Science Interviews


Sun, 18th May 2008

Kitchen Science - Food Poisoning and Passing Bacterial Wind

Simon Park, University of Surrey

Listen Now    Download as mp3 Part 1,2 from the show Your Bacterial Body

Ben - For this weekís Kitchen Science Iíve come to the university of Surrey in Guildford and Iíve met up with Dr Simon Park. Hi Simon.

Simon - Hello.

CampylobacterBen - Simon works on campylobacter and this is actually the most likely cause of food poisoning in the UK.  But not many people know about it so Simon, how does campylobacter get into us?

Simon - It lives in the farm environment, in all the poultry flocks. So poultry flocks in the UK are actually endemically contaminated with campylobacter. When it infects chickens itís perfectly at home in that environment and the chickens are perfectly healthy so itís a commensal of chickens. During the slaughtering process the gut contents of the chicken contaminate the external meat and the carcass of the chicken. It goes into the supermarkets, we take it into our homes and itís really from that major source that we get campylobacter infection.

Ben - What does it do to us when it does get in?

Simon - When it gets in it causes a very painful diarrhoea. Itís one of the most painful types of food poisoning. A lot of people that have the infection are mistakenly diagnosed as having appendicitis. It causes profuse, watery and occasionally bloody diarrhoea. In most people that have acquired the infection that clears up naturally over a two week period. Occasionally you can get relapses, stomach pain that can last up to 2 or 3 months afterwards.

Ben - Usually the stomach acid and the enzymes in our stomachs would break down the bacteria that we get on our food so how does campylobacter survive?

Simon - Unlike a lot of other organisms like salmonella and Ecoli O157, itís very sensitive in the laboratory. If you subject it to acid conditions in the laboratory it dies very quickly. What you have to remember is that the stomach can have a very low pH. It can be very acidic around pH1, pH2. Itís only that acidic at certain times, when thereís not a lot of food in there. When you eat the campylobacter itís quite likely that it can be protected within lumps of food and lumps of chicken and thereby survive the process of going through the stomach.

Ben - We also know that all of our digestive system is lined with its own complex spectrum of different bacteria; many of which we live with very happily that donít make us ill. How does campylobacter establish a colony amongst all this other bacteria?

Simon - Itís quite a specialised organism. It has quite a different shape compared to a lot of bacteria. What you see when you look down a microscope is a very fine corkscrew-like organism that moves through liquid as if it were a corkscrew, spinning through an environment. That gives it a relatively unique ability to move through viscous environments. When it comes into the gut of a human thatís consumed it what it does is it follows a path or a trace of chemicals that lead it to the wall of the gut. Whilst the lumen of the gut is packed full of bacteria the very narrow environment between the tissue of the gut and the faeces is relatively unoccupied. It swims towards that and its corkscrew shape and its drilling ability allows it to penetrate the tissue. It has a specialised niche that it occupies in the gut.

Ben - Once itís take hold of that niche, how does it actually do the damage? Does it multiply so quickly that its sheer numbers hurt us or does it release a toxin?

Simon - It certainly multiplies into huge numbers but as to how it causes illness - I started working with it about 20 years ago and we still donít know. It does produce a toxin and it also has been shown to invade gut tissue. These are two possible mechanisms. Thirdly, it maybe that because you get such high numbers of the organism there the immune over-responds to the infection and it damages the gut tissue in terms of collateral effect. The actual symptoms of diarrhoea, inflammation and pain may be generated by your immune system overreacting to the infection.

Ben - Well, it certainly sounds like something we should avoid. Is there any way we can avoid it?

Raw ChickenSimon - Itís very difficult to avoid if you eat meat and particularly if you eat chicken. It contaminates, depending on what study you read, up to 70-90% of supermarket chicken. You must be aware of that and when you handle things like raw chicken you need to use separate chopping boards and separate knives to do that. Also, be very careful when youíre washing your hands. If, for example, you take a piece of chicken out of the fridge, you touch it, you start chopping it up into joints then think about washing your hands. The first thing you do is you go over to the sink, turn the taps on and you touch the taps. You then wash your hands and the next thing you do is turn the tap off. You immediately re-contaminate yourself because you touch the tap.

Ben - On the subject of transmitting bacteria itís really the reason Iíve come to see you because for this weekís Kitchen Science. We know that coughs and sneezes spread diseases and thatís how respiratory infections actually get transferred. You were thinking there might be another way that bacteria could be transmitted.

Simon - Yes, I have two sons. Joe and Josh who are aged about 5 and 7 and theyíve developed and obsession with this homemade biological prank: farting. I thought, why do we find this so offensive and why is it dangerous. Can I demonstrate this to my children to stop them doing it? I thought of some experiments where I could actually prove whether or not farts could transmit bacteria. What Iíve done is Iíve taken some Conkey agar plates that are very good at culturing faecal bacteria. Iíve done some very crude experiments where weíve exposed the plates to people farting in terms of a naked fart (no pants and no jeans on) and also people farting with underpants and jeans on.

Ben - So youíve set this up by passing wind, shall we say, on whatís called a MacConkey agar plate.  I believe that you actually have some of these plates to actually show us.

MacConkey Plate - Pants On

MacConkey Plate - Pants Off

Plate 1 - Exposed to flatulence through underwear and jeans

Plate  - Exposed to flatulence without underwear and jeans

Part 2 - now in Simon Park's Lab

Ben -   One of these plates was farted on through jeans and pants. The other one was exposed to flatulence completely bare. We d like a bit of Naked Science here, of course. There are two plates. One of them clearly has some colonies on but the other one is completely clean. So, Simon, which oneís which?

Simon - The plate thatís totally clear is the one that was exposed with pants and jeans on. Obviously the pants and jeans are being very effective at filtering out any faecal bacteria. The plate that was exposed to the naked emission has a splattering of red colonies on it. Theyíre very indicative of Ecoli thatís a very common faecal bacteria. Itís a very good indicator of faecal contamination.

Ben - So we are definitely transmitting bacteria with every flatulence.

Simon - Yes absolutely. Thereís such huge numbers of bacteria in a stool that itís inevitable that we would transmit bacteria after flatulence.

Ben - Weíve been able to catch these bacteria on an agar plate which is designed to feed them and enable them to grow. But theyíve been living inside us so theyíve been living in an environment thatís quite low on oxygen, thereís quite a bit of methane and hydrogen sulphide. Would these have actually survived if we hadnít encouraged them?

Simon - Yes. Thereís a lot of bacteria in the gut and the vast majority are strictly anaerobic so they canít grow in the presence of a normal atmosphere. They can only grow where thereís no oxygen. Obviously those bacteria, whilst they might have landed on the agar plate, they wouldnít have been able to grow on the agar plate. The ones that weíve isolated are probably Ecoli or coliforms that are very common in the gut. They are very robust bacteria so they will grow in air, without air and on agar plates so these are capable of surviving outside in the environment for hours if not days.

Ben - could this mean that people who choose not to wear underwear, for example Scotsmen wearing a kilt or naturists, could actually be transmitting more bacteria every time they fart?

Simon - Because thereís no protection or filtering I guess thatís true, yes.

Ben - So, we now know that jeans filter out some of the bacteria that might otherwise get transmitted through flatulence but could there be anything else that gets transmitted? Is there anything that might get through the jeans?

Simon - There are obviously viruses that are many orders of magnitude smaller than bacteria. Things like the norovirus which is a very common cause of vomiting and some of the astroviruses that are common in causing diarrhoea are quite likely to pass through the fine holes in things like underpants and jeans.

Ben - And did you show your sons? Have you convinced them now that farting in the house is not right?

Simon - They were quite shocked. One of the first things they asked me was Ďwere they friendly bacteria or bad bacteria. I had to tell them they were relatively friendly bacteria.

Ben - So obviously coughs and sneezes spread diseases, itís possible that farts do as well. Do you think we should ban farting in hospitals?

Simon - Possibly. Itís very difficult to ban actually because everybody does it. Generally, on average itís about a pint glass full of gas that we emit every day. Most of us actually fart during our sleep when all of our muscles are relaxed. Even those of us that donít fart during the day: almost all those fart during the night unknowingly. Itís very difficult to prevent in a hospital environment.

Ben - So itís best we just stick to normal personal hygiene Ė keeping our hands washed with alcohol and that sort of thing. I think the overall lesson we can take from this is it may not be best to go to a naturist's barbecue.



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