podcast: the microbiology of your christmas dinner

posted on december 19, 2022   by charlotte hartley

in this festive episode of microbe talk, charlotte speaks to dr lorna lancaster about the harmful and helpful microbes involved in making christmas food.

music: adeline yeo (hp) - tis the season to be jolly 

transcript

charlotte
hello. you're listening to microbe talk, the podcast from the 英格兰vs美国谁会赢？ . i'm charlotte. and in this christmas episode, i'm talking to dr lorna lancaster from the university of lincoln in the uk. lorna has an interest in bacteria and antibacterial compounds. so today we're going to discuss all these things, but with a bit of a festive twist.

lorna
hi, i'm dr lorna lancaster and i am at the university of lincoln within the school of pharmacy. i am a researcher, and i look at the competition between bacterial species and i am particularly interested in bacteriocins and how they interact within the environment and how we can use them to control infections, especially in an antibiotic resistant world.

charlotte
thinking about bacteria, this time of year has a big focus around food and food preparation. the big example being christmas dinner. so what are some of the bad bacteria we should be aware of when we are preparing christmas dinner?

lorna
the biggest culprit of food poisoning is probably the turkey or the chicken, depending on what you're having. we'll go with turkey, with it being christmas time. and there are three main bacteria that cause most infections, food poisoning infections in particular over the christmas period.

so the biggest one, the most common is campylobacter. and this is a bacteria that is everywhere in the world and lives in the gastrointestinal tract of most animals. it causes severe diarrhea, which is lovely, for about 2 to 7 days. it doesn't come with vomiting and nausea. so you've got that bonus.

charlotte
yeah, it's not what you want on christmas!

lorna
i think it doesn't usually start until about two days after. so it's more of a boxing day infection. so but still, you want to be sitting around eating chocolate and watching christmas movies, not sat on the toilet, i'm sure, on boxing day.

the other big one are the second most common food poisoning agent is salmonella, which i'm sure we've all heard of as well. and that one, it's very much like e. coli and its structure and its function, but it produces a toxin which causes pretty much nausea, vomiting and diarrhea. and it kicks in about 12 hours after contamination. and it takes very little for contamination to happen and illness to happen. and you do know about it quite quickly after eating it and it lasts again, 2 to 5 days of being feeling pretty poorly.

charlotte
yes. so something you probably want to avoid if at all possible.

lorna
definitely! and with these to one of the big things is making sure all your meat is cooked like properly and over 70 degrees and all the way through to the center and also preparing your meats correctly, making sure they're separate from any foods you're not going to be cooking and making sure that you wash your hands after touching the meat.

there is the third most common bacterial species that causes food poisoning, and that is clostridium perfringens. and that's one that's not heard about as much i don't think, certainly in mainstream media.

charlotte
so i think that's one that i'm definitely less familiar with. and maybe also for some of our listeners whose work focuses less on bacteria.

lorna
yeah. so it causes a number of different diseases, but food poisoning is one of them and it's the third most common agent for causing food poisoning, especially in meat and poultry. again, you can control it by making sure everything is cooked properly and preparing foods in an appropriate manner.

one thing you've got to watch with this one is it's also storage. that's a big problem. so even if you cook your meat very well, you then have to stored it properly and make make sure you put it in the fridge and not let it sit around at nice warm temperatures.

charlotte
so is that because the bacteria will grow better in these warm temperatures?

lorna
yeah. so basically because clostridium perfringens is a spore forming bacteria and the spores are resistant to heat. so by cooking, although you would kill off the live bacteria, the spores can hang around. then if you let the meat sit for a little while at nice bacteria friendly temperatures, the spores can then germinate into live bacteria and start growing again, producing the toxins which can then lead to food poisoned conditions.

with chlostridium perfringens, it tends to be just diarrhea. you don't tend to get a fever. that can last for 2 to 4 days. so again, not something you want to be having on your boxing day.

charlotte
so clostridium perfringens is one of the species you work with. can you tell me a little bit about this research.

lorna
yes, clostridium perfringens is something that affects us in food poisoning. so we want to avoid that. it can also cause infections like gas gangrene. so we want to try and remove that. it also causes necrotising enterocolitis in neonates and those that are immunocompromised. so we need to find ways of controlling that.

but actually, clostridium perfringens causes disease in the poultry themselves. so campylobacter and salmonella actually can cause disease in animals but is less common. whereas clostridium perfringens causes necrotising enterocolitis in poultry, which means that poultry that are being prepared for food and or dinner have to be culled on a fairly regular basis because of infections from clostridium perfringens.

and we saw numbers go down when we used antibiotics on a regular basis within poultry farming practices, but because of antibiotic resistance, that's not allowed anymore. and so we're seeing a reemergence of infections. and we have been looking at ways to control some of that.

charlotte
so is there a risk that there are already antibiotic resistant strains because of this prior use of antibiotics?

lorna
yeah, and that's actually some of the research we've been doing. we've been looking at the different resistance profiles of these bacterial strains. and there are many different strains of clostridium perfringens and with all different plasmid based differences. but yeah, antibiotic resistance is a big problem and we are seeing we're having to change a lot of the antibiotics that we use or introducing new antibiotics. bacitracin, that's a common one at the minute.

charlotte
okay. so we've talked a lot about lots of really nasty sounding bacterial infections, but obviously we know that not all bacteria are bad for us. and in fact, some of them are really useful, especially in the context of food and food production. so i'm thinking of the obvious example around christmas time being cheese.

lorna
yeah. so we need the bacteria to actually turn the milk into cheese and they do that by different processes. but it's really turning the fat of the milk into more solid forms. there are three well three main ones that are used.

so we've got lactococci and this is used to make cheddar, other streptococci which is used to make mozzarella. and we have a lactobacilli which is made to use swiss cheese. and the bacteria are chosen depending on how hard you want your cheese to be, but also some of the flavors as well. and so we can actually use bacteria or fungi as well to make the flavor of the cheese differently.

so you've got the bacteria to make the solid impact of the cheese and then you've got adjunct cultures which are there to bring in flavors. so for example, another lactobacillus, lactobacillus helveticus brings in a sweet, nutty flavor.

but propionibacterium freudenreichii, which actually produces the holes and the swiss cheese, which is quite interesting. so it creates air and gases and that puts the holes into the cheese. and so that's the bacteria. then we've got the fungi, which is so penicillium camembert and that's actually the white mold on the surface of camembert. and that provides a lot of the flavor because camembert centre is actually not that, the mold on the outside is where the flavor comes in. and then there's penicillium roqueforti which is the blue mold. so that's again, that's the bit that makes the flavor of the cheese.

so bacteria are really important in, in actually the whole cheese process, the creation of the solid form of the milk and then the creating the flavors that are part of it.

charlotte
yeah, because i think most people are probably aware that we need microbes to actually produce cheese. but i had no idea how important it is to the flavor as well. and i never knew that the holes in swiss cheese are caused by bacteria.

lorna
yeah.

charlotte
but then obviously there are some harmful bacteria associated with cheese, for example, camembert, which you mentioned and, you know, soft cheeses.

lorna
so again, that's another food poisoning agent, which is mostly affecting those that are immunocompromised or pregnancy in particular.

so that's listeria monocytogenes and it causes food poisoning symptoms of vomiting and diarrhea, but also it can spread to the meninges and cause meningitis and colitis in severe cases. it can also cause spontaneous abortions and miscarriages in pregnant women and it can when it goes to systemic infection, you get flu like symptoms.

and that's where you really need to be very cautious and treat effectively.

charlotte
so that's why it's generally recommended to avoid soft cheeses during pregnancy.

lorna
it certainly is. yeah.

charlotte
but then some of your research is focused on making soft cheeses safer for pregnant or immunocompromised people.

lorna
yes. so some of this work has already started and we are already seeing some use of bacteriocins within cheese making products. so we're just trying to increase the number of options that we have within the cheese making process.

so i've been looking at different what's known as enterocins, which are bacterial cells produced by enterococci, that are effective against listeria monocytogenes. and we can't really put enterococcus into the cheese because they can also cause disease. however, we're looking at the genetics and seeing whether we can then transfer that into the starter cultures or the adjunct cultures to there to bring in the citizens into the cheese to prevent the listeria growth in the first place, which means that pregnant women and immunocompromised people can have some beautiful camembert.

charlotte
yes. so that sounds great, but i wonder if we could just explain in a little bit more detail what bacteriocins are?

lorna
so bacteriocins are proteins or peptides that are produced by all varieties or species of bacteria. so basically it's been found in 99% of bacterial species identified and they are designed by the bacteria to kill off like or competitive bacteria in the surrounding area.

so it's basically bacteria like to continuously live in a fighting environment. so you have some that are resistant and some that are producing bacteriocins. and they like to, when food is short, they will produce these bacteriocins to reduce the competition in the surrounding area so that their strain will gain from the nutrients that are there.

charlotte
and so we can use these naturally occurring compounds for our own benefit. in this case, to kill off the more dangerous bacterial strains in soft cheeses, the ones that can infect humans.

lorna
yes, it's a natural way to enhance control of bacterial growth. so you're not having to then use antibiotics either down the line through infection or as a preventative measure and in the growth of cheese.

charlotte
thank you so much, lorna. it really does go to show that microbes are everywhere and they affect our lives in so many big and small ways. even at christmas time.

thank you for listening to microbe talk. as usual, we love to hear your thoughts so please leave us a comment, maybe listening. and i'd like to wish you all a very merry christmas if you're celebrating and a happy new year.