Introduction to Medical Microbiology

Introduction to Medical Microbiology

• Microbiology is the study of microbes, or microorganisms, which are tiny living organisms often invisible to the naked eye.
• Some microbes are pathogenic (cause disease), while others are beneficial.
• Examples of microbes include bacteria, fungi, protozoa, algae, and viruses.
• Medical microbiology is the study of causative agents of infectious human diseases and their responses to these infections.
• It covers etiology, pathogenesis, laboratory diagnosis, specific treatment, and control of infection/immunization.

Learning Objectives

• Understanding basic concepts of microbiology and its history.
• Distinguishing between different groups of microorganisms.
• Identifying prokaryotic and eukaryotic cells.
• Knowing the general characteristics of bacteria, parasites, viruses, and fungi.

What is Microbiology?

• Microbes are minute living things usually too small to see with the naked eye.
• Examples of microbes include bacteria, fungi, protozoa, algae, and viruses.
• Some microbes are pathogenic, causing disease.
• Many microbes are beneficial, playing important roles in ecosystems, including food production, digestion, and environmental processes.

History of Microbiology

• Ancient civilizations (Egyptians) used salt for preservation and as an antiseptic.
• Hippocrates (460-377 BC) emphasized observation and attributed diseases to disturbances in the body's vital fluids.
• The field of Microbiology developed by using scientific techniques during the Renaissance.
• The development of experimental observation and research led to a more scientific understanding of disease transmission, prevention and treatment.

First Steps

• Early efforts to control infections included hand-washing, wound treatments, and awareness of harmful substances in the environment.
• Physicians recognised that diseases can be caused by toxic substances in the soil or swamps, and that certain substances or measures that could prevent disease.

Middle Ages

• The views of Hippocrates and Galen became widely accepted.
• People began to make associations between diseases or sicknesses to certain things like food or air.
• Girolamo Fracastoro (1546) proposed that contagious diseases were transmitted by living germs or organisms, which changed or led to a better understanding of disease transmission, contributing also to the microbes theory.

Spontaneous Generation (Abiogenesis)

• The ancient belief that living organisms could arise spontaneously from non-living matter.
• William Harvey and Francesco Redi challenged this concept with experiments on maggots and flies.

The Germ Theory of Disease

• The theory that infectious diseases are caused by microorganisms.
• Joseph Lister used chemical disinfectants to prevent surgical wound infections.
• Louis Pasteur's experiments disproved spontaneous generation and showed that microbes were responsible for fermentation and disease.

Anton van Leeuwenhoek (1674)

• First person to actually see living microorganisms.
• He observed microorganisms in teeth scrapings, rainwater, and peppercorn infusions using early microscopes.

Louis Pasteur (1822-1895)

• Disproved spontaneous generation and demonstrated the role of microorganisms in fermentation, food spoilage, and disease.
• Developed methods (Pasteurization, Sterilization, and Aseptic techniques) to control the spread of diseases in food and medicine, significantly benefiting human life.

Koch's Postulates

• Criteria to establish a causal link between a microorganism and a disease.
• Steps to verify the causality of a microbe to a particular disease.
• The postulates were very important in microbiology.

Molecular Koch's Postulates

• Modern criteria to link a gene to a disease phenotype and pathogenicity

• Involve identifying, mutating or disabling the causative gene, observing its correlation to disease, and re-establishing the gene's function.

Microorganisms

• Microorganisms are present in diverse environments and interact with multicellular organisms (especially humans) in close associations.
• Some microbes are pathogenic, causing infectious diseases.
• Microorganisms play important roles in ecosystems and human lives.

Cell Size

• Illustrates the extremely small size of microbes compared to larger organisms and cells.
• Microscopes needed to view microbes.

Typical Bacteria

• Most bacteria have rod-shaped, spherical, or spiral shapes.
• Cell walls provide structure and determine gram-positivity or gram-negativity.
• Bacteria reproduce by binary fission.
• Genetic information exchange can occur via plasmids.

Atypical Bacteria

• Groups of bacteria that deviate from typical bacterial traits (e.g., lacking cell walls, special metabolic traits) include Mycoplasma, Chlamydia, and Rickettsia.

Fungi

• Non-photosynthetic eukaryotes (with membranes) that can be either multicellular (filamentous) or unicellular (eukaryotic).
• Reproduction via spores (asexual or sexual).
• Some cause infections in humans.

Protozoa

• Single-celled eukaryotic organisms.
• Many are free-living, some are pathogenic.
• They can infect various tissues and organs.
• Transmission mechanisms vary (e.g., ingestion, insect bites).

Helminths

• Multicellular eukaryotic worms (parasites).
• Classified into tapeworms, flukes, and roundworms.

Viruses

• Obligate intracellular parasites.
• Lack cellular structure and rely on host cells for replication.
• Consist of genetic material (DNA or RNA) enclosed in a protein coat.
• Some viruses have an envelope derived from the host cell membrane.
• Viruses can cause various diseases.

Important Definitions

• Infection: Microorganisms contact an organism and cause disease.
• Infectious diseases: Diseases caused by an infection.
• Pathogenicity: Ability of a microorganism to cause disease.
• Virulence: Severity of the disease caused by a microorganism.

How Infectious Disease Starts

• Colonization-establishment of microorganisms on the skin or mucous membranes.
• Infection-introduction of organisms into the bloodstream or internal organs.

Microbial Colonization

• Results in elimination of the microbe, with no impact on the host.
• Results in infection, with organism multiplication and host response.
• Results in infectious disease (tissue damage and impairment of body function).

Host-Parasite Relationships

• The term refers to the relationship between the host and the parasite, and the competition for supremacy that takes place between them.
• Disease should not be confused with infection (a person can be infected, but not develop the disease).
• Symbiosis describes an association in biology between organisms, often categorized as mutualism, commensalism, or parasitism.

Types of Symbiotic Associations

• Mutualism (+,+): Both organisms benefit from the interaction. Need to live together.
• Commensalism (+,0): One organism benefits, the other is not affected.
• Parasitism (+,-): One organism benefits at the expense of the other.

Prokaryotic Pathogens

• All prokaryotic organisms are classified as bacteria.
• Eubacteria and archaebacteria.

Eukaryotic Cells

• Key differences between eukaryotic and prokaryotic cells: features like cell wall, chromosomal structure, nucleus and presence of organelles such as ribosomes, and mitochondria.

Typical Bacteria

• Most have basic shapes (rod, sphere, or spiral).
• Cell walls impact gram-positivity/negativity.
• Reproduction using binary fission.
• Plasmids facilitate genetic exchange.

Atypical Bacteria

• Exceptions to common bacterial characteristics (e.g., Mycoplasma, Chlamydia, Rickettsia): lack cell walls or possess special metabolic properties.

This quiz explores the fundamental concepts of medical microbiology, including the types of microorganisms, their characteristics, and their roles in human disease. Learn about the pathogens, etiology, and the laboratory diagnosis of infectious diseases. Test your knowledge on prokaryotic and eukaryotic cells, as well as the treatment and immunization techniques.