turkey
 
A turkey of a turkey
Bezillions of bugs!
Meat of the matter
Antibiotics in agriculture
Replacing antibiotics in feed?
Freaky food stories -- all true
 
bacteria


 


strands of dna













 















ground meat-closeup

Foul food

ground beef Mortified by microbes?
Let's start by mentioning that microbes are everywhere -- in the dirt, on our skin, in our food -- even in our guts. Scientists say the bacteria in your intestines outnumber the cells in your body. Since you're alive, most of those bacteria must be harmless or helpful.

Some bacteria, however, are living nightmares, and an increasing variety of them are showing up in our food. Since the deadly Escherichia coli (E coli) O157:H7 first surfaced in the 1980s, we have learned that only 10 to 100 cells can cause grave illness (most organisms need many more to become infectious). Salmonella, the long-time king of food-borne bacteria, is showing up in more and more foods, including unbroken eggs.

Add it up: Now we have to worry about new bugs -- and old bugs in new places.

Where do antibiotic-resistant bacteria come from?

    bacteriaSome arise from random mutations that allow one bug to overcome a particular drug. The mutation may decompose the antibiotic or eliminate whatever part of the bacterium's metabolism the drug attacks.

    bacteriaMore ominous -- and probably more common -- is the sharing of chunks of DNA among bacteria. These chunks of DNA can confer resistance to many antibiotics. So instead of having to evolve resistance to, say, streptomycins, penicillins and the other common classes of antibiotics, a pathogen may get multiple resistance as a malignant gift from an organism -- even from another species -- that's already resistant.

In any case, when animals are taking antibiotics, only the resistant bacteria survive the drug, so new generations will likewise be resistant. That's why doctors tell you to take a full antibiotic prescription -- to make sure even the bugs with some limited degree of resistance are killed.

Antibiotics + bacteria = a classic example of survival of the fittest -- on a microscopic scale.

A toxic tale
Generally, bacteria cause illness by creating powerful chemicals called toxins that gum up some necessary function in the body. Toxins may interfere with nerves, muscles, digestion or blood flow, and can kill, even in minute quantities.

It's unclear why bacteria make toxins. They may have evolved as a means of self-protection, but Charles Kaspar, who studies the deadly E coli O157:H7 at the University of Wisconsin-Madison, says chance is a more likely explanation. "It's probably an accident of some sort, because I can't see a competitive advantage of causing a lethal effect on the host."

In other words, why would more bacteria survive by killing their hosts? In evolutionary terms, a better strategy would be to let your host live so you can continue your detestable, parasitic, sponging existence forever.

A strange sort of ally
Before you get yourself in a high dudgeon about bacterial toxins, look at the bright side. Toxins -- whether made by snakes, insects or bacteria -- are exquisitely targeted biological molecules that, perfected by evolution, work in tiny doses. This makes toxins, oddly enough, useful in medicine.

The seven botulism toxins, made by a food-spoilage organism, are incredibly powerful. According to the Merck Index, the minimum lethal dose of botulinum toxin A in mice is 0.3 nanograms (0.0000000003 grams!) per kilogram of body weight.

Botulism toxins kill by jamming nerve signals and paralyzing muscles. Fear of botulism explains why you shouldn't eat food from a swollen can. But non-lethal doses can treat abnormal muscle contractions, and now, according to one doctor, migraine headaches (see "Taking a New..." in the bibliography).

Another killer, E coli O157:H7, produces a substance called verotoxin that can kill by destroying the kidney. But Canadian scientists recently used verotoxin to waste cancer cells in the laboratory (see "Poisonous Friend" in the bibliography).

Before we get too far off course, please serve up the scoop on food-borne disease!


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