Study of Thermophilic Campylobacter Contamination of a Broiler Batch at Slaughter

Background: Broilers are a reservoir of Campylobacter (C.), an important causal agent of gastroenteritis mostly associated to handling and consumption of broiler meat. The majority of broiler flocks are colonized by thermophilic Campylobacter at the slaughter age, and carcasses might be contaminated throughout the processing line. Since surveillance is crucial to evaluate and improve approaches to reduce Campylobacter spread during broiler processing, a cross-sectional study was carried out to detect the level of Campylobacter contamination in a broiler at slaughter. Materials, Methods & Results: Cloacal swabs, caeca and whole carcasses were taken from a broiler flock slaughtered in Southern Brazil. Samples were individually inoculated in Bolton Broth (BB) and incubated at 41.5 degrees C in a microaerobic atmosphere for 44 h, when the enriched culture was inoculated onto modified Charcoal Cefoperazone Deoxycholate Agar (mCCDA) and Campy-Cefex Agar (CCA) plates. All plates were incubated at 41.5 degrees C in the microaerobic atmosphere for 44 h. Aliquots of each enriched BB were collected and submitted to polymerase chain reaction (PCR), while the genetic relatedness of isolates was analyzed by pulsed-field gel electrophoresis (PFGE). A total of 3 (9.4%) cloacal swabs were positive for C. jejuni. No Campylobacter was isolated from any of the caecal contents or broiler carcasses analyzed. In addition, negative mCCDA and CCA plates showed an abundant growth of contaminant cells. The PCR assay detected all thermophilic Campylobacter reference strains tested and also the Arcobacter species. No amplified product was obtained from the non-related bacterial species analyzed. It was possible to identify 29 (90.6%) cloacal swabs, 32 (97.0%) caecal contents and 31 (100%) broiler carcasses Campylobacter-positive by PCR analysis. PFGE typing of the C. jejuni isolated resulted in two clearly distinguished genotypes which were grouped into different clusters. Discussion: The detection of C. jejuni in only few cloacal swabs sampled contrasts with higher frequencies of Campylobacter previously described in broilers. However, the enrichment culture of fecal samples might be compromised by the many competing non-target bacteria present, which may have prevented the detection of Campylobacter-positive samples. In addition, the BB and selective media containing cefoperazone might have allowed the growth of cefoperazone-resistant contaminant cells from fecal and carcasses samples, which masked Campylobacter cells onto mCCDA and CCA. To improve the detection of Campylobacter in broiler samples, alternative antimicrobial supplements or reduction of the time of enrichment has already been suggested. PCR showed a higher number of positive samples, which might reflect the increased ability of the PCR assay to detect either injured cells in conventional enrichment culture or Campylobacter that were masked by the proliferation of competing cells onto selective media used. The PCR assay was able to detect all the reference strains of thermophilic Campylobacter, but also the related Arcobacter species. However, the temperature of incubation of the enriched cultures associated to the selective pressure of the antimicrobials present in the BB restricts the growth of Arcobacter and the false-positive results observed using PCR. The subtypes of the C. jejuni strains isolated showed that the target broiler flock was simultaneously colonized by more than one C. jejuni strain which might be the result of introduction of Campylobacter from different sources at farm. PCR analysis showed high Campylobacter contamination level of the target flock at slaughter, pointing to the need for additional studies to investigate Campylobacter sources at broiler processing.