Transcription
[Music] Let's talk a little bit about pathogens and foodborne illness, and how, how it works; in other words, how do these things happen? How do these illnesses occur with this contamination in foods? There are really two scenarios that we can think of for bacterial illness. In both cases, we have a pathogen, or a disease-causing organism, that is present in the food.
In one case, the pathogen is actually able to grow; it reaches an infectious dose, the level or threshold at which, beyond, beyond which it can cause illness in a person, or it produces a toxin that makes that person sick. The food is then ingested, and the illness occurs. The other possibility is that the pathogen is present in the food but does not grow. The food is consumed, and the organism, because it is so infectious, is actually able to multiply within the host organism, or the host individual themselves, causing an infection. That infection, infection in turn can cause damage, as infections will do, or a toxin produced by the infectious agent can then make someone ill. Understanding infection and intoxication is important to understanding foodborne illness.
In the case of infection, we're dealing with an illness that is caused by a living pathogen. The food is consumed; the pathogen either induces illness right away, or it multiplies inside the body and then induces illness. In the case of intoxication, it's caused by a toxin or metabolic product of the pathogen growing in that food, and the pathogen may not actually be alive in that food. Um, it creates this toxin; the toxin gets into the body and causes someone to be ill, or it can also grow in the person's body if it is still alive and create the toxin, but in this case, it is really the chemical itself causing the illness and not the organism per se.
Detecting foodborne illness outbreaks is a big challenge, challenge. It takes a lot of people being exposed to a food that is contaminated to even cause a certain number of those folks to become ill. Of the ones that become ill, many will become well on their own or recover at home; they won't seek medical care. But there will be some who are more severely ill than others, and they will seek medical attention. In that case, there may be a specimen taken from that person that is sent to the laboratory and is identified as a confirmed case of a foodborne illness outbreak. So we can see that the number of confirmed cases of a foodborne illness outbreak is a gross underestimation of the number of people that may have been exposed to that contaminant, and then that confirmed case on, in turn, is reported to the health department and the Centers for Disease Control, where it can then be confirmed as having been from a certain type of food.
Now, how long does it take for that whole process, from the bottom of the pyramid to the top of the pyramid, to occur? It can take a long time, and actually one of the big risk factors, or one of the big challenges, uh, faced in these investigations is the amount of time it takes from the time someone ingested a contaminant to when they're actually ill. In the case of something like salmonella, it's relatively fast, anywhere from 6 to 48 hours. With E. coli, it might take upwards of a week, 1 to 8 days. Listeria can be especially challenging; it can take anywhere from 2 weeks to 70 days after that product is consumed before the person actually falls ill. So that's a great challenge, trying to find out what that person ate, especially if it was 70 days ago. Staphylococcus aureus produces a toxin that makes people sick, and that happens quickly, in 1 to 6 hours. Clostridium botulinum also produces a very devastating and deadly toxin; it takes 12 to 72 hours for someone to show signs of that illness. And the chart to the right of us on this, uh, slide is actually available from the FDA, and it summarizes some of the symptoms and ways to diagnose the common foodborne illnesses.
Let's talk a little bit about a pathogen versus a spoilage organism. Not all microbes are pathogens; there are many common organisms that are present in our foods that are perfectly harmless to us. Um, many of them will cause spoilage; we've all been familiar with opening the container of milk from our refrigerator and realizing that it had gone sour. Food can smell or look bad and not necessarily induce illness; it might just simply be spoiled and not taste very good. However, on the flip side, food can seem perfectly fine and still make you ill. The people that, uh, ate the romaine lettuce, for example, in this recent outbreak this spring with E. coli O157, the lettuce probably tasted perfectly fine; it didn't take very many of those organisms to make someone sick. It's a key point to understand your enemy; remember the food doesn't have to look or smell bad in order to make someone ill.
Let's talk a little bit about, about bacterial growth and understand how it is that these organisms are able to multiply. This is kind of a fun exercise and one that relates to me as I ate plenty of pizzas leftover in college. Let's think about this: you leave three pizzas on the counter overnight. Which one is the safest one to eat next morning? One that was cheese, meat only, or a combo meat and vegetables? Well, let's think about the risk assessment of this situation. In the case of a cheese pizza, we have a relatively low moisture; it has been baked; we know that cheese is cultured, and the sauce is acidic, so that seems fairly low risk in that regard. Look at the pizza with meat; is the meat more risky? You know, it's still very low moisture; it's been cured or salted or preserved if it's pepperoni, um, so it's still a fairly low-risk event. But if we look at the combo, what's the difference? Moisture. The combo has the highest risk; remember we have those fresh vegetables laying on top, so there might be tomatoes, there might be bell peppers that have been sliced and laid on top; they also did not receive any kill step when they were put on the pizza, so potentially if they survived the cooking process, we might have a pathogen that was able to grow overnight on that pizza. We have to think about this factor: FAT TOM. FAT TOM is an acronym that is commonly used in microbiology in foods; it stands for food, in other words the type of food that we're dealing with; acidity, how acid is that food, how low is its pH; time, how much time have we allowed this food to be in a scenario where there could be growth; temperature, is the food kept in a cold condition, very warm condition, or something intermediate where microbes can grow; oxygen, is oxygen available, uh, will it enable the organism to grow faster if it is present; and moisture, if there's enough moisture present, microbes are able to grow. At lower moistures, typically, uh, microbial growth is slowed. So FAT TOM does not necessarily refer to, uh, a big pudgy cat or myself if I've eaten too much food; it actually refers to the conditions that we can think of when we're talking about microbial spoilage.
Let's start with temperature. We often refer to something as the 41-40 rule, uh, and this really refers to what I call the danger zone; it's that intermediate temperature between 40° and 140° F where many microbes are able to grow rapidly. Below, above 140°, um, it's really pretty warm; many microbes will actually die, and, uh, it's very difficult for them to grow; it denatures the proteins that they need to grow in their cells. Below 40°, it's very, very cold; microbes don't have any way to control their internal temperature and slow, when, so when it gets that cold, everything slows way down, and of course, even when we get down to the level of freezing, some of the microbes may survive, but they won't be able to grow. So our goal is always to try and avoid very much time for food to dwell in that danger zone between 40 and 140 degrees Fahrenheit; that's where most microbes are happy and able to grow the best.
Let's talk about acidity; remember that was the A in FAT TOM. pH and growth. pH is the scale that we use to determine acidity or measure acidity. A pH of seven is considered neutral; above seven is considered alkaline; below seven is considered acidic. And it's important to know what the capability of microbes are to deal with acidity. As we can see from this chart, molds are incredibly good at growing over a wide range of acidities; they're very effective at, uh, kind of overcoming the barrier of acidity. Yeasts are also pretty effective, but, but less so than molds, and we can see some of the different pathogens that we've discussed, such as Salmonella, Clostridium botulinum, and Campylobacter; they have much more limited ranges of pH that they can grow on, typically centered roughly around neutrality; may be able to grow a little above it or a little below it, but acidity is, of course, one of the time-honored ways that people use in food processing to control microbial growth. This is a pH of some of the common foods that we might encounter in our everyday diet. Ground beef, for example, slightly acidic; chicken, again, slightly on the acidic side, but basically neutral; butter, cheese, milk, vegetables, uh, and we can see that some of the products that we deal with, such as fruits and vegetables, can have wide-ranging, uh, pH differences and often are on the acidic side. Look at vegetables; go all the way down to 4.2; fruits, all the way to a pH of 2, which is fairly acidic. This helps them be more resistant to the growth of pathogens and microorganisms. Now, as the, the text says on the right-hand side, we know that cheese is made from milk, and if we look at the pH of cheese, it's about 4.9 to 5.9, whereas the pH of milk is much higher, 6.6 to 7. Why is its pH different? There's a very good answer for that; cheese is basically a fermented food product; in other words, microbes are involved in the preserving of, um, cheese and making of cheese; they're basically converting lactic, the, the lactose sugar into lactic acid. So it's, it's a microbially produced food, and it's becoming, um, a different product. Now, is it more or less microbiologically stable than milk? Well, the answer to that, to that is it is more stable because it's a little more acidic, so some of those organisms that can't grow at that lower pH are knocked out of the picture, and we make an actually more stable, shelf-stable food product. This is why making cheese is one of the earliest ways that man was able to preserve milk products.
Let's talk about how bacteria grow in the right conditions. Imagine that there's a single bacterium or a single cell sitting on, uh, your food product or your equipment; given the right conditions, it can grow in less than a day into over a million cells. And this kind of describes the growth cycle that we typically see with bacteria. This early phase we call the lag phase; the bacterium is just kind of getting used to its environment and gearing up to grow; sometimes it has to turn on certain genes or switch off others in order to be able to grow properly on that set of conditions. During the time we call log phase, it's growing exponentially; sometimes bacteria can replicate or make new copies of themselves every 20 minutes, and this is the period of time in which microbial growth occurs very, very quickly, and eventually it reaches a stationary phase or the carrying capacity of that environment; you know, it's, it's basically maxed out that environment; it can't grow anymore, and so you just have a stable population sort of sitting there. Eventually, it goes into a decline phase as there's a buildup of waste products from those cells, a lack of nutrients, and the cells start to die off. But even in that decline phase, the numbers of microbes can stay very, very high, and especially if that product has been stored under conditions such as cold storage, you might have those microbes sitting around for a long time, still able to cause disease.
Let's talk a little bit about log reductions, and by this we don't mean, uh, cutting down trees; there's no lumber involved. Log reductions is something we often talk about when we talk about food processing and ways to control or kill pathogens; it simply refers to a 10-fold drop in the population, and we will often say that, say a pasteurization process might be a four or five log drop; that basically means it's a 10,000 or 100,000-fold reduction in the population. So let's say we look at, um, this example; we have a very, very high population that is sitting there; we have a one log reduction, two log, 3, 4, 5, and 6 log. But you can see that even after a six log reduction, which is a pretty rigorous pasteurization, we've gone from this massive population down to a single cell. So we have to remember that the starting population in a food product will help us determine how effective our log reduction or pasteurization is.
Let's talk a little bit about spore-formers versus non-spore-formers. This is another factor for you to think about as you look at and evaluate biological hazards. Some bacterial species are able to form spores, and this is a stress response; it's like a bacterial seed; the cell is basically dormant and kind of hunkered down until favorable conditions develop for it to grow and germinate. These spores can be very hard to kill. Working in the laboratory, one of the ways that we would test our steam sterilizers was using a species of Bacillus; at 250° Fahrenheit, 15 PSI per square inch of, of saturated steam, uh, it takes 15 minutes to kill those spores. So this is an organism that can, um, be pretty hardy and can survive literally for hundreds of years under the right conditions. Because spores are very hard to kill, we have to use special measures in, in such items as canned foods to make sure that we're not going to have anything like botulism present. We list below some of the vegetative bacteria or non-spore-formers that we typically deal with; these are Listeria, E. coli, Salmonella. We're a bit relieved that those bacteria don't produce spores because that means that they can potentially be much easier to kill, but we also have to worry about the spore-formers that I just mentioned, Bacillus cereus, Clostridium botulinum being examples. These bacteria are able to form spores and can, can be very, very resistant to heat processes. Okay, let's talk a bit about addressing these biological hazards in your food safety plan. How do you go about that now that we know a little bit about these organisms, some of the things that can impact their growth, and some of the different types of organisms that we're talking about? How do we address them?
Some common pathogen examples based on our past history with these foods include things like Salmonella in eggs, chicken, uh, black pepper, tree nuts, lettuce. So Salmonella can occur in a number of different food items. Campylobacter, which we typically associate with poultry products, raw poultry products. E. coli is common in beef, uh, vegetables; we've seen it also in fruit juices because some of the E. coli strains are very acid-resistant, as well as some tree nuts and fresh produce such as lettuce. Uh, vegetables can also be impacted, for example, by E. coli, Salmonella, and E. coli. Um, milk products can have various contaminants; if you think about it, this comes from a cow; cows can have various, uh, infectious agents in them; they can also be exposed to various things in the, the growth environment, uh, of the, the cow or in the farm environment. So there are a number of different pathogens, including many of the ones that we've just listed with the other food products. Seafood has some unique pathogens, including Vibrio, Clostridium botulinum, and certain types of parasites. Um, we mentioned lettuce already; E. coli, Listeria, Salmonella again, very common, and the tree nuts; not only are they affected by Salmonella and E. coli, but Listeria as well. So these are some examples that we see in some major categories of foods.
What organisms do you include in your plan when you're coming up with your food safety plan and evaluating the biological hazards? Well, you really have to look at the whole environment that's going to be, um, exposed, when, or the food is going to be exposed to when you're, you're doing your process. You have to think of the history of the ingredients that you're going to use in that food process; the type of packaging, which will impact things like oxygen and moisture; um, you also have to base some of this on past recalls or plant history. So did the food processing facility that you're doing this product in have a past history of some issue that became a concern, uh, for example, there was a food processing facility dealing with cereal products that had Salmonella as a resident strain in that facility; it appeared to be hiding out in the bricks of the actual walls. So they had repeated incidents with salmonellosis related to the cereal products produced in that plant over many decades. So it's good, it pays to know the actual history of the facility you're working with. Also, regulatory guidance is something to look at as well; there's a lot of good information out there that FDA has available for you. We also have to think about, uh, the equipment that we're using to do our food processing; do we have past results from our environmental monitoring programs where we actually go out and swab and look for contamination? Are there known risk factors for those products? You know, thinking back to our FAT TOM example, do we know something about the characteristics of the food that make them more susceptible to certain types of organisms? You also have to equipment consider your equipment design; any niche areas, for example, on, um, conveyor belts; you might have something like a hollow roller that is able to, to make the belt roll, but in, in the process of, uh, making that roller, they may not have sealed it up properly, so there's a void inside that could enable something like Listeria to become established on that food processing line. And again, even with the equipment, there could be ped issues or regulatory guidance. Um, the FDA will often publish the results of their investigations when they're looking at a foodborne illness incident, and you can actually go online and find some of the information in there where they actually list the contributing factors that may have caused a foodborne illness outbreak and how they're related to the equipment. This is a very good resource that is currently available. FDA's preventive controls guidance in Appendix 1; it talks a great deal about FDA's historical data that they have collected, um, based on their past recalls, their past investigations; it identifies the risk by different types of product groups, and it breaks down those risks into each of the three core types of hazards that you might look at: biological, chemical, and process-related hazards.
Some tips on biological hazards and identifying them: be as specific as possible; look at the raw materials that you're using; look at your processes and, and get it down to as low a level as you possibly can so that you can have really good U parameters describing, uh, what are the conditions that could possibly cause a hazard; and be consistent with your current scientific knowledge. Remember, there's a, a lot of information out there; many of it, many of these things are easily accessible online, and try to get the most lat, the latest and most up-to-date information. Uh, you can group biological hazards together to make it easier to manage in your HACCP plan, but remember you can only do that if there is no significant difference in the parameters that are related to that hazard; things like acidity, pH, um, presence or absence of oxygen; these are all different factors that might be similar for different organisms, and it may pay to actually lump them together and make it easier to control, but you have to make sure that those are the same sets of conditions that affect each of those [Music] organisms.