What’s with the Weird, Scary Cloverleaf Bacteria?

Huh, I guess we took a little break there for a while. Sorry about that. We don’t even have a good excuse for why we haven’t been updating. It’s not like we had a death in the family, or a medical crises. We didn’t even go on vacation. Well, here’s a cute picture of a dog in a sleeping bag:


All better now?

Anyway, on to what I really wanted to talk about today: Antibiotic resistant superbugs!

The CDC recently sent out a press release calling for immediate action to halt the spread of antibiotic-resistant bacteria that they’re calling CRE. The acronym stands for Carbapenem-Resistant Enterobacteriaceae, or in plain English, bacterial strains that normally live in our intestines but can wreak havoc when they get into the blood, bladder, or in wounds, and have acquired the ability to withstand our most-effective antibiotics. Apparently these antibiotic-resistant strains have been on the rise for about 10 years now, but they are finally becoming widespread and are incredibly lethal, killing about half of those who are infected. These strains do not pose a great threat to an average, healthy person who spends little time in the hospital, but can be very dangerous to your elderly grandmother, or anyone staying in a hospital or long-term care facility.


But now I will get to what I really really want to talk about today: The image that accompanies the CDC press release. It’s a backlit agar plate, held by blue-gloved disembodied hands. The bacteria growing on the plate makes four unusual clover leaf shapes. Somehow the picture comes across as threatening, even though few people know what those clover leafs actually mean. I have an advanced degree in microbiology and I still had to look it up.

Turns out that cloverleaf plate is the end result of a Modified Hodge Test, which is really just an adaptation of the cloverleaf test developed by Kjellander and Myrbäch back in 1964. The test tells you whether or not a certain bacterial strain is secreting an enzyme that can break down a specific antibiotic, which tells you if it is resistant to that antibiotic. If your strain makes a nice, well-defined clover leaf shape, then it is resistant to the antibiotic. If the plate looks more like a dark circle with a cross through it, then the strain is susceptible to the drug.

How does it work? Well, first you cover the plate with a solution of garden-variety E. coli. Why E. coli? This bacteria is susceptible to the antibiotic and makes a yellowish lawn all over the plate, except for a circle around the little white disk, which is impregnated with the antibiotic. The antibiotic from the disc seeps into the surrounding agar and prevents any E. coli from growing there. Next, you streak a line of a bacteria that is resistant to the antibiotic coming out from the white disc, as well as a strain that is susceptible. These are the positive and negative controls, respectively. Then, you streak a line of your unknown bacteria. I think the CDC did this part twice so that the plates would look like luck four-leaf clovers, instead of the three-leaf ones, but it does look nifty, so I suppose you can’t blame them. Then, you culture the plates at around 98 degrees and see what grows.

First of all, the E. coli will grow everywhere, except for where there are antibiotics leeching into the agar. The other bacterial strains that produce the antibiotic-eating enzymes will be surrounded by E. coli growth, since the enzymes make the agar safe for the E. coli This creates the round leaf shape. Strains that are susceptible to the antibiotic and do not make these enzymes will grow poorly next to the disk, and will not be surrounded by E. coli, so the dark (bacteria-free) part will look more like a piece of pie.

And that’s why that picture of the cloverleaf plate is so scary, but it shows several strains of bacteria that are circulating in our hospitals that don’t give a *bleep* about our antibiotics. Even scarier, is that these bacteria have the potential to spread the genes for these antibiotic-eating enzymes to other bacteria, which could results in all sorts of new, deadly “superbugs.”

What can YOU do about CRE? Unfortunately, not much. The responsibility is going to fall on the hospitals to institute stricter cleaning regimes and isolation of CRE-positive patients to prevent its spread. Also, public health labs will need to do more antibiotic resistance testing (AKA Clover leaf plates!) to find the CRE-resistant strains, track their movement, and to make sure that they are not treated with useless antibiotics.

BUT! You can act wisely toward the bacterial strains that are still susceptible to antibiotics.

-ALWAYS finish ALL of your prescribed antibiotics.

-NEVER take antibiotics for a viral infection – and don’t pester your doctor about it, because sometimes they give out antibiotics just because they’re tired of being hounded when whiny kids have ear aches.

-Buy organic meats and dairy products that do not come from animals that have been treated with unnecessary, constant antibiotics.

-Do not buy antibacterial soaps or other antibacterial products. The antibiotic in these products does not make you any safer, and tends to accumulate in the environment, where bacteria form a resistance to it.   If you much, alcohol-based hand sanitizer is ok.

The superbugs may still win in the end, but at least we can stave off their dominion for as long as possible…

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