Performance testing of six chromogenic ALOA-type media for the detection of Listeria monocytogenes.
OBJECTIVE
The aim of the study was to test the performance of commercially available chromogenic plating media for detection and enumeration of the food-borne pathogen Listeria monocytogenes. A wide range of chromogenic media similar to Agar Listeria according to Ottaviani and Agosti (ALOA) were compared using PALCAM agar, according to van Netten et al.


RESULTS
Six chromogenic media similar to ALOA were challenged for inclusivity and exclusivity. Additionally, the ability of chromogenic agars to facilitate growth of stressed L. monocytogenes strains and mixed cultures with competitive non-Listeria strains was estimated. Finally, we tested the detection and enumeration of L. monocytogenes in artificially inoculated and naturally contaminated food samples. The results of this study indicated that chromogenic media are a good supplementation to PALCAM agar. A single application is not advisable, as the specificity of chromogenic agars is frequently insufficient (50.0-88.9%), particularly in food samples with a complex microflora.


CONCLUSIONS
The competitive flora of food samples is able to overgrow low numbers of L. monocytogenes, especially in half-Fraser enrichment. This might lead to the underestimation of L. monocytogenes positive samples.


CONCLUSIONS
Although many evaluation studies of chromogenic agar have been published recently, harmonized validation strategies are lacking. This survey provides a new concept for stepwise testing of plating media.
Stessl
B
B
Department of Veterinary Public Health and Food Science, Institute of Milk Hygiene, Milk Technology, and Food Science, University of Veterinary Medicine, Vienna, Austria.
Luf
W
W
Wagner
M
M
Schoder
D
D
D000362:Agar; D001431:Bacteriological Techniques; D002863:Chromogenic Compounds / Q000737:chemistry; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry*; D005506:Food Contamination; D005516:Food Microbiology; D006358:Hot Temperature; D008089:Listeria monocytogenes / Q000254:growth & development / Q000302:isolation & purification*
D002863:Chromogenic Compounds; D003470:Culture Media; D000362:Agar