Super-bad super-bugs
Bacteria are making love to make war
Neil Owens
Consider for a moment that a healthy person carries around 10 little bacteria for every human cell they have. Most of these bacteria lead short, happy lives on our skin and various other places and actually help to keep us healthy. But then, of course, there are always a few visitors who try to ruin the party and make us sick, in some cases, extremely sick. Our efforts to control these unfriendly bacteria had been working for several decades, but now several so-called “super-bugs” are showing super-resistance to conventional treatment.
The response from the medical community has been to keep a close watch on the emergence of these super-bugs and learn how some bacteria have developed the ability to evade our antibiotics. A leader in the field is George Zhanel, who chairs the Canadian Antimicrobial Resistance Alliance and is a professor in the department of medical microbiology at the University of Manitoba. He said that the close attention being paid to these bacteria is very important.
“We, in terms of scientists and the medical community, are quite scared. We know that there are a lot of multi-drug resistant super-bugs that are moving across Canada and the United States and internationally all the time. They are causing significant morbidity and mortality; they are very difficult to treat, so we are quite worried,” said Zhanel.
Bacteria are foreign cells lacking a nucleus and they have the capacity to reproduce indefinitely when presented with sufficient nutrients and a suitable environment, like the human body. Healthful bacteria are those that achieve a balance with the surrounding system and are permitted by the immune system, whereas infectious bacteria replicate beyond the well-being of the host.
Two common types of infectious bacteria — “Staphylococcus aureus” and “Enterococcus” — have developed the ability to defeat two powerful antibiotics: methicillin and vancomycin. As a result, they are now known as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), a.k.a. super-bugs.
Initially, these were found only in hospitals but now they are showing up in young, healthy people, which, as explained by Zhanel, is adding to the concern.
“They used to be just in the hospitals, so we focused there. Unfortunately, in the last few years [these bacteria] moved out, growingly into the community. And some of these new scary pathogens, the community associated (CA) MRSA, are really scary because this is a super-bug that doesn’t just live in the hospitals. It has moved out into the real world and affects athletes, military, the aboriginal reserves, day-care centres, nursing homes, cruise ships, the IV drug abusers and the homeless.”
While the spread of these bacteria is a concern, fortunately these super-bugs are still helpless against good hygiene. “Washing your hands is the single biggest way to prevent the spread of viruses and resistant bacteria, fungi, etc. Whether it’s soap and water or these alcohol hand rubs, the biggest way these pathogens move around is by touching. The simplest way to prevent getting infections and to prevent transmitting these pathogens is to wash you hands, very simple,” said Zhanel.
He added that another way for people to avoid the super-bugs is to become vaccinated against the flu. While the vaccine does not affect the bacteria directly, it does help the body’s immune system.
“We have been touting annual influenza shots for every Manitoban. This is one of most powerful strategies we have to prevent these infectious diseases. It’s a great way to prevent not just influenza but also prevents you getting a resistant pathogen that infects you while you have influenza. That happens frequently; people get influenza, and now they’re more susceptible to getting an antibiotic resistant bacterial pathogen.”
Prevention is key, since once these drug-resistant bacteria get a foothold the infections can be very hard to treat. Sadly, the consequences of infection are sometimes tragic. In February of 2006, a 17-year-old high school student turned up at a Scarborough, Ont. emergency room with a high fever and shortness of breath. Diagnosed with severe pneumonia, his condition quickly deteriorated and, despite treatment with a variety of antibiotics, succumbed to his infection five days later. According to a report by the Public Health Agency of Canada, tests later indicated he had been infected with MRSA.
Thankfully, the risk of contracting these multi-drug resistant bacteria is relatively low in Canada. According to Zhanel, “We in Canada, relatively speaking to other parts of the world like the United States, are much better off. Our resistance rates for some of these really bad super-bugs like MRSA and VRE that we talk about are much, much, much lower here than they are in the United States.”
How these bacteria were able to develop mechanisms to resist antibiotics is in dispute, but it is generally agreed on that years of indiscriminate use of conventional antibiotics has been the driving force behind the current problem, said Zhanel.
“Someone would come to the family doctor with a cold or virus, and the doc would give them an antibiotic to get them out of the office, figuring, ‘Well, it’s not going to help you, but it’s not going to hurt you.’”
It does, however, promote natural selection for bacteria that can survive antibiotic treatment and also has an impact on our healthy bacteria — something that hasn’t always been considered.
“Fifteen years ago, we didn’t think about how antibiotics affected the healthy bacteria. They’re there for a reason: to prevent other things from overgrowing,” said Zhanel. “If you had a resistant organism on your skin, in your mouth, [removing health bacteria] allows it to overgrow. You’re killing the normal stuff, and now [the drug-resistant bacteria] has a selective advantage. It creates a vacuum, where now you can become colonized with the resistant bug through touching somebody, through someone coughing on you . . . and now it has no antagonism.”
Researchers have also discovered that multi-drug resistant bacteria can share their resistant genes with other strains of bacteria, which adds to the scope of the problem. Genes are units of DNA that code for different traits of an organism. While the mechanisms for gene-sharing are not completely understood, several interesting factors are implicated.
“There’s an enormous amount we don’t know, but what we do know is that there are three major ways how bacteria evolve; that is, acquiring DNA. We think the most common is: bacteria having sex together. Two bacteria have sex together and they exchange DNA; the new bacteria can say, ‘Oh, this is a resistance gene, I can use this!’ And they evolve and become stronger.”
Zhanel explained that viruses also play a role in the spread of resistance genes. “Viruses come along that infect the bacteria and the viruses can actually take a chunk of the bacterial DNA, stick it into a different bacteria and they move around resistance genes. The third way is when bacteria die; DNA is very stable, so bacteria actually take up the free-floating DNA and they look at it, and they say, ‘Can this help me?’ And if it helps them, they can actually integrate it into their chromosome and pick up resistance genes.”
Not only do bacteria share their newfound resistance genes, but the current view is that, when super-bugs share DNA, they also throw in some other nasty genes.
“We think that these bacteria are evolving to actually link antibiotic resistant genes with what are called virulence traits: things to make them more powerful at causing infection. They adhere better, they make more toxins to kill the host. These genes are coupled together, so you use antibiotics and you’re driving selection of not just a resistance gene to that drug, but maybe one or two or three other genes that will make the bug more powerful.”
The fact that bacteria are evolving methods to survive should come as no surprise, as they are thought to have dominated the planet for three billion years. That didn’t happen by accident, since bacteria are deceptively intelligent and adapt to their environment, as concluded by Zhanel, “They are enormous communicators, they communicate with other cells, they communicate with other organisms that are different than them . . . and they are adapting much faster than they should if it was all random. They’re very smart. Our question is: how long can we keep them at bay? But they have to win . . . because they’re just faster, and probably smarter.”
