Food Protection Trends - March 2009 - 149

650,000 pounds of artisanal cheeses, and that approximately 10% of these cheeses reached consumers by way of mail order (34). This means that many consumers of farmstead cheeses are located in cities, states, or even countries other than where the cheeses are made. The Internet makes it easier for businesses of all types, including producers of perishable products such as cheese, to sell their products to the world in the global marketplace. While dairy products collectively have been identified by the Centers for Disease Control and Prevention (CDC) as causing less than 1.5% of all foodborne disease outbreaks (33), cheeses are perishable products that can potentially harbor bacterial pathogens that can cause severe illness or even death. Some types of cheese, in particular soft cheeses made from raw milk have been implicated in outbreaks more often than others (21). The bacterial pathogens most often found in contaminated cheeses implicated in outbreaks of illness include Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Staphylococcus aureus (1). Farmstead cheesemakers, compared to other cheesemakers, must take additional precautions to prevent the contamination of their product with these pathogens, which are commonly found in the animal farming environment. Because of the seriousness of illness these pathogens can cause, regulations (federal and state) are in place to help assure the safety of these products for the consumer. One of the federal regulations that applies to cheeses produced in all states, in place since 1949, addresses the safety of cheeses made from raw milk by requiring that these cheeses be aged for a minimum of 60 days prior to their release for sale to consumers (35). State regulations related to making and selling these cheeses vary from state to state. The objective of this study was to evaluate the microbiological safety, relative to standards of Virginia state regulations, of farmstead cheeses made in various places across the United States, by testing cheeses available for purchase via online shopping. the following terms, or a combination of these terms: farmstead, small farm, cheese, artisanal, gourmet, raw, unpasteurized, and pasteurized. The cheeses for this project were purchased via the Internet, either directly from the cheese maker or through a retail distributor of gourmet food products. All of the cheeses selected for purchase were described by the cheese maker as being made on the farm where the animals producing the milk are maintained. These farmstead cheeses were purchased entirely by electronic means (Web site “shopping carts”). All cheeses were delivered to a single address in Virginia, evaluated for condition upon arrival, and placed in refrigeration at 0–4.4°C until microbiological analyses were performed. Procedure for detection of E. coli O157:H7 The VIDAS, E. coli O157 (ECO) test kit (bioMérieux, Inc., Durham, NC), an enzyme-linked fluorescent assay (ELFA) designed to detect the presence of E. coli O157 antigens, was used with a mini VIDAS instrument (bioMérieux) to evaluate the cheese samples qualitatively for contamination with E. coli O157. A 25-g portion of each cheese sample was incubated in the appropriate enrichment broths according to the ECO test kit instructions, and prepared for analysis. The prepared sample broths were analyzed for E. coli O157 antigens, following test kit instructions. Sample broths testing positive by the VIDAS ECO test were subjected to a confirmation procedure using the VIDAS Immuno-Concentration E. coli O157 (ICE) test kit (bioMérieux) according to the kit instructions, followed by plating on Rainbow Agar O157 (Biolog, Inc., Hayward, CA), Chromagar O157 (Hardy Diagnostics, Santa Maria, CA), Sorbitol MacConkey Agar (SMAC), and Cefixime Tellurite supplemented SMAC agar (CT-SMac). Absence on these selective/differential media of colonies typical of E. coli O157 (as described by the technical information for Rainbow O157 agar, FDA’s Bacteriological Analytical Manual [BAM] for SMAC and CT-SMac agars, and the technical information for Chromagar O157) was considered a negative confirmation result (4, 5, 13). Procedure for detection of Salmonella spp. To determine the presence or absence of Salmonella in the cheese samples, the VIDAS Immuno-Concentration Salmonella (ICS) (bioMérieux) and the VIDAS Salmonella (SLM) (bioMérieux) were used in combination. The ICS kit, which uses Salmonella specific antibodies (O and H antigens) to capture and concentrate any Salmonella present, was used first to increase the sensitivity of the SLM test, which, like the ECO test, uses the ELFA technique to detect the target organism. A 25-g portion of each cheese was incubated in enrichment broth according to instructions included with the ICS and SLM kits and prepared for analysis. The prepared sample broths were analyzed on the mini VIDAS instrument for Salmonella antigens, and broths testing positive by the VIDAS SLM test were subjected to a confirmation procedure. To confirm the presence of Salmonella, Xylose Lysine Deoxycholate (XLD) agar (Remel, Inc., Lenexa, KS) and Brilliant Green (BG) agar (Remel) were used. After incubation, the plates were examined for colonies typical of Salmonella (for BG agar, pink, opaque colonies with red zones in the surrounding media; for XLD agar, black, red with black center, or red colonies) (3, 6). Colonies typical of Salmonella were inoculated in Triple Sugar Iron Agar slants (Remel) and Lysine Iron Agar slants (Remel), incubated, and examined for reactions consistent with Salmonella. Isolates determined to be Salmonella were serogrouped using the Wellcolex Colour Salmonella test (Remel). Procedure for detection of Listeria monocytogenes Another ELFA test, the VIDAS Listeria (LIS) (bioMérieux), was used, according to AOAC Official Method 999.06, with a mini VIDAS instrument to qualitatively detect Listeria spp. antigens in a 25-g portion of each cheese sample. Sample broths testing positive by the VIDAS LIS assay were subjected to a confirmation procedure according to methods described in BAM, using both Palcam agar (Hardy) and Oxford agar (Remel) (18). MATERIALS AND METHODS Sampling of cheeses Determining the various sources of farmstead cheeses for this project was done by performing Internet searches using MARCH 2009 | FOOD PROTECTION TRENDS 149

Food Protection Trends - March 2009

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