Slide 1Normal MicrobiotaSlide 3Microbial Pathogens can be divided into two classesPrimary PathogensPrimary Pathogens - SummaryOpportunistic PathogensPseudomonas aeruginosaOpportunistic Pathogens - summaryPathogenicityMedian Infectious Dose (ID50)Infectious Dose of various foodborne bacterial pathogensStages of Bacterial PathogenesisModes of TransmissionPortals of EntrySome Pathogens that Cross the PlacentaPortals of ExitReservoirs of InfectionAnimal ReservoirsHuman CarriersNonliving ReservoirsSlide 22Evasion of the Host Immune SystemVirulence DeterminantsSurface Virulence FactorsSurface Virulence FactorsSlide 27ExotoxinsSlide 29Slide 30Slide 31Exceptions to Koch’s PostulatesSlide 33Extent of Host InvolvementEpidemiologySlide 36Slide 37Slide 38Slide 39Slide 40Nosocomial InfectionsControl of Nosocomial InfectionsTake home pointsMICROBIAL PATHOGENESIS MIKE BALDWIN [email protected] is colonized by numerous mutualistic and commensal symbiontsMicrobes that colonize the body’s surfaces without normally causing disease constitute the body’s normal microbiotaMany organisms are beneficial, certain E. coli strains produce Vitamin KNORMAL MICROBIOTARESIDENT MICROBIOTATRANSIENT MICROBIOTA•Resident microbiota remain a part of the normal microbiota throughout our lives•These organisms are found on our skin and the mucous membranes of the Respiratory system; GI tract; distal portion of the male urinary and reproductive system; and the vagina •Transient microbiota remain in the body for only a few hours, days or weeksMICROBIAL PATHOGENS CAN BE DIVIDED INTO TWO CLASSES Primary PathogensOpportunistic PathogensPRIMARY PATHOGENSPrimary pathogens cause disease as a result of their presence within the normal, healthy hostObligate pathogens: primary pathogens which are restricted to a single host, e.g. N. gonorrhoeae / Humans (Most human diseases)Strict pathogens: primary pathogens which cause disease in more than one host organism, e.g. B. anthracis / cattle, humansPRIMARY PATHOGENS - SUMMARY•High potential for causing disease•Can be prevented by immunization•Responsible for significant morbidity and mortality in the developing worldA usually harmless microbe that becomes pathogenic under favorable conditions; Often a member of the normal microbial floraConditions that provide opportunities for pathogens •Immune suppression (various causes)•Changes in relative abundance of normal microbiota (antibiotic treatments)•Introduction of normal microbiota into unusual site in the body (medical devices)OPPORTUNISTIC PATHOGENSPseudomonas aeruginosa is a prototypic example of an opportunistic pathogen of humansWhile healthy individuals are rarely infected with P.a., those with compromised immune systems (diabetics, cancer patients, burn victims) are highly susceptiblePseudomonas aeruginosaDiabetic Ulcer Tissue infected with P.a.Due to poor circulation/ intrinsic antibiotic resistance of P.a., prognosis is poorOPPORTUNISTIC PATHOGENS - SUMMARY•Low probability of causing disease in normal healthy host•Increased probability of causing disease in immunocompromised host•Responsible for high morbidity and mortality in the developed worldPATHOGENICITYPathogenicity: the ability of a microorganism to cause disease within a hostVirulence: the relative ability of an microorganism to cause disease within the same hostPathogenicity is the product of an organism’s virulence factorsThe virulence of strains within a species can vary:•H. influenzae: otitis media, sinusitis•H. influenzae type b: meningitisMEDIAN INFECTIOUS DOSE (ID50)Median infectious dose (ID50): the number of microorganisms required to cause an infection in half the members of a tested population High virulence  few microorganisms sufficient to initiate disease (\ low ID50 ≡ highly contagious organism)Low/ moderate virulence  many microorganisms required to initiate disease (\ high ID50 ≡ moderately contagious organism)Summary:  Number of organisms   likelihood of diseaseINFECTIOUS DOSE OF VARIOUS FOODBORNE BACTERIAL PATHOGENSEscherichia coli : very large (106 - 108 of organisms)Salmonella : quite large ( > 105 of organisms)Campylobacter jejuni : low (500 organisms)Shigella : very low (~10 organisms) i.e. Shigella is highly virulent with a Low ID50STAGES OF BACTERIAL PATHOGENESISTransmission Penetration of the barrierAdherenceProliferation  colonizationClinical manifestations Host responseRecovery or deathMODES OF TRANSMISSIONMode of Transmission Diseases Spread Include:Contact TransmissionDirect contact: handshaking, kissing, sex, bitesIndirect contact: shared utensils, toothbrushes, toys, respiratory droplets (within 1 meter)cutaneous anthrax, genital warts, herpes, rabies, staphylococcal infections, syphiliscommon cold, enterovirus infections, influenza, measles, tetanus, whooping coughVehicle TransmissionAirborne: dust particlesWaterborne: streams, swimming pools, water fountainsFoodborne: poultry, seafoodchicken pox, influenza, measles, pulmonary anthrax, tuberculosischolera, Campylobacter, Giardiabotulism, hepatitis A, listeriosis, tapeworms, typhoid feverVector TransmissionMechanical: transferred on body partsBiological: bites (arthropods)E. coli diarrhea, salmonellosis, trachomaChagas’s disease, Lyme disease, malaria, plague, RMSFPORTALS OF ENTRY A Portal of Entry is the route a pathogen takes to enter a hostTypical routes include: •mucous membranes (respiratory-, gastrointestinal-, & genitourinary-tracts, the eyes) •skin (highly impermeable to majority of pathogens, entry via natural openings such as hair follicles or sweat glands)•Parenteral (a parenteral portal of entry is one of direct deposit of pathogens into body cavities or wounds – hypodermic needles, cuts/ abrasions in skin) •Bloodstream/ placentaTable 14.3SOME PATHOGENS THAT CROSS THE PLACENTAThe Placenta typically forms an effective barrier to bacterial/ viral pathogens as the two blood supplies are not in physical contactPORTALS OF EXITMost pathogens cannot survive long outside of their hostSites where pathogens are maintained and serve as sources of infection are termed reservoirs 3 types of reservoirs:•Animal reservoir•Human carriers•Nonliving reservoirRESERVOIRS OF INFECTIONZoonoses: diseases that are naturally spread from their usual animal host to humansAcquire zoonoses through various routes•Direct contact with animal or its waste•Eating animal meat•Bloodsucking arthropodsHumans are