Methods for detecting Listeria monocytogenes
A method of detecting Listeria monocytogenes . The method comprises providing a culture device with a selective culture medium and a detection article comprising a first indicator system. The selective culture medium facilitates the growth of Listeria microorganisms. When a Listeria microorganism is detected in a sample contacted with the culture medium, the detection article is contacted with the culture medium to detect Listeria monocytogenes.
1. A method for detecting a Listeria microorganism in a sample, the method comprising:
providing:
a culture device including a culture medium comprising ingredients selected to facilitate growth of a Listeria microorganism;
a detection article comprising a first indicator system, the first indicator system selected to detect Listeria monocytogenes;
wherein the Listeria microorganism is detected by its ability to convert the first indicator system from a first state to a second state;
a second indicator system selected to detect the Listeria microorganism; and
a sample;
inoculating the culture device with the sample;
placing the second indicator system in fluid communication with the culture medium;
incubating the inoculated culture device for a period of time sufficient to permit growth of the Listeria microorganism, if the Listeria microorganism is present in the sample;
observing the culture device to detect at least one Listeria microorganism;
wherein observing the culture device for an indication of the presence of the at least one Listeria microorganism comprises detecting a conversion of the second indicator system from a first state to a second state;
contacting the culture medium of the incubated culture device with the first indicator system of the detection article only if the at least one Listeria microorganism is detected; and
observing the article-contacted culture device to detect a conversion of the first indicator system from a first state to a second state by the at least one Listeria microorganism;
wherein the first and second indicator systems are distinct;
wherein conversion of the first indicator system from the first state to the second state by the at least one Listeria microorganism indicates the at least one Listeria -microorganism is Listeria monocytogenes.
2. The method of claim 1 , wherein providing the culture device further comprises providing a culture device that comprises a hydrogel or a dry, cold-water-soluble gelling agent.
3. The method of claim 1 , wherein providing a culture device further comprises providing a culture device that includes the second indicator system.
4. The method of claim 1 , wherein the first indicator system comprises a reagent to detect α-mannopyranosidase and/or phosphatidylinositol-specific phospholipase C enzyme activity.
5. The method of claim 1 , wherein observing the culture device or the article-contacted culture device comprises observing the culture device visually.
6. The method of claim 1 , wherein observing the culture device or the article-contacted culture device comprises observing the culture device using an imaging device.
7. The method of claim 1 , further comprising enumerating Listeria microorganism colony-forming units in the culture device.
8. The method of claim 1 , further comprising enumerating Listeria monocytogenes microorganism colony-forming units in the culture device.
9. The method of claim 1 , wherein contacting the culture medium with the detection article further comprises contacting the culture medium with the detection article at a predetermined temperature.