RESUMO
Simultaneous and individual enumeration of Salmonella, Shigella and Listeria monocytogenes was compared on inoculated Roma tomatoes and Serrano peppers using an Most Probable Number (MPN) technique. Samples consisting of tomatoes (4 units) or peppers (8 units) were individually inoculated with a cocktail of three strains of Salmonella, Shigella or L. monocytogenes, or by simultaneous inoculation of three strains of each pathogen, at low (1.2-1.7 log CFU/sample) and high (2.2-2.7 log CFU/sample) inocula. Samples were analyzed by an MPN technique using universal pre-enrichment (UP) broth at 35⯰C for 24⯱â¯2â¯h. The UP tubes from each MPN series were transferred to enrichment and plating media following adequate conventional methods for isolating each pathogen. Data were analyzed using multifactorial analysis of variance (pâ¯<â¯0.05) and LSD multiple rang test. There were differences (pâ¯<â¯0.05) in recovery of simultaneous and individual bacteria inoculated (individualâ¯>â¯simultaneous), type of bacteria (Salmonellaâ¯>â¯Shigella and L. monocytogenes), type of sample (UP brothâ¯>â¯pepper and tomato), and inoculum level (highâ¯>â¯low). The MPN technique was effective for Salmonella on both commodities. Shigella counts were higher on tomatoes compared to peppers, (pâ¯<â¯0.05), and for L. monocytogenes on peppers (pâ¯<â¯0.05).
Assuntos
Capsicum/microbiologia , Listeria monocytogenes/crescimento & desenvolvimento , Salmonella/crescimento & desenvolvimento , Shigella/crescimento & desenvolvimento , Solanum lycopersicum/microbiologia , Contagem de Colônia Microbiana , Contaminação de Alimentos/análise , Frutas/microbiologia , Verduras/microbiologiaRESUMO
Polymyxin Ceftazidime Oxford Medium (PCOM), a novel selective and differential plating medium for Listeria monocytogenes was compared with Modified Oxford Agar (MOX) for efficacy to isolate L. monocytogenes and other Listeria spp. naturally present in non-pasteurized Mexican-style cheese (n = 50), non-pasteurized fresh squeezed orange juice (n = 50), raw beef chunks (n = 36), and fresh cabbage (n = 125). Samples were collected from retail markets and farms in Mexico and tested following the US Department of Agriculture enrichment technique. Listeria spp. were isolated from 23.4% of analyzed samples, and from those, 75.0% corresponded to raw beef chunks, 38.0% to non-pasteurized Mexican-style cheese, and 30.0% to fresh squeezed orange juice. No Listeria spp. were isolated from fresh cabbage samples. L. monocytogenes was recovered from 15.3% of food samples analyzed. Non-pasteurized Mexican-style cheese showed the highest proportion of L. monocytogenes positive samples (36.0%), followed by orange juice (26.0%) and raw beef (25.0%). The frequency of isolation of Listeria spp. and L. monocytogenes was not different (P > 0.05) between PCOM and MOX. The advantages of using PCOM when comparing to MOX, include the easier way to identify Listeria species, the lower cost per plate and the availability of its ingredients for Latin-American countries.
Assuntos
Bebidas/microbiologia , Brassica/microbiologia , Queijo/microbiologia , Meios de Cultura/metabolismo , Listeria monocytogenes/crescimento & desenvolvimento , Carne/microbiologia , Animais , Bovinos , Meios de Cultura/química , Contaminação de Alimentos/análise , Microbiologia de Alimentos , Listeria monocytogenes/isolamento & purificação , Listeria monocytogenes/metabolismo , México , Polimixinas/metabolismoRESUMO
Salmonella is a foodborne pathogen that commonly inhabits the gastrointestinal tract of a healthy feedlot cattle and can be transferred to the carcass surface during hide removal and evisceration procedures. Numerous investigations on Salmonella prevalence throughout different stages of the beef chain have been conducted. In contrast, limited studies are available on quantitative determinations of Salmonella at different steps in raw meat production. Quantitative data, particularly for pathogenic bacteria such as Salmonella are important for quantitative risk assessment. Salmonella spp. and Escherichia coli populations were enumerated on beef carcass samples collected at abattoirs and also in beef chunks and ground beef samples collected from butcher's shops at retail in Jalisco State, Mexico. Sponge samples from beef carcass sides (n=142) were collected immediately after final water wash and before chilling at three non-federally inspected abattoirs following USDA-FSIS sampling protocols. Beef chunks (n=84) and ground beef (n=65) samples were obtained from 86 butcher's shops. Salmonella enumeration was conducted by the Most Probable Number method and E. coli counts were determined using Petrifilm plates. Salmonella was isolated from 18% of beef carcasses, 39% of beef chunks and 71% of ground beef samples. Salmonella mean counts were 1.3±0.9 Log MPN/300 cm(2) on beef carcasses, 1.9±0.9 and 2.3±1.1 Log MPN/25 g in beef chunks and ground beef samples, respectively. Twenty-six Salmonella serotypes and 11 serogroups were identified among 432 isolates recovered. Salmonella typhimurium (14%), Salmonella sinstorf (12%) and S. Group E1 monophasic (10%) were the most frequent. Escherichia coli was present on 97, 84 and 100% of beef carcasses, beef chunks and ground beef samples, respectively. Escherichia coli mean counts were 3.2±0.7 Log CFU/300 cm(2), 3.9±1.1 and 4.5±1.2 Log CFU/25 g on beef carcasses, beef chunks and ground beef, respectively. Salmonella prevalence and mean counts found in raw beef were higher than previously reported in studies from other countries. The data collected in this study show a trend in the prevalence of Salmonella to be higher as meat processing is extended at retail. This, together with the diversity of serotypes found, indicates that raw meat is exposed to multiple contamination sources during slaughter and retail processing and highlights the necessity to implement Sanitation Standard Operating Procedures for those establishments. Finally, this study provides quantitative information for future risk assessments associated with the risk of human salmonellosis.
Assuntos
Escherichia coli/fisiologia , Microbiologia de Alimentos , Carne/microbiologia , Salmonella/fisiologia , Matadouros , Animais , Bovinos , Escherichia coli/isolamento & purificação , México , Prevalência , Medição de Risco , Salmonella/isolamento & purificaçãoRESUMO
The Polymyxin Ceftazidime Oxford Medium (PCOM) was developed to recover Listeria monocytogenes from raw or unpasteurized foods. It contains esculin-ferric ammonium citrate as indicator system for Listeria growth, and ceftazidime and polymyxin B as selective agents, which are available in several Latin American countries. Comparison of PCOM, Modified Oxford Medium (MOX) and Tryptic Soy agar with 0.6% yeast extract (TSAYE) indicated that both selective media were equally effective at recovering four individual strains of L. monocytogenes (Scott A, V7, California and broccoli), and a mixture of these strains (LMM) (P > 0.05). The ability of PCOM, MOX, TSAYE and TSAYE supplemented with 4% NaCl to recover heat, acid and freeze-damaged LMM was similar for all media (P > 0.05). The PCOM proved to be effective at isolating colonies of LMM from inoculated raw beef chunks, unpasteurized orange juice, cabbage, and Mexican-style cheese by direct plating and by the US Department of Agriculture's Food Safety and Inspection Service enrichment method. Differentiation of L. monocytogenes colonies was easier on PCOM than on MOX for foods with high levels of background microbiota. Based on the evaluations performed on foods naturally contaminated with L. monocytogenes, PCOM was a more economical alternative than MOX for selective and differential isolation of Listeria from raw or unpasteurized foods.
Assuntos
Contagem de Colônia Microbiana/métodos , Meios de Cultura/metabolismo , Microbiologia de Alimentos , Listeria monocytogenes/isolamento & purificação , Animais , Brassica/microbiologia , Bovinos , Ceftazidima/farmacologia , Queijo/microbiologia , Contagem de Colônia Microbiana/instrumentação , Meios de Cultura/química , Listeria monocytogenes/efeitos dos fármacos , Listeria monocytogenes/crescimento & desenvolvimento , Listeria monocytogenes/metabolismo , Leite/microbiologiaRESUMO
In-plant validation of an alternative washing and sanitizing method was conducted at a cantaloupe packing operation in Mexico. This method consisted of a spray water wash followed by spraying warm (55 to 60 degrees C) 2% (L)-lactic acid solution and was compared with the existing method of spray washing the melons with tap water followed by immersion in a chlorinated water tank. Surface samples (100 cm(2)) were collected from 160 melons subjected to each processing method and tested for counts of aerobic bacteria, coliforms, and Escherichia coli. The aerobic plate counts from cantaloupes washed in the dump tank ranged from 3.6 to 5.2 log CFU/cm(2) and were significantly higher (P < 0.05) than those from melons treated with the alternative spray method, which ranged from 1.8 to 2.6 log CFU/cm(2). Coliform counts for cantaloupes treated in the dump tank were 0.2 to 2.2 log CFU/cm(2) and were below the detection level (-6.0 log CFU/cm(2)) on cantaloupes treated by the spray method. Growth of E. coli was observed in 2.5% of the samples of cantaloupes treated in the dump tank and in none of the samples of cantaloupes treated by lactic acid spray (P < 0.05). These results support the elimination of dump tanks in cantaloupe packing operations established by the Mexican government for certification of firms exporting cantaloupes to the United States. When a sanitizer is to be applied to the product, lactic acid seems to be a viable option, at least for products such as cantaloupes whose quality is not affected by an acid wash.
Assuntos
Cucumis melo/microbiologia , Manipulação de Alimentos/métodos , Embalagem de Alimentos/métodos , Conservação de Alimentos/métodos , Saneamento/normas , Bactérias Aeróbias/isolamento & purificação , Contagem de Colônia Microbiana , Qualidade de Produtos para o Consumidor , Desinfetantes/farmacologia , Manipulação de Alimentos/normas , Embalagem de Alimentos/normas , Conservação de Alimentos/normas , Humanos , Higiene , Ácido Láctico/farmacologia , MéxicoRESUMO
The effect of different washing or sanitizing agents was compared for preventing or reducing surface and internal contamination of tomatoes by Salmonella Typhimurium and Escherichia coli O157:H7. The tomatoes were inoculated by dipping them in a bacterial suspension containing approximately 6.0 log CFU/ml of each pathogen and then rinsing them with tap water, hypochlorite solution (250 mg/liter), or lactic acid solution (2%, wt/vol). All treatments were applied by dipping or spraying, and solutions were applied at 5, 25, 35, and 55 degrees C. With the exception of the lactic acid dip at 5 degrees C, all treatments reduced both pathogens on the surfaces of the tomatoes by at least 2.9 cycles. No significantly different results were obtained (P > 0.05) with the dipping and spraying techniques. For internalized pathogens, the mean counts for tomatoes treated with water alone or with chlorine ranged from 0.8 to 2.1 log CFU/g. In contrast, after lactic acid spray treatment, all core samples of tomatoes tested negative for Salmonella Typhimurium and, except for one sample with a low but detectable count, all samples tested negative for E. coli O157:H7 with a plate count method. When the absence of pathogens was verified by an enrichment method, Salmonella was not recovered from any samples, whereas two of four samples tested positive for E. coli O157:H7 even though the counts were negative. Few cells of internalized pathogens were able to survive in the center of the tomato during storage at room temperature (25 to 28 degrees C). The average superficial pH of tomatoes treated with tap water, chlorine, or lactic acid was 4.9 to 5.2, 4.1 to 4.3, and 2.5, respectively (P < 0.05), whereas no differences were observed in the internal pH (3.6 to 3.7) of the tomatoes treated with different sanitizers. The general practice in the tomato industry is to wash the tomatoes in chlorinated water. However, chlorine is rapidly degraded by organic matter usually present in produce. Therefore, lactic acid sprays may be a more effective alternative for decontaminating tomato surfaces. The use of warm (55 degrees C) sprays could reduce pathogen internalization during washing.
Assuntos
Desinfetantes/farmacologia , Escherichia coli O157/crescimento & desenvolvimento , Ácido Hipocloroso/farmacologia , Ácido Láctico/farmacologia , Salmonella typhimurium/crescimento & desenvolvimento , Solanum lycopersicum/microbiologia , Contagem de Colônia Microbiana , Escherichia coli O157/efeitos dos fármacos , Contaminação de Alimentos/prevenção & controle , Microbiologia de Alimentos , Concentração de Íons de Hidrogênio , Oxidantes/farmacologia , Salmonella typhimurium/efeitos dos fármacos , Temperatura , ÁguaRESUMO
To study the potential of three bacterial pathogens to cross-contaminate orange juice during extraction, normal operation conditions during juice preparation at food service establishments were simulated. The spread of Salmonella enterica serovar Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes from inoculated oranges to work surfaces and to the final product was determined. The transference of these three bacterial pathogens to orange juice made from uninoculated oranges with the use of contaminated utensils was also studied. Fresh oranges were inoculated with a marker strain of rifampicin-resistant Salmonella Typhimurium, E. coli O157:H7, or L. monocytogenes. Final pathogen levels in juice were compared as a function of the use of electric or mechanical juice extractors to squeeze orange juice from inoculated oranges. Pathogen populations on different contact surfaces during orange juice extraction were determined on sulfite-phenol red-rifampicin plates for Salmonella Typhimurium and E. coli O157:H7 and on tryptic soy agar supplemented with 0.1 g of rifampicin per liter for L. monocytogenes. After inoculation, the average pathogen counts for the orange rind surface were 2.3 log10 CFU/cm2 for Salmonella Typhimurium, 3.6 log10 CFU/cm2 for E. coli O157:H7, and 4.4 log10 CFU/cm2 for L. monocytogenes. This contamination was spread over all utensils used in orange juice squeezing. Mean pathogen counts for the cutting board, the knife, and the extractor ranged from -0.3 to 2.1 log10 CFU/cm2, and the juice contained 1.0 log10 CFU of Salmonella Typhimurium per ml, 2.3 log10 CFU of E. coli O157:H7 per ml, and 2.7 log10 CFU of L. monocytogenes per ml. Contact with contaminated surfaces resulted in the presence of all pathogens in orange juice made from uninoculated oranges. These results give emphasis to the importance of fresh oranges as a source of pathogens in orange juice.