Bacterial Pathogenesis. The term infection describes the process that pathogenic microorganisms multiply,release toxin within the body and produce a change in the normal physiology of the body. Section 1 Normal flora and opportunistic pathogens.
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Metabolic substances by normal flora: e.g., bacteriocins, antibiotics, etc.
normal flora share many antigenic determinants with pathogenic organisms
Definition: the state in which the proportion of bacterial species and the number of the normal flora colonizing in certain site of a host present large-scale alteration.
From the organism’s perspectives
The number of organisms
The virulence of these organisms
From the host’s perspective
involved in mediating attachment of some bacteria to mammalian cell surfaces
Including the filamentous haemagglutinin of Bordetella pertussia,a mannose-resistant haemagglutinin from Salmonella serotype Typhimurium and a fibrillar haemagglutinin from helecobacte pylori
Pili: e.g., Neisseria gonorrhoeae
Other surface structures of bacteria: LTA
e.g.Coagulase:working in conjunction with serum factors to coagulate plasma.contributes to the formation of fibrin walls around staphylococcal lesions.
Definition: a specific antibody capable of neutralizing the exotoxin that stimulates its production.
Definition: a modified exotoxin that has been treated to destroy its toxicity and remains immunogenicity.
Toxicity: high and even fatal; highly tissue specificity
Cytotoxins: exotoxins that destroy the target cells directly by various mechanisms.
Neurotoxins: exotoxins that affect nerve transmission of the nerve system.
Enterotoxins: exotoxins that stimulate hypersecretion of water and electrolytes from the intestinal epithelium and produce watery diarrhea.
Tetanus toxin ,clostridium tetani
glycine spastic paralysis
Botulinum toxin, clostridium botulinum
acetylcholine flaccid paralysis
Cytotoxin diphtheria toxin inhibits
Enterotoxins v. cholerae
perturb the processes that regulate ion and water exchange across the intestinal epithelium
produced only by Gram-negative bacteria and released only when bacteria lyze.
lipopolysaccharide of the outer membrane of Gram-negative bacteria; heat-stable
lipid A is the primary toxic component
all endotoxins present similar biologic effects.
Endotoxemia and endotoxin shock
DIC (dissemiated intravascular coagulation)
(especially lipid A))
Fever and hypotension
Persons or animals with frank symptomatic infection are obvious sources of infection
Convalescent carriers: those who recover from infectious disease and in whom the pathogens remain and multiply without causing overt symptoms.
Healthy carriers: those who do not have the clinical symptoms but carry pathogens indeed.
Typhoid Mary (Mary Mallon)
the tiny particles of liquid released into the air form aerosols or droplets
C.Patterns of infection
When an infection causes pathological changes leading to disease,it is often accompanied by a variety of signs and symptoms
Infectons that come on rapidly,with severe but short-lived effects,are called acute infections
The infection persists several months to several years called chronic infection
Localized infection stands for the case that the microbe enters the body and remains confined to a specific tissue
special toxic symptom
pathogenic bacterium can grow in blood
Organism is seriously dadamaged, toxic symptom all over the body。
When Pyosis bacteria cause Septicemia，multiple pyosis focus of infection will happen.e.g. staphylococci aureus
New pyosis focus of infection
Skin & mucous membranes
Fatty acids sebaceous glands
Mucous membrane of respiratory tract
Inflammatory response & phagocytosis
(early host responses to bacteria infection)
Bacteria infection→vasoactive factors →
the increased permeability
Chemokines → Neutrophils and macrophages
Inflammatory response & phagocytosis
antibody to aggressin
antibody to toxin
lymphokines (IFN- γ)