Slide 1Why is this important?Symbiotic Relationships Between Microbes and Their HostsSymbiotic Relationships Between Microbes and Their HostsNormal Microbiota in HostsResident MicrobiotaTransient MicrobiotaAcquisition of Normal MicrobiotaHow Normal Microbiota Become Opportunistic PathogensSlide 10Immune SuppressionChanges in the Normal MicrobiotaCapabilities of a PathogenMaintain a ReservoirAnimal ReservoirsAnimal ReservoirsHuman CarriersNonliving ReservoirsModes of Infectious Disease TransmissionModes of Infectious Disease TransmissionContact TransmissionContact TransmissionVehicle TransmissionVehicle TransmissionVector TransmissionVector TransmissionExposure to Microbes: Contamination and InfectionPortals of EntrySkinMucous MembranesPlacentaParenteral RouteThe Role of Adhesion in InfectionThe Role of Adhesion in InfectionThe Nature of Infectious DiseaseVirulence Factors of Infectious AgentsVirulence Factors of Infectious AgentsExtracellular EnzymesToxinsExotoxinsEndotoxinAntiphagocytic FactorsManifestations of DiseaseThe Movement of Pathogens Out of Hosts: Portals of ExitThe Stages of Infectious DiseaseFrequency of DiseaseHospital Epidemiology: Nosocomial InfectionsFactors Influencing Nosocomial InfectionsControl of Nosocomial InfectionsM I C R O B I O L O G YWITH DISEASES BY BODY SYSTEM SECOND EDITIONChapter 14Infection, Infectious Diseases, and Epidemiology THIRDWhy is this important?•Beginning of discussion of how microbes affect our bodies•Microbes are simply living their lives – undergoing metabolism, binary fission, etc. – and are not on a mission to harm humansSymbiotic Relationships Between Microbes and Their Hosts•Symbiosis means “to live together”•We have symbiotic relationships with countless microorganisms that live in and on our bodies•Types of symbiosis–Mutualism–Commensalism–ParasitismSymbiotic Relationships Between Microbes and Their HostsNormal Microbiota in Hosts•Although many parts of your body are axenic other parts shelter millions of mutualistic and commensalistic symbionts•Normal flora – the microbes that colonize the surfaces of the body without normally causing disease–Also termed normal flora and indigenous microbiota•Two types–Resident microbiota–Transient microbiotaResident Microbiota•Remain a part of the normal microbiota of a person throughout life•Most are commensal–Feed on excreted cellular wastes and dead cells without causing harm•Exact combination of species and size may vary somewhat, but resident flora are characteristic and permanentTransient Microbiota•Remain in the body for only a few hours, days, or months before disappearing•Found in the same regions as resident members•Cannot persist in the body–Competition from other microorganisms–Elimination by the body’s defense cells–Chemical or physical changes in the body that dislodge themAcquisition of Normal Microbiota•The womb is generally an axenic environment•Microbiota begins to develop during the birthing process•Much of one’s resident microbiota is established during the first months of lifeHow Normal Microbiota Become Opportunistic Pathogens•Opportunistic pathogens are normal microbiota or other normally harmless microbes that can cause disease under certain circumstances•Conditions that provide opportunities for pathogens –Introduction of normal microbiota into unusual site in the body–Immune suppression–Changes in the normal microbiotaIntroduction of a Member of the Normal Microbiota into an Unusual Body Site•Normal microbiota are present only in certain body sites and each body site contains only certain species of microbiota•If a member of the normal microbiota is introduced into a site it normally does not inhabit, the organism may become an opportunistic pathogenImmune Suppression•Anything that suppresses the body’s immune system–Disease–Malnutrition–Emotional or physical stress–Extremes of age–Use of radiation or chemotherapy–Use of immunosuppressive drugs•Microbial antagonism or microbial competition – normal flora use nutrients, take up space, and release toxic waste products–Make it less likely that other microbes can compete well enough to become established•Changes in relative abundance of normal microbiota may allow one member of the normal microbiota to become an opportunistic pathogen–Long-term antimicrobial treatment–Hormonal changes–Stress–Changes in diet–Exposure to overwhelming numbers of pathogensChanges in the Normal MicrobiotaCapabilities of a Pathogen•Maintain a reservoir•Leave the reservoir (transmission) •Enter a host through a portal of entry (infection) and adhere to the surface of the host•Evade defenses, multiply, and affect body function•Leave the body and return to its reservoir or enter a new hostMaintain a Reservoir•Most pathogens cannot survive for long outside of their host•Sites where pathogens are maintained as a source of infection are termed reservoirs of infection •Three types of reservoirs–Animal reservoir–Human reservoirs–Humans with active disease–Carriers–Nonliving reservoirAnimal Reservoirs•Many pathogens that infect domesticated or wild animals also infect humans–The more similar the animal’s physiology to that of humans, the more likely the pathogen is to infect humans•Zoonoses – diseases that are naturally spread from their usual animal host to humans•Acquire zoonoses through various routes–Direct contact with animals or their waste–Eating animals–Bloodsucking arthropods•Human infections with zoonoses are difficult to eradicate because extensive animal reservoirs are often involved•Humans are usually dead-end host to zoonotic pathogensAnimal ReservoirsHuman Carriers•Humans with active disease•People with no obvious symptoms before or after an obvious disease may be infective (carriers) and some may be asymptomatic and infective for years–Some individuals will eventually develop illness –Others remain a continued source of infection without ever becoming sick–Healthy carriers may have defensive systems that protect them from illnessNonliving Reservoirs •Soil, water, and food can be reservoirs of infection–Presence of microorganisms is often due to contamination by feces or urineModes of Infectious Disease Transmission •Transmission is either from a reservoir or a portal of exit to another host’s portal of entry•Three groups of transmission–Contact