Microorganisms are tiny organisms found throughout nature, characterized by their small size and simple structure, visible only under magnification by light or electron microscopes. They inhabit diverse environments such as rivers, lakes, oceans, soils, minerals, and the air, each with varying types and quantities of microorganisms. Pathogenic microorganisms specifically refer to those capable of invading and causing infections or infectious diseases in humans or animals.

Pathogenic microorganisms encompass a broad category, primarily referring to microorganisms capable of causing diseases in humans or animals. This group typically includes viruses and bacteria, which are commonly recognized as pathogenic. However, it also encompasses various other types such as fungi, chlamydia, mycoplasma, rickettsia, spirochetes, prions, parasites, and more. Among these, bacteria and viruses are often considered the most detrimental in terms of their potential impact on health.

Bacteria

Bacteria are single-celled prokaryotic microorganisms characterized by their small size and simple morphology. They are among the most abundant organisms on Earth. Bacteria exhibit diverse shapes, including spherical (cocci), rod-shaped (bacilli), and spiral-shaped (spirilla).

Bacteria are responsible for causing numerous diseases, such as tuberculosis, gonorrhea, anthrax, syphilis, plague, trachoma, and various other infections.

Viruses

Viruses are non-cellular microorganisms devoid of a typical cellular structure and lack an enzyme system for energy production. They rely on living cells to grow and multiply. The pathogenic effects of viruses often include cytolytic processes, where the virus enters a cell, replicates within it, and ultimately destroys the cell. Upon cell destruction, a large number of viruses are released into the surrounding environment, facilitating their spread to other cells. This can lead to tissue damage, inflammation, and the manifestation of symptoms.

Viruses such as measles, AIDS, influenza, smallpox, as well as more recent examples like COVID-19 and monkeypox, are all caused by viruses.

How Pathogenic Microorganisms Cause Infections

Pathogenic microorganisms require infectious sources (such as patients, asymptomatic carriers, infected animals, and plants), suitable transmission routes (such as air, water, surface contact, etc.), and susceptible populations (such as individuals with compromised health, pregnant women, infants, children, and the elderly) to initiate infections. The higher the concentration of pathogenic microorganisms, the greater their virulence, and consequently, the increased likelihood of causing disease.

Viruses primarily induce disease by disrupting the nutrition and metabolism of host cells, leading to damage and dysfunction of host tissues and organs. Toxins, on the other hand, are classified into two types based on their properties, effects, and production: exotoxins and endotoxins.

Whether pathogenic microorganisms can cause disease also depends on the route of transmission

- Airborne transmission is significantly more contagious compared to other routes. For instance, the new coronavirus spreads through airborne transmission, making it highly contagious.

- Transmission through the digestive tract, as seen with pathogens like rotavirus and dysentery bacillus, typically occurs via contaminated food and water sources.

- Transmission through contact, exemplified by pathogens like the varicella virus and tetanus bacillus, typically occurs through direct contact. This involves skin-to-skin contact or contact of exposed wounds with bacteria or viruses, leading to potential infection.

In addition to the common transmission routes, bacterial and viral infections can also occur through other routes such as blood-borne transmission, sexual contact, aerosol transmission, and more.

According to the World Health Organization (WHO), more than 17 million people worldwide die each year due to infections caused by microorganisms, accounting for approximately one-third of global deaths. Beyond human health impacts, some pathogenic microorganisms also contribute to the corrosion, spoilage, and deterioration of industrial products, agricultural goods, and everyday items.

For example, they can degrade the physical and chemical properties of metals, instruments, telecommunications equipment, and textiles upon contact, leading to aging and decay. Additionally, these microorganisms are responsible for various animal diseases such as avian influenza, chicken cholera, and bovine anthrax, as well as plant diseases like rice leaf blight, wheat scab, and soybean virus diseases.