Mike the Mad Biologist

An outbreak of vancomycin resistant MRSA, or VMRSA, would be the ‘perfect microbiological storm’, even worse than vancomycin resistant Staphylococcus aureus (VRSA). The only currently available antibiotics that would be effective against it would have to be used off-label, and are not very effective against sepsis (bloodstream) infections. Fortunately, VRSA is observed only anecdotally: a single patient, usually on long-term vancomycin therapy, is infected with it, and it is not spread to other patients or healthy people.

One reason is that most patients with VRSA are already in hospitals, usually in isolation. We’re fortunate that these infections evolve in these settings (and that vancomycin is administered intravenously, making it hard for fucking morons who don’t know medicine to misuse this drug–Got Cipro?).

A second reason is described in a recent article: it’s very hard to evolve vancomycin resistance in a methicillin resistant S. aureus. When MRSA is evolved in a vancomycin-containing medium, it loses the methicillin resistance genes. And when the researchers knocked out the methicillin genes, they found that these S. aureus grew faster. The reason appears to be that these resistance genes are very poorly regulated; they’re never turned completely off, even when they’re not needed (i.e., there’s no vancomycin around). While the mechanism is unclear, these genes do appear to lower growth rates.

So the good news is that it appears very difficult to evolve a VMRSA.

For now.

At some point, with all of the MRSA strains out there, one (or more) of them is going to evolve a better regulated methicillin resistance gene.

Cited article: Noto MJ, Fox PM, Archer GL. 2008. Spontaneous Deletion of the Methicillin Resistance Determinant, mecA, Partially Compensates for the Fitness Cost Associated with High-Level Vancomycin Resistance in Staphylococcus aureus. Antimicrob Agents Chemother. 52(4):1221-9. doi: 10.1128/AAC.01164-07.

Comments

  1. #1 TK Kenyon
    April 24, 2008

    *When MRSA is evolved in a vancomycin-containing medium, it loses the methicillin resistance genes. And when the researchers knocked out the methicillin genes, they found that these S. aureus grew faster.*

    *Please* tell me that these people used a glovebox or higher biocontainment level! Geez, Louise! I wrote about a fictional scientist doing crazed experiments in my novel, Rabid, (think: green, glowing rabiesvirus,) but this is just plain insane.

    It’s nice to know that it’s evolutionarily difficult for an MRSA to also acquire VR, but this is a pathogen that I don’t want to meet in the lab, let alone in the wild.

    TK Kenyon, http://www.tkkenyon.com , http://science4non-majors.blogspot.com/
    Author of RABID ( http://www.amazon.com/gp/product/1601640021 ) and CALLOUS ( http://www.amazon.com/gp/product/1601640226 ): Two novels about science and religion, with some sex, murder, and GFP-labeled rabiesviruses.

  2. #2 Bob the Microbiologist
    April 27, 2008

    Hi Mike – love your science blog – I work in a clinical lab in Detroit – I am a med tech w/specialty in micro) with 20+ years experience. We recently isolated a VRSA (the 8th in the US) and it was fairly sensitive to alot of antibiotics (cipro, sxt, tetracycline) even though it was vanco resistant. There was no spread – even though our infection control dept. went batshit crazy. It looked and acted like any SA, this spec was from a woman that was on IV vanco for a foot wound. Our pathologist was such a stickler for exact ID that the word didnt go out for a week because he thought that the bug might be Staph. intermedius, a SA lookalike that animals (in the patients case, a dog she had and might have picked it up from) harbor. This bug can be Vanco resistant and people can get it. The PYR reaction is different though. Anyway, like you said, this was no superduper bad bug, very easily treated, and again, no spread. The hysteria that this bug produces is hilarious – have you checked out the comic Rex Morgan, MD lately? The sheer terror the people in the strip have is really funny, and the misinformation is mind-numbing. Thanks for all the great info you put out! Bob

  3. #3 Snarly
    May 20, 2008

    My friend phoned me this evening to inform me that her sister, who is critically ill, has VMRSA as well as VRE. She is at one of the premier hospitals in the country and the doctor informed this poor, 22 year old girl that she’s going to go home on comfort measures.

    Anyone know of any great, unknown, antibiotics?

  4. #4 Bernadine Elfand
    July 23, 2008

    I have been infected by a stap since 1997, at which time my
    mom that I cared for at home was on Vancomicin provalactly for VRSA. She died in 1998, and I have been sick ever since. In 1998 I was given vancomin 1000mg a day for two weeks after they had opened me and found 8 puss sacks in my adomin. I have been on numerous antibiotics ever since. Even the new drug Vyox(spell?)until my blood platlets went to low. I have tried everything. I drank edible peroide, the only thing that has kept me alive are healers that help me drain the lymphatic system. I have had one heart attach from the awful toxins this infection puts in my blood. I drink pomigranit and cranberry for my kidneys and take cranberry pills which I sware by. I continually suffer from bladder infections and can feel these large sacks form in my adomin. I have sores that form on my scalp and lower extremedies. I work hard to survive hopeing
    they will come up with a cure. I believe many people are infected with this and don’t know it. Anything new out?
    Thanks, just one of God’s Angels.

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