What’s Listeria?

Image Credit: Clay Irving.

By now you’ve surely heard about the latest food-borne illness freak-out: cantaloupes contaminated by Listeria monocytogenes. Originating in Colorado’s Jensen Farms, the fruits have already caused 72 illnesses and 13 deaths in a total of 18 U.S. states. And those are just the numbers as of this writing, they’ll probably be higher by the time you read this. For reasons that I’ll explain momentarily, cases are expected to keep rising for some time.

Listeria doesn’t make headlines very often. Usually it’s the more familiar pathogens E. Coli and Salmonella that are responsible for outbreaks of food poisoning. As with these more famous cooties, Listeria is a bacterium with a propensity for turning up in animal feces (though it can also be found in soil), which then comes in contact with our food. But it has a few additional qualities that distinguish it from our friends E. Coli and Salmonella. For one thing, Listeria can reproduce in colder conditions, rendering it unfazed by all our fancy refrigeration technology. A dash of Listeria on a cantaloupe (or on the cheese or cold cuts that more typically serve as its intermediate home*) will gleefully multiply into a teeming hoard of bacteria without ever being improperly stored.

Another important difference is the Listeria bacterium’s lengthy incubation period in the gut of its human host. It can take several weeks for someone who ingested the microorganisms to manifest symptoms of Listeriosis – the actual illness caused by Listeria. The good news is that most people who eat Listeria-tainted food won’t get this malady; a healthy immune system generally destroys these pathogens before they have a chance to do any real damage. But in those with weaker internal defenses – older adults, pregnant women (and their newborn babies) and anyone with a compromised immune system – Listeria can escape the intestinal tract and cause serious illness. Symptoms include fever, muscle aches and diarrhea, but life-threatening complications like meningitis can also occur.

Given that the initial symptoms of Listeriosis are best described as “flu like”, we’re ensured an extra special flu season this year, as every under-the-weather individual with recollections of cantaloupe consumption rushes to the ER. Not that they shouldn’t. Listeria may not account for many food-borne disease outbreaks, but when it does cause illness, the fatalities are high, even when treated with antibiotics. When dealing with E. Coli and Salmonella, we’re accustomed to hearing figures in which hundreds or thousands of people are sickened but only a handful die. Listeriosis, on the other hand, can be fatal in as many as 25% of cases. If I’m doing my math correctly, this current outbreak is at about 18%. Pretty scary.

The textured rind of a cantaloupe. Image Credit: Bruno Girin.

And what can you do to protect yourself from killer cantaloupe? Clearly peeling it doesn’t do the trick. The trouble with produce of this sort is specifically that it does have a thick rind. People tend to view it as safe and forgo the more thorough washing they would give to something like lettuce. I’ve been scrubbing fruits with peels for ages (except bananas, one has to draw the line somewhere) and others in the kitchen act like I’m insane. But as I’ve explained again and again, the peel touches things that touch other things that end up in your mouth. It touches the knife that slices through the rind and right into the fruity center, it touches the plate onto which you place the sliced fruit, it touches your hands. Ugh, cooties everywhere! Just wash your fruit, okay. And if you fall into any of the high risk groups mentioned above, I’d recommend also having a look at the CDC’s prevention page for Listeria for a complete list of foodstuffs to avoid. It’s a pathogenic world out there.

* This is the first case of Listeria being found on cantaloupe.

Why Florida should stick to cats and dogs

As someone who spends a lot of time researching animals, I’ve read my share of articles on invasive species and I’ve noticed a certain pattern. In peer-reviewed journals and Cracked top-10 lists alike one word comes up again and again: Florida. I’ve been speculating as much for ages and now scientific research has confirmed that Florida does, in fact, have the worst invasive reptile and amphibian problem on the entire planet.

A recent study published in the journal Zootaxa after almost two decades of critter cataloging came up with a startling total of 137 introduced herpetofauna (a fancy, though also easier to type, word for retiles and amphibians) lurking in Florida’s great outdoors. An additional 3 species were intercepted before they could get too comfortable. Of the 137 outdoor dwelling herpetofauna, 56 are “established”, meaning they’re reproducing and, in many cases, pretty much taking over the place.

How did all these non-native beasties end up in the wild? The study examined animal introduction incidents in the Sunshine State from 1863 through 2010 and found that for the first half of the timeline, invasive species mostly trickled in as accidental stowaways on cargo ships, much like Guam’s infamous brown tree snake. But once the exotic pet trade took off in the latter 20^th century, things got a lot messier. Whether the animals got outside through stealth or by owner abandonment – some of these animals prove to be far higher maintenance than their owners anticipated – the pet trade ultimately accounted for 125 (about 84%) of the 137 species described in the study.

Part of the problem is Florida’s laws regarding such pets. While it is illegal in the state to release non-native animals into the wild without a permit, this is obviously not the easiest law to enforce. The authors of the study stress the importance of creating better legislation to prevent further species introduction. Personally, if I were running the show in Florida, I would just go ahead and immediately ban the acquisition of any new exotic pets. It’s just too accommodating of a climate for fugitive herpetofauna. The warm, humid weather, the luxurious tree coverage, the abundant insects… it’s ectotherm paradise. Ironically, some colder states like New York, where delicate exotic pets would freeze to death or get run over by a taxi within an hour of their escape into the world, have stricter laws about animal ownership.

Some of Florida’s more well-publicized invasive herpetofauna include the Burmese python, which grows to an average of 12 feet in length and can strangle prey as large as an alligator, and the Nile monitor – a muscular 6-foot long lizard with alarming sharp teeth and claws, not to mention its formidable swimming, climbing and running abilities. It is lizards that comprise most of the troublesome species plaguing Florida – 43 of 56 established invaders (and the state only has 16 native lizard species). While viewed by many people with less dread than snakes, lizards can be the more destructive of the two reptiles, devouring both plants and animals and compromising manmade structures with their incessant burrowing.

The charming Nile monitor. Image Credit: Chris Eason

The study’s authors begin by noting that, “Introduced species are second in negative effects only to human-mediated effects on native species, habitats, and whole ecosystems.” It’s a reminder that for all the accidental monsters visited upon the native flora and fauna of Florida, the biggest problems are ultimately created by the same invasive species that has caused widespread damage to so many other parts of the world – Homo sapiens.

Advice from mice, trade in your weekend benders for moderate daily tippling

Image Credit: Daniel Farrell.

Is consuming alcohol good for you or bad for you? The research often seems contradictory. Drinking is linked to health benefits one day and ghastly diseases the next. Amount of alcohol consumed seems to be one predictor of relative help or harm, but how much is too much? For example, is 14 drinks per week a lot or a little? Before you answer that question, you may want to ask about when (and how often) those drinks are being drunk, as patterns of drinking may play as large a role in determining how alcohol affects health as the actual amount consumed. To better understand the relationship between drinking and cardiovascular disease, University of Rochester scientists recently spent a month sousing up mice and found that different drinking schedules yielded very different health impacts.*

The advantage of working with mice is that, unlike human subjects who tend to choose when and how much to drink, alcohol consumption of experimental rodents is determined solely by their lab-coated bartenders. The mice were thus divided into three groups. A “daily-moderate” group received the mousey equivalent of two drinks per day seven days a week, while a “weekend-binge” group were instead assigned seven rodent-sized cocktails in a sitting, but on only two days each week.† A control group of teetotalling mice received a non-alcoholic cornstarch mixture (in order to match the caloric intake of the boozers). Additionally, all three groups were subjected to an “atherogenic diet” a high calorie, high fat menu designed to induce atherosclerosis – a thickening or “hardening” of the walls of the arteries caused by fatty deposits, which impedes blood flow and potentially leads to heart attacks and strokes. Essentially, they ate like average Americans.

While the daily-moderate mice consumed the same total amount of alcohol per week as the weekend-binge group (and ate the same unhealthy meals), their bodies fared considerably better. Mice in the moderate group actually emerged with healthier blood vessels than those in the non-drinking control group on the same diet, with 40% less build-up of plaque on their arteries. Meanwhile, the binge group had pretty dismal numbers with a 60% increase in arterial plaque build-up compared to the control mice.

The binge-drinking mice not only sustained more damage to their arteries, they also got the fattest. While all three groups were fed the same junk food diets, changes in body weight varied with different alcohol intake schedules. Over the course of 4 weeks, non-alcoholic control mice increased in mass by about 8.5%, while the moderate-daily-drinking mice only increased by about 5%, a modest improvement. The binge drinkers, however, gained double the weight of the control group and more than triple that of the moderate drinking mice, adding a mighty 17.5% to their initial body weight.

How can the same amount of alcohol protect the cardiovascular health (and figures) of the daily drinkers while doing so much damage to the bingers? While exact mechanisms of action are yet undetermined, part of the difference lies in how the two patterns affect cholesterol in the blood. While both groups of boozing mice experienced an increase in HDL (the “good cholesterol” associated with removing build-up from arterial walls) their drinking regimens produced opposite effects in LDL levels (“bad cholesterol” that can cause build-up). Relative to the control group, the daily-moderate group showed a 40% decrease in LDL while the unfortunate binge group experienced a 20% increase in LDL.

Alcohol metabolism itself differs in moderate versus binge drinking episodes. While much to-do has been made over demon alcohol, its metabolite acetaldehyde is the more damaging molecule. When alcohol is consumed, the body breaks it down so that it can be removed. It’s a two-step process, first to acetaldehyde and then to acetate (a nontoxic chemical similar to vinegar). This is all fine and well except that the supplies needed to do the second step (breaking down nasty acetaldehyde into benign acetate) run out after a few drinks worth of metabolizing. So with binge drinking, acetaldehyde hangs around causing problems until the materials required to deal with it can be replenished.‡

Of course cardiovascular disease isn’t the only health concern out there. This study does not aim to address the overall effect of drinking patterns on all systems in the body. But it’s information worth noting for those who believe that abstaining from alcohol during the week is sufficient to balance out weekend bacchanalian excesses. That and it might be a good idea to lay off the cheese fries.

* The study will be published in a forthcoming issue of the journal Atherosclerosis. If you’re too impatient to wait for it, you can download the accepted manuscript in all its unformatted, un-copyedited majesty.

† The blood alcohol levels attained by moderate vs. binge drinking mice were roughly 0.07% and 0.23% respectively. This placed the moderate daily drinkers at a level where they could still legally drive in most U.S. states….if they weren’t mice, that is.

‡  Lingering acetaldehyde is also a major contributor to hangovers.