Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/14/2008
Publication Date: 8/1/2008
Citation: Brito, J.R., Santos, E.M., Oliveira, M.M., Arcuri, E.F., Lange, C.C., Brito, M.A., Souza, G.N., Beltran, J.M., Call, J.E., Liu, Y., Porto Fett, A.C., Luchansky, J.B. 2008. A retail survey of brazilian milk and minas frescal cheese, and a contaminated dairy plant, to establish the prevalence, relatedness, and sources of listeria monocytogenes. Applied and Environmental Microbiology. Vol.74, No.15. pg 4954-4961. Interpretive Summary: Latin-style fresh cheese, such as Queso Fresco (QF) and Minas Frescal (MF), are very popular variety of cheese. However, they provide a favorable environment for the growth/survival of Listeria monocytogenes (Lm), a food borne pathogen that causes listeriosis. This study was conducted to determine the prevalence and levels of the pathogen at processing plants and retail markets located in the city of Juiz de Fora, Brazil. Any Lm that were recovered were further characterized to determine if they were genetically related or not related, as well as to help identify possible sources of contamination. All milk samples and all samples from 9 of 10 MF brands tested negative for Lm. However, one brand of MF that was obtained from two retail establishments tested positive for Lm. The processing plant that produced the contaminated cheese was subsequently sampled. A number of environmental samples from the cheese processing plant and all of the MF samples tested positive for the pathogen. In addition, each of the Lm that were collected from the plant processing environment and the MF samples were genetically related. It was also determined that the coolers/refrigeration units were the source within the processing plant that contaminated the MF. Based on this information and in conjunction with Brazilian authorities, sanitation and design flaws of the processing plant were identified and corrected. Following these corrections, environmental and MF samples were taken on multiple visits to the processing plant and MF samples were taken on multiple visits to retail markets. All of these samples tested negative for the pathogen over a 12-month period. The results of this study will be helpful for processors and retailers to develop ways to better control the contamination of this type of cheese with Lm.
Technical Abstract: A study was designed to recover Listeria monocytogenes from pasteurized milk and Minas Frescal cheese (MFC) sampled at retail and to identify the source(s) of contaminated products in the corresponding dairy processing plant and farm. Fifty milk samples (9 brands, 5-7 samples/brand) and 55 MFC samples (9 brands, 5 samples/brand; 1 brand, 10 samples/brand) were tested between June and October of 2005 from retail sites located in 8 areas of Juiz de Fora, Minas Gerais, Brazil. The 50 pasteurized milk samples and all 45 samples from 9 of 10 MFC brands tested negative for L. monocytogenes following a one-step enrichment procedure and plating onto two different selective media. However, “Brand F” of MFC obtained from retail establishments #119 (4 of 6 samples positive over 4 visits) and #159 (2 of 4 samples positive over 2 visits) tested positive for L. monocytogenes. Thus, in October of 2005 the farm/dairy that produced Brand F MFC was sampled; all 5 samples from the milking parlor tested negative for L. monocytogenes, whereas 10 of 23 sites/samples from the processing plant environment and 5 of 5 MFC samples obtained directly at Plant F tested positive for the pathogen. Levels of L. monocytogenes recovered from the 5 positive MFC obtained directly from Plant F ranged from ca. 2.5 to 4.3 log10 CFU/g. All 344 isolates (5-20 isolates per each positive sample) recovered from retail MFC (6 positive samples), Plant F MFC (5 positive samples), and Plant F environmental samples (10 positive samples) were serotype 1/2a and displayed the same AscI pulsed-field restriction profile. These results also established that the coolers/refrigeration units served as the point source within Plant F that contaminated the MFC. Based on these findings, and in collaboration with both the producer and the State Service for Veterinary and Phyto-sanitary Supervision (IMA, MG), failures in the hygienic process and plant design were identified and subsequently corrected. The plant remained closed from October through December of 2005 until the corrective renovations of the facility were completed. Immediately following renovation in December of 2005, 29 samples, including samples from sites that previously tested positive for the pathogen, were collected from the processing environment; all tested negative for L. monocytogenes. On 3 subsequent visits to Plant F between March and October of 2006 an additional 97 environmental and 15 MFC samples from Plant F all tested negative for L. monocytogenes. In addition, on 2 visits to retail establishment #159 (1 sample per visit) and 4 visits to retail establishment #119 (6 samples total) between January and March of 2006, all 8 samples of MFC tested negative for the pathogen. Studies are ongoing to quantify the prevalence, levels, and types of L. monocytogenes in MFC and associated processing plants to lessen the likelihood of food borne listeriosis in Brazil.