Comparison of Culture, Conventional and Real-time PCR Methods for Listeria monocytogenes in Foods

Abstract

We compared standard culture methods as well as conventional PCR and real-time PCR for the detection of Listeria monocytogenes (L. monocytogenes) in milk, cheese, fresh-cut vegetables, and raw beef that have different levels of background microflora. No statistical differences were observed in sensitivity between the two selective media in all foods. In total, real-time PCR assay exhibited statistically excellent detection sensitivity (p<0.05) and was less time consuming and laborious as compared with standard culture methods. Conventional culture methods showed poor performance in detecting L. monocytogenes in food with high levels of background microflora, generating numerous false negative results. While the detection of L. monocytogenes in fresh cut vegetable by culture methods was hindered only by L. innocua, various background microflora, such as L. innocua, L. welshimeri, L. grayi, and Enterococcus faecalis appeared on the two selective media as presumptive positive colonies in raw beef indicating the necessity of improvement of current selective media. It appears that real-time PCR is an effective and sensitive presumptive screening tool for L. monocytogenes in various types of foods, especially foods samples with high levels of background microflora, thus complementing standard culture methodologies.

Prevalence and toxin type of Clostridium perfringens in beef from four different types of meat markets in Seoul, Korea

“…The average level of background microflora of the 82 beef samples was 4.53±2.67 log CFU per gram, suggesting that the real-time PCR assay could detect the targeted organism even when it was hidden by other background organisms in the culture media. The same phenomenon was observed in the real-time PCR assays for the detection of Listeria monocytogenes and Lactobacillus kefiranofaciens in food samples with high levels of background microflora (10,19). In addition, the results of the real-time PCR assay for detection of C. perfringens could be obtained within 30 h, whereas the conventional culture method requires 96 h (Fig.…”

“…The culture method is regarded as the standard method for the detection of C. perfringens from food samples, but it is timeconsuming and labor-intensive (9). Furthermore, the detection performance of this method can be profoundly diminished by the presence of competing flora in foods (10). To overcome these drawbacks, we previously developed a real-time PCR assay for the detection and enumeration of C. perfringens in foods (9).…”

Real-Time Quantitative PCR as a Tool for Monitoring Microbiological Quality of Food

“…In addition, the result of real-time PCR was obtained in 2 days, while the traditional method took 4-8 days [24]. Another study comparing standard culture methods, conventional PCR, and real-time PCR for the detection of Listeria monocytogenes in milk, cheese, fresh vegetables, and raw meat showed that the real-time PCR assay was statistically more sensitive, reducing the time of analysis and laborious work [25]. The targeted gene coding for a protein of the ribosome large subunit was used in qPCR for quantifying Enterobacteriaceae in 51 food products naturally contaminated.…”

Improvement of Enterobacteriaceae enrichment broth by supplementation with sodium citrate for detection of Cronobacter sakazakii using real-time PCR

“…All samples were purchased from a local grocery store in Seoul, Korea and were found to be free of C. sakazakii by standard culture methods. A plate count of the background flora of each food type was conducted as described earlier (9)(10)(11).…”