Pathogenics / Listeria and Pregnancy / Pasteurization?

[Zoey]

A lot of eye-catchers in that topic.
Well, what I've been listing out in my head is:

- Pathogens don't survive longer than 60 days.
- Listeria is usually found in raw milk products
- Hence pasteurization kills listeria
- Listeria is dangerous to pregnant women and little children

I'm not pregnant, but since I'm planning to make cheese making a constant part of my life, which will hopefully include reproduction in the pretty-near future, I'm already wondering about these issues (funny what some pregnant friends do to you)...

So I have these questions in my head, feel free to comment, I won't hold you responsible for any results...

- Is the 60-day-rule a sure cure, or are there still circumstances in which pathogens could survive?
- Pathogens refers to bacteria only, right? Could other dangerous microflora persist after 60 days? Molds, etc, especially ones that are hard to recognise?
- Is it possible to recontaminate the cheese with listeria even when using pasteurised milk? What are the odds?
- Would you risk using home-made dairy products while pregnant (or males: offer them to someone pregnant with your child)? If so, would you rule out some products?

The discussion is open...

[FRANCOIS]

Having owned a raw milk dairy, made raw milk cheeses and now pasteurized....I would only make raw milk cheeses and consume them while pregnant if I milked the animals myself and had them tested.  Otherwise I would pasteurize all milk before making cheese, even store bought.

[linuxboy]

The 60 day rule is for "normal" conditions. If you have a high population of listeria in the milk, say 10^2 cfu/g, that cheese can still kill after 60 days.

A pathogen is anything that can cause illness. It can be a chemical or organism. Common ones in dairy products are E. coli, Salmonella, Listeria, bovine Tuberculosis and Brucella. Molds are usually not a problem, they just cause offtastes and spoilage.

Yes, you can contaminate pasteurized milk. To get it to a lethal dose, you need to contaminate very deliberately. For most operations, it's not an issue. Where it becomes a problem is if there's a contamination that is small combined with poor hygiene practices. For example, if the contaminated cheese is brined, and that brine reused. Listeria can survive in brine.

I would only make products from a trusted source with good practices for raw milk, or pasteurize the milk for pregnant women. Personally, that means I would need to raise the animals and milk them myself. Contaminated cheese is more an issue with mexican bathtub cheese than artisan cheesemakers who practice proper cheesemaking and affinage.

[linuxboy]

If you're really paranoid, look into using protective cultures as additives. Common ones are L plantarum, rhamnosus, sakei, paracasei, and propioni. They help control general gram+ pathogens (like listeria).

[Zoey]

Thanks a lot Francois and linuxboy, your answers are really useful!

I got really interested on that issue on milking practises and testing of cows. If I would test my cow (if I own one some day), would a negative result on listeria mean there can not be listeria in the milk either? So does the cow have to have the disease for bacteria to appear in the milk? That would sound logical, of course...

My plan is to produce my own milk in the future, it's just that I don't know what the adequate safety procedures would be...

Probably it's only possible to test listeria contamination in milk if you have a laboratorium available? Otherwise I would happily do that.

And anyway, if I'm clean on listeria, couldn't I still have some other pathogens? Or is listeria the main thing to worry about?

[Sailor Con Queso]

The 60 day rule is not an absolute and is really coming into question in many states. I suspect that we will see even more states banning the sale of raw milk to consumers.

Theoretically, the good bacteria eat up all the available food resources within 60 days so there is nothing left for bad bacteria to feed on. HOWEVER some bacterial strains, especially those that acidify really quickly, are slowed down by the lowering pH and do NOT complete lactose breakdown. So additional strains may be required in the starter mix that will complete the process.

S. thermophilus (a thermophile) does not complete sugar break down. So if you are just using a basic TA61 starter for example, there MAY be some long term risk during aging. Adding a little LH 100 which includes L. lactis & L. helveticus will complete the sugar breakdown. The important thing is the RATIO. Different cheeses with different fat contents, etc.. age differently and have different environments for organisms to grow in. These ratios and exact strains are no doubt closely guarded secrets with the big time cheesemakers - just like they are with fine wine.

Raw milk was originally banned in many places because of the association with tuberculosis. It was never proven that raw milk itself was the source. Microbiologists generally agree that the tuberculosis came from dairy workers and unsanitary conditions. The rate of illness from raw milk is almost nonexistent. Compare that to the number of cases of E. coli from "pasteurized" milk.

This is a very complex subject that bureaucrats can't usually understand. So for public policy, they simply listen to the big milk producers, ban raw milk and be done with it.
 

[linuxboy]

Common tests for cows include ones for mastitis and listeriosis. Positive indicators would show that the animal is not healthy, and its milk cannot be used.

The test for milk is a separate issue. You can have a healthy cow and unclean milking equipment, or unclean tank, or listeria contamination somewhere else in the milk handling equipment. What I mean is that milk may become contaminated. You need to test animals for their health and milk for its health.

Safety procedure is to test animals and milk regularly, and sanitize everything, and pasteurize milk. If you gently pasteurize, you can still make great cheese. Plenty of award winning cheeses are made with pasteurized cheese.

Yes, it is tough to test for pathogens without a lab. You'd need to do a dot blot, agglutination, or ELISA test for listeria.

And there are many types of pathogens that can infect milk. I already posted the list earlier of the deadly ones. Other types of bacteria aren't deadly, but they cause spoilage, or bad cheese. And quick refrigeration or pasteurization doesn't always kill them. For example, there's psychotrophic bacteria that live at very low temps and can infect milk holding tanks. Cooling milk quickly is not enough to protect it from psychotrophs.

The best way to control pathogens is proper hygiene and knowing in detail what conditions each bacteria like so you can watch for those conditions and remove them. For example, e.coli is a fecal pathogen. If your cow is clean and if you keep the barn clean so there's no feces, especially when milking, you minimize chance of contamination.