat meats have garnered considerable attention in Canada over the past decade as a result of foodborne outbreaks and product recalls that continue to transpire. A number of factors suggest that ready-to-eat meats and Listeria monocytogenes are a wicked problem. They include (among others) the number of stakeholders involved in the processing, distribution and inspection of ready-to-eat meats in Ontario, the ubiquitous and hardy nature of the organism and the challenges associated with eliminating it from ready-to-eat meat products and processing environments. Since Ontario public health units play an integral part in the inspection of ready-to-eat meats in the province, it is important to determine their current role in the wicked problem in order to identify possible solutions for change. Purpose: The purposes of the study were: (1) to determine how Ontario public health units address the wicked problem of Listeria monocytogenes and ready-to-eat meats in their food safety inspection programs using the provincial regulatory framework in addition to the use of research, knowledge translation and innovation; and (2) to develop a theory that identifies gaps (if any) in public health unit inspection practices, provincial legislation or food safety research that serves to generate recommendations to reduce incidence of listeriosis resulting from consumption of RTE meat products. Methodology: The research design used the principles of grounded theory to lead the interview and survey methodology and subsequent data analyses. The study was completed in three phases. Interviews were conducted in the first 2 phases of the study while a survey was conducted in the last phase. Interviews were conducted with public health unit ‘food safety leads’ that met pre-determined eligibility criteria. Following methods used in previous studies,interview data were analyzed in 4 stages of theory development using a grounded theory approach. Through substantive coding and constant comparative methods, core categories were identified in each of the study phases. As a result, theoretical saturation was reached leading to the process of theoretical coding and the emergence of the study theory. Results: In total, 27 public health units of 36 participated in the study. Eleven public health units participated in the first 2 phases of the interviews while 25 public health units (for a total of 45 participants) participated in the survey. The study core category, 'reactive and regulatory practice' evolved from the results of the interviews and survey. As a result, it was determined that: (1) the Ontario provincial regulatory framework including the Food Premises Regulation is almost exclusively responsible for directing food safety inspection practices in food premises; (2) food safety inspection and investigation activities associated with listeriosis outbreaks are the focus of Listeria monocytogenes and ready-to-eat meat research; and (3) innovation and knowledge translation are not currently influenced by inspection practice as a result of the food safety framework which does not require or encourage it. Using the processes of theoretical integration and theoretical coding, the following theory emerged from the data analyses; Ontario public health units manage ready-to-eat meats and Listeria monocytogenes through general population and reactive regulatory processes that focus on local-level, end-product, hazard reduction strategies for established risks in inspected food premises. Strengths and Limitations: The study had several strengths including being the first of its kind to associate ready-to-eat meats and Listeria monocytogenes as a part of a wicked problem. It was also the first study to use grounded theory to illuminate the function and role of Ontario public health units in managing Listeria monocytogenes and ready-to-eat meats. There are a number of limitations to the study including the study sample size, participant inclusion process through provincial public health unit senior management, the generalizability of study results, and method of interviews conducted with participants. Implications: The results of the study have implications for public health researchers and policy/regulatory makers in the province of Ontario. It stresses improved management of Listeria monocytogenes and ready-to-eat meats in food premises using a proactive approach. Conclusions: Using a grounded theory approach, this study demonstrated that Ontario public health units manage ready-to-eat meats and Listeria monocytogenes through reactive and regulatory food safety inspection practices. Survey and interview results indicate that study participants aspire for evidence-based regulatory and program amendments that will allow for proactive and targeted microbial risk-reduction activities at the local level that focus on vulnerable populations. The study substantiates that amendments to the Ontario Food Safety program and in particular, the Food Premises Regulation are necessary.

Background: Listeria monocytogenes and ready-to-eat meats have garnered considerable attention in Canada over the past decade as a result of foodborne outbreaks and product recalls that continue to transpire. A number of factors suggest that ready-to-eat meats and Listeria monocytogenes are a wicked problem. They include (among others) the number of stakeholders involved in the processing, distribution and inspection of ready-to-eat meats in Ontario, the ubiquitous and hardy nature of the organism and the challenges associated with eliminating it from ready-to-eat meat products and processing environments. Since Ontario public health units play an integral part in the inspection of ready-to-eat meats in the province, it is important to determine their current role in the wicked problem in order to identify possible solutions for change. Purpose: The purposes of the study were: (1) to determine how Ontario public health units address the wicked problem of Listeria monocytogenes and ready-to-eat meats in their food safety inspection programs using the provincial regulatory framework in addition to the use of research, knowledge translation and innovation; and (2) to develop a theory that identifies gaps (if any) in public health unit inspection practices, provincial legislation or food safety research that serves to generate recommendations to reduce incidence of listeriosis resulting from consumption of RTE meat products. Methodology: The research design used the principles of grounded theory to lead the interview and survey methodology and subsequent data analyses. The study was completed in three phases. Interviews were conducted in the first 2 phases of the study while a survey was conducted in the last phase. Interviews were conducted with public health unit ‘food safety leads’ that met pre-determined eligibility criteria. Following methods used in previous studies,interview data were analyzed in 4 stages of theory development using a grounded theory approach. Through substantive coding and constant comparative methods, core categories were identified in each of the study phases. As a result, theoretical saturation was reached leading to the process of theoretical coding and the emergence of the study theory. Results: In total, 27 public health units of 36 participated in the study. Eleven public health units participated in the first 2 phases of the interviews while 25 public health units (for a total of 45 participants) participated in the survey. The study core category, 'reactive and regulatory practice' evolved from the results of the interviews and survey. As a result, it was determined that: (1) the Ontario provincial regulatory framework including the Food Premises Regulation is almost exclusively responsible for directing food safety inspection practices in food premises; (2) food safety inspection and investigation activities associated with listeriosis outbreaks are the focus of Listeria monocytogenes and ready-to-eat meat research; and (3) innovation and knowledge translation are not currently influenced by inspection practice as a result of the food safety framework which does not require or encourage it. Using the processes of theoretical integration and theoretical coding, the following theory emerged from the data analyses; Ontario public health units manage ready-to-eat meats and Listeria monocytogenes through general population and reactive regulatory processes that focus on local-level, end-product, hazard reduction strategies for established risks in inspected food premises. Strengths and Limitations: The study had several strengths including being the first of its kind to associate ready-to-eat meats and Listeria monocytogenes as a part of a wicked problem. It was also the first study to use grounded theory to illuminate the function and role of Ontario public health units in managing Listeria monocytogenes and ready-to-eat meats. There are a number of limitations to the study including the study sample size, participant inclusion process through provincial public health unit senior management, the generalizability of study results, and method of interviews conducted with participants. Implications: The results of the study have implications for public health researchers and policy/regulatory makers in the province of Ontario. It stresses improved management of Listeria monocytogenes and ready-to-eat meats in food premises using a proactive approach. Conclusions: Using a grounded theory approach, this study demonstrated that Ontario public health units manage ready-to-eat meats and Listeria monocytogenes through reactive and regulatory food safety inspection practices. Survey and interview results indicate that study participants aspire for evidence-based regulatory and program amendments that will allow for proactive and targeted microbial risk-reduction activities at the local level that focus on vulnerable populations. The study substantiates that amendments to the Ontario Food Safety program and in particular, the Food Premises Regulation are necessary.

Master of Science / Food Science Institute / Elizabeth Boyle / Consumer demand for clean-label and 'all natural' food products has created the need to investigate antimicrobials derived from natural sources. Multifunctional ingredients are food additives that have multiple properties to reduce fat, limit salt, retard oxidation, increase water-holding capacity and inhibit bacterial growth in foods. Multifunctional ingredients that exhibit antimicrobial effects in meat and poultry products can facilitate consumers demand for clean and 'all natural' labels while reducing foodborne illness risk. Previous scientific research has shown that plant essential oils are known to contain active components to prevent oxidation in meat products, but emerging data have shown that these plant-based ingredients also contain antimicrobial properties. Plant essential oils such as basil oil has shown limited Salmonella Enteritidis inhibition in meat model systems and thyme oil has shown Listeria monocytogenes inhibition in low fat beef hotdogs. Intrinsic and extrinsic parameters of meat systems can alter the antimicrobial efficacy of plant essential oils. Although antimicrobial effects were observed with plant essential oils, effective usage levels may be limited to sensory characteristics in certain meat and poultry products. Natural extracts have shown potential antimicrobial properties in meat and poultry applications. Rosemary extract has been shown to suppress the growth of Enterobacteriaceae, Pseudomonas, and yeast and molds in fresh sausage. Grapefruit seed extract has shown inhibition against Campylobacter jejuni in poultry skin and meat models and E. coli O157:H7 in moisture enhanced beef homogenate models. The addition green tea extract in ground beef has been shown to reduce D-values while cooking and inhibit outgrowth of C. perfringens spores during extended chilling of cooked ground beef. Grape seed extract has been shown to reduce Listeria monocytogenes, E. coli O157:H7 and Salmonella Typhimurium populations in cooked lean ground beef stored for 9 days at 4°C. Scientific research findings for plant essential oils and extracts confirm that multifunctional ingredients are relevant to meat and poultry products as potential food additives to control undesirable pathogen and spoilage bacteria while meeting consumer demand for natural, clean-label ingredients.

Understanding potential cross contamination pathways is essential to reducing the risk of food product contamination. The use of a fluorescing abiotic surrogate (GloGermTM) to visualize the potential spread of bacteria may be beneficial to researchers. To quantify cross contamination during experimental trials in a mock retail deli, a rating method for visualization of fluorescence levels using a trained sensory panel was developed. Panelists feedback led to a pre-defined strategy allowing for characterization of contamination seen in photographs and reduced variability within responses. Following validation, GloGermTM was used to visually represent how bacteria may spread through a deli environment. Six origination sites (slicer blade, meat chub, floor drain, preparation table, employee's glove, employee's hands) were evaluated separately and spread was photographed throughout the mock deli. The trained sensory panel then analyzed the photographs. Five of the six contamination origination sites transferred GloGermTM to surfaces throughout the mock deli. Contamination from the floor drain did not spread to any food contact surfaces. To determine the potential of using a GloGermTM/ bacteria mixture to simultaneously track and sample contamination spread; surfaces were co-inoculated with GloGermTM and bacteria to determine if co-inoculation would affect the recoverability of microorganisms from these surfaces. Three common foodborne bacteria (E. coli O157:H7,Salmonella enterica ser. Enteritidis, Listeria monocytogenes, Listeria innocua) were inoculated on 2 by 2 stainless steel coupons alone and with GloGermTM . There was no significant difference found (p > 0.05) between the recovery of bacteria alone and the mixture for all bacteria. Finally, the use of co-inoculation was further explored by inoculating two contamination origination sites with either bacteria alone (L. monocytogenes and L. innocua) or a GloGermTM/bacteria cocktail. Nine recipient sites were sampled after a series of deli procedures were performed. Generally, no significant differences (p>0.05) were seen between the transfer of bacteria inoculated alone and the transfer of bacteria inoculated with GloGermTM to the selected recipient sites, regardless of contamination source or bacteria. These results suggest there may be potential in using L. innocua in combination with GloGermTM to visually track and sample contamination from a known source throughout a retail deli environment. / Ph. D.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Douglas Powell / Randall Phebus / Not-ready-to-eat entrées purchased at retail and prepared in the home have been identified as a risk factor for salmonellosis. From 1998 to 2010, ten outbreaks implicated undercooked not-ready-to-eat entrées. In each outbreak, affected individuals prepared entrées in a microwave oven, did not follow recommended cooking instructions, and failed to take the internal temperature of the cooked product. This dissertation surveyed grocery stores for product availability, evaluated consumers’ preparation practices of raw, breaded, frozen chicken entrées, and validated on-package label instructions. The survey of retail revealed that several manufacturers fail to provide consumers clear preparation instructions. A video capture system was used to observe food preparation practices of 41 consumers–21 primary meal preparers and 20 adolescents–in a mock domestic kitchen using uncooked, frozen, breaded chicken products, and determined if differences exist between consumers’ reported safe food handling practices and actual food handling behavior as prescribed on product labels. Differences between self-report and observed food safety behaviors were identified between groups. Many participants reported owning a food thermometer (73 percent) and reported using one when cooking raw, breaded chicken entrées (19.5 percent); however, only five participants (12.2 percent) were observed measuring the final internal temperature with a food thermometer despite instructions on the product packaging to do so. Food handling errors identified during the meal preparation sessions were then mimicked in a controlled laboratory setting to determine the impact of such deviations on end-product temperature. For all products, highly variable internal temperatures were recorded across entrées when prepared in a 600W microwave oven. Microwave cooking of raw breaded poultry products is unpredictable in achieving uniform target end-point temperatures; however, a 1000W microwave oven consistently produced a safe end product. Data collected through direct observation more accurately reflected consumer food handling behaviors than data collected through self-reported surveys. Low wattage microwave ovens failed to produce a safe end product. Processors should validate instructions for not-ready-eat entrées using a range of microwave ovens rather than a single wattage, develop a unique set of instructions for entrées, and provide consumers clear cooking instructions that result in a safe end product.

A preferência por produtos prontos para consumo pode implicar em aumento do risco de doenças transmitidas por alimentos (DTAs) e uma grande preocupação, nesse caso, é a presença da Listeria monocytogenes. A infecção por essa bactéria apresenta baixa taxa de morbidade, porém alta de mortalidade, representando maior risco para gestantes, idosos, crianças e indivíduos imunodeprimidos. Os produtos considerados de maior risco são aqueles prontos para o consumo, mantidos sob refrigeração e com longa vida útil. Face ao exposto, foi pesquisada a ocorrência de L. monocytogenes em dois grupos de produtos cárneos fatiados: presunto cozido e salame. Cento e trinta amostras de cada tipo de produto, adquiridas no comércio varejista do Município de São Paulo, foram submetidas a análises laboratoriais. Tais análises foram conduzidas em dois momentos: no terço inicial e no final de vida útil dos produtos. Nos casos de positividade, foram realizadas a quantificação e a sorotipagem da bactéria em cada um dos produtos, a fim de avaliar se os resultados obtidos poderiam oferecer risco à saúde. O salame apresentou prevalência significativamente maior para a L. monocytogenes, 6,2 por cento (8/130), enquanto no presunto a prevalência foi de 0,8 por cento (1/130). As contagens nas amostras de salame apresentaram valores entre <10 a 1900 UFC/g. Os sorotipos identificados, considerando os dois tipos de produtos, apresentaram as seguintes freqüências: 4b= 37,5 por cento (3/8), 1/2b= 25 por cento (2/8), 3b= 25 por cento (2/8) e 1/2c= 12,5 por cento (1/8). Os resultados encontrados permitem inferir que, para os produtos analisados, o risco de listeriose decorrente do consumo de salame é maior do que o associado ao consumo de presunto cozido / The preference for ready-to-eat products can raise the risk of diseases transmitted by food and in this case there is a main concern about the presence of Listeria monocytogenes. The infection caused by these bacteria presents low morbidity but high mortality rate, representing higher risk to pregnants, elderly, children and immunodepressed people. Products considered to have higher risk are the ready-to-eat kept under refrigeration and with longer shelf life. Considering this, it has been searched the occurrence of L. monocytogenes in two groups of sliced meat: cooked jam and salami. There were submitted to laboratorial analyses, to identification of L. monocytogenes, 130 samples of each product, acquired from São Paulo retailing market. Analyses were conducted in two times, in the starting third part life of product and in the end of shelf live. For the positive cases it was realized quantification and serotype from this bacterium, in order to evaluate if found results can offer risk to health. Salami has presented occurrence significantly higher for L. monocytogenes, 6.2 per cent (8/130), while cooked jam has presented 0.8 per cent (1/130). Counts of salami have shown results from <10 to 1900 CFU/g. Identified serotypes, considering both types of products, presented the following frequencies: 4b= 37,5 per cent (3/8), 1/2b= 25 per cent (2/8), 3b= 25 per cent (2/8) e 1/2c= 12,5 per cent (1/8). Presented results allow us to infer, to the tested products, that the risk of listeriosis from consuming salami is higher than the risk associate to consuming cooked jam