Listeria spp.

Listeria monocytogenes (Gram Positive)

Enriched sample in UVM 1 broth
Incubate 30˚C, 24Hrs
Draw 1 ml into Fraser broth, Incubate 35˚C 24hrs
Do a streak plate on MOX and PALCAM
Incubate 35˚C for 24 Hrs.
From each plate pick 1 colony and streak onto TSAYE agar ( Half for MOX and Half for PALCAM)

Positive TSAYE agar will yield 0.2 to 1.5mm blue grey colony

From Each plate choose another colony stab into TSA blood agar

Positive TSA blood agar will yield clear zones in colony
From TSAYE agar, do a gram stain
From TSAYE agar, do a catalase test

Positive catalase test will yield oxygen bubble

With all the positive test, it can then be confirm that Listeria spp. is present. Above test can be confirm at the genus level only.

PALCAM agar medium
Contains Lithium Chloride, polymyxin, ceftazidime are antimicrobial agents that will inhibits other microorganisim, my Listeria spp. are resistant to it.
Listeria spp. hydrolyses Esculin, which will react with ferric amminium citrate. Esculin-Ferric ammonium citrate yield black ppt. Therefore Esculin differentiates Listeria spp. from other microorganisim.
Manitol and phenol red differentiates Manitol fermenting microorganism which will be in yellow colour

Trypton Soy Agar (TSA) with Blood

Listeria spp. haemolyses blood which will give a colony with clear zone.

TSA Yeast Extract

It’s a non selective enriched media. Clear media allows the examination of colony morphology that will undergo catalase reaction


University of Vermont Broth (UVM 1 broth)
· Nalidxic acid inhibits G-.
· Acrflavin suppresses other G+, but not Listeria spp.

Modified Oxford Agar (MOX)
· Contains Lithium chloride ,esculine, ferric ammonium citrate, colistin sulfate and moxalactam.
· The above are antimicrobial agents against G- and other G+, but not Listeria spp.Lithium Chloride select for osmotolerants like Listeria spp.