Development and evaluation of a real-time polymerase chain reaction assay targeting iap for the detection of Listeria monocytogenes in select food matrices.

Listeria monocytogenes is an intracellular foodborne pathogen that has been associated with severe human illnesses. Various rapid detection methods have been developed for the specific detection of this pathogen. In the present study, a real-time quantitative polymerase chain reaction (PCR) assay targeting iap, a gene encoding extracellular protein p60, was developed for L. monocytogenes. The PCR efficiency is above 85% and the limit of detection (LOD) is 30 copies of genome per reaction for all strains tested. The assay exhibited 100% inclusivity and exclusivity rates. The detection of L. monocytogenes in five food matrices, whole milk, soft cheese, turkey deli meat, smoked salmon, and alfalfa sprouts, was evaluated with and without enrichment. Without enrichment, the LOD for all food matrices were 4×10(3) CFU/mL food enrichment mix for whole milk and 4×10(4) CFU/mL for all other foods. With 24 h incubation in Buffered Listeria Enrichment Broth, the LOD was 3 CFU/25 g food for whole milk, turkey deli meat, and smoked salmon and 9 CFU/25 g food for soft cheese and alfalfa sprouts. With 48 h incubation, the LOD was 3 CFU/25 g food for all matrices. This quantitative PCR appears to be a promising alternative for rapid detection of L. monocytogenes in select foods.

Survival of Salmonella Typhi and Shigella dysenteriae in dehydrated infant formula.

UNLABELLED: Powdered infant formula has previously been linked to the transmission of various bacterial pathogens in infants resulting in life-threatening disease and death. Survival studies of 2 common foodborne pathogens, Salmonella enterica serovar Typhi and Shigella dysenteriae, in powdered infant formula have not been previously studied despite the potentially devastating consequences from ingestion of these organisms, particularly by newborns, in case of a natural or deliberate contamination event. Therefore, to better predict the risk of S. Typhi and S. dysenteriae infection from consumption of infant formula, the present study was undertaken to determine survival of these microorganisms in dry infant formula under varying atmospheric conditions. A 2-strain cocktail of S. Typhi and a 3-strain cocktail of S. dysenteriae were stored for up to 12 wk in dehydrated infant formula in an ambient air or nitrogen atmosphere. Viable counts of S. Typhi at 12 wk in infant formula revealed a 2.9- and 1.69-log decrease in ambient air and nitrogen atmosphere, respectively. Viable counts of S. dysenteriae at 12 wk in infant formula revealed a 0.81- and 0.42-log decrease in ambient air and nitrogen atmosphere, respectively. These results show that S. Typhi and S. dysenteriae can remain viable for prolonged periods of time in powdered infant formula, and the presence of nitrogen enhances survival. PRACTICAL APPLICATION: Our goal in this work was to study the survival of S. Typhi and S. dysenteriae in dehydrated storage conditions in infant formula. This interest is partially generated by the possibility of using these 2 microorganisms to deliberately contaminate the food supply. The outcome of this study will help us to have a better idea how to respond and react to the risk of deliberate food contamination.

Detection of Yersinia enterocolitica in alfalfa, mung bean, cilantro, and mamey sapote (Pouteria sapota) food matrices using DNA microarray chip hybridization.

Four different food matrices (alfalfa, cilantro, mamey sapote, and mung bean) were contaminated with three different dilutions 10(6), 10(4), and 10(3) cfu/g of Yersinia enterocolitica. DNA was isolated from each food mix and used in chromosomal amplifications. The amplified DNA was used as templates in single PCR reactions of the four genes (virF, ail, yst, and blaA) followed by mixing the four reactions for one PCR primer extension reaction. The presence and the limit of detection of four genes in four food matrices were established by microarray hybridization. Data revealed the diversity of signal intensities. Neither the microarray chip hybridization nor the single PCR amplification could detect virF's presence located on a plasmid. Ail was detected in 10(3) cfu/g, whereas blaA and yst were detected from 10(5) to 10(6) cfu/g in all food matrices. Therefore, the ail gene could be the gene of choice in identifying Y. enterocolitica in alfalfa, cilantro, mamey, and mung bean. Other genes--blaA, yst, virF--exhibited wide variability in hybridization signals, highlighting the need of a better DNA purification step prior to DNA microarray hybridization.