Author: Lensyl Urbano

Horizontal Gene Transfer: Plasmids

Peter Eisler has a somewhat scary article on the development of drug resistance in bacteria at the University of Virginia Medical Center. The bacteria were resistant to all of their antibiotics. Everything. And the bacteria were able to pass the genes that gave them their resistance to other bacteria: not just to their offspring, but horizontally to other species of bacteria by exchanging bits of DNA called plasmids.

One bacteria cell passes a piece of DNA (called a plasmid) to another. From USA Today — Image links to more complete information.

When genes are passed on from parent to offspring, or even from one microbe to another by cell splitting, it’s called vertical gene transfer. Horizontal transfer, on the other hand, involves different individual organisms passing genes from one to the other. It would be as if two people could exchange genes by shaking hands.

When the doctors began analyzing the bacteria in their first patient, who’d transferred from a hospital in Pennsylvania, they found not one, but two different strains of CRE bacteria. And as more patients turned up sick, lab tests showed that some carried yet another.

“We were really frustrated; we hadn’t seen anything like this in the literature,” says Costi Sifri, the hospital epidemiologist. “The fact that we had different bacteria told us these cases were not related, but the shoe leather epidemiology suggested to us that all these (infections) came from the same patient. … We realized we might be seeing a mobile genetic event.”

In other words, it looked like a single resistance gene was jumping among different bacteria from the Enterobacteriaceae family, creating new bugs before their eyes.

— Eisler 2012: Deadly ‘superbugs’ invade U.S. health care facilities in USA Today.

The really scary part:

There is little chance that an effective drug to kill [drug resistant] CRE bacteria will be produced in the coming years. Manufacturers have no new antibiotics in development that show promise, according to federal officials and industry experts, and there’s little financial incentive because the bacteria adapt quickly to resist new drugs.

Breeding Drug Resistant Bacteria at Farms

Modern commercial farming uses a lot of antibiotics, and, as a consequence, we’re beginning to see them breeding drug resistant bacteria (see here for exponential growth demo). Jeremy Laurance reports on one bug (MRSA ST398) now being found in milk.

Three classes of antibiotics rated as “critically important to human medicine” by the World Health Organisation – cephalosporins, fluoroquinolones and macrolides – have increased in use in the animal population by eightfold in the last decade.

The more antibiotics are used, the greater the likelihood that antibiotic-resistant bacteria, such as MRSA, will evolve.

…

The MRSA superbug can cause serious infections in humans which are difficult to treat, require stronger antibiotics, and take longer to resolve. Human cases of infection with the new strain have been found in Scotland and northern England

— Laurance (2012): New MRSA superbug strain found in UK milk supply in The Independent.

Note that consumers of milk don’t have to worry because the milk is pasteurized.

A Global Warming Primer

The Discovery Channel has an interesting series of videos about the effects of global warming on: polar bears; the Antarctic Ice Sheets; the Amazon rainforest; and the Great Barrier Reef. They also have a nice bit on what goes into the average American carbon footprint.

Natural Selection and Polar vs. Grizzly Bears

What I end up seeing, in this quintessentially 21st century creature, is a glimpse of the future.

— Gamble (2012): One, two, three, er…many. in The Last Word on Nothing.

The effect of rapid Arctic warming on polar bears has been a theme this year in Environmental Science, so this article on the hybridization of polar bears and grizzly bears caught my eye.

As caribou migration routes have moved North, grizzlies have followed and started mating with polar bears. Not only have they produced hybrid young, but those young are fertile. Polar bears and grizzlies only diverged about 150,000 years ago and haven’t developed many genetic differences, despite quite dramatic visual dissimilarities. Second-generation hybrids have now been confirmed in the wild.

This article is also of note to my Middle School science class because we’ve talked about speciation — the divergent evolution of two populations into separate species — before when we looked at the phylogenetic tree and bison evolution in particular. This seems to be a re-convergence after separation. As the climate warms the grizzly bears are able to range further north, while the polar bears are more restricted to the shores by the melted sea ice, so the two populations encounter each other more and more. Thus polar bears, may eventually disappear as they are re-incorporated into the grizzly population.

The author, Jessa Gamble, thinks this is a glimpse of things to come.

↬ The Dish.

Warming of the West Antarctic Ice Sheet

… a breakup of the ice sheet, … could raise global sea levels by 10 feet, possibly more.

— Gillis (2012): Scientists Report Faster Warming in Antarctica in The New York Times.

In an excellent article, Justin Gillis highlights a new paper that shows the West Antarctic Ice sheet to be one of the fastest warming places on Earth.

The black star shows the Byrd Station. The colors show the number of melting days over Antarctica in January 2005. This number increases with warming temperatures (image from supplementary material in Bromwich et al., 2012).

Note to math students: The scientists use linear regression to get the rate of temperature increase.

The record reveals a linear increase in annual temperature between 1958 and 2010 by 2.4±1.2 °C, establishing central West Antarctica as one of the fastest-warming regions globally.

— Bromwich et al., (2012): Central West Antarctica among the most rapidly warming regions on Earth in Nature.

Anti-biotic Brass

Interesting research shows that brass and other copper metal alloy surfaces kill bacteria and degrade their DNA much better than stainless steel or plastic.

Plastic and stainless steel surfaces, which are now widely used in hospitals and public settings, allow bacteria to survive and spread when people touch them.

Even if the bacteria die, DNA that gives them resistance to antibiotics can survive and be passed on to other bacteria on these surfaces. Copper and brass, however, can kill the bacteria and also destroy this DNA.

— Grey (2012): Fit brass fixtures to cut superbugs, say scientists in The Telegraph.