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


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.


CONCLUSIONS
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 non-pathogenic Listeria species act as markers for the likelihood of presence of L. monocytogenes and allow preventive action to be taken to avoid its presence.
Greenwood
M
M
Wessex Environmental Microbiology Services, Health Protection Agency, Southampton, UK.
Willis
C
C
Doswell
P
P
Allen
G
G
Pathak
K
K
D000362:Agar; D000818:Animals; D002611:Cheese; D002863:Chromogenic Compounds; D015169:Colony Count, Microbial; D005396:Fish Products; D005399:Fishes; D005506:Food Contamination; D005516:Food Microbiology; D006801:Humans; D018545:Lactuca; D008087:Listeria / Q000302:isolation & purification*; D008460:Meat; D008461:Meat Products
D002863:Chromogenic Compounds; D000362:Agar