liveonearth (liveonearth) wrote,

Microbiology: Why Pregnant Women Shouldn't Eat Soft Cheese

There's this lovely bacterium called Listeria monocytogenes that is gram positive and likes to grow in dairy products. It doesn't produce any toxins or spores, it just gets in your cells and kills them. It gets started invading your body via the gut (gastroenteritis), but can take over much more of your body (invasive disease) given enough time. It is one of just a few bacteria that gets inside of your own cells (though this is standard practice for viruses) using a "zipper" mechanism. Once Listeria is inside your cells, the normal macrophage cleanup crew can't find it. It swims inside of host cells by making actin polymers! Listeria can grow at 4 degrees celcius, and is one good reason to we keep meats frozen.

Some 500 deaths/year are caused by Lysteria, and the pregnant woman and baby are most suceptible. The most common way for a pregnant mother to be exposed is by eating soft cheese. The first signs/symptoms of gastroenteritis are watery diarrhea (no blood), fever and headache, myalgias (flu-like). No vomiting. If a 1-4 week old newborn has meningitis, suspect Listeria. It can also get in the placenta during pregnancy and cause sepsis and abortion. Tx for invasive disease: ampicillin.

Clostridium is a strict anaerobe, forms spores and has exotoxins. The four relevant genera are difficile, botulinum, perfringes and tetani.

Clostridium tetani is what is sounds like; it causes tetanus, aka "lock jaw". I get vaccinated for it every 10 years or so, seems like. Advanced tetanus is a state of strong muscle spasms that don't let up---like a siezure that doesn't fluctute or end. The toxin blocks inhibitory neurotransmitters GABA and glycine, so the nerves can't stop telling the muscles to fire.

Clostridium botulinum is the bug you get from eating food out of bulged cans. It forms spores so it can survive for a very long time in all kinds of conditions. The bacterium is common in soil and water and the bug of many animals. Botulinum can be found in improperly home-canned foods with low acid content, (such as carrot juice, asparagus, green beans, beets, and corn). It can be killed and the toxin disarmed by cooking for 3 minutes at 250 degrees F.

Botulism is familiar to me because my dog Loki got it once. I got to watch the progress of the entire illness, and the process of finding out what it was. Definitive diagnosis is difficult because it's hard to culture. Botulinum bacterium is slow growing and needs hours of warmth in an airless environment to be fruitful and multiply--and make toxins sufficient to paralyze anything. The toxin blocks the release of acetylcholine from nerve endings. According to my prof the toxin is heat labile. Boiling your food for 10 minutes will kill the bacteria and destroy the toxin.

Symptoms include dry mouth, double and/or blurred vision, difficulty swallowing, muscle weakness, drooping eyelids, difficult breathing, slurred speech, vomiting and sometimes diarrhea. These symptoms may continue to cause paralytic ileus with severe constipation, and will lead to paralysis. The pattern of nerve damage occurs because the toxin affects nerves that are firing more often. The respiratory muscles are affected, and may cause death due to respiratory failure. Loki's hind legs were the first part to stop working, though he also had slurred speech.

The other two kinds of botulism (besides foodbourne) are infant and wound types. Infant botulism is caused by eating the spores which then grow in the intestines and release toxin (something about HONEY as if it is an acronym).

Clostridium perfringes grows anaerobically, and causes either food poisoning or gas gangrene. Gas gangrene seems to happen to people who have been in motor vehicle accidents. The spores are in the soil, and when they get into human tissue and germinate they make gasses which are trapped in the tissue. Gas gangrene refers to this gas, which has a certain feel and sound (crepitus) when palpated. If not treated it causes jaundice, hemolysis and has a high mortality rate.

There is no vaccine for C. perfringes, it is treated with penicillin and good wound care. It's normally present in the colon and vagine.

Clostridium dificile infects the colon. It is probably present normally, but with high levels of antibiotic use, a person may kill off their normal gut flora and leave themselves exposed to an invasion by this species.
Tags: bacteria, digestion, food poisoning, microbes, pregnancy, public health

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