Vaccsbook

Microbes, Micro-Organisms, and "Not-Microbes"

Microbe is a general term for something too small to be seen by the naked eye. Micro-Organisms are very small living microbes, many of which cause disease in humans and other species.

This is an idiot's guide to microbes and micro-organisms (which because of the placing of the apostrophe in "idiot's" means a guide written by a specific idiot).

The important categories of micro-organisms are bacteria, protozoa, and yeasts.
Viruses are microbes but not considered micro-organisms because viruses are not capable of living independently (a distinction without a difference, or maybe the other way round !).

Other organsims can also cause infectious disease either directly or indirectly.
Some are microbes, but many are big enough to be seen with the naked eye so are Not-Microbes. Most of these these are grouped under the term parasite.
Btw, Not-Microbes are not called "Macrobes"; a macrobe is essentially just a collection of like microbes.

Viruses

A Virus consists of just DNA or RNA (pure genetic material) inside a shell called a "capsid"; the components (organelles) usually found inside living cells are absent.
Viruses come in many different shapes, and usually 1/5000th to 1/1000th of a millimeter in size.
The capsid contains spikes which can match receptors on the surfaces of specific living cells and thereby gain entry into the tissues of the body (similar to a house key matching the lock on a door and allowing entry into that house, but only that house).
With the right spike, viruses can enter the cells of almost all other living organism: humans, animals, birds, plants, and even bacteria.

Once inside a cell, viruses use that cell's own organelles to rapidly multiply. This upsets the cell's function, often kills the cell, and provokes a response from the immune system. (Once inside the house, viruses trash the place or burn it down, then the alarm goes off, the cops arrive and it's Bonnie and Clyde all over again.)

Safe and effective vaccines exist for many common viral infections. Some viruses can also be treated with specific anti-viral medications which can be taken by mouth or injection. Antibiotics used to treat bacterial infections are, with a few rare exceptions, useless against viruses.

Viruses were suspected (and named as such) as infectious agents in the 1890s, but none could be visualized and differentiated until the invention of the Electon Microscope in the 1930s.
So . . . during the influenza "virus" pandemic of 1918-19, no one actually knew what was causing it.

Bacteria

Bacteria are micro-organisms consisting of a single cell (humans are composed of many trillion cells).
Bacteria cells have components (organelles) which allow them to exist independently of other living things; however, they are much less sophisticated than human cells.
Most bacteria are shaped as spheres, cyclinders, or spirals, and are 1/2000th to 1/200th of a millimeter in size.

Many individual bacterium appear in multiples forming characteristic shapes under the light microscope.
Bacteria can also be distinguished by whether they become red/purple or stay colourless, when subjected to a chemical process called "Gram Staining", invented by a Mr. Gram about 150 years ago.
Bacteria are further classified by their metabolism; whether they need oxygen to survive (aerobic), whether they can live without oxygen (anaerobic), or whethere they actually die if exposed to oxygen (obligate anaerobic).
Many individual species of bacteria have been identified by microscopy; those with similar characteristics are grouped as a Genus (technical word !) .

Some bacteria are harmful; different bacteria have different preference for which organ they infect.
Some bacteria are harmful to one living species, but not to others.
Some bacteria are harmful when found in one organ of the human body, e.g. the lungs, but not in others e.g. the skin or bowels.
Many bacteria are harmless and even perform useful functions when in or on another living species; e.g. Vitamin K is made by bacteria in the human bowel.

Many classes of antibiotic medication exist (better called anti-bacterials); a few occur naturally but most are synthesized in laboratories. Each class is usually effective against a certain class of bacteria, i.e. of a certain shape, "Gram" colour, or metabolism.
Vaccines are available to prevent infections by a few specific bacteria.

When harmful bacteria invade an organ, the body's immune system usually kills the bacteria, particularly with the help of antibiotic medications. However, some bacteria destroy human cells so rapidly that death results.
Diagnosis of the species bacteria causing an infection can usually be made by taking a sample of infected bodily fluid or tissue. But this can take time and/or is not always practical.
So . . . when initially treating an infection with an anti-bacterial , physicians need to use their expertise to match the choice of anti-bacterial to the species most likely to be causing the particular infection in the particular organ.

Some anti-bacterials can be effective against several species of bacteria. These are called broad spectrum anti-bacterials, but are often "Jack of all trades, master of none" in terms of their effectiveness.
Many species of bacteria undergo mutation causing a class of anti-bacterials to no longer be effective; these bacteria are known as resistant to that anti-bacterial.
The more an anti-bacterial is used against a species of bacteria, the more likely the bacteria become reistant.

Anti-bacterial resistant bacteria are often called Superbugs. However, superbugs usually only cause disease in people who are already very ill from some other cause, so not really very super at all.

Yeasts (and Fungi)

Yeasts are micro-organisms comprised of a single cell. (Fungi develop when yeast cells multiply and connect with each other; fungi can be seen with the naked eye so strictly speaking are not microbes.)
Yeast cells are much more complicated than bacteria and their components are more like those of human cells. A single yeast cell is about 1/200th of a millimeter in size (about 1/10th the diameter of human hair).

Many yeasts are used in food and beverage production, and do not cause disease.
Reference is often made to fungal infections, and while the fungal form can be isolated in specimens, technically the infection is caused by the yeast form.

Yeasts commonly cause comparitively minor infections of the skin, mouth or genitals.
Inhalation of yeast spores can cause both acute and chronic lung infections, and occasionally progress to meningitis.
In those with poor immune systems e.g. due to chemotherapy, yeasts entering the bloodstream from the skin have a high mortatily.

Due to differences in the membrane surrounding a yeast cell, anti-bacterial medications are ineffective against yeast. However, there are a limited number of anti-fungal medications, both topically applied and given by mouth or intravenously.

Protozoa

Protozoa are micro-organisms comprised of a single cell (humans are composed of many trillion cells). Their cells are among the most complicated of all micro-organisms; many protoza can move independently
They can be as small as 1/1000 of a millimetre (like the malaria parasites), 1/20th of a millimetre (like amoebas), and as large as 200 millimetres (usually found on the ocean floor).

Some protoza live independently in water or soil; others (parasites) live on or in other organisms.
Some protozoa are harmless to humans; some cause mild disease, e.g. Trichomoniasis, Beaver Fever, others cause significant diseases e.g. Malaria or Amoebic Dysentery.

Many protozoal infections are transmitted by insects, others by ingestion of contaminated food or water.
A few anti-bacterials are actually effective against protozoal infections.

Parasites

Parasites are organsims (some micro-, some not) that live on or in other species, and cause infectious disease. As mentioned above, protozoa are considered to be parasites.

Helminthic (worm) infections can usually be seen with the naked eye and so are "Not Microbes".
They can be acquired by ingestion, insect bites, or from direct invasion of the skin.
Most helminth infections can be treated successfully with medications, in locations where these are available.
Untreated infections can lead to chronic malnutrition, anemia, and fatigue.
One serious infection, Schistosomiasis (flatworm), can result in liver and kidney damage and be fatal; only Malaria causes more parasitic deaths.

Arthropods (mosquitos, spiders, ticks, mites, lice, fleas, scorpions) are also "Not Microbes". They cause disease by transmitting other micro-organisms, or injecting venom or toxins, through bites or stings.
For example, Lyme disease is caused by a bacteria injected into the skin by a bite from the Ixodes species of Tick.
Treatments are directed at the bacteria or toxin, rather than the arthropod itself.