Module 1 (Introduction To The Study Of Pathogenic Bacteria) Flashcards
The presence of a particular pathogen in a host animal. It refers to the entry of a living agent into an animal’s body and sets up disturbance in the body functions
Infection
It refers to a condition that marks the alteration or deviation of the normal state of an animal body that disturbs or interrupts the proper performance of physiological functions.
Disease
It refers to the communication of disease from one person to another by close contact.
Contagion
Two causes of diseases
- External causes of diseases:
living bacteria, protozoa, viruses, trauma, heat, cold, vitamin, trace element deficiencies and chemical poisons. - Internal etiologies of diseases:
metabolic and endocrine abnormalities, organ degeneration, neoplasms, genetic defects and autoimmunity.
Sources of Infection
- Direct or immediate contact with a diseased animal
- Contact through fomites
- Contact with disease carriers which may serve as carriers of infection
- Infection from the environment
- Infection from food and water
- Air-borne infections
- Infections from blood sucking arthropods
- Iatrogenic infections
- Nosocomial infections
- Endogenous infection
Portals of entry
The routes or pathways by which pathogens enter the body and initiate infection.
- Through cuts and abrasions of the skin
- Through the mucus membranes of the respiratory tract
- Through the eyes, mouth, gastro-intestinal tract and genito-urinary tract
Fates of infecting pathogens
- Destruction of the pathogen by the host’s tissues
- Elimination of the pathogen in the host’s secretions and excretions
- Destruction of the pathogen with the host’s carcass
- Organism and host can reach an impasse
A property of pathogenic bacteria that refers to the degree of pathogenecity. It is defined as the relative ability of a microorganism to overcome host defenses, or the degree of pathogenicity within a group or species of pathogens.
Virulence
Virulence factors in bacteria
a. Adhesins
b. Toxins
c. Anti-phagocytic factors
d. IgA proteases
e. Resistance to the bactericidal effect of a complement
f. Ability to sequester iron
g. Ability to penetrate epithelium
h. Ability to multiply and survive in macrophages
Gene-controlled virulence of bacteria
a. Antibiotic resistance due to the presence of R-factors
b. Heavy metal resistance
c. Toxin production
d. Heat stability
e. Production of heat-labile enterotoxin
f. Cell penetration
g. Iron penetration
h. Iron chelation
i. Adhesin production
j. Colonization factor
k. Edema disease toxin
l. Colisin production
m. Hemolysin factor
Plasmid-related virulence of bacteria
a. Colonizing antigens (fimbriae and capsule-associated antigens like
K88 (F4) and K99 (F5) of E. coli
b. Enterotoxin production (ST, heat-stable and LT, heat-labile
enterotoxins)
c. Edema disease toxin
d. Resistance to complement –mediated killing
e. Iron scavenging
f. Hemolysin
g. Anthrax capsule and toxin
h. Tetanus, hematoxins and neurotoxins
i. Entero-invasive ability (Salmonella spp.)
j. Invasive ability (Yersinia spp.)
3 Properties of Pathogenic Bacteria
- Virulence
- Ability of a pathogen to propagate in tissues and on body surfaces
- Ability of a pathogen to produce other active substances that enhance microbial virulence
Elements in the production of an infectious disease
- Attachment of pathogens to host surfaces (Organ colonization)
- Penetration of host surfaces that involves passage of bacteria in between epithelial cells.
- Dissemination which is aided by enzymes (like collagenase and
hyaluronidase) produced by bacteria. - Microbial growth in tissues is made possible when a pathogen tries to
neutralize host defenses and initiate relevant adaptations.
Bacteria that exhibit organ colonization
a. E. coli K88 and K99-positive strains that adhere to the mucosa of the
small intestines of swine
b. B. bronchiseptica that adheres to the tracheal cilia and bronchi of dogs
c. Mycoplasma gallisepticum attachment to the bronchial epithelium of chickens
d. Streptococcus equi attachment to the pharyngeal epithelium of horses
e. Staphylococcus aureus adherence to the epithelial cells of the mammary ducts of cows
Bacteria-related injury to tissues
- Production of potent toxins that circulate throughout the body via the blood (neurotoxin and tetanospasmin of C. tetani)
- Release of bacterial enzymes that damage cell membranes and body
components (lecithinase and phospholipids) - Production of bacterial cell wall components that exert a cascade of
pathological conditions on host (endotoxins)
