Variation in Campylobacter Multilocus Sequence Typing Subtypes from Chickens as Detected on Three Plating Media

Prevalence and Subtype Characterization of Campylobacter in Ceca of Commercial Broiler Chickens at Processing - A 452 Flock, Seven-year Survey

Human Campylobacter infections have been associated with chicken and other poultry meat products. Environmental conditions such as temperature and season can affect Campylobacter recoverability from chicken meat products. In the presented study, we sought to investigate the relationship between ambient weather conditions and the isolation of Campylobacter from chicken flocks, as well as the subtype of these isolates. Campylobacter was isolated from the ceca of broilers collected in a commercial processing facility over 7 years, representing 452 flocks. Isolates were subjected to whole-genome sequencing and subtyping by multilocus sequence typing (MLST). Approximately 60% (269/452) of flocks sampled were positive for Campylobacter. There was no significant effect on the presence of detectable Campylobacter by month, season, temperature, or rainfall during grow-out or transportation. Sixty-eight different STs were detected; 45 C. jejuni and 23 C. coli. Diversity as measured by Shannon's diversity index was higher in the spring and fall than in mid-winter and summer. We concluded that in the warm temperate climate of the Southeastern U.S., seasonality does not affect the rate of Campylobacter isolation from broilers, but the diversity of isolates was higher in the milder spring and fall seasons.

Enrichment and Direct Plating for Detection of Campylobacter in Chicken Liver Rinse and Exudate

ABSTRACT

Foodborne campylobacteriosis has been traced to undercooked chicken liver dishes; thus, it is important to use the best available culture methods when testing for the presence of Campylobacter. We compared two Campylobacter enrichment broths-Bolton formulation and Neogen formulation-in combination with three selective plating media-Campy-Cefex, Campy-Line and RF Campylobacter agars-for detection of Campylobacter from fresh retail chicken livers. In each of three experiments, nine replicate tubs of chicken livers were sampled by drawing exudate and a pooled rinse of five whole liver lobes. Results are reported as number positive and compared by Fisher's exact test. In experiment 1, no combination of enrichment and plating media significantly outperformed another for detection of Campylobacter (P > 0.05); all tubs were found to include Campylobacter in both exudate and liver rinse. In experiment 2, serial dilutions of samples were plated before and after enrichment. Exudate was found to be significantly more likely than rinse to support detection of Campylobacter by direct plating (P < 0.05); most exudate samples included at least 10 CFU Campylobacter per mL. Enrichment improved detection from rinse, but not exudate; all enrichment and plating combinations resulted ≥1,000 CFU/mL from most enriched samples. In experiment 3, samples were diluted before enrichment to determine effect of enrichment on ever lower numbers of Campylobacter. Enrichment did not improve recovery of Campylobacter from exudate or undiluted rinse (P > 0.05). However, when rinse samples were diluted to lower Campylobacter numbers, enrichment improved detection (P < 0.05). Overall, all media combinations tested were equivalent for detection of Campylobacter from chicken livers; sensitivity for detection seemed to be increased by using liver exudate compared with a pooled rinse of liver lobes.

HIGHLIGHTS

Campylobacter subtypes detected in broiler ceca and livers collected at slaughter1

Foodborne campylobacteriosis has been linked to undercooked chicken liver. We have detected Campylobacter in chicken livers available at retail. The objective of the current project was to determine the prevalence and subtype of Campylobacter associated with livers and ceca of the same broiler carcasses at commercial slaughter. Within 2 min of commercial evisceration, we collected liver and ceca of one broiler carcass from each of 70 discreet flocks over a 12-mo period. Liver surface, liver internal tissue, and cecal contents were cultured for Campylobacter using standard methods. One example of the predominant colony type was selected from each positive sample for whole genome sequencing and multilocus sequence typing. We detected Campylobacter in at least one sample from 58 of 70 (83%) carcasses/flocks; 41 ceca, 57 liver surface samples, and 19 liver internal tissue samples were positive. For 11 of 18 carcasses from which all samples were positive, the predominant colony types were indistinguishable. However, some carcasses did have multiple subtypes of Campylobacter. Of carcasses with Campylobacter on the surface of the liver and within the ceca, it was more likely that the subtypes be the same than different (P < 0.01). However, Campylobacter subtypes detected in internal liver tissue were not more likely to be the same as those detected in ceca (P > 0.05). We detected different subtypes of Campylobacter from internal liver tissue and liver surface of seven broiler carcasses/flocks. Livers from a large percentage of broiler carcasses/flocks can have one or more subtypes of Campylobacter.

Multilocus Sequence Subtypes of Campylobacter Detected on the Surface and from Internal Tissues of Retail Chicken Livers

Foodborne campylobacteriosis has been traced to undercooked chicken liver. The objectives of this study were to determine the prevalence of Campylobacter associated with chicken livers at retail and to determine which subtypes are detected on the surface and in the internal tissues of the livers. Fifteen packages of fresh chicken livers, each representing a unique combination of processing plant and sell-by date, were collected at each of three retail grocery stores in Georgia. Three intact, undamaged livers per container ( n = 45) were selected and sampled using each three methods: outside swab, inside swab accessed by pressing through a heat-sterilized outer surface, and whole liver blended in enrichment broth. Each liver sample with 0.1 mL of exudate from packages was cultured for Campylobacter by plating on Campy-Cefex agar. The most prevalent Campylobacter colony type from each positive sample was subjected to whole genome sequencing and multilocus sequence typing. Campylobacter was detected in at least one sample from every package. Surface swabs were positive for 29 of 45 livers, but significantly fewer swabs of internal tissue were positive, 14 of 45 ( P < 0.01). Campylobacter was detected in 30 of 45 blended whole liver samples. Multiple subtypes were detected from eight livers. In four livers, a different subtype was dominant on the surface than was dominant internally. In one liver, three subtypes were detected. Various subtypes of Campylobacter can be readily isolated from fresh retail chicken livers; therefore, undercooked chicken livers pose a food safety risk.

Passage of Campylobacter jejuni and Campylobacter coli Subtypes through 0.45- and 0.65-Micrometer-Pore-Size Nitrocellulose Filters

Campylobacter can be difficult to recover from complex samples due to overgrowth by background bacteria. A 0.45- or 0.65-μm-pore-size filter overlaid on agar plates can be used as a means to separate Campylobacter from confounding non-Campylobacter cells, facilitating detection on solid plating media. It is unclear what percentage of cells in a Campylobacter suspension passes through a filter and results in visible colonies. The objective of this study was to compare the number of Campylobacter cells detected by the filter method with those detected by direct plating and determine if the filter method can be used to estimate cellular density of an unknown Campylobacter in suspension. Overnight liquid cultures of six subtypes of Campylobacter jejuni and six of Campylobacter coli, all originally detected in chicken samples, were used for this study. Motility of isolates was tested by using a stab into soft agar, incubating plates, and measuring colony size. Each subtype was applied to Campy-Cefex agar directly and through a 0.45- or 0.65-μm-pore-size filter. Filters were removed, plates were incubated, and colonies were counted; three replications were conducted. Mean recovery by direct plating was 8.3 log CFU/mL. Regardless of pore size, the overall mean number of Campylobacter detected by using the filter method was significantly less than that using direct plating (P < 0.05). The mean difference between direct plating and plating though a 0.65-μm-pore-size filter for motile Campylobacter was log 2.4 CFU/mL, with a 95% confidence interval of ±0.2 log CFU/mL.