36 replies to this topic

[Simon]

I know eating food contaminated with food poisoning bacteria, viruses etc. can make you very ill and I also know that good hygiene practice and commonsense can avoid or reduce the risk.

However, in our quest to learn more about the invisible enemy (and to give the food microbiology forum a little jump start) I wanted to stimulate some discussions beginning with our friend Listeria monocytogenes.

With regard to Listeria monocytogenes in particular:

- What does it look like?
- What foods can it be found on and in?
- Where does it come from?
- What illness or physical symptoms can it cause in humans?
- How do we prevent, control and eradicate it?
- Has it ever caused you or someone you know harm?
- What is its toughness rating – please vote!

[cazyncymru]

Listeria has 5 clearly distinguished species (L.monocytogenes, L. innocua, L. welshimeri, L.seeligeri and L. ivanovii)There are others in the genus such as L.grayi and L.murrayi but they are not species in their own right.
The most common occuring in food are L.innocua and L.monocytogenes

L.monocytogenes is recognized as a pathogen and has been implicated in a number of outbreaks. The illness caused by L.monocytogenes is often referred to as Listeriosis

There are a number of infection routes.
Zoonotic Infections are local infection of skin lesions and can self resolve. Time of onset is 1-2days.

Neonatal infection occurs when newborn babies are infected by the mother during birth or cross infection from 1 baby to another. this can be severe and can result in meningites and death. Time of onset is 1-2 days.

Infection during pregnancy from consuming contaminated foods can give mild flu like symptoms in the mother but can have serious implications on the foetus, including spontaneous abortion, foetal death, stillbirth or menengitis. Onset time can be 1day to several months.

Meningitis can also affect the immunocompromised or elderly

Food poisioning by Listeria can occur when there are exceptionally high levels of L.monocytogenes in food (10⁷ per ml). This can bring on vomiting and diarrohea <24hours after consumption.

Outbreaks of listeriosis has occured from food stuffs as diverse as coleslaw to smoked mussels. .

Listeria can survive for many weeks at frozen temperatures and can grow slowly at refrigeration temperatures, it is not very heat resistant

Integrity of raw material is paramount, especially if there is to be no heat treatment of the raw material (ie cold smoking raw fish, or unpasteurised cheeses)

Cleaning in factories is also important as listeria can thrive in dirty, broken drains, unclean equipment such as brushes etc and personnel (boots collect moist debris and this can act as harbourages of Listeria species)



I'm no microbiologist, but i must admit usually if you say Listeria some adopt Hysteria!
My rule of thumb is, if i'm not panicing, then theres no need for others to!

Caz x

[Penard]

interesting information, let's keep in mind that the H1N1 flu isn't the only one curse all around the world...but if I want my wife to sleep correctly I'm not sure I will talk her about all these details tonight (she's pregnant) !

Regards,

Emmanuel

[rosie]

 Listeria_mono.pdf   90.23KB   210 downloadsHi

Some info on Listeria monocytogenes:

Edited by rosieNI, 03 August 2009 - 07:44 PM.

[Simon]

Thanks everyone for your input. So pretty much a heavy weight then. We'll let the poll run for a litle while and then we can move onto another.

Has anyone been made ill by Listeria? Or would you actually know which bacteria had made you ill - pehaps not?

Regards,
Simon

[Charles.C]

Dear Simon,

As HACCP would say, It must relate to the product and the consumer..

Sometimes heavy, sometimes light. I entered light.

Rgds / Charles.C

[Sirius]

I gave it a Tyson and with good reason.

Dealing in food service to a vulnerable population, this bug has seen at least two confirmed deaths (and one litigation still in progress) from our supply chain in the last five years. Our controls have improved vastly since then but we are still at the mercy of a three day turnaround on any test swabs we submit to IMVS Labs. Since my time here, we have eliminated Listeria on all our own made goods through extensive cleaning procedures and, sadly, eliminating a lot of high risk foods from our menu (goodbye eggs and smallgoods). The only time we're caught out is when a supplier provides us with infected foods, we sample (as part of our SOP), product goes out whilst awaiting results and when we get results back we find high counts. Sheesh.

Listeria has also seen major smallgoods suppliers (Conroy's and Garibaldi) fall into major financial and civil action hardship after contaminated product from their outlets was consumed.

[Tony-C]

Middle weight for me. Although it has a decent punch it gets knocked out easily enough.

Also factored in the fact it doesn't spread from person to person.

Regards,

Tony

[Tony-C]

This popped up today almost on cue!

Processors under spotlight as food ingredient suspected in listeria outbreak

Listeria Outbreak in Australia

Regards

Tony

[MRios]

From Caz´ post I´d say it´s a middleweight. If it´s not very heat resistant, then it´s not so scary. What does scare me is meeting it in the middle of a pregnancy!!! I read that in the US, they found a correlation between stillbirths and Hispanic women. Turns out these women had been eating cheese made from nonpasteurized milk, which was contaminated with Listeria.
So Emmanuel, don´t tell your wife anything. Just make sure any cheese she has was made from pasteurized milk. (I´m under the impression that some artisan cheese makers in France are against pasteurizing milk because it changes the flavor of aged cheese.)
As for Listeria in the general population, at least in Central America, I´m pretty sure that amoebas, giardias and Taenia saginata are much more prevalent. Most people here have learned to live with occasional diarreah.

[Charles.C]

If it´s not very heat resistant

This is a relative term. One of the reasons for it's choice as a reference (by some authorities) for various foods is due to it's (relative) difficulty for destruction. This aspect is involved in the safety arguments regarding typical UK vs US hotdogs.

Didn't do an exhaustive look but some (representative ?) relative data here -

 heat_resistance_data.jpg   32.35KB   76 downloads
(Food Microbiology, Adams)

(D is time in mins for 90% bacterial population reduction at the specified temp./matrix etc, z is the temp. change in degC required to cause a 10 fold (!!) change in D.)

Using comparable temperatures for a given matrix is crucial.

BTW, For cheese, this link might be of interest -
http://www.ontarioch...se_safety_2.php


Rgds / Charles.C

[Tony-C]

This is a relative term. One of the reasons for it's choice as a reference (by some authorities) for various foods is due to it's (relative) difficulty for destruction. This aspect is involved in the safety arguments regarding typical UK vs US hotdogs.

I agree with you Charles it is a relative term

Heat Resistance of Listeria monocytogenes in Dairy Products

The D-values obtained for both strains resuspended in all the dairy products would result in efficient elimination of the pathogen at 72·7 °C for 15 s

Output from simulations confirmed that pasteurization at the IDF standard conditions of 72°C for 15 sec can ensure at least an 11-log reduction of L. monocytogenes.

Most of the plants I know hold for 25 seconds due to the possible survival of Mycobacterium avium subsp. paratuberculosis on a 15 second hold.

Regards,

Tony

[Simon]

I'm really pleased with the input here. Thanks everyone I've learned a lot and I'm sure this thread will be helpful to newbies looking for information on Listeria monocytogenes.

Regards,
Simon

[Charles.C]

Dear Tony,

Thanks for the milk links. I noticed that (if I read correctly) the D values in these articles are approx 10x in disagreement with the value given in the link for milk / cheese in my post [the comment in its main text specifically illustrates this also]. I’m sure yr data is correct, just curious where the discrepancy (blunder?) originated.

Also interesting that the heat requirements for milk are seemingly fortuitously lower than officially prescribed for the “typical” food product (min 2mins / 70degC which is predicated for a 6D reduction in L.mono....) According to the standard table in an earlier post here, the 6D also corresponds to 1min@72degC which if my arithmetic has not let me down indicates a D value of 10sec. Maybe a substantial safety factor has been added ( ).

Rgds / Charles.C

[Kamwenji Njuma]

Hi,
Listeria problem is most found on wet floors and condensate from evaporator fans.Also vegetables mostly leeks are mostly contaminated.

Regards,
Jeremy,
Kenya

[Tony-C]

Listeria problem is most found ............... condensate from evaporator fans
Regards,
Jeremy,
Kenya

Good point Jeremy and evaporator fans not so easy to clean

Regards,

Tony

[Penard]

Not a lot of bacteria remaining as mandatory in the 'new' european legislation (2073/2005), but the listeria still present - like salmonella. I don't think it's just because of a lobby, customs or just a forgetting.
As written above it's very easy to find it the food industry (overall raw materials) despite all the improvements done for the process, and so difficult to eradicate it once established.

(right MRios my wife can't eat any unpasteurized cheese with a red wine glass anymore, such a pity...but she has already asked me to prepare some of these special dishes when she will leave the maternity hospital !)
Regards,

Emmanuel

[Tony-C]

Not a lot of bacteria remaining as mandatory in the 'new' european legislation (2073/2005), but the listeria still present - like salmonella.

EU Legislation 2073/2005 Microbiological Criteria for Food

Not a great fan of this document:

Off topic I know but I would like someone to explain to me how the maximum level for E.coli in ready to eat fruit and vegetables is 1000/g ?

Regards,

Tony

[Simon]

Off topic I know but I would like someone to explain to me how the maximum level for E.coli in ready to eat fruit and vegetables is 1000/g ?

I have split into own topic for you Tony:
How is the maximum level for E.coli in ready to eat fruit and vegetables 1000/g?

[Tony-C]

I thought this was generally well known and as such waste of research money but link here:

Listeria risks from high pressure cleaning

Regards

Tony

[cazyncymru]

Dear Tony,

Thanks for the milk links. I noticed that (if I read correctly) the D values in these articles are approx 10x in disagreement with the value given in the link for milk / cheese in my post [the comment in its main text specifically illustrates this also]. I’m sure yr data is correct, just curious where the discrepancy (blunder?) originated.

Also interesting that the heat requirements for milk are seemingly fortuitously lower than officially prescribed for the “typical” food product (min 2mins / 70degC which is predicated for a 6D reduction in L.mono....) According to the standard table in an earlier post here, the 6D also corresponds to 1min@72degC which if my arithmetic has not let me down indicates a D value of 10sec. Maybe a substantial safety factor has been added ( ).

Rgds / Charles.C

Hi Charles

As Tony rightly says, the Dairy industry uses a heat treatment of 25 seconds although legally pasteurisation temperature is 71.7 degrees C for 15 seconds. Even 15 seconds HTST (High Temp / Short Time) allows a log 5 reduction killing 99.99% of viable micro-organisms.

I have a very good document somewhere regarding HTST, i'll have to dig it out, although i'm sure Tony has it too!

[Tony-C]

Hi Charles

As Tony rightly says, the Dairy industry uses a heat treatment of 25 seconds although legally pasteurisation temperature is 71.7 degrees C for 15 seconds. Even 15 seconds HTST (High Temp / Short Time) allows a log 5 reduction killing 99.99% of viable micro-organisms.

I have a very good document somewhere regarding HTST, i'll have to dig it out, although i'm sure Tony has it too!

Sorry Caz/Charles don't have anything useful loaded on my laptop and I'm away until December. There are a few bits and pieces on the Dairy UK website.

Regards,

Tony

[Tony-C]

This popped up today almost on cue!

Processors under spotlight as food ingredient suspected in listeria outbreak

Listeria Outbreak in Australia

Update on this Australian listeria source identified

Regards

Tony

[Simon]

Just a quick question - if you cook chicken at a high enough temperature for a decent length of time do you kill Listeria?

[Charles.C]

Dear Tony,

(only slightly OT) - This other link within yr excellent first one ( ) is also very interesting -

http://www.ap-foodte...ady-to-eat-food

It does rather look as the whole issue of the risk from L.mono is heating up again, ie official "backs" are being analysed for coverage again.

@ Simon - yes (99.9% anyway) but perhaps no eatable chicken left after the "decent" time. (This is the continuous problem of course)

Rgds / Charles.C