Transcript Chapter 14a
Host-Microbe Interactions Chapter 14 • Disease • Etiology • Pathogen – Primary vs. opportunistic • Virulence • Contamination • Infection vs. Infestation • Pathogenesis • Pathology • Symptoms • Signs • Syndrome • Sequelae Anatomical Barriers as Ecosystems • Skin and mucous membranes are physical barriers to infection – May supply foundation for microbial ecosystem • Humans are usually sterile in utero • Exposed to microbes during and immediately after birth – microbial populations begin to establish • Normal flora – Resident flora – Transient flora • Probiotics • Isolated colonies in specific body regions •Dominant type of organism may change with age and situation • Factors that influence distribution of Flora: – Nutrient availability, salinity, oxygen availability, host defenses and mechanical factors – Normal flora may offer protection from disease-causing organisms – microbial antagonism – Competitive exclusion – Bacteriocins • Symbiotic relationships form between microorganism and host – Relationships may change depending on state of host and attributes of microbes – Mutualism (++) • both partners benefit – Intestinal bacteria – Probiotics – Commensalisms (+ neutral) • one partner benefits and other is unharmed – Flora on skin and conjunctiva – Parasitism (+-) • microbe benefits at expense of host – Pathogens Pathogenicity – State of host resistance usually determines extent of infection • primary infection • secondary infection • Sub-clinical or in-apparent infection • Many people are carriers of pathogens – Viruses; Neisseria; Salmonella; Streptococcus • Why are they not affected? • Predisposing factors: – gender – genetic background – climate and weather – inadequate nutrition – age – habits and lifestyle – chemotherapy – emotional disturbances • Characteristics of infectious disease: – communicable • contagious • Often reflects ID50 – non-communicable disease Etiology of Infectious Diseases • Robert Koch demonstrated that specific microbes caused specific diseases – experimented with grazing animals infected with anthrax – Later work with TB got more interest • Koch developed a series of steps (Koch’s postulates): – Same pathogen must be present in each case of disease – Pathogen is isolated from diseased host and grown in pure culture – Pure culture must cause disease when inoculated into healthy animal – Pathogen must be re-isolated from inoculated animal • Exceptions to Koch’s postulates – some bacteria have unique culture requirements – some diseases are caused by multiple pathogens • Polymicrobial diseases (mixed infections) – Ethical considerations Stages of an Infectious Disease Duration of a Disease – acute diseases – chronic diseases – latent disease Distribution of pathogens – Local infections – Systemic infections • Bacteremia • Toxemia • Viremia – Septicemia