Microorganisms in Nature and Their Parasitic Nature in Humans

Microorganisms (MOs) are ubiquitous in nature, inhabiting environments ranging from soil and water to air, plants, and the bodies of animals and humans. They play crucial roles in biological cycles, but some can also cause disease in humans.

The Role of MOs in Medicine:

Studying disease-causing MOs in the environment and their distribution in the human body is crucial for developing effective disease prevention measures.

Classification of MOs:

• MOs in Nature:

• MOs in Soil:

• Autotrophic MOs: Utilize inorganic substances to synthesize organic matter for their own growth.

• Heterotrophic MOs: Thrive on organic matter, decomposing dead plants and animals in the soil.

• Pathogenic MOs: Spread from corpses, animal carcasses, or excreta of infected humans and animals. They require specific environmental conditions for survival and are easily eliminated.

• Spore-forming bacteria can persist in soil for extended periods.

• Soil MOs can be transmitted indirectly to humans through contaminated fruits and vegetables.

• Studying soil MOs is particularly crucial in areas associated with waste disposal.

• MOs in Water:

• MOs enter water from soil, dust, air, and the waste products of humans and animals.

• The quantity and types of MOs vary depending on the water’s level of contamination.

• Water is a dangerous source of infection, especially for MOs transmitted through the gastrointestinal tract, such as Salmonella and Shigella.

• MOs can persist in water for a specific duration.

• The presence of E.coli in water indicates fecal contamination. (E.coli is commonly used to assess fecal contamination levels in water).

• MOs in Air:

• MOs in the air are expelled from humans through coughing and sneezing, or they originate from dust and soil pollution.

• The number of MOs varies depending on the location.

• Pathogenic bacteria such as Mycobacterium tuberculosis, Corynebacterium diphtheriae, Streptococcus, Staphylococcus aureus, influenza viruses, and measles viruses, can be released into the air from infected individuals or carriers.

• MOs on the Human Body:

• Skin and Mucous Membranes:

• Normal Flora: A balanced composition and quantity of MOs, quickly re-establishing themselves if disrupted. This flora acts as a biological barrier, preventing the invasion of pathogenic MOs. In the gut, it contributes to vitamin K, B1, and B6 synthesis, assisting in food digestion. These normal flora can cause disease when they leave their usual habitat.

• Transient Flora: Includes MOs with or without disease-causing potential, originating from the surrounding environment. They may thrive and cause disease when the normal flora is disrupted.

• Skin MOs:

• Normal Flora: Coagulase-negative Staphylococcus, Streptococcus viridans, gram-positive bacilli, yeasts, Mycobacterium.

• Pathogenic MOs: S. aureus, P. aeruginosa, etc.

• Factors Affecting Skin MOs: Low pH, fatty acids in mucus, lysozyme.

• Respiratory Tract MOs:

• Nose: Corynebacterium diphtheriae, Staphylococcus. Around 20-50% of healthy individuals carry Staphylococcus aureus in their noses.

• Nasopharynx: Streptococcus viridans persists throughout life after birth (4-12 hours).

• Tonsils: Group A beta-hemolytic streptococcus.

• Trachea and Bronchi: Due to the presence of mucus and macrophages, the lower respiratory tract harbors fewer MOs.

• Gastrointestinal Tract MOs:

• At Birth: The gastrointestinal tract is sterile.

• After Birth: MOs enter through food.

• Adults:

• Mouth and Esophagus: A balanced ecological relationship exists between bacteria (gram-positive and gram-negative cocci, gram-positive bacilli, spirochetes).

• Stomach: Low pH limits the presence of MOs (only Mycobacterium tuberculosis can survive).

• Helicobacter pylori: A spiral bacterium that thrives in the stomach lining, causing gastritis and peptic ulcers.

• Intestines:

• Small Intestine: Limited MOs, such as Enterococcus, Lactobacillus, Diphter, Candida.

• Large Intestine: Predominantly anaerobic bacteria like Bacteroides, Lactobaci.

• Children:

• Newborn: No MOs present.

• Within Hours of Birth: MOs from the external environment enter, primarily Lactobacillus followed by E.coli.

• Formula-fed Infants: Harbor more MOs.

• Urinary Tract MOs:

• Normally: The urinary tract is sterile.

• Urine: No MOs present.

• Genitourinary Tract MOs:

• Immediately After Birth: Lactobacillus acidophillus (Doderlein’s bacilli) is present in the vagina.

• Later: Cocci and bacilli appear.

Conclusion:

Microorganisms play vital roles in the environment and within the human body. Understanding these microorganisms is crucial for preventing diseases, safeguarding individual health, and protecting the health of the community.