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Title: Passage of Campylobacter subtypes through 0.45 and 0.65 µm filters.

Author
item Berrang, Mark
item Meinersmann, Richard - Rick
item Cox Jr, Nelson

Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/17/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Introduction A 0.45 or 0.65 µm filter can be used as a means to separate Campylobacter from complex samples allowing 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. Purpose The objective of this study was to compare the number 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 suspension. Methods Overnight liquid cultures of five subtypes of C. jejuni and 5 of C. coli, all originally detected in chicken samples, were used for this study. Each subtype was applied to Campy-cefex agar directly, and through a 0.45 or 0.65 µm filter. All plates were allowed to dry for 45 minutes, filters were removed, plates were incubated, and colonies were counted; data is presented as log cfu/mL. Three replications were conducted for all 10 isolates. Results Mean recovery by direct plating was 8.1 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) : 5.4 log cfu by 0.45 µm and 5.5 with the 0.65 µm filter. When analyzed by subtype, significant differences (P<0.05) in ability to travel through the filter was noted, ranging from 3.0 to 6.3 log cfu/mL. Significance The number of Campylobacter cells that can pass through a filter and make a colony on underlying solid media is dependent on subtype. The filter method does not appear to be reliable for determination of actual numbers of an unknown Campylobacter per mL.

Technical Abstract: Introduction A 0.45 or 0.65 µm filter can be used as a means to separate Campylobacter from complex samples allowing 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. Purpose The objective of this study was to compare the number 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 suspension. Methods Overnight liquid cultures of five subtypes of C. jejuni and 5 of C. coli, all originally detected in chicken samples, were used for this study. Each subtype was applied to Campy-cefex agar directly, and through a 0.45 or 0.65 µm filter. All plates were allowed to dry for 45 minutes, filters were removed, plates were incubated, and colonies were counted; data is presented as log cfu/mL. Three replications were conducted for all 10 isolates. Results Mean recovery by direct plating was 8.1 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) : 5.4 log cfu by 0.45 µm and 5.5 with the 0.65 µm filter. When analyzed by subtype, significant differences (P<0.05) in ability to travel through the filter was noted, ranging from 3.0 to 6.3 log cfu/mL. Significance The number of Campylobacter cells that can pass through a filter and make a colony on underlying solid media is dependent on subtype. The filter method does not appear to be reliable for determination of actual numbers of an unknown Campylobacter per mL.