Food Protection Trends - November 2009 - 784

from 3.31°C to 9.03°C in the six summer shipments and -2.44°C to 9.42°C in the six winter shipments. Campylobacter species were not isolated from any of the 1,200 packages of retail ground beef. PCR detection of campylobacters Of the 142 samples tested using PCR, 65 (46%) were positive for DNA of Campylobacter spp. origin while 77 were negative (Table 1). Two of the 142 samples tested with use of PCR could not be linked to store or chain and were omitted from all subsequent analyses. The remaining 140 ground beef samples represented 52 different stores. Twelve stores had more than one meat sample tested from the same collection period. Of these 12 stores, only four stores had more than one meat sample positive for DNA of Campylobacter spp. origin. Ten of these 12 stores had either four or five samples from the same collection period tested with PCR, and the most any store had positive for DNA of Campylobacter spp. origin was two samples. Campylobacter spp. by PCR. The odds of a retail ground beef package testing positive for Campylobacter spp. DNA was 5.6 times greater if the package was from collection period 2 than if it was from collection period 1 (OR 5.6, 95% CI 1.8–17.5). Further, a package had 12 times greater odds of testing positive for Campylobacter spp. DNA if it was from collection period 3 than if it was from collection period 1 (OR 12.0, 95% CI 3.5–42.0). Ground beef from collection period 4 was not statistically different from beef from collection period 1 (OR 0.6, 95% CI 0.2–2.0). DISCUSSION The samples from this large retail ground beef survey represented four different supermarket chains and three cities in southern Alberta. Random selection of packages in stores, multiple collection periods, and limiting the number of packages purchased per store were used to avoid oversampling the same meat batches. In 2005, source beef for ground beef likely came from the six federally inspected slaughter plants in Alberta (1), or from provincially inspected facilities. Because retail chains likely purchased meat from the same plants or processors, it was expected that variation within each chain would be small. As a result, only five packages of ground beef were purchased from each store at each collection time. Hazard analysis critical control points (HACCP) have been identified and programs implemented in all federally registered beef slaughter plants in Canada (5). In previous surveys in cattle, poultry and swine, significant reductions in Campylobacter isolation rates from slaughter to post-chill have been reported (20, 24, 26). Protocols in cattle slaughter plants, including hide-on-carcass, lactic acid, hot water, and carcass washes, chilling, and the ability to remove potentially contaminating components (e.g., hides and intestinal tracts) quickly and intact may have all contributed to bacterial numbers below detectable levels in the retail ground beef surveyed here. It can be difficult to compare laboratory protocols with other published research because many incubation and temperature protocols, culture media, and antimicrobial supplements are avail- Factors associated with PCR detection of Campylobacter spp. For one sample, data were missing for whether or not the source store cut poultry. This sample was included in risk factor analysis, and designated ‘missing’ in the “poultry” analysis. Supermarket chain did not explain an important part of the variance in the null model (chain level variance 0.000, standard error 0.000) and was not included as a random effect in the final analysis. After accounting for clustering within the store of origin, only the package type and the collection period variables were selected for consideration in the development of a final model (P ≤ 0.25) (Table 2). None of the other risk factors considered (chain, city, inclusion of frozen portions, on-site poultry cutting practices, kinds of trim in the ground beef or package weight) were associated with the odds of detecting campylobacters by PCR (Table 2). When package type (regular or lean) and collection period (1: Nov 21–23, 2004, 2: Jan 9–11, 2005, 3: May 30–31, June 1, 2005, and 4: July 18–20, 2005) were examined together, only the collection period was significantly associated (P ≤ 0.05) with detection of able, and because viable but non culturable Campylobacter strains may exist (8, 23). Using the culture technique described, we were able to isolate C. jejuni at 1×101 CFU/g in experimentally inoculated ground beef samples; this level is below the estimated dose required for human infection (3, 14). However, none of the 1,200 packages of retail ground beef collected as part of this study were culture positive for viable Campylobacter spp., an encouraging finding for public health in Alberta. The very low prevalence of culturable Campylobacter levels in retail ground beef observed in this study is similar to those seen in other North American ground beef surveys (4, 28) and lower than the 60–90% prevalences reported in raw retail chicken (4, 30, 31). In a survey in the United States from 2002–2005, campylobacters were identified in only 1 of 2,073 packages of ground beef using culture (28), and a smaller Alberta survey found zero of 100 packages positive (4). However, it is possible that the laboratory sensitivity of the culture method used here may not have been high enough to pick up very low numbers of organisms. Further, if campylobacters were sufficiently stressed, it is possible the method was not able to resuscitate these pathogens sufficiently for growth with culture. Three of the meat shipments dipped below the 0°C mark during shipping; however, campylobacters have been isolated from ground beef frozen at -18°C for 90 days (10), and culture recovery in our study did not vary between summer and winter samplings. Traditionally, PCR has been used to confirm isolates as campylobacters rather than as a survey tool in retail meat studies (13, 30, 31). This is because from a food safety point of view, viable campylobacters are usually the targets of interest and the identification of Campylobacter DNA by use of PCR does not ensure viability. However, from our direct PCR results, C. jejuni, C. coli, and C. hyointestinalis were identified in the retail ground beef. None of the samples were positive for C. fetus or C. lanienae, species which may be carried by cattle, or for C. concisus or C. upsaliensis, which are pathogens responsible for infections in people but are putatively not carried by livestock (14, 21). Finding 27% (38/142) of samples PCR positive for 784 FOOD PROTECTION TRENDS | NOVEMBER 2009
Food Protection Trends - November 2009

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