Understanding Microbes Can Temper Panic - and Help People Understand Treatments for Various Diseases

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Professor of Biology, University of Southern Maine

In the fall 2014, the news was dominated by stories of the Ebola virus causing illnesses for people entering various U.S. states, with politicians whipping up public fears. Kaci Hickox, a nurse returning from treating Ebola victims in Africa, was even penned up for a time in a tent, after New Jersey Governor Chris Christie dramatically announced emergency measures well beyond any steps recommended by public health experts.

Not just Ebola, but influenza and other diseases caused by microbial pathogens are very real threats to public health. Serious illnesses are caused by pathogenic microbes, even as other kinds of microbes prove non-threatening or even helpful to human bodies. A basic understanding of various types of microbes and how they function can help alleviate fears and prevent panic.

Living Organisms

What exactly is a pathogen? Are all microscopic organisms pathogens? The term pathogen simply means something that causes disease. Most people think of pathogens as “germs,” “bacteria” and “viruses,” but these are not all the same – and not all bacteria or viruses are disease causing. Not all are pathogenic.

Let’s move step by step to sort out types of microbes. All living organisms are composed of cells. “Unicellular” organisms are made up of a single cell, while “multicellular” organisms like plants and animals are made up of many cells tied together and functioning in concert.

Humans like to categorize or organize things that they find complex, and beyond the basic distinction between uni- and multicellular, there are various ways to categorize organisms, such as into categories based on how they look. But this approach is not sufficient to make sense of micro-organisms, because many of them look the same yet are known to have different capabilities. Scientists have learned that organisms can be classified according to the sequences of their genetic material, their DNA (deoxyribonucleic acid), that codes all of the proteins required to make particular kinds of organisms.

Microscopic Organisms – Including Parasites and Bacteria

The term bacteria is often used for any microscopic organism, but this isn’t correct. All bacteria are microscopic, but not all microorganisms are bacteria. Cellular life can be separated into organisms that have a nuclear membrane surrounding their DNA within the cell – those are called “eukaryotes” – versus organisms that do not have a nuclear membrane surrounding their DNA – called “prokaryotes.”

  • Some unicellular, eukaryotic organisms are referred to as parasites because they infect other cellular life. Examples include the protozoan Plasmodium, which is transferred to humans by mosquitos and causes Malaria, and Toxoplasma, which humans can get through infected cat feces in kitty litter boxes.

  • In a further kind of difference lies between the “Bacteria domain” and “Archaea domain.” Both of these microorganisms with similar cell structures and no nuclear membrane are actually as different from each other genetically as bacteria are from eukaryotic organisms. Only some bacteria are pathogenic – and there are no known pathogenic Archaea domain organisms. 

Virus Basics

Viruses are fundamentally different from cellular life. In the simplest sense, viruses are genetic material protected by proteins. Like cellular organisms, viruses contain genetic material that provides the codes for proteins necessary for protecting their genetic material. That is, viruses have protein “coats,” and those coats allow viruses to infect particular kinds of host cells in living organisms. But in a crucial difference from cellular life, viruses generally do not have the ability to replicate themselves. They cannot on their own make new genetic material and new protein. To replicate, viruses must infect host cells – and each type of virus can only enter a certain kind of host cell. This means that a certain sort of pathogenic virus that causes one sort of disease has to find appropriate host cells in a living creature – and that sort of virus cannot enter other types of cells or cause other kinds of diseases.

Why Does This Information Matter?

Not all microbes cause human illnesses, and various treatments are required for those that do.

  • Microbial diversity is vast – not all microorganisms are pathogenic. In fact, the vast majority of microorganisms do not cause disease in humans. Some live in extreme environments where few humans exist. Others ferment and make byproducts that humans like, such as lactic acid bacteria used to make yogurt, which are considered “good” bacteria for human digestive systems. Still other bacteria photosynthesize and were the evolutionary precursors to chloroplasts in plants. Some archaea make methane, a greenhouse gas, and certain bacteria can even make tiny particles of gold.

  • When microbes are pathogenic, different types require specific treatments. Prokaryotes can be treated with antibiotics, but eukaryotes and viruses cannot be treated that way. Antibiotics are compounds either naturally made by organisms, or made by humans using natural antibiotics as models. Typically, antibiotics target specific processes or proteins found only in prokaryotes, such as targeting the enzyme that makes the cell wall around prokaryotes. Antibiotics do not work to counter virally caused diseases, but there are some antiviral medications – such as Tamiflu – that have been developed to target specific viral proteins or mechanisms, resulting in the destruction of the virus. 

Understanding basic information about amazingly diverse microorganisms allows people to put pathogens in perspective and deal with them knowledgeably rather than fearfully. Many microorganisms help humans. For those that cause illness, knowing exactly what type of microbe causes the threat helps scientists, health care providers, and patients find the right treatment to defeat that specific pathogen.

Further information about microbes can be found through organizations such as the American Society for Microbiology, the Centers for Disease Control and Prevention, and on the MicrobeWiki.