Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2017
Publication Date: 11/15/2017
Citation: Berrang, M.E., Meinersmann, R.J., Cox Jr, N.A. 2017. Passage of Campylobacter jejuni and Campylobacter coli subtypes through 0.45 and 0.65 µm pore size nitro-cellulose filters. Journal of Food Protection. 80(12):2029-2032. https://doi.org/10.4315/0362-028X.JFP-17-211.
Interpretive Summary: Campylobacter is a human bacterial pathogen that has been associated with poultry and poultry meat products. This organism can be difficult to detect in samples that have a high number of non-Campylobacter background bacteria. A method has been developed to separate Campylobacter from other bacteria by use of a filter placed on top of the nutrient plating media. A sample is applied to the filter and Campylobacter, which is highly motile, can wiggle through he filter while most other bacteria can not. It is not clear what percentage of a population of Campylobacter can pass thought the filter or if all subtypes of Campylobacter can pass to the same extent. A study was conducted to compare twelve different subtypes of Campylobacter for passage through filters. Each subtype was applied to either a 0.45 or 0.65 µm pore size filter. Numbers detected were compared to those detected by traditional methods. Regardless of pore size, the overall mean number of Campylobacter detected using the filter method was significantly less than direct plating (P<0.05). The mean difference between direct plating and plating though a 0.65 µm filter for motile Campylobacter was log 2.4 CFU/mL with a 95% confidence interval of ± 0.2 log CFU/mL. These findings will allow researchers using the filter technique to more accurately estimate Campylobacter numbers in complex highly contaminated samples.
Technical Abstract: 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 pass through a filter and result in visible colonies. The objective of this study was to compare the number of Campylobacter cells detected by the filter method to those detected by direct plating and determine if the filter method can be used as a means to estimate cellular density of an unknown Campylobacter in suspension. Overnight liquid cultures of six subtypes of C. jejuni and six of C. coli, all originally detected in chicken samples were used for this study. Motility of isolates was tested 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 using the filter method was significantly less than 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.