31 Figure 14.7 Koch’s postulates The suspected agent must be present in every case of the disease.Agent not typically found in healthy subjectsDiseased subjectsHealthy subjectsPetri plateBacterial coloniesThe agent must be isolated and grown in pure culture.Streaked platesInjectionThe cultured agent must cause the disease when it is inoculated into a healthy, susceptible experimental host (animal or plant).The same agent must be reisolated from the diseased experimental host.
36 Figure 14.9a Some virulence factors: Extracellular enzymes Hyaluronidase and collagenaseCoagulase and kinaseBacteriumHyaluronidaseBacteriumCoagulaseClotClotting proteinKinaseEpithelial cellsCollagenaseCollagen layerInvasive bacteria reach epithelial surface.Bacteria produce hyaluronidase and collagenase.Bacteria invade deeper tissues.Bacteria produce coagulase.Clot forms.Bacteria later produce kinase, dissolving clot and releasing bacteria.Extracellular enzymes
38 Figure 14.9b Some virulence factors: Toxins ExotoxinEndotoxinBacteriumExotoxinPhagocytePhagocytized Gram bacteriaExocytosisEndotoxinDead Gram bacteriaBlood vesselBacteria secrete exotoxins, in this case a cytotoxin.Cytotoxin kills host’s cells.Dead Gram-negative bacteria release endotoxin (lipid A), which induces effects such as fever, inflammation, diaarrhea, shock, and blood coagulation.Toxins
42 Figure 14.9c Some virulence factors: Antiphagocytic factors Phagocytosis blocked by capsuleIncomplete phagocytosisCapsule around bacteriumCapsule around bacteriumBacteria reproducePhagocytic vesiclePhagocyteLysosomeAntiphagocytic factors
45 Figure 14.10 The stages of infectious diseases Incubation period (no signs or symptoms)Prodromal period (vague, general symptoms)Illness (most severe signs and symptoms)Decline (declining signs and symptoms)Convalescence (no signs or symptoms)Number of microorganisms or intensity of signs or symptomsTime
60 Figure 14.17 Epidemics may have fewer cases than nonepidemics Number of cases per 100,000 individualsEpidemic 2Epidemic 1TimeExpected number of casesActual number of cases Disease AActual number of cases Disease B
61 Figure 14.18 A page from the CDC’s Morbidity and Mortality Weekly Report (MMWR)
68 Presence of microorganisms in hospital environment Figure The interplay of factors that result in nosocomial infectionsPresence of microorganisms in hospital environmentImmunocompromised patientsNosocomial infectionTransmission of pathogens between staff and patients and among patients