J. K. Northcutt

Variations in external and internal microbial populations in shell eggs during extended storage.

The current project was conducted to determine the microbial quality of commercially processed shell eggs during extended storage. Unwashed eggs were collected at the accumulator before entering the processing line. Washed eggs were retrieved after placement in flats. All eggs were stored on pulp flats at 4 degrees C for 10 weeks. Twelve eggs from each treatment were rinsed on the day of collection and during each week of storage. After rinsing, eggs were sanitized in ethanol, and contents were aseptically collected. Total aerobes, yeasts and molds, Enterobacteriaceae, and pseudomonads were enumerated from shell rinses and pooled egg contents. During storage, no differences were found between unwashed and washed eggs for Enterobacteriaceae and pseudomonads in either shell rinses or contents. No differences were found between treatments for population levels of total aerobes or yeasts and molds in the egg contents throughout the storage period. Significant differences between treatments were found at each week of storage for external shell contamination by total aerobes. The highest unwashed egg contamination occurred at week 8 of storage and the lowest was at weeks 0 and 1 of storage. The highest shell contamination with aerobic bacteria on the washed eggs was found at week 0 of storage and the lowest was at week 7. Yeast and mold contamination determined by shell rinses was also significantly different between treatments at each week of storage. Commercially washed eggs were significantly less contaminated than were unwashed eggs for the populations monitored.

Molecular Characterization of Listeria monocytogenes Isolated from a Poultry Further Processing Facility and from Fully Cooked Product

This study was undertaken to explore environmental sources of Listeria monocytogenes in a commercial chicken further processing facility and to compare the isolates obtained from this facility with others obtained from fully cooked product. In a survey conducted at the processing facility, 40 environmental sites (encompassing two production lines and representing areas in which raw and cooked products are processed) were cultured for L. monocytogenes. The resulting isolates were subjected to molecular subtyping by ribotyping, and these isolates were compared with 25 isolates collected by plant personnel from product contact surfaces and from fully cooked product. Eighty-nine environmental and product isolates were divided into 15 distinct ribogroups. Two ribogroups included isolates from fully cooked product; the members of these two ribogroups were subjected to further analysis by pulsed-field gel electrophoresis, resulting in four clusters. L. monocytogenes isolates from fully cooked product produced on line 1 were found to be indistinguishable from isolates collected from (i) drains on the raw-product side of line 1 and (ii) the floor surface in the cooked-product area of line 1. L. monocytogenes isolates from fully cooked product from line 2 were found to be indistinguishable from isolates collected from (i) the spiral freezer exit conveyor on line 2, (ii) raw product contact surfaces on line 1, and (iii) drains in the cooked-product area of line 1. These data suggest that L. monocytogenes can colonize a poultry further processing facility and eventually be transferred to fully cooked product.

Identification of Enterobacteriaceae from Washed and Unwashed Commercial Shell Eggs

To evaluate the effect of processing on the safety and quality of retail shell eggs, a storage study was conducted with unwashed and commercially washed eggs. This work demonstrated that commercial processing decreased microbial contamination of eggshells. To know which species persisted during storage on washed or unwashed eggs, Enterobacteriaceae isolates were selected and identified biochemically. For each of three replications, shell eggs were purchased from a commercial processing plant, transported back to the laboratory, and stored at 4 degrees C. Once a week for 6 weeks, 12 eggs for each treatment (washed and unwashed control) were rinsed in sterile phosphate-buffered saline. A 1-ml aliquot of each sample was plated onto violet red bile glucose agar with overlay and incubated at 37 degrees C for 24 h. Following incubation, plates were observed for colonies characteristic of the family Enterobacteriaceae. A maximum of 10 isolates per positive sample were streaked for isolation before being identified to the genus or species level using commercially available biochemical strips. Although most of the isolates from the unwashed control eggs belonged to the genera Escherichia or Enterobacter, many other genera and species were identified. These included Citrobacter, Klebsiella, Kluyvera, Pantoea, Providencia, Rahnella, Salmonella, Serratia, and Yersinia. Non-Enterobacteriaceae also recovered from the unwashed egg samples included Xanthomonas and Flavimonas. Very few washed egg samples were contaminated with any of these bacteria. These data provide useful information on the effectiveness of processing in removing microorganisms from commercial shell eggs.

Effect of dry air or immersion chilling on recovery of bacteria from broiler carcasses.

A study was conducted to investigate the effect of chilling method (air or immersion) on concentration and prevalence of Escherichia coli, coliforms, Campylobacter, and Salmonella recovered from broiler chicken carcasses. For each of four replications, 60 broilers were inoculated orally and intracloacally with 1 ml of a suspension containing Campylobacter at approximately 10(8) cells per ml. After 1 day, broilers were inoculated with 1 ml of a suspension containing Salmonella at approximately 10(8) cells per ml. Broilers were processed, and carcasses were cooled with dry air (3.5 m/s at -1.1 degrees C for 150 min) or by immersion chilling in ice water (0.6 degrees C for 50 min). Concentrations of E. coli, coliforms, Campylobacter, and Salmonella recovered from prechill carcasses averaged 3.5, 3.7, 3.4, and 1.4 log CFU/ml of rinse, respectively. Overall, both chilling methods significantly reduced bacterial concentrations on the carcasses, and no difference in concentrations of bacteria was observed between the two chilling methods (P < 0.05). Both chilling methods reduced E. coli and coliforms by 0.9 to 1.0 log CFU/ml. Air and immersion chilling reduced Campylobacter by 1.4 and 1.0 log CFU/ml and reduced Salmonella by 1.0 and 0.6 log CFU/ml, respectively. Chilling method had no effect on the prevalence of Campylobacter and Salmonella recovered from carcasses. These results demonstrate that air- and immersion-chilled carcasses without chemical intervention are microbiologically comparable, and a 90% reduction in concentrations of E. coli, coliforms, and Campylobacter can be obtained by chilling.

Impact of commercial processing on the microbiology of shell eggs.

Shell egg microbiology has been studied extensively, but little information is available on how modern U.S. processing conditions impact microbial populations. As regulations are being drafted for the industry, such information can be important for determining processing steps critical to product safety. Five different shell egg surface microbial populations (aerobic bacteria, yeasts and molds, Enterobacteriaceae, Escherichia coli, and Salmonella) were monitored at 12 points along the processing line (accumulator, prewash rinse, washer 1, washer 2, sanitizer, dryer, oiler, scales, two packer head lanes, rewash entrance, and rewash exit). Three commercial facilities were each visited three times, a total of 990 eggs were sampled, and 5,220 microbiological samples were subsequently analyzed. Although variations existed in concentrations of microorganisms recovered from each plant, the patterns of fluctuation for each population were similar at each plant. On average, aerobes, yeasts and molds, Enterobacteriaceae, and E. coli prevalence were reduced by 30, 20, 50, and 30%, respectively, by the end of processing. The microbial concentrations (log CFU per milliliter) in the egg rinse collected from packer head lanes were decreased by 3.3, 1.3, 1.3, and 0.5, respectively, when compared with those of rinses collected from eggs at the accumulator. Salmonella was recovered from 0 to 48% of pooled samples in the three repetitions. Higher concentrations of Salmonella were recovered from preprocessed than from in-process or ready-to-pack eggs. These data indicate that current commercial practices decrease microbial contamination of egg shell surfaces.

Microbiology of Broiler Carcasses and Chemistry of Chiller Water as Affected by Water Reuse

A study was conducted to determine the effects of treating and reusing poultry chiller water in a commercial poultry processing facility. Broiler carcasses and chiller water were obtained from a commercial processing facility which had recently installed a TOMCO Pathogen Management System to recycle water in sections 2 and 3 of two 3-compartment chillers. In this system, reused water is blended with fresh water to maintain the chiller volume. Carcasses were sampled prechill and postchill (final exit), and chiller water was sampled from the beginning and end of each of the 3 sections. Carcasses were subjected to a whole carcass rinse (WCR) in 0.1% peptone. Numbers of Escherichia coli (EC), coliforms (CF), and Campylobacter (CPY) were determined from the WCR and chiller water samples. Prevalence of Salmonella (SAL) was also determined on the WCR and chiller water samples. On average, prechill levels of bacteria recovered from rinses were 2.6, 2.9, and 2.6 log10 cfu/mL for EC, CF, and CPY, respectively. Ten out of 40 (25%) prechill carcasses were positive for SAL. After chilling, numbers of EC, CF, and CPY recovered from carcass rinses decreased by 1.5, 1.5, and 2.0 log10 cfu/mL, respectively. However, 9 out of 40 (22%) postchill carcasses were positive for SAL. When the chiller water samples were tested, counts of EC, CF, and CPY were found only in water collected from the first section of the chiller (inlet and outlet). Two of 4 water samples collected from the inlet of the first section tested positive for SAL. This study shows that fresh and reused water can be used to cool poultry in chiller systems to achieve a reduction in numbers of bacteria (EC, CF, and CPY) or equivalent prevalence (SAL) of bacteria recovered from broiler carcasses.

Enterobacteriaceae and Related Organisms Isolated from Shell Eggs Collected During Commercial Processing

In the United States, commercial shell eggs are washed and graded before retail. Since passage of the Egg Products Inspection Act in 1971, processing guidelines have been set to ensure that external and internal characteristics are maintained. However, less is known about how commercial processing affects the safety of shell eggs. To identify enteric bacteria entering plants and persisting throughout processing, eggs were collected from 3 US commercial shell egg-processing plants on 3 separate visits. On each plant visit, 12 eggs were collected from each of 12 sites along the processing line: accumulator, prewash rinse, first washer, second washer, sanitizer rinse, dryer, oiler, check detection/scales, 2 egg grader/packer head lanes, rewash belt entrance, and rewash belt exit. Each egg was sampled by a rinse technique, and the rinsate was plated onto violet red bile glucose agar with overlay for the detection and enumeration of Enterobacteriaceae. From each plate, up to 5 colonies were randomly selected and isolated for identification to genus or species by using biochemical tests. Several genera and species were detected at each of the 3 plants. Sites from which the greatest numbers of isolates were identified were those collected from eggs during preprocessing (accumulator, prewash rinse) or from eggs judged as dirty (rewash belt entrance or exit). Sites yielding the smallest number of isolates were those during or at the end of processing. Escherichia coli and Enterobacter spp. were isolated from each of the 9 plant visits. Other genera isolated from at least 1 of the 3 plants included Cedecea, Citrobacter, Erwinia, Hafnia, Klebsiella, Kluyvera, Leclercia, Morganella, Proteus, Providencia, Rahnella, Salmonella, and Serratia. Non-Enterobacteriaceae isolated and identified included Aeromonas, Chryseomonas, Listonella, Pseudomonas, Sphingobacterium, Vibrio, and Xanthomonas. All of the genera and species were recovered less frequently from fully processed eggs than from unwashed eggs, indicating that shell eggs are less contaminated with bacteria as a result of commercial washing procedures.

Pale poultry muscle syndrome

Muscle that exhibits a pale color, soft texture, and exudative nature (PSE) was first described by the swine industry. Some turkey breast muscle has been found to be lighter or paler than what is considered normal. A comparable phenomenon has also been observed in broiler chicken breast muscle. Similar to PSE pork, pale poultry muscles may have reduced water-holding capacity and higher drip loss than normal muscles. However, the lighter color poultry may also have normal water-holding and drip loss. Based on these findings, researchers have adopted the PSE term to describe pale avian muscle. The scientific literature describes porcine PSE as a much more severe meat quality defect than the poultry version. The genetic basis for the PSE syndrome between turkey and pork muscle also appears to differ. Finally, the halothane screening method used to detect PSE-susceptible live swine does not work when used to screen suspect turkeys or chickens. Most of the PSE-like avian muscle is usually chosen by researchers based on the color of the muscle. However, many factors affect muscle color and the literature shows substantial differences in research relative to the definition of pale and normal avian muscles. Therefore, we propose using other terminology than PSE when describing avian breast muscle that exhibits some degree of paleness, reduced water-holding capacity, and increased drip loss. Two recommendations are: pale chicken muscle or pale poultry muscle syndrome. Continued use of PSE to describe pale poultry meat may be misleading because the conditions in swine and avian resulting in the defect are not the same.

Shell Rinse and Shell Crush Methods for the Recovery of Aerobic Microorganisms and Enterobacteriaceae from Shell Eggs

Recovery of bacteria from shell eggs is important for evaluating the efficacy of processing and the quality and safety of the final product. Shell rinse (SR) techniques are easy to perform and widely used. An alternative sampling method involves crushing and rubbing the shell (CR). To determine the most appropriate method for recovering microorganisms from shell eggs, 358 shell eggs were collected from a commercial egg processor and sampled by SR and CR techniques. Total aerobic mesophiles and Enterobacteriaceae were enumerated on plate count and violet red bile glucose agar plates, respectively. Unwashed, in process, and postprocess eggs were evaluated in the study. Aerobic microorganism prevalence for eggshells sampled was similar for both methods (approximately 100%), but the log CFU per milliliter values were higher in the SR than the CR samples (3.2 and 2.2, respectively). Average Enterobacteriaceae recovery was similar for both methods (45 versus 40% for the SR and CR methods, respectively) when all eggs were considered together. This population was detected more often by SR when unwashed eggs were sampled (90 versus 56% for the SR and CR methods, respectively), equally by SR and CR for in-process eggs (30 versus 29.3% for the SR and CR methods, respectively), but more often by CR for postprocess eggs (10 versus 36% for the SR and CR methods, respectively). The SR technique was easier to perform and recovered larger numbers of aerobic organisms, particularly for unwashed eggs. However, the CR technique was more efficient for recovery of Enterobacteriaceae from postprocess eggs. Stage of shell egg processing may be an important consideration when choosing egg sampling methods.

Partitioning of external and internal bacteria carried by broiler chickens before processing

Broiler chickens from the loading dock of a commercial processing plant were sampled to determine the incidence and counts of coliforms, Escherichia coli, and pathogenic bacteria. Feathers were removed by hand from ten 6-week-old chickens from each of seven different flocks and rinsed in 400 ml of 0.1% peptone water. Heads and feet were removed and rinsed, and the picked carcass was also rinsed, each in 200 ml. The ceca, colon, and crop were aseptically removed and stomached separately in 100 ml of peptone water. Campylobacter was present in six of the seven flocks. Salmonella was isolated from 50 of the 70 carcasses, with at least 2 positive carcasses in each flock, and five-tube most-probable-number (MPN) assays were performed on positive samples. Significantly (P < 0.05) more coliforms and E. coli were found in the ceca than in the feathers, which in turn carried more than the other samples, but total external and internal counts were roughly equivalent. Counts of Campylobacter were higher in the ceca and colon than in the other samples. Salmonella was isolated in external samples from 46 of the 50 positive carcasses compared with 26 positive internal samples or 17 positives in the ceca alone. The total MPN of Salmonella was approximately equivalent in all samples, indicating that contamination was distributed through all external and internal sampling locations. Salmonella-positive samples did not carry higher counts of coliforms or E. coli, and there were no significant correlations between the indicators and pathogens in any sample. Campylobacter numbers in the ceca were correlated with Campylobacter numbers in the feathers and colon, but Salmonella numbers in those samples were not correlated. The pattern of bacterial contamination before processing is complex and highly variable.