Microbiology & Infectious Diseases: Introduction

Introduction to Microbiology and Infectious Disease

• Microbiology is the study of microorganisms associated with human diseases.
• Host response is the interaction between the host and the infectious agent.
• Germ theory states that microorganisms cause certain human diseases.
• Koch's postulates describe criteria for identifying the causative agent of a disease. These include finding the microbe in all cases of the disease, isolating and growing the microbe in a pure culture, reproducing the disease when inoculating the pure culture into a susceptible animal, and recovering the microbe from the inoculated animal.
• Important pathogens are viruses and bacteria, while fungi and protozoan parasites are less common.
• Microorganisms vary in size, from viruses less than 200 nanometers to larger organisms that can be seen with the naked eye.
• Viruses are intracellular parasites, needing infected cells for replication, and cause intracellular infections.
• Bacteria are prokaryotic organisms that typically multiply by binary fission, causing either intracellular or extracellular infections.
• Fungi are eukaryotic organisms.

Portals of Entry and Sources of Infection

• Entry portals include respiratory, alimentary, genital, skin, conjunctiva, blood transfusion, injections, and organ transplants.
• Exogenous infections come from outside factors which could be contaminated food, water, or other objects.
• Endogenous infections arise from a person's own microorganisms/flora that become pathogenic. This could be caused by disruption of normal flora, release of bacteria in compartments (e.g., intestine), or opportunistic pathogens overgrowing due to immunosuppression.

Modes of Transmission and Infection Sources

• Infectious agents can be transmitted directly (like inhalation of aerosols) or indirectly through fomites, water, food, soil, or vectors (arthropods).
• Healthcare-associated infections can be from medical/surgical procedures, contaminated medical equipment, transfusions, transplants, and needlesticks.

Clinical Signs of Infection and Diagnostic Tools

• Systemic signs include fever, chills, myalgia, fatigue, loss of appetite.
• Organ-specific signs involve localized pain, swelling, redness, warmth, and inflammation.
• Complete blood counts (CBC) identify different blood cells (red blood cells, white blood cells, and platelets) to understand the types and numbers for possible diagnosis.

Important Factors in Diagnosing and Treating Infectious Diseases

• Deductive reasoning involves patient history, physical examination, and lab tests to identify the most likely infectious agent.
• Consider the clinical manifestation of a given microorganism to help with diagnosis and treatment.
• Determine the most likely causative microorganism given a particular presentation of symptoms in a patient.
• Understand factors influencing host-pathogen interactions, like the immune system.

Important Infections Syndromes

• Infectious syndromes can affect many body systems, including upper respiratory tract, pleuropulmonary/bronchial, urinary tract, sepsis, intraabdominal, cardiovascular, central nervous system, skin and soft tissues, gastrointestinal, bone and joint, diseases of the reproductive system, eye infections, hepatitis, acquired immunodeficiency disease (AIDS), eosinophilia, and dental infections.

Overview of Microbiology: host response, germ theory, and Koch's postulates. Common pathogens include viruses and bacteria, while fungi and protozoan parasites are less common. Microorganisms vary greatly, viruses are intracellular parasites, while bacteria are prokaryotic organisms.