DETECTION OF SALMONELLA FROM NATURALLY CONTAMINATED CHICKEN CARCASS RINSE SAMPLES USING THE AUTOMATED BAX PCR SYSTEM

Authors: Bailey, Joseph; Berrang, Mark; COX, J - UNIVERSITY OF NEW S WALES

Submitted to: Poultry Science Association Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/18/2006
Publication Date: 7/16/2006
Citation: Bailey, J.S., Berrang, M.E., Cox, J.M. 2006. Detection of salmonella from naturally contaminated chicken carcass rinse samples using the automated bax pcr system. Poultry Science Association Meeting Abstract. 58(1):172.

Interpretive Summary:

Technical Abstract: Salmonella is a major cause of human enteric disease commonly associated with poultry meat. Efficient detection of Salmonella is important in managing the pathogen during poultry production and processing. The automated BAX system, a technology based on the polymerase chain reaction (PCR) was compared to the standard USDA cultural method for detection of Salmonella. After overnight enrichment at 37°C of 30mL of rinse with 30mL buffered peptone water (BPW), a 50'L aliquot was taken into the BAX system, and processed according to manufacturer’s instructions. BPW enrichment (0.5mL and 0.1mL respectively) was enriched selectively overnight at 42°C in Rappaport-Vassiliadis medium and Hajna’s tetrathionate broth, then each streaked for isolation to brilliant green sulfa agar and modified lysine iron agar. Presumptive isolates were confirmed using biochemical tests and latex agglutination. Of the 360 broiler carcass rinses tested, from 16 commercial processing plants, the BAX yielded 213 positive results while conventional enrichment and plating detected the bacterium in only 193 samples. Based on comparison of paired data, the BAX yielded 181 true positive, 135 true negative, 32 false positive and 12 false negative results. The false-negative results are definitive as salmonellae were isolated by culture. The false-positive results are much harder to interpret. No salmonellae were isolated from the same enrichment used in the BAX analysis, even though that BPW enrichment was further enriched in two different selective broths, and they were plated to different agar media. This suggests that the BAX false positives are indeed false-positives. However, the sensitivity of the PCR may be sufficient to yield a positive result even though the numbers of salmonellae present may not be detected by culture, or salmonellae present in the BPW enrichment may have been lost during selective enrichment. Thus, at least some of these BAX-positive results may represent true positives, with culture yielding false-negative results. Despite the differences in results, there was 94% agreement based on paired positive data between BAX and culture, indicating BAX is suitable as a rapid method for the detection of Salmonella in chicken carcass rinses.