Quantification of low and high levels of Salmonella enterica serovar Typhimurium on leaves

Microarray-Based Screening of Differentially Expressed Genes of E. coli O157:H7 Sakai during Preharvest Survival on Butterhead Lettuce

“…Serial dilutions were made in PBS and the appropriate dilutions were plated onto SMAC (24 h, 37˝C). Maceration does not recover all of the interacting bacteria, but it is still one of the best methods for direct plate counts [12]. For each experiment two samples were analyzed (n = 2) and the experiment was performed three times.…”

Factors affecting cell population density during enrichment and subsequent molecular detection of Salmonella enterica and Escherichia coli O157:H7 on lettuce contaminated during field production

“…Furthermore, there may be substantial interference, difficult to predict in a nonvalidated matrix, of plant or food components that can cause inhibition of the PCR reaction (Harris & Griffiths, 1992;Jacobson, Gill, Irvin, Wang, & Hammack, 2012;Kim et al, 2012;Taskila, Toumola, & Ojamo, 2012). Commonly, low numbers of cells are present on contaminated samples that, alone, make detection difficult, but cells can also be sub-lethally injured or stressed which may delay recovery and reaching the critical detection threshold during an enrichment step (Havelaar et al, 2010;Kisluk, Hoover, Kneil, & Yaron, 2012;Stevens & Jaykus, 2004;Taskila et al, 2012). Although not currently a factor in lot acceptance decisions in fresh produce, enrichment greatly limits the opportunity to accurately quantify or even estimate the presence of a target pathogen.…”

“…Most commercial kits based on PCR reactions are coupled to cultural enrichment, a physical or immuno-capture concentration step or both. Most methods require the enrichment end-point cell population density of target pathogens to reach about log 3 to log 4 CFU/mL for detection, thus in the majority of cases, pre-enrichment prior to application of even sensitive detection platforms is needed (Bennett, Greenwood, Tennant, Banks, & Betts, 1998;Franco, Hsu, & Simonne, 2010;Kisluk et al, 2012). The variation of culture enrichment among commercial and published methods is enormous, and it can involve nonselective enrichment, followed by a selective enrichment step, it can also be as short as 6 h or a minimum of 24 h depending on the target microorganism (D'Lima & Suslow, 2009;Taskila et al, 2012;Weber, Stephan, Druggan, Joosten, & Iversen, 2009).…”

“…The variation of culture enrichment among commercial and published methods is enormous, and it can involve nonselective enrichment, followed by a selective enrichment step, it can also be as short as 6 h or a minimum of 24 h depending on the target microorganism (D'Lima & Suslow, 2009;Taskila et al, 2012;Weber, Stephan, Druggan, Joosten, & Iversen, 2009). When nonselective enrichment media are utilized, primarily to minimize stress-cell inhibition but also to keep commercial test costs low, the risk of overgrowth from native microbiota due to nutrient competition increases (Kisluk et al, 2012;Weber et al, 2009). The general effect is to reduce the propensity for target pathogens to sufficiently increase their population to a cell density necessary to ensure transfer in the analytical volume required for the test kit, often 2e5 ml, thus resulting in a false negative outcome.…”

PCR Assay for Detection of Staphylococcus aureus in Fresh Lettuce (Lactuca sativa)

“…Despite these foods being ready to eat, it has been reported that their quality is not satisfactory in Vienna, Austria [23], Johannesburg, South Africa [24], Korea [25], and Catalonia, Spain [26]. Reports show that the main pathogens in ready-to-eat foods include Listeria monocytogenes, S. aureus, Bacillus cereus, Salmonella spp., and Escherichia coli O157:H7, the last two being involved in most outbreaks caused by fresh fruits and vegetables [27,28] reported in low doses of 10 and 2-2000 cells, respectively [29,30].…”