Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2005
Publication Date: 2/1/2006
Citation: Georgsson, F., Porkelsson, A.E., Geirsdottir, M., Stern, N.J. 2006. The influence of freezing and duration of storage on campylobacter and indicator bacteria in broiler carcasses. International Journal of Food Microbiology. 23(7):677-683. Interpretive Summary: Campylobacter jejuni is the most frequent cause of food-borne bacterial infection in many developed countries (Altekruse, et al., 1999; Friedman et al., 2000). The organism has been isolated from various food sources such as: poultry, red meat, and raw milk (Atanassova and Ring, 1999). Epidemiological studies indicate that handling raw poultry or eating undercooked poultry are important risk factors for transmitting campylobacteriosis in many industrialized countries. Additional identified risk factors for humans include consumption of meats other than poultry, drinking untreated surface water, or drinking unpasteurized milk and dairy products (Friedman et al., 2000). High frequencies of Campylobacter spp. in poultry products have been reported among numerous developed countries. Atanassova and Ring reported an incidence of 45.9% contamination in broiler carcasses in Germany (1999). Ono and Yamamoto reported a prevalence of 45.8% in domestic retail poultry in Japan (1999). Madden and co-workers reported a 38% frequency in cut-up chicken portions in Northern Ireland (1998). (Icelandic data). Various levels of Campylobacter have been reported in poultry products. Berrang et al. (2001) reported concentrations ranging from 2 to 3 log 10 CFU g-1 of Campylobacter in breast skin, thigh skin and drumstick skin samples and significantly lower concentration in the corresponding meat samples. Whyte et al. (2001) recovered 1.88 to 3.59 log 10 CFU g-1 of Campylobacter from neck skins, depending on the makeup of a water bath in which poultry carcasses were immersed. Stern and Robach (2003) reported the average level of Campylobacter as 104.11 CFU carcass-1 in 1995 being reduced to 103.05 CFU carcass-1 in 2001 among north Georgia (United States), processed whole broiler rinses. Although the levels were greatly reduced, the frequency remained quite high, with approximately 85% of the carcasses sampled being contaminated. A positive relationship between the exposure to pathogenic Campylobacter cells and the probability of infection has been published (Black et al., 1998). This relationship suggests that a significant reduction of viable Campylobacter spp. in commercial poultry products could result in a reduced incidence of Campylobacter infections in humans. A number of chemical or physical decontamination methods have been investigated to control the level of Campylobacter and other human pathogens on broiler carcasses including ozonation, super-chlorination, organic acids and steam pasteurization (Whyte et al., 2003). While Campylobacter spp. routinely demonstrate survival on broiler carcasses held under refrigeration (Stern, 1995), freezing is known to decrease the viability of some bacteria including Campylobacter. The loss of viability has been attributed to ice nucleation and dehydration. Stead and Park (2000) demonstrated that Campylobacter encounter oxidative stress during freezing and thawing and that superoxide dismutase plays an important role as a resistance mechanism for cells to overcome this stress. Studies, both in pure broth cultures (Humphrey and Cruickshank, 1985) and on naturally contaminated broiler carcasses (Stern et al., 1985), ground beef livers (Hänninen, M.-L., 1981) and artificially contaminated beef trimmings (Moorhead, 2002), which were frozen and thawed, showed reductions in levels of C. jejuni or C. coli. Moore et al. (2002) observed that 94% of fresh poultry samples (n=63) vs. 77% of frozen samples (n=44) indicated the reduction of Campylobacter spp. during the poultry freezing process. Lee et al. (1998) demonstrated that C. jejuni artificially inoculated onto chicken skin survives freezing under various atmospheric conditions. Their data did indicate a rapid reduction in survival during the first two weeks of '20°C storage. Campylobacteriosis reached epidemic proportions in Iceland in
Technical Abstract: In total, 215 commercially processed broiler carcasses were examined to determine optimum cultural enumeration, the effects of freezing, method of thawing, and duration of frozen storage on levels of Campylobacter spp. and fecal coliforms. Enumeration studies compared MPN procedures to direct plating onto selective mCCDA agar and indicated equivalency for quantitation of Campylobacter spp. Levels of Campylobacter and fecal coliforms were subsequently estimated by direct plating of carcass rinses. Freezing of naturally contaminated carcasses followed by storage at '20°C for 31, 73, 122 and 220 days showed statistically significant (P<0.05) reductions in Campylobacter counts initially as compared with counts found on fresh product. Among 5 lots of broilers, levels of Campylobacter on carcasses were reduced by log mean values ranging from 0.65 to 2.87 after freezing and 31 days of storage. Similar reductions due to freezing were not observed for fecal coliforms counts. The level of Campylobacter was reduced by approximately one log immediately after freezing, and remained relatively constant during the 31 to 220 days of frozen storage. The levels were constant during 7 days of refrigerated storage. After 31 days of frozen storage there was a reduced rate in reduction of counts among broilers thawed at 7°C as compared to thawing at 22°C with either cultural method (MPN and mCCDA). These findings warrant consideration of the public health benefits related to freezing contaminated poultry prior to commercial distribution to reduce Campylobacter exposure levels associated with contaminated carcasses.