Campylobacter jejuni in Poultry: Zoonotic Risks, Food Safety, and Thermophilic Characteristics

Introduction

Campylobacter jejuni is a Gram-negative, microaerophilic, thermophilic bacterium recognized as a leading cause of bacterial gastroenteritis worldwide, with poultry serving as the principal reservoir and vector for human infection [1, 44, 49, 66]. The organism colonizes the intestinal tract of avian species, particularly chickens and turkeys, without inducing clinical disease, resulting in high shedding rates and contamination of carcasses during processing [2, 3, 4]. The zoonotic potential of C. jejuni is amplified by its ability to survive across the poultry production continuum, from farm to fork, and by the emergence of multidrug-resistant strains [5, 6, 26]. This review provides a detailed examination of the thermophilic characteristics, colonization biology, food safety implications, antimicrobial resistance profiles, and intervention strategies associated with C. jejuni in poultry.

Taxonomy and Thermophilic Characteristics

Campylobacter jejuni belongs to the family Campylobacteraceae within the order Campylobacterales [44]. It is classified as a thermophilic campylobacter due to its optimal growth temperature of 42 degrees Celsius, which corresponds to the core body temperature of avian hosts [44, 110]. The organism requires microaerobic conditions (5% oxygen, 10% carbon dioxide, 85% nitrogen) and is strictly fermentative, utilizing amino acids and tricarboxylic acid cycle intermediates rather than carbohydrates as carbon sources [49, 132].

Thermotolerance in C. jejuni is mediated by the ClpB chaperone, which functions as a protein disaggregase independent of the DnaK system [110]. ClpB enables the bacterium to withstand heat stress encountered during poultry processing, such as scalding at 54 degrees Celsius [110]. Multilocus sequence typing (MLST) clonal complexes (CCs) CC-443 and CC-607 are overrepresented among heat-tolerant strains, suggesting a phylogenetic association with thermotolerance [110]. Additionally, aerotolerance varies among isolates: hyperaerotolerant strains exhibit less than a 2-log reduction in viability after 120 hours of aerobic incubation at 37 degrees Celsius, whereas non-aerotolerant strains decline more rapidly [7, 134]. Encapsulated iron availability influences growth kinetics under iron-limited conditions, further affecting survival in the poultry gastrointestinal tract [135].

Biofilm formation is a critical survival strategy for C. jejuni in poultry processing environments. The organism forms biofilms on stainless steel, polyethylene, and polystyrene surfaces, with significantly higher cell densities and biofilm density at 42 degrees Celsius compared to room temperature, regardless of oxygen tension [80, 96]. Flagellar proteins (FlaA, FlaB, FlaG) and adhesins (CadF, FlpA) are essential for biofilm development [56, 88]. Mixed-species biofilms containing Salmonella Enteritidis, Escherichia coli, and C. jejuni are common on slaughterhouse surfaces, with C. jejuni adhesion being lower than that of E. coli or Salmonella but still sufficient to enable persistence [86, 92].

Colonization of the Poultry Gastrointestinal Tract

Campylobacter jejuni colonizes the avian cecum and colon without causing overt pathology, establishing high bacterial loads often exceeding 10^8 colony-forming units per gram of cecal content [4, 44, 133]. Colonization occurs via oral ingestion of contaminated feed, water, or litter, with bird-to-bird transmission through the fecal-oral route [4, 128]. The bacterium adheres to intestinal epithelial cells using surface adhesins such as CadF, FlpA, and JlpA, and subsequently invades via the Type VI secretion system and flagellar export apparatus [56, 71, 76].

The cecal microbial community composition influences colonization dynamics. Pre-existing microbiota diversity, particularly the presence of Lactobacillus species, can reduce C. jejuni loads [4, 122]. Co-colonization with Salmonella spp. enhances C. jejuni survival under aerobic conditions through inter-species interactions [138]. Age-related susceptibility varies: young broilers (less than 3 weeks old) are less readily colonized, but once colonized, they shed high numbers for several weeks [8, 44]. Water disinfection programs using hydrogen peroxide and peracetic acid reduce cecal C. jejuni counts and translocation to the liver [73].

Zoonotic Transmission Routes

Human campylobacteriosis is primarily foodborne, with undercooked poultry meat accounting for 50% to 80% of sporadic cases [9, 32, 48, 49]. Contamination occurs at multiple points: on-farm colonization leads to carcass contamination during slaughter, and cross-contamination of ready-to-eat foods occurs through kitchen utensils and cutting boards [3, 10, 94]. Direct contact with infected poultry, particularly in backyard flocks and live bird markets, constitutes a non-foodborne transmission route [11, 33, 37, 72]. Quantitative risk assessments have estimated that the probability of infection per serving of street-vended poultry can exceed 10^-3, with predicted illness rates of over 10^6 cases per population [94].

Children, the elderly, and immunocompromised individuals are at elevated risk, with severe manifestations including bloody diarrhea, reactive arthritis, and neurological sequelae such as Guillain-Barre syndrome, which is associated with lipooligosaccharide ganglioside mimicry [65, 66]. Longitudinal studies in Ethiopia, Uganda, and Cambodia have identified poultry density, consumption patterns, and hygiene practices as key risk factors for human infection [5, 10, 31, 34].

Food Safety: Prevalence and Contamination in Poultry Products

The prevalence of C. jejuni in broiler flocks at slaughter is high across geographic regions. In a longitudinal study in the southeastern United States, prevalence exceeded 90% in some integrated complexes [8]. In Ecuador, 95.5% of cecal samples from poultry farms and 72.5% of retail chicken carcasses were positive for thermophilic Campylobacter, with C. coli dominating in some settings and C. jejuni in others [78]. In Nigeria, 20% of broiler fecal samples yielded Campylobacter, with C. coli more frequent than C. jejuni [74]. A meta-analysis of Nigerian studies reported pooled prevalence estimates of 18.5% across food-producing animals and humans [9].

Chicken livers constitute a particular risk: in Spain, 77.9% of surface liver samples and 35.7% of inner tissue samples were positive for Campylobacter, with C. jejuni as the predominant species [109]. Translocation from ceca to liver was demonstrated by identical RFLP profiles in paired samples [109]. Eggshells can also harbor viable C. jejuni, with cross-contamination to egg white (68%) and yolk (14%) occurring during manual separation using the shell [120].

Slaughterhouse practices influence contamination levels. Chilling reduces bacterial counts, and backyard slaughterhouses that do not incorporate ice exhibit higher contamination than commercial facilities [124]. Adhesion to stainless steel and plastic surfaces is a major concern; predictive models have been developed to simulate biofilm removal using citric acid and benzalkonium chloride [86, 92].

Antimicrobial Resistance in Poultry Isolates

Antimicrobial resistance (AMR) in C. jejuni is a severe and growing problem [6, 66]. Resistance to fluoroquinolones (ciprofloxacin) and tetracyclines is common globally, with rates frequently exceeding 80% in poultry isolates [2, 12, 7, 77, 95, 102]. Macrolide resistance, particularly to erythromycin, is more variable but can exceed 40% in some regions [5, 74, 77]. Multidrug resistance (MDR), defined as resistance to three or more antimicrobial classes, has been detected in 18% to 97% of poultry isolates depending on the study [2, 7, 74, 77].

The genetic basis of AMR in C. jejuni involves point mutations, acquired resistance genes, and efflux pumps. Fluoroquinolone resistance is primarily conferred by the T86I mutation in GyrA, with a rare T86V variant also reported [57, 102]. Tetracycline resistance is mediated by the tet(O) gene, which encodes a ribosomal protection protein [57, 95]. The CmeABC efflux pump, particularly the RE-CmeABC variant, contributes to multidrug resistance, including reduced susceptibility to fluoroquinolones, macrolides, and tetracyclines [13, 60]. Beta-lactam resistance is associated with BlaOXA genes, with BlaOXA-61 and BlaOXA-184 being highly prevalent [93, 98, 102]. Genes conferring resistance to phenicols and oxazolidinones (optrA, fexB) have been detected in avian C. jejuni in Tunisia, indicating interspecies gene transfer from Gram-positive bacteria [89]. The lnu(C) gene, encoding lincosamide resistance, is globally distributed in C. jejuni from food animals and humans, with ST573 as a predominant genotype [111].

Horizontal transfer of AMR determinants between C. jejuni and C. coli is frequent, as evidenced by the sharing of CmeRABC alleles and the presence of identical sequence types across species [60, 127]. The detection of carbapenemase genes (NDM, OXA-48, VIM) in avian Campylobacter isolates in Tunisia represents an alarming development [14].

Virulence Factors and Pathogenesis

Campylobacter jejuni possesses a repertoire of virulence factors that enable colonization and cause disease in humans. Adhesins (CadF, FlpA, JlpA, PebA) facilitate binding to fibronectin and other extracellular matrix components [56, 84, 100]. Flagella mediate motility and also function as a secretion system for invasion proteins [99, 125]. The cytolethal distending toxin (CDT) operon (cdtA, cdtB, cdtC) is nearly universal in C. jejuni isolates from poultry, with detection rates of 100% for all three genes in some studies [88, 99]. The invasion-associated gene virB11 is present in a variable proportion of isolates (0% to 74%), with poultry isolates often showing higher carriage than human isolates [84, 100].

The HtrA protease, expressed on the bacterial surface, cleaves tight junction proteins (occludin, claudin-8) and adherens junction proteins (E-cadherin), enabling paracellular transmigration [71]. Capsular polysaccharide and lipooligosaccharide genes, including those involved in ganglioside mimicry (neuA1, cstIII), are associated with strains that cause Guillain-Barre syndrome [15, 57, 106]. The Type VI secretion system, marked by the hcp gene, is present in some C. jejuni strains and absent in C. coli from the same poultry sources [69].

Molecular Detection and Genotyping

Culture-based isolation of C. jejuni from poultry samples is achieved using selective media such as modified charcoal-cefoperazone-deoxycholate agar, often with enrichment in Bolton broth [85, 105]. The ISO 10272:2017 protocol is standard, but overgrowth by Extended-Spectrum Beta-Lactamase-producing E. coli may require tazobactam supplementation at 4 mg/L for effective isolation [130]. Real-time PCR targeting the mapA or hipO genes enables rapid quantification, with limits of detection as low as 2.56 log10 CFU/mL in enriched samples [105, 114].

Genotyping methods provide insight into the population structure and transmission dynamics of C. jejuni in poultry. MLST based on seven housekeeping genes has identified numerous sequence types and clonal complexes, with CC-21, CC-45, CC-257, CC-443, and CC-828 frequently isolated from poultry sources [57, 68, 121, 131]. Whole-genome sequencing and core-genome MLST offer higher resolution and have revealed geographical clustering of C. coli (dominated by ST-828 complex) versus more diffuse distribution of C. jejuni across South and Southeast Asia [68]. Pulsed-field gel electrophoresis and ERIC-PCR are also employed for subtyping [75, 125]. Rapid on-site sequencing using portable devices can identify C. jejuni in less than five hours, enabling real-time surveillance at the farm level [137].

Control Strategies

Reducing C. jejuni colonization in poultry is a key target for food safety interventions. Vaccination approaches include subunit vaccines (FlpA, glycoconjugates), outer membrane vesicles, and recombinant Lactococcus lactis based multivalent vaccines [16, 61, 82, 104, 123, 136]. While some vaccines induce IgA responses and reduce cecal colonization by 1 to 3 log10, results have been inconsistent across trials, likely due to antigenic diversity and host-specific variables [82, 123]. Polymyxin B treatment of outer membrane vesicles reduces endotoxicity without compromising immunogenicity [136].

Probiotics and feed additives are promising alternatives. Lactobacillus salivarius SMXD51 reduces C. jejuni loads in broilers [30]. Leuconostoc mesenteroides and other lactic acid bacteria inhibit growth in vitro through organic acid production [62]. Fermented rapeseed meal reduces caecal C. jejuni concentration and downregulates L-tryptophan and L-histidine biosynthesis pathways [122]. Hyperimmunized egg yolk antibodies (IgY) at 0.5% dietary inclusion significantly lower cecal C. jejuni counts and improve intestinal villus morphology [58].

Bacteriophage therapy using broad-host-range phages (e.g., CBP1, CBP2) lyse both C. jejuni and C. coli and reduce loads on artificially contaminated chicken meat [107]. Phage cocktails have been efficacious in Galleria mellonella models and are being developed for poultry biocontrol [112]. Metallic nanoparticles, including Al2O3 and ZnO, exhibit antimicrobial activity against planktonic and biofilm-associated C. jejuni, with additive and synergistic effects when combined with plant-derived compounds like carvacrol [54, 55].

Biosecurity measures on farms, including stringent hygiene, water treatment, and prevention of carryover from previous flocks, are critical for reducing colonization [53, 128]. Mathematical models integrating cold tolerance data into quantitative microbial risk assessment are being developed to refine performance objectives for C. jejuni in poultry meat [59, 79].

flowchart TD
    A[Poultry flock on farm] --> B[Biosecurity measures]
    B --> C{Colonization by C. jejuni?}
    C -->|Yes| D[Cecal shedding >10^8 CFU/g]
    C -->|No| E[Low prevalence at slaughter]
    D --> F[Slaughter and processing]
    F --> G[Carcass contamination]
    G --> H[Chilling and intervention steps]
    H --> I{Pathogen reduction achieved?}
    I -->|Yes| J[Retail meat with low load]
    I -->|No| K[High-risk product]
    J --> L[Consumer handling and cooking]
    K --> L
    L --> M[Risk of human campylobacteriosis]
    M --> N[Surveillance and AMR monitoring]
    N --> O[One Health feedback loop to farm]

Summary of Key Data from Selected Studies

Conclusion

Campylobacter jejuni remains a major zoonotic pathogen associated with poultry production, characterized by its thermophilic growth, ability to form biofilms, and high prevalence in broiler flocks worldwide. The increasing rates of multidrug resistance, including to clinically important antibiotics, underscore the need for integrated control measures that encompass farm biosecurity, vaccination, probiotics, bacteriophage therapy, and improved slaughterhouse hygiene. Continuous molecular surveillance using high-resolution typing methods is essential for tracking the dissemination of virulent and resistant strains along the food chain and for informing One Health interventions aimed at reducing the burden of campylobacteriosis.

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Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.