C-EnterNet 2007 Annual Report

National Integrated Enteric Pathogen Surveillance Program

Appendix C: Enumeration Results

TABLE C: Enumeration results for retail meat samples collected within Sentinel Site 1 in 2007

	# Samples Tested for Presence/ Absence	# Positive Samples by Presence/ Absence	MPN/g of sample
			Below Detection (< 0.3)	0.3-10	11-100	101-1000	>1000
Campylobacter
Pork	187	3	3
Chicken	187	55	49	6
Beef	187	1	1
Salmonella
Pork	187	6	5	1
Chicken	187	61	52	7	2
Beef	187	1	1
Listeria
Pork	187	21	14	5	2
Chicken	187	64	48	11	3		2
Beef	187	44	37	7
Yersinia
Pork	187	8	8

Summary of MPN technique

Primary isolation was initiated on each meat package purchased by removing a representative 50-gram portion from each sample and stomaching it for two minutes in a selective enrichment media, specific for each pathogen. The Most Probable Number (MPN) method, which estimates the number of bacteria per gram of sample, was performed on meat samples that tested positive by primary isolation. For Salmonella, L. monocytogenes and Yersinia spp., 50 mL of the stomached rinsate used in the MPN procedure was stored at refrigeration temperature until the results of the primary isolation were known. For Campylobacter spp., 50 g of meat was stored under microaerophilic conditions at 4ºC for MPN analyses if the primary isolation results were positive. The three-tube MPN series was prepared for each of the pathogens tested, by transferring 10 mL of the sample enrichment broth into three tubes containing 9 mL of broth, 1mL of the sample homogenate into three tubes containing 9 mL of broth, 1 mL of a 10^-1 dilution into three tubes containing 9 mL of broth, and 1 mL of a 10^-2 dilution into three tubes containing 9 mL of broth. This method is sensitive to 0.3 MPN per gram of sample. The MPN table used for these analyses was obtained from the FDA Bacteriological Analytical Manual (http://www.cfsan.fda.gov/~ebam/bam-toc.html).

A majority of the samples had levels below the MPN detection limit. These samples most likely represent a lower public health risk since the level of these organisms were sufficient for detection following growth in enrichment culture, but not high enough (<0.3 MPN/g) without enrichment for a positive enumeration result.