The effect of pre-enrichment protocol on the sensitivity and specificity of PCR for detection of naturally contaminated Salmonella in raw poultry compared to conventional culture.

Salmonella spp. are the leading cause of foodborne illness worldwide. Conventional culture techniques for the detection of Salmonella spp. are labor intensive and time consuming. Several rapid detection methods have been developed over the past few years. However, standard methods for sample handling and preparation have not been established and limited data are available on the sensitivity and specificity of these methods for detection of Salmonella in naturally contaminated retail meat. Using culture as the gold standard for Salmonella detection in naturally contaminated raw poultry products, the sensitivity and specificity of a polymerase chain reaction (PCR) detection method was determined under varying enrichment protocols. Chicken meat samples (ground, boneless/skinless breast meat, and bone-in breast meat with skin) from retail grocery stores were pre-enriched in buffered peptone water (BPW) and Salmonella specific primers ST 11 and ST 15 were used to amplify a 429 bp region of random fragment target specific to all Salmonella spp. There was a significant decrease (P-value<0.001) in the sensitivity of the PCR test when BPW pre-enrichment alone (85%) was used compared to the sensitivity achieved after both BPW enrichment and selective enrichment with RV and TT-H (100%). PCR failed to detect any positive samples when no pre-enrichment was conducted. A minimum of 12h pre-enrichment was required for detection of Salmonella by PCR at a limit of 100 colony forming unit (cfu)/1 ml of sample. No detectable amplification product was seen in those naturally contaminated meat samples testing negative by culture methods.

The effect of subclinical Mycobacterium paratuberculosis infection on milk production in Michigan dairy cows.

The objective of this study was to determine the effect of subclinical Mycobacterium paratuberculosis infection on mature equivalent milk, protein, and fat production in a sample of Michigan dairy herds with a history of cows positive for M. paratuberculosis diagnosed by fecal culture. A prospective two-group cohort study was conducted. Participating herds were tested, and productivity and reproduction records were monitored for 18 mo. All cows aged 24 mo and greater were tested for M. paratuberculosis infection using the ELISA and radiometric fecal culture (RFC) techniques. Using both tests in parallel, the overall sample apparent prevalence for M. paratuberculosis infection was 41.8%. Adjusting for diagnostic sensitivity and specificity resulted in a calculated sample true prevalence of 59.9%. Subclinical paratuberculosis test-positive status had no statistically significant effect on mature equivalent milk, fat, or protein production. The results of this study concur with the findings of other studies, reporting that the magnitude and direction of the association between subclinical paratuberculosis infection and milk production depends upon the parity of the animal, stage of disease, and the stage in lactation being monitored. Assessment of the impact of subclinical paratuberculosis on milk production must consider the average parity of the sample population. In herds that have an average parity of 2 or less, subclinical paratuberculosis infection may have little impact on milk production.