Evaluation of chromogenic media for the detection of Listeria species in food

Abstract

Aims: The aim of this study was to evaluate the performance of chromogenic agars, Agar Listeria according to Ottaviani and Agosti (ALOA) and Rapid L. mono agar, compared with Oxford agar for the enumeration and detection of Listeria species in food. Methods and Results: A total of 170 food samples were examined using the three plating media. Listeria species were isolated from 63 samples. In contrast to Oxford agar, detection of Listeria colonies on chromogenic media was as good after 24 h of incubation of plates as after 48 h. While there was no significant difference in recovery of Listeria monocytogenes on the three media, recovery of other Listeria species was significantly poorer on Rapid L. mono agar compared with Oxford and ALOA agars. Recovery of species other than L. monocytogenes was significantly improved by including a secondary enrichment stage in the detection method. Conclusions: Using chromogenic agars, presumptive identification of L. monocytogenes is possible after 24 h, compared with 3-4 days using Oxford agar. However, the poor detection of species other than L. monocytogenes on Rapid L. mono agar is a disadvantage of this medium. Significance and Impact of the Study: This study provides new information regarding the isolation of Listeria species other than L. monocytogenes from food using chromogenic plating media. This is important, as nonpathogenic Listeria species act as markers for the likelihood of presence of L. monocytogenes and allow preventive action to be taken to avoid its presence.

Comparison of PI-PLC based assays and PCR along with in vivo pathogenicity tests for rapid detection of pathogenic Listeria monocytogenes

“…other than L. monocytogenes and L. ivanovii. Similar results were reported by others (Greenwood et al, 2005;Notermans, Dufrenne, Leimeister-Wachter, et al, 1991).…”

“…Agar Listeria according to Ottaviani and Agosti (ALOA) is based on detecting phosphatidylinositol specific phospholipase C (PI-PLC) activity of L. monocytogenes (Greenwood et al, 2005). Phospholipases of L. monocytogenes are essential determinants of pathogenicity (Marquis, Doshi, & Portnoy, 1995;Smith et al, 1995) and activity of PI-PLC is expressed only by pathogenic L. monocytogenes (Notermans, Dufrenne, Leimeister-Wachter, Domann, &L.…”

“…Presently, a variety of chromogenic agars are commercially available which aim at shortening time for the detection of pathogenic L. monocytogenes (Greenwood, Willis, Doswell, Allen, & Pathak, 2005). Agar Listeria according to Ottaviani and Agosti (ALOA) is based on detecting phosphatidylinositol specific phospholipase C (PI-PLC) activity of L. monocytogenes (Greenwood et al, 2005).…”

Reliability of Listeria monocytogenes Identification by Specific PCR Assessed by Phenotypic and Genotypic Techniques

“…These results are in accordance with the results reported by other authors (Gouws and Liedemann 2005;Furrer et al 1991) showing a high frequency of Listeria species isolation, mainly L. innocua, from Oxford and PALCAM agar. This has been witnessed in comparative studies using alternative isolation media (Vlaemynck et al 2000;Karpísková et al 2000;Greenwood et al 2005;Pinto et al 2001) and has led to the introduction of improved selective-differential isolation media, such as ALOA (Vlaemynck et al 2000), in updated standard isolation procedures (Anon 2005b), thus enhancing the detection ratio for L. monocytogenes. The isolates under study were recovered between 1999 and 2002, and following the regulations in force at that time, Oxford and PALCAM were used as selective media instead of ALOA, which explains the high recovery of other Listeria spp.…”

The Effect of Thawing and Storage Temperature on the Microbial Quality of Commercial Frozen Ready Meals and Experimental Reduced Salt Frozen Ready Meals

“…Indeed the commercial regular salt chicken curry meal was the only meal where general growth of psychrotrophs was evident. Although L. grayii is regarded as non-pathogenic it may indicate deterioration in hygiene standards or inadequate process conditions, leading to an increased risk of contamination by other pathogenic Listeria species (Greenwood et al, 2005). Lekroengsin et al (2007) demonstrated that cooking processes, i.e.…”