Controlling Listeria in hatcheries and plants

Listeria is rare on the farm, but when it enters the processing plant it can potentially contaminate equipment and other birds.

Listeria contamination is only infrequently associated with the farm and is carried into the processing plant by live broilers. (Dr_Microbe | BigStock.com)
Listeria contamination is only infrequently associated with the farm and is carried into the processing plant by live broilers. (Dr_Microbe | BigStock.com)

Listeria is rare on the farm, but when it enters the processing plant it can potentially contaminate equipment and other birds.

Listeria

Listeriosis is uncommon in poultry. It rarely causes morbidity or mortality during commercial broiler production.

Earlier research conclusively shows the hatchery is an important source of Salmonella in chicks and the grow-out house. These findings led us to wonder if a commercial hatchery may contribute to the colonization of live broilers with Listeria monocytogenes and if live broilers may introduce L. monocytogenes to a commercial slaughter plant.  

Additionally, we wanted to measure the potential for increased prevalence of L. monocytogenes on broiler carcasses due to commercial processing and presentation at retail. We conducted two industry surveys separated by approximately five years to find out.

Hatchery sampling

In the first project, we conducted seven replicate sampling trips to three commercial broiler hatcheries in Georgia. On each trip, 10 to 20 eggshell samples, each consisting of two shell halves, and 10 to 20 soiled chick transport tray pads were collected for a total of 100 of each sample type. Conventional cultural methodology was used to identify presumptive Listeria spp. positive samples.  

Isolates were further confirmed as L. monocytogenes by hemolysis on horse blood overlay plates, CAMP reaction on 5% sheep blood plates, and positive results on a Remel Micro-ID Listeria identification system. Results from the hatchery sampling are presented in Table 1. Six of 100 eggshell samples and one of 100 chick pad samples were positive for L. monocytogenes.

Considering that our cultural methods are sensitive and each chick pad is a screen of 100 baby chicks, it appears the hatchery is not a critically important source of L. monocytogenes for day-old chicks. It’s possible the slightly higher prevalence of L. monocytogenes noted on eggshell samples than on chick pads is more a function of environmental contamination than of hen or chick colonization.  

Plant sampling

We collected samples in two different commercial broiler slaughter plants. For this part of the project, we collected ceca and rinses from the pre-scald carcasses – representing what entered the plant with the live birds – as well as rinses from post-chill carcasses to determine any change in L. monocytogenes prevalence due to passage through the processing plant.

In total, 115 ceca and pre-scald carcasses were tested while 105 post-chill carcasses were tested. All samples were cultured, and suspect isolates confirmed as L. monocytogenes as described above.  

Processing plant results from the first project are presented in Table 2. We found one positive out of 115 feathered carcass rinses. None of the ceca yielded L. monocytogenes. However, 23% of post chill carcasses were positive for L. monocytogenes suggesting an amplification of prevalence along the processing line. A snapshot of carcasses at retail revealed 40% of fresh whole carcasses tested were positive for L. monocytogenes.  

Follow-up study

As part of a follow-up study conducted five years later, the same two plants were surveyed using similar methods.

In the interim, both plants updated their processing parameters with increased use of antimicrobial processing aids. One plant also underwent a substantial renovation including new processing equipment.

The data from the second study in Table 3 shows an increase in prevalence of L. monocytogenes on broiler meat products due to processing, which was lesser than previously reported in the same two slaughter plants.

Conclusions    

From these data, we conclude Listeria contamination is only infrequently associated with the farm and is carried into the processing plant by live birds. However, once in the plant, Listeria may be able to contaminate equipment and the processing plant environment, resulting in cross-contamination of other carcasses.  

If present, L. monocytogenes may persist on broiler meat products during retail display and potentially contaminate the kitchen. If processors are aware of the problem and take steps to thoroughly clean, renovate and update processing procedures, L. monocytogenes can be controlled in broiler slaughter plants.


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