Introduction to Pathogenic Microorganisms

Introduction to Pathogenic Microorganisms

• Most microorganisms are harmless, but some have the potential to cause disease
• Infection is the invasion or colonization of the body by a microorganism
• Disease is an infection that results in a detrimental change in the health of the host
• Pathogenesis refers to the process by which disease develops
• Not all microbes cause disease, and some only do so under certain circumstances (opportunistic pathogens)
• Pathogenic microorganisms possess mechanisms to manipulate host immune systems to promote disease

Types of Infections

• Subclinical: Infection with no detectable symptoms, often referred to as an asymptomatic carrier
• Latent: Dormant infection that can reactivate with reoccurring symptoms
• Opportunistic: Infection caused by an organism that doesn't typically cause disease but can in individuals with compromised immune systems
• Primary: Initial infection that can become latent and later cause other disease manifestations
• Secondary: Reactivation of a latent infection or the second stage of an infection
• Mixed: Infection by two or more bacteria infecting the same tissue

Koch's Postulates

• Series of criteria developed by Robert Koch to establish a causal relationship between a microorganism and a disease
• Developed to standardize the identification of the specific cause of an infectious disease
• Convinced microbiologists to use rigorous criteria before claiming a causal relationship between a microorganism and a disease
• Limitations: Some pathogens cannot be grown in pure culture, animal models might not be available for all pathogens, and ethical concerns arise

Molecular Koch's Postulates

• Used to identify genes involved in microbial pathogenicity
• Postulate 1: The phenotype or property under investigation should be significantly linked with pathogenic strains of a species and not with non-pathogenic strains.
• Postulate 2: Specific inactivation of the gene/s associated with the suspected virulence trait should lead to a measurable decrease in pathogenicity or virulence (note that not all genes from pathogenic microorganisms play a role in pathogenicity or virulence).
• Postulate 3: Reversion or replacement of the mutated gene with the wild type gene should restore pathogenicity or virulence.

Useful Resources

• CDC (Centers for Disease Control and Prevention) articles on emerging infectious diseases
• CDC A-Z index on diseases and conditions
• WHO (World Health Organization) fact sheets on infectious diseases
• "Contagion" - A Warner Bros movie depicting an outbreak of a novel, virulent infectious disease, offering a comparison to the COVID-19 pandemic.

Explore the fascinating world of pathogenic microorganisms and their role in causing diseases. This quiz delves into the processes of infection, types of infections, and the mechanisms employed by pathogens to evade host immune responses. Test your understanding of how these microorganisms impact health and disease.