Bacteria Pathogenicity

Bacteria pathogenicity

Glossary  Infection

: multiplication of an infectious agent within the body .  Pathogenicity: The ability of an infectious agent to cause disease

 Pathogen:

A micro organism capable of causing

disease.  Non-pathogenic: A micro organism 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 (i.e., when the patient is “immunocompromised”).  Normal microbial flora : the population of micro organisms that inhabit the skin and mucous membranes of healthy normal persons

LD 50 (age /sex /health /route of entry, etc )  LD50: The number of pathogens required to cause lethal disease in half of the exposed hosts is 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

Role of the resident( normal ) flora

1. 2.

3. 4. 5.

synthesize nutrient vitamin K and aid in the absorption of nutrients. prevent colonization by pathogens and possible disease through “bacterial interference”. antagonize other bacteria stimulates the development of certain tissues, stimulate the production of cross-reactive antibodies.

The Mechanisms of Bacterial Pathogenicity Virulence:

a term which refers to the degree of pathogenicity of the microbe. Amount of invasive bacteria Pathway of invasive bacteria

 There

are two broad qualities of pathogenic bacteria underlie the means by which they cause disease: invasiveness and toxigenesis. – 1. Invasiveness : The ability to invade tissues, 2. Toxigenesis : The ability to produce toxins. Bacteria produce two types of toxins called exotoxins and endotoxins.

1.Factors of Invasiveness  capsule  Adhesin

= pili, hair-like appendages  invasive substances tissue-degrading enzymes

Adhesion BACTERIUM

adhesin receptor

EPITHELIUM

E. coli with fimbriae

E. coli fimbriae Type 1 mannose

P

• galactose – glycolipids – glycoproteins

S. pyogenes lipoteichoic acid F-protein

fibronectin

BACTERIAL VIRULENCE FACTORS

2. Toxins  Exotoxins  Endotoxins

Exotoxins Like enzymes, bacterial exotoxins: •are proteins •are denatured by heat, acid, proteolytic enzymes •have a high biological activity (most act catalytically) •exhibit specificity of action

Exotoxins •strongly antigenic •In vivo, specific antibody (antitoxin) neutralizes the toxicity of these bacterial proteins.

Exotoxins •Toxoids •Protein toxins are inherently unstable: in time they lose their toxic properties but retain their antigenic ones. Toxoids are detoxified toxins which retain their antigenicity and their immunizing capacity.( formalin)

A-B toxins Cell surface

Active

Binding

A

B

Endotoxins  LPS

Lipopolysaccharide: core or backbone of CHO side chains of CHO: "O" antigen Lipid A  Cell wall lysis required  formaldehyde and heat resistant  poor antigen as free molecule

Endotoxins Endotoxin

effects

Fever-pyrogen 1 microgram/ kg Leukopenia and leukocytosis necrosis Shwartzman phenomenon and disseminated intravascular coagulation (DIC). Endotoxemia and shock

Original and devolopment of Bacterial Infection

Source of infection  Exogenous

infection : patient, carrier, diseased animal or animal carrier.  Endogenous condition : most are normal flora, cause infection under abnormal condition.

Transmission • Airborne droplets • Food • Water • Sexual contact

Routes of infection  Respiratory  Gastroenteric  Genitourinary

tract  closely contact  insect bitting  blood transfusion  Parenteral route  Mucous membranes

According to infectious state  In

apparent or subclinical infection  Latent infection  Apparent infection : cause apparent clinic syndrome  Carrier state: carrier

  1. 2. 3. 4.

5.

According to infectious sites

Local infection Generalized or systemic infection Toxemia : is the presence of exotoxins in the blood. Endotoxemia : is the presence of endotoxins in the blood. Bacteremia : is an invasion of the bloodstream by bacteria. Septicemia : illness that occurs when poisonous substances (toxins) produced by certain bacteria enter the bloodstream. Pyemia : is caused by pyogenic microorganisms in the blood.