Scientists show some bacteria decrease during poultry processing

Researchers have assessed the impact of processing on the presence and transfer of antimicrobial resistant bacteria on chicken meat.

Findings showed that while Campylobacter and E. coli were present in birds entering the plants, their presence and numbers significantly declined along the poultry processing line, especially following procedures such as defeathering and evisceration.

Previous studies looking at the relationship between antimicrobial resistant (AMR) bacteria on incoming birds and outgoing meat appear to show that AMR and antimicrobial resistance genes (ARGs) are connected to incoming birds, so are related to farm drivers rather than contamination from equipment within a plant.

In the current work, funded by the Food Standards Agency (FSA), resistance of Campylobacter isolates to five antimicrobial agents and E. coli isolates against 11 antimicrobials were tested. Campylobacter showed the highest resistance to tetracycline and lowest to erythromycin, while E. coli had high resistance to ampicillin and low to chloramphenicol. Notably, 7 percent of Campylobacter and 60 percent of E. coli isolates were resistant to three or more antimicrobial classes, indicating multidrug resistance (MDR).

Two studied sites
Of the 376 samples collected from the poultry plants, 65.1 percent were positive for Campylobacter and 95.6 percent were positive for E. coli. Chicken litter showed the highest levels for both bacteria. Campylobacter decreased from samples along the processing stages, to non-detectable levels while E. coli remained detectable in samples from later stages, despite a general decrease.

The study took samples along the processing chain of two large scale UK chicken sites producing whole chickens and chicken meat for major retailers on three occasions in March, June, and October into November 2023. The first site had a line speed of 217 birds per minute and the second ran at 175 birds per minute. June datasets showed higher contamination levels compared to October or November.  

“The consistent differences between sites and seasons suggest that processors should consider both location-specific factors (such as equipment design, processing methods, or local environmental conditions) and seasonal variations when developing and implementing food safety measures,” according to the research.

Steam was used to reduce pathogen contamination on chicken carcasses at both factories. The number of farms supplying birds on each visit ranged from five to seven.

Whole Genome Sequencing (WGS) analysis of Campylobacter jejuni and E. coli isolates revealed genetic diversity across sampling points and periods, with E. coli showing greater variability in sequence types (STs). Five Campylobacter jejuni STs, including ST 6175, which was most prevalent, were identified. E. coli isolates demonstrated high genetic diversity with 36 STs identified, including STs 10, 155, and 6448.

Samples, including swabs, liquids, and neck skin, were collected from various stages of poultry processing. Each sample was analyzed for the presence, levels and AMR characteristics of Campylobacter and E. coli isolates. WGS was then performed on some isolates to evaluate the presence of ARGs.

“We were able to conclude that the target organisms were readily recovered from the process chain at early stages but following several identified processing stages reduced numbers of Campylobacter and E. coli were recovered,” said researchers.

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