How the bugs that make you sick dodge the drugs designed to fight them

Sarah Ajeel
6 August 2015

Above: Image © istockphoto.com/AlexRaths

Chances are that you’re very familiar with symptoms like a runny or blocked nose, coughing, sore throat, and fever. The diseases responsible for common symptoms like these can be caused by two very different kinds of microbes: bacteria and viruses. Thankfully, there are antimicrobial drugs called antibiotics and antivirals that can destroy, or at least inhibit the growth of bacteria and viruses. Your doctor just has to be sure to choose the treatment that matches what’s really causing your illness.

Did you know? In Latin, the word “virus” means poison or venom.Of course, when you’re lying in bed feeling miserable, you might not care very much about the difference between bacteria and viruses. But if you head to the clinic for help with your symptoms, you’ll actually be on the front lines of a battle against antimicrobial resistance. Antimicrobial resistance describes bacteria and viruses that can’t be treated with existing antibiotics and antivirals. And the misuse of antivirals and especially antibiotics can actually contribute to antimicrobial resistance, how your illness is diagnosed and treated is extremely important.

Bacteria and viruses are two different types of microbes. Bacteria are single-celled organisms that live just about everywhere, including inside your body. Not all bacteria are harmful. For example, there are ones that live in your gut and help you digest food. But other bacteria are pathogenic, which means they can cause disease. For example, strep throat is caused by the bacterium Streptococcus pyogenes. Unlike bacteria, viruses do not benefit your body in any way. Instead, they invade your cells so they can multiply and produce more viruses. Common viruses include rhinoviruses, which cause the common cold, and influenza (the flu). Other well-known viruses include HIV and HPV.

When they visit their doctor with symptoms like the ones mentioned above, many people automatically expect to get a prescription for antibiotics. But your doctor needs to be sure that your infection is bacterial and not viral. Otherwise, there's a good chance the antibiotics will do more harm than good. To begin with, the unnecessary use of antibiotics kills the “good” bacteria in your system. It also encourages the development and spread of one form of antimicrobial resistance: antibiotic-resistant superbugs. Sadly, unnecessary antibiotic prescriptions are a growing trend and superbugs have become a global problem.

Did you know? Every year, between 3 to 5 million people worldwide catch the seasonal flu, and between 250,000 and 500,000 people die as a result.In any case, antibiotics will not help if you have a viral infection. Antibiotics kill bacteria by preventing them from building their cell walls properly. But viruses simply do not have cell walls that for an antimicrobial drug to interfere with. So antivirals have to use a different approach. Instead of trying to destroy the virus, they try to prevent it from reproducing inside a host cell. There are several different ways of doing this. For example, some antivirals prevent viruses from penetrating a host cell. Others block vital proteins that viruses need to reproduce.

However, when viruses like influenza do reproduce, mutations can occur that make them resistant to antivirals. When viruses infect a host like your body, they use the host’s genetic machinery to make copies of themselves. In the process, the genetic makeup of the virus may be altered. The influenza virus in particular is constantly changing its shape and genetic content from one season to the next—and sometimes even during the same flu season. Along with random mutations, influenza can also evolve through a process called Antigenic Shift, two or more influenza strains combine to form a new and more virulent hybrid virus.Whatever the source of the mutations, there’s always a chance that they will make a new strain of the virus that is resistant to existing antivirals. In fact, these resistant strains will survive and flourish in people being treated with antivirals that attack non-resistant strains.

Researchers are constantly on the lookout for new antibiotics and antivirals that are effective against different pathogenic bacteria and viruses. In the case of drug-resistant bacteria, several new technologies are also being explored, from fecal transplants to DNA sequences called CRISPRs. For antivirals to remain effective, research will need to continue into better understanding the viruses themselves and how they interact with drugs.

Learn more!

Websites with general information on antimicrobial resistance:

Influenza Antiviral Drug Resistance (2015)
US Centers for Disease Control and Prevention.

Fact Sheet: Antimicrobial resistance (2014)
World Health Organization

Antibiotic resistance: delaying the inevitable
University of California: Museum of Paleontology

Scientific article on seasonal influenza mutation:

Influenza seasonality causes and modeling theories (2007)
E. Lofgren, N. H. Fefferman, Y. N. Naumov. J. Gorski & E. N. Naumova,  Journal of Virology 81

Scientific article on antiviral resistance:

Antiviral Drug Resistance: Mechanisms and Clinical Implications (2010)
L Strasfel & S. Chou, Infectious Disease Clinics of North America 24
Link to preview. Registration or subscription required to view full text.

Scientific article on antiviral treatments for influenza:

Inhibition of Influenza Virus Infections by Sialylgalactose-Binding Peptides Selected from a Phage Library (2009)
T. Matsubara et al., Journal of the Medicinal Chemistry 52
Link to abstract. Registration or subscription required to view full text.

Sarah Ajeel

Hello this is Sarah. I am a third year undergraduate student studying Biology at the University of Waterloo. I am passionate about Microbiology and hope to continue doing graduate studies on Viruses. Besides my passion about biology, I enjoy crafting and reading science fiction books. I'm also a big fan of Doctor Who!



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