Background

It has long been known that beef and dairy cattle are a primary reservoir of E. coli O157:H7. Faith et al. (1996) and Hancock et al. (1994) showed that fecal material acts as the vehicle of transmission of E. coli O157:H7 from animal to animal and from animal to human. Gill et al. (1999) showed that carcass contamination is most likely to occur during the dehiding process when the exterior hide surface accidentally roles over and contaminates the previously sterile carcass surface. The present studies were conducted to identify chemical interventions that could potentially be used on the hide surface to minimize pathogenic contamination.

Although not federally approved for food contact surfaces, cetylpyridinium chloride (CPC) has reduced bacterial counts on beef carcasses by as much as 6 log CFU/cm² (Cutter et al., 2000). In addition, Ransom et al. (2002) demonstrated that CPC reduced E. coli O157:H7 populations by 4.8 and 2.1 log CFU/cm², respectively on beef adipose tissue and beef trimmings.

When CSU preliminary studies were first initiated, populations of E. coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes were reduced by 6 to 7 log CFU/cm² on hide surfaces; however, we realized that the residual CPC in the plated sample was preventing the bacteria from growing on the agar plates. Thus, subsequent studies were conducted using Dey-Engley Broth, which immediately stops the antimicrobial action of CPC. 

Hide samples were cut to approximately 50 cm², then inoculated with 8 log CFU/ml of a five-strain cocktail of E. coli O157:H7. Following inoculation, the bacteria were allowed 30 minutes to attach to the hide surface. After attachment, the samples were dipped and rotated in the CPC solution for 30 seconds; then, neutralizing broth was added to stop the antimicrobial activity of CPC. Bacterial populations were reduced immediately following treatment and, in general, reductions in E. coli O157:H7 and total bacterial populations were observed following the 30 second CPC treatment period. The effectiveness of CPC increased as the time following 30-second treatment period increased. For example, the reduction of E. coli O157:H7 increased from 2.1 log CFU/cm² after the 30-second treatment time to 3.3 log CFU/cm² after 30 minutes following the original CPC treatment (Table 1). Each sample from each time period was plated in duplicate and replicated twice.

A second study was conducted to determine if the length of exposure time in the CPC solution would affect the survival of both pathogen and total bacterial populations on the hide surfaces. Increasing the length of time before neutralization after 30 seconds of exposure during treatment application, increased (P < 0.05) the reduction of both pathogen and total bacterial populations by 0.9 log CFU/cm². Moreover, increasing the length of expose to the CPC solution, increased (P < 0.05) the effectiveness of CPC on E. coli O157:H7 and total bacterial populations. Unfortunately, the most commonly reported data on hides is for prevalence, rather than logarithmic quantification, of E. coli O157:H7, thus the level of pathogenic bacteria on beef hides during entry to the harvest facility is currently unknown. Further investigation of CPC on live animal hides is warranted and could prove to be beneficial in reducing the potential for bacterial contamination and ultimately foodborne illness. 

The stated objectives for this work were: To determine the efficacy of cetylpyridinium chloride (CPC) in reducing total plate count and pathogen populations on beef hide surfaces, as well as on subsequent carcasses.

Methodology

As cattle enter the incline “S”-ramp outside of the slaughter plant, they were divided in one of two treatment groups: (1) control or (2) CPC (1%) treated. When the cattle moved by the last section of the incline ramp, they were identified with livestock marking chalk (All-Weather PAINTSTICK®, LA-CO Industries, Elk Grove Village, IL) as being in either the control or CPC treated group so they would be easily identified for sampling later in the slaughter process. Once the cattle to be treated were identified, five were treated with 1% CPC. The  treatment was applied from the top of the rump, down to the cod/twist  (anal/hock area) area, using a hand held spray-washing system (The Fuller Brush Company, Great Bend, KS) with pressures of up to 50 psi and with a flow rate of 1 gallon per 5 seconds, as initially approved for this study by FSIS-USDA. One of the difficulties of applying the CPC treatment, was the variation of the speed of the animals as they moved by the treatment application station. Three to five animals were placed between treatments in order to prevent the control cattle from coming in contact with the treated cattle. Of the five animals that were designated as control or CPC treated, the one in the middle was sampled. As the animals that had been marked with the chalk went through the slaughter process, they were easily identified by the color of the chalk.  

Hides and carcasses were sampled using sponge-swabbing kits (International Bioproducts, Bothell, Wash.). Sponges were hydrated with 25 mL of Dey/Engley neutralizing buffer (Difco Laboratories, Detroit, Mich) in order to neutralize the effect of the CPC. Four hundred hide samples (200 control and 200 CPC treated) were collected at the first station in the dehiding area. Hide sponge samples were collected by swabbing a 100 cm² area of the rump on the pattern-mark. The same treated and control cattle which were sampled hide-on, were followed through the slaughter process, then sampled again using the MRU-MARC anal/hock sampling method. All samples (hides and carcasses) were analyzed for the presence or absence of E. coli O157:H7, and the quantification of Enterobacteriaceae and aerobic plate counts. Treatment effects of the CPC decontamination were evaluated by comparing numbers of samples testing positive for E. coli O157:H7 with those obtained for negative controls. In addition, Enterobacteriaceae populations and aerobic plate counts were enumerated for each sample to allow analysis of variance for treatment effects.  

Findings

Hides treated with CPC resulted in the reduction (P < 0.05) of aerobic plates counts (APC) and Enterobacteriaceae (EB) populations by 0.8 and 0.5 log CFU/cm², respectively, when compared to the control (non-treated) hides. In addition, the results were similar for carcasses, as shown by reductions in APC and EB populations of 0.7 and 0.6 log CFU/cm², respectively, when the hides were treated with CPC. With respect to isolation of E. coli O157:H7, sponge samples from hides treated with CPC resulted in significantly (P < 0.05) fewer positive samples than the controls, 11 and 29, respectively, for CPC treated versus control hides. With this, it could be speculated that there would be fewer E. coli O157:H7 positive carcass samples; conversely, there were significantly (P < 0.05) more positive carcasses when the hides were CPC treated than when they were not. In retrospect, it was possible that the fluidity of the CPC treatment allowed contamination to roll onto the carcass as the hide was opened, thus contaminating the carcass surface. More research should be conducted to determine the cause of this phenomenon.

Implications

Cetylpyridinium chloride was tested to determine its effectiveness as a pre-harvest animal wash. Data from this study show that it can significantly reduce the aerobic plate count populations, 

Enterobacteriaceae populations and the prevalence of E. coli O157:H7 on the hide surface. More research should be conducted to determine its ultimate effectiveness on the safety of beef products.