Bacterial Infection and immunit Xiao-KuiGuo
Bacterial Infection and Immunity Xiao-Kui GUO
Symbioses ● Commensalism:one partner benefits and the other is neither harmed nor benefited ● Mutualism:both partners benefit. o Parasitism: one partner benefits at the expense of區出”“ the other
Symbioses ⚫ Commensalism: one partner benefits and the other is neither harmed nor benefited. ⚫ Mutualism: both partners benefit. ⚫ Parasitism: one partner benefits at the expense of the other
Role of the resident flora Members of the resident fora in the intestinal tract synthesize vitamin K and aid in the absorption of nutrients Members of the resident flora on mucous mem branes and skin may prevent colonization by pathogens and possible disease through"bacterial interference The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species The normal flora stimulates the development of certain tissues, i.e., the caecum and certain lymphatic tissues(Peyer's patches) in the GI tract The normal flora stimulate the production of cross reactive antibodies
Role of the resident flora • Members of the resident flora in the intestinal tract synthesize vitamin K and aid in the absorption of nutrients. • Members of the resident flora on mucous membranes and skin may prevent colonization by pathogens and possible disease through “bacterial interference”. • The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species. • The normal flora stimulates the development of certain tissues, i.e., the caecum and certain lymphatic tissues (Peyer's patches) in the GI tract • The normal flora stimulate the production of crossreactive antibodies
o Hospital acquired infection: Infections acquired during hospital stays o Pathgen: A microorganism capable of causing sisease Nonpathogen: a microorganism that does not cause disease; may be part of the normal flora o Opportunistic pathogen: An agent capable of causing disease only when the host's resistance is impaired (ie, when the patient is"immunocompromised) o Pathogenicity: The ability of an infectious agent to cause disease o Virulence: The quantitative ability of an agent to cause disease. Virulent agents cause disease when introduced into the host in small numbers. Virulence involves invasion and toxigenicity LD so(age/sex/health /route of entry, etc o LD50: The number of pathogens required to cause lethal disease in half of the exposed hosts is called an Ldso ID50: The number of pathogens required to cause disease(or, at least, infection) in half of the exposed hosts is called the ID o Adherence(adhesion, attachment) the process by which bacteria stick to the surfaces of host cells Once bacteria have entered the body, adherence is a major initial step in the infection process. The terms adherence, adhesion, and attachment are often used interchangeabl o Invasion: The process whereby bacteria, animal parasites, fungi, and viruses enter host cells or tissues and spread in the body Toxigenicity: The ability of a microorganism to produce a toxin that contributes to the development of disease
⚫ Hospital acquired infection:Infections acquired during hospital stays. ⚫ Pathgen: A microorganism capable of causing sisease. ⚫ Nonpathogen: A microorganism that does not cause disease; may be part of the normal flora. ⚫ Opportunistic pathogen: An agent capable of causing disease only when the host’s resistance is impaired (ie, when the patient is “immunocompromised”). ⚫ Pathogenicity: The ability of an infectious agent to cause disease ⚫ Virulence: The quantitative ability of an agent to cause disease. Virulent agents cause disease when introduced into the host in small numbers. Virulence involves invasion and toxigenicity. LD 50 (age /sex /health /route of entry, etc ) ⚫ LD50: The number of pathogens required to cause lethal disease in half of the exposed hostsis called an LD50. ⚫ ID50: The number of pathogens required to cause disease (or, at least, infection) in half of the exposed hosts is called the ID50 ⚫ Adherence(adhesion, attachment): the process by which bacteria stick to the surfaces of host cells. Once bacteria have entered the body, adherence is a major initial step in the infection process. The terms adherence, adhesion, and attachment are often used interchangeably. ⚫ Invasion: The process whereby bacteria, animal parasites, fungi, and viruses enter host cells or tissues and spread in the body. ⚫ Toxigenicity: The ability of a microorganism to produce a toxin that contributes to the development of disease
Koch's postulates oo Isolated ●Koch’ s Postulates diseased not health Molecular Koch’s people Postulates Growth o Molecular guidelines for pure culture Establishing Microbial ● Induce disease Disease causation susceptible animals ● Re-isolated susceptible animals
⚫ Koch’s Postulates ⚫ Molecular Koch’s Postulates ⚫ Molecular Guidelines for Establishing Microbial Disease Causation Koch's postulates ⚫ Isolated – diseased not healthy people ⚫ Growth – pure culture ⚫ Induce disease – susceptible animals ⚫ Re-isolated – susceptible animals
Pathogenesis o Pathogenesis is a multi-factorial process which depends on the immune status of the host, the nature of the species or strain(virulence factors)and the number of organisms in the InItial exposure
Pathogenesis ⚫ Pathogenesis is a multi-factorial process which depends on the immune status of the host, the nature of the species or strain (virulence factors) and the number of organisms in the initial exposure
Source of infection o Exogenous infection: patient, carrier, diseased animal or animal carrier o Endogenous condition: most are normal flora cause infection under abnormal condition Routes of infection Transmission Respiratory Gastroenteric Airborne droplets ● Genitourinary tract Food ● closely contact Water insectbitting ● blood transfuse0m Sexual contact ● Parenteral route ● Mucous membranes
Source of infection ⚫ Exogenous infection : patient, carrier, diseased animal or animal carrier. ⚫ Endogenous condition : most are normal flora, cause infection under abnormal condition. • Airborne droplets • Food • Water • Sexual contact Transmission ⚫ Respiratory ⚫ Gastroenteric ⚫ Genitourinary tract ⚫ closely contact ⚫ insect bitting ⚫ blood transfusion ⚫ Parenteral route ⚫ Mucous membranes Routes of infection
According to According to infectious state infectious sites Local infection o Inapparent or subclinical infection e Generalized or systemic Latent infection infection 1. Toxemia: is the presence of parent infection: cause exotoxins in the blood apparent clinic syndrome 2. Endotoxemia: is the presence e Carrierstate: carrier of endotoxins in the blood 3. Bacteremia is an invasion of the bloodstream by bacteria 4. Septicemia: illness that occurs when poisonous substances (toxins) produced by certain bacteria enter the bloodstream 5. Pyemia: is caused by pyogenic microorganisms in the blood
According to infectious sites ⚫ Local infection ⚫ Generalized or systemic infection 1. Toxemia : is the presence of exotoxins in the blood. 2. Endotoxemia : is the presence of endotoxins in the blood. 3. Bacteremia : is an invasion of the bloodstream by bacteria. 4. Septicemia : illness that occurs when poisonous substances (toxins) produced by certain bacteria enter the bloodstream. 5. Pyemia : is caused by pyogenic microorganisms in the blood. ⚫ Inapparent or subclinical infection ⚫ Latent infection ⚫ Apparent infection : cause apparent clinic syndrome ⚫ Carrier state: carrier According to infectious state
TABLE 7-1 Types of Bacterial Infections Type of Infection Examples apparent (subclinical) No detectable clinical symptoms Asymptomie gonorrhea in women of infection and men Dormant (latent Carmer state ephod cartier Zoonosis or environmental or Anthrax, cryptococcal infection. inadvertent exposures and laboratory exposure, respectively Opportunistic I by normal flora 洲m nf or Candida infection of the nar tract Prima invasion and in body tissues using local tissue injury) Microbial invasion subsequent to serial pneumonia primary intection wing viral lung infection Mixed wo or more microbes infecting Anaerobic abscess the same tissue (E col and Bacteroides fragilis) Acute Rapid onset (hours or days) Diphtheria bnef duration(days or weeks) Prolonged duration (months or years) Localized Confined to a small area or to an argar Staphylococcal boil Generalized Disseminated lo many body regions Tam.n egative bacteremia PUS-forming Staphyloccal and Retrograde s ascending in a duct or tube E cof urinary tract infection the fiow of secretions Fulminant elections that occur suddenly Airbome Yersina pest and intensely (pneumonic plague)
BACTERIAL VIRULENCE FACTORS ADHESION EXOTOXIN CAPSULE VIRULENT SURFACE PROTEINS VIRULENGE PLAMID E VIRULENT ENZYME BINDING PROTEIN LPs FLAGELLA Environmental signals often control the expression of the virulence genes Common signals include: Temperrature/ron availability: C diphtheriae Alow ion/Osmolality/Growth phase/pH/Specific ions
Environmental signals often control the expression of the virulence genes. Common signals include:Temperrature/Iron availability : C diphtheriae /low ion/Osmolality /Growth phase/pH/Specific ions BACTERIAL VIRULENCE FACTORS
