New research from North Carolina State University has found that Campylobacter bacteria persist throughout poultry production - from farm to grocery shelves - and that two of the most common strains are exchanging genetic material, which could result in more antibiotic-resistant and infectious Campylobacter strains.
Campylobacter is a well-known group of foodborne bacteria, spread primarily through consumption of contaminated food products. In humans it causes symptoms commonly associated with food poisoning, such as diarrhea, fever and cramps. However, Campylobacter infections also constitute one of the leading precursors of Guillain-Barré syndrome, a serious complication that can cause permanent disability and paralysis. Poultry is a known reservoir of the bacteria.
"There are two strains of Campylobacter that we're concerned with: C. coli and C. jejuni," says Maj. Dawn Hull, Army veterinarian, current Ph.D. student at NC State and lead author of the study. "C. jejuni causes up to 90% of human Campylobacter infections, but the good news is that this strain is less likely to carry multidrug-resistant genes. C. coli is twice as likely to contain multidrug-resistant genes, but it's a less effective human pathogen. Multidrug resistant means that the bacteria have genes that are resistant to three or more antimicrobial classes."
Both strains are commonly found throughout the poultry production process in North Carolina, according to corresponding author Sid Thakur, professor of population health and pathobiology and director of global health programs at NC State and the College of Veterinary Medicine.
"Since Campylobacter has a fairly 'plastic' genome, the strains can exchange genetic material," Thakur says. "If C. coli starts to take in a lot of C. jejuni's genetic material and increases its virulence, then it will cause larger numbers of infections that are antibiotic resistant, which could become a big public health issue. Likewise, if C. jejuni takes up antibiotic-resistant genes from C. coli, the same thing happens."
The team sampled chicken and turkey from retail grocery stores across North Carolina during 2018-2019. They compared Campylobacter isolates from the meat to USDA samples taken from poultry farms and production facilities in North Carolina. C. coli was most prevalent on farms and production facilities, at 54% and 60% for chicken isolates respectively, while C. jejuni was found in 69% of retail chicken meat.
They then tested the isolates from food animals and meat for antimicrobial-resistant (AMR) genes and found that 90% of both C. coli and C. jejuni contained at least one AMR gene while 43% contained resistance genes to three or more antibiotic drug classes. Twenty-four percent of C. jejuni included resistance genes to fluoroquinolones, the "last line of defense" against Campylobacter.
Finally, the team noted the appearance of a significantly higher number of new Campylobacter strains - 21 - in 2019 compared to only two in 2018. This indicates extensive changes occurring in the Campylobacter genome that have the potential to increase its virulence and drug resistance profile.
"If you go to a supermarket and pick 10 different chicken breasts, four will have Campylobacter, and of those four at least one will have a fluoroquinolone-resistant Campylobacter," Thakur says. "This trend has been pretty consistent over the last 10 years. Seeing a sudden jump in resistant sequence types is concerning."
"This study shows that genomic exchange is happening between C. coli and C. jejuni, and that there is increasing antimicrobial resistance in Campylobacter found in N.C. poultry production," Hull says. "Campylobacter is the worldwide leading cause for foodborne illness, so tracking this exchange is crucial to preventing transmission and providing future treatments."
The research appears in PLOS ONE and was supported by the Food and Drug Administration (Grant # 1U01FD007145-01, National Antimicrobial Resistance Monitoring System) and the United States Department of Agriculture. Erin Harrell and Maria Correa of NC State and Arnoud van Vliet of the University of Surrey, U.K., also contributed to the work.
Note to editors: An abstract follows.
"Antimicrobial resistance and interspecies gene transfer in Campylobacter coli and Campylobacter jejuni isolated from food animals, poultry processing, and retail meat in North Carolina, 2018-2019"
Authors: Dawn Hull, Erin Harrell, Maria Correa, Siddhartha Thakur, North Carolina State University; Arnoud van Vliet, University of Surrey, U.K.
Published: Online Feb. 11, 2021 in PLOS One
The Center for Disease Control and Prevention identifies antimicrobial resistant (AMR) Campylobacter as a serious threat to U.S. public health due to high community burden, increased transmissibility, and limited treatability. The National Antimicrobial Resistance Monitoring System (NARMS) plays an important role in surveillance of AMR bacterial pathogens in humans, food animals and retail meats. This study investigated C. coli and C. jejuni from live food animals, poultry carcasses at production, and retail meat in North Carolina between January 2018-December 2019. Whole genome sequencing and bioinformatics were used for phenotypic and genotypic characterization to compare AMR profiles, virulence factors associated with Guillain-Barré Syndrome (GBS) (neuABC and cst-II or cst-III), and phylogenic linkage between 541 Campylobacter isolates (C. coli n=343, C. jejuni n=198). Overall, 90.4% (489/541) Campylobacter isolates tested positive for AMR genes, while 43% (233/541) carried resistance genes for three or more antibiotic classes and were classified molecularly multidrug resistant. AMR gene frequencies were highest against tetracyclines (64.3%), beta-lactams (63.6%), aminoglycosides (38.6%), macrolides (34.8%), quinolones (24.4%), lincosamides (13.5%), and streptothricins (5%). A total of 57.6% (114/198) C. jejuni carried GBS virulence factors, while three C. coli carried the C. jejuni-like lipooligosaccharide locus, neuABC and cst-II. Further evidence of C. coli and C. jejuni interspecies genomic exchange was observed in identical multilocus sequence typing, shared sequence type (ST) 7818 clonal complex 828, and identical species-indicator genes mapA, ceuE, and hipO. There was a significant increase in novel STs from 2018 to 2019 (2 in 2018 and 21 in 2019, p<0.002), illustrating variable Campylobacter genomes within food animal production. Introgression between C. coli and C. jejuni may aid pathogen adaption, lead to higher AMR and increase Campylobacter persistence in food processing. Future studies should further characterize interspecies gene transfer and evolutionary trends in food animal production to track evolving risks to public health.