Clinically Relevant Campylobacter jejuni Subtypes Are Readily Found and Transmitted within the Cattle Production Continuum but Present a Limited Foodborne Risk

Abstract

Increasing evidence exists for the role that cattle play in the epidemiology of campylobacteriosis. In this study, the prevalence and distribution of Campylobacter jejuni were longitudinally examined at the subspecies level in the beef cattle production continuum. Animals were subdivided into two groups: those that were not administered antibiotics and those that were administered the antimicrobial growth promoter chlortetracycline and sulfamethazine (AS700). Samples were longitudinally collected throughout the confined feeding operation (CFO) period and during the slaughter process, and C. jejuni was isolated and genotyped to assess subtype richness and to elucidate transmission dynamics from farm to fork. The bacterium was frequently isolated from cattle, and the bacterial densities shed in feces increased over the CFO period. Campylobacter jejuni was also isolated from digesta, hides, the abattoir environment, and carcasses. The administration of AS700 did not conspicuously reduce the C. jejuni densities in feces or within the intestine but significantly reduced the bacterial densities and the diversity of subtypes on abattoir samples. All cattle carried multiple subtypes, including clinically relevant subtypes known to represent a risk to human health. Instances of intra-animal longitudinal transmission were observed. Although clinically relevant subtypes were transmitted to carcasses via direct contact and aerosols, the bacterium could not be isolated nor could its DNA be detected in ground beef regardless of treatment. Although the evidence indicated that beef cattle represent a significant reservoir for C. jejuni, including high-risk subtypes strongly associated with the bovine host, they do not appear to represent a significant risk for direct foodborne transmission. This implicates alternate routes of human transmission. IMPORTANCE Limited information is available on the transmission of Campylobacter jejuni subtypes in the beef production continuum and the foodborne risk posed to humans. Cattle were colonized by diverse subtypes of C. jejuni, and the densities of the bacterium shed in feces increased during the confined feeding period. Campylobacter jejuni was readily associated with the digesta, feces, and hides of cattle entering the abattoir, as well as the local environment. Moreover, C. jejuni cells were deposited on carcasses via direct contact and aerosols, but the bacterium was not detected in the ground beef generated from contaminated carcasses. We conclude that C. jejuni bacterial cells associated with beef cattle do not represent a significant risk through food consumption and suggest that clinically relevant subtypes are transmitted through alternate routes of exposure.

Tetracycline Resistant Campylobacter jejuni Subtypes Emanating from Beef Cattle Administered Non-Therapeutic Chlortetracycline are Longitudinally Transmitted within the Production Continuum but are Not Detected in Ground Beef

“…Intestinal segments were aseptically excised and digesta was removed as described previously [30]. Feces and digesta were placed in a 10 times volume of CB and the sample homogenized.…”

“…Ground beef was stomached in 200 mL of CB for 2 min on high setting using a Stomacher 400 (Seward Laboratory Systems Inc.), and the suspension was concentrated by centrifugation as for the sponge samples. An aliquot (25 µL) of the homogenate/stomached suspension was spread in duplicate onto Campylobacter blood-free selective medium (CCDA) with CCDA selective supplement CM739 (CS; Oxoid Inc.), and KKA, and maintained in a microaerobic atmosphere at 42 • C for 48 and 72 h as described previously [30]. Samples from ground beef were enriched in Bolton Broth (Oxoid Inc.) with selective supplement, SR0183 (BBS; Oxoid Inc.) [30].…”

“…An aliquot (25 µL) of the homogenate/stomached suspension was spread in duplicate onto Campylobacter blood-free selective medium (CCDA) with CCDA selective supplement CM739 (CS; Oxoid Inc.), and KKA, and maintained in a microaerobic atmosphere at 42 • C for 48 and 72 h as described previously [30]. Samples from ground beef were enriched in Bolton Broth (Oxoid Inc.) with selective supplement, SR0183 (BBS; Oxoid Inc.) [30]. Where applicable, cell biomass from each of two colonies per colony morphology characteristic of Campylobacter were streaked onto KA, and maintained at 37 • C in a microaerobic atmosphere.…”

“…All recovered C. jejuni isolates were fingerprinted using a 40-locus comparative genomic fingerprinting (CGF) method [30,35]. To ascertain health risk of C. jejuni subtypes, the CGF40 profiles of tetracycline resistant and susceptible subtypes recovered from beef cattle and diarrheic human beings in the study region from 2004 to 2017 (n = 1171) were compared; the susceptibility of isolates recovered from people to tetracycline was determined using the same agar dilution method protocol with a breakpoint MIC of ≥16 µg/mL [25,36].…”

“…Campylobacter jejuni in/on feces, digesta, carcasses, and ground beef was quantified by PCR as described previously [30,38]. Briefly, a Stratagene Mx3005 (Stratagene Products, La Jolla, CA, USA) was used.…”