What are the best examples of Listeria monocytogenes (L. monocytogenes) culture plates?

From the Guidelines

The best examples of Listeria monocytogenes culture plates are those using selective media like PALCAM or Oxford agar, which show distinctive colony morphology, as recommended by recent studies 1. When it comes to culturing Listeria monocytogenes, the choice of media is crucial for accurate identification and diagnosis.

• Selective media like PALCAM or Oxford agar are ideal for L. monocytogenes culture, as they allow for the growth of the organism while inhibiting the growth of other bacteria.
• On PALCAM agar, L. monocytogenes appears as small grayish-green colonies with black centers and a black halo against a cherry-red background after 24-48 hours of incubation.
• On Oxford agar, colonies appear as small black colonies surrounded by a black halo due to esculin hydrolysis.
• Blood agar is also useful, where L. monocytogenes produces small colonies with a characteristic narrow zone of beta-hemolysis after 24-48 hours at 35-37°C.
• Chromogenic media like CHROMagar Listeria show L. monocytogenes as blue-turquoise colonies with a white halo, allowing differentiation from other Listeria species. Proper incubation conditions (35-37°C for 24-48 hours) and appropriate quality control strains are essential for reliable identification, as highlighted in a study on culture media for clinical bacteriology in low- and middle-income countries 1. In terms of best practices, it is recommended to select a small panel of well-described media that is supported by the national reference laboratory and look for products from reputable manufacturers 1. Overall, the use of selective media like PALCAM or Oxford agar, combined with proper incubation conditions and quality control measures, is the best approach for culturing Listeria monocytogenes.

From the Research

Listeria Monocytogenes Culture Plate Examples

• PALCAM agar is a selective and differential medium for the isolation and enumeration of L. monocytogenes, as described in 2.
• The medium is based on Columbia agar with added selective agents, and L. monocytogenes colonies are approximately 2 mm grey-green with a black sunken centre and a black halo on a cherry-red background.
• Other media, such as L-PALCAMY, Oxford, and Rapid' L. mono, have also been developed for the detection of L. monocytogenes, as discussed in 3 and 2.
• Listeria monocytogenes blood agar (LMBA) is another medium that has been compared to PALCAM and Oxford media for the detection and enumeration of L. monocytogenes, with LMBA showing superior results in some cases, as reported in 4.
• The choice of medium depends on the type of sample, number and nature of competing flora, and cost, as guided in 5.

Characteristics of Listeria Monocytogenes Colonies

• On PALCAM agar, L. monocytogenes colonies are approximately 2 mm grey-green with a black sunken centre and a black halo on a cherry-red background, as described in 2.
• On LMBA, L. monocytogenes can be distinguished from other Listeria species by detection of beta-hemolysis, as reported in 4.
• The appearance of colonies can vary depending on the medium used, with some media allowing for the detection of specific characteristics, such as PI-PLC activity, as discussed in 3.

Comparison of Media for Listeria Monocytogenes Detection

• PALCAM agar, Oxford agar, and nalidixic acid agar have been compared for the detection of L. monocytogenes in foods, with PALCAM agar and Oxford agar offering advantages in reducing contaminating microflora and ease of reading, as reported in 6.
• LMBA has been compared to PALCAM and Oxford media, showing superior results in detection after enrichment and enumeration, as described in 4.
• The choice of medium depends on the specific requirements of the analysis, including the type of sample and the level of contamination, as guided in 5.