Dairy Cattle, a Potential Reservoir of Human Campylobacteriosis: Epidemiological and Molecular Characterization of Campylobacter jejuni From Cattle Farms

Abstract

Campylobacter jejuni is a major foodborne pathogen that is increasingly found worldwide and that is transmitted to humans through meat or dairy products. A detailed understanding of the prevalence and characteristics of C. jejuni in dairy cattle farms, which are likely to become sources of contamination, is imperative and is currently lacking. In this study, a total of 295 dairy cattle farm samples from 15 farms (24 visits) in Korea were collected. C. jejuni prevalence at the farm level was 60% (9/15) and at the animal level was 23.8% (68/266). Using the multivariable generalized estimating equation (GEE) model based on farm-environmental factors, we estimated that a high density of cattle and average environmental temperature (7 days prior to sampling) below 24°C affects the presence and survival of C. jejuni in the farm environment. Cattle isolates, together with C. jejuni from other sources (chicken and human), were genetically characterized based on analysis of 10 virulence and survival genes. A total of 19 virulence profile types were identified, with type 01 carrying eight genes (all except hcp and virB11) being the most prevalent. The prevalence of virB11 and hcp was significantly higher in isolates from cattle than in those from other sources (p < 0.05). Multilocus sequence typing (MLST) of C. jejuni isolates from three different sources mainly clustered in the CC-21 and CC-48. Within the CC-21 and CC-48 clusters, cattle isolates shared an indistinguishable pattern with human isolates according to pulsed-field gel electrophoresis (PFGE) and flaA-restriction fragment length polymorphism (RFLP) typing. This suggests that CC-21 and CC-48 C. jejuni from dairy cattle are genetically related to clinical campylobacteriosis isolates. In conclusion, the farm environment influences the presence and survival of C. jejuni, which may play an important role in cycles of cattle re-infection, and dairy cattle represent potential reservoirs of human campylobacteriosis. Thus, environmental management practices could be implemented on cattle farms to reduce the shedding of C. jejuni from cattle, subsequently reducing the potential risk of the spread of cattle-derived C. jejuni to humans through the food chain.

Keywords: Campylobacter jejuni; dairy cattle farms; molecular subtyping; prevalence; risk factor analysis; virulence genes.

FIGURE 1

UPGMA dendrogram based on virulence profile types. Virulence-associated genes for each type are indicated in different colors for each gene. Blank, not detected.

FIGURE 2

Proportion of MLST clonal complexes in each source. UA, unassigned ST; NT, non-typable ST (including eight different non-typable STs).

FIGURE 3

Clonal distribution analysis of C. jejuni isolates from all three sources. (A) Minimum spanning tree based on MLST data from 146 strains. Each number represents a sequence type, and the size of the node indicates the number of strains belonging to the ST (red: cattle, green: chicken, and purple: human). A bold solid line indicates that there is one allele difference between STs, and a thin solid line indicates that two and three alleles are different according to the length. Four to six allele differences are represented by a wide-interval dotted line, and seven are indicated by a narrow-interval dotted line. Nodes with fewer than two different alleles have been placed in the same cluster. Each cluster contains at least five entries and at least one node. The number shows the sequence type of each node. The color of the shadow represents the major source of the cluster, while a gray shadow indicates no primary source. (B) UPGMA dendrogram based on 51 different STs identified through MLST in a total of 146 strains, and detection rate of 10 virulence-associated genes of C. jejuni belonging to each ST. Pie chart shows the number of strains belonging to each ST (red: cattle, green: chicken, and purple: human), and the major CC is indicated by a thick, solid, colored line and the ST background color. In addition, the positivity rates of pathogenicity-associated genes in the strains belonging to each ST are shown.

FIGURE 4

UPGMA dendrogram based on PFGE and flaA-RFLP band pattern composite analysis for strains belonging to CC-21 and CC-48. (A) Strains belonging to CC-21. (B) Strains belonging to CC-48. Dendrograms were generated based on 2% optimization and 1.5% tolerance based on unweighted pair group method with arithmetic mean. Boxes indicate clusters created based on 90% similarity. The letter next to the farm number indicates the visit number (a – first visit and b – second visit).