Bacterial colonization, tissue invasion and clinical disease Flashcards
A number of bacterial species can reside in animal hosts, either as?
commensals or as potential pathogens
are host to an enormous number of resident microbes
Mammals
can interact with host tissues in ways that result in disease
Pathogenic bacteria
What are commensals?
-Commensal organisms, acquired soon after birth, are able to adhere to body surfaces.
Commensal organisms form stable polymicrobial communities that are present throughout life as ___________
on the skin and in the hollow organs surfaces and cavities are open to the environment.
normal microflora
the composition of the microbial communities tends to be?
- host specific
- within hosts
- organ specific
it is beneficial to the host in many ways
stable microflora
it relies on the normal microflora to drgrade ingested material in the rumen of cattle and sheep, in the caecum and colon of horses, and in the colon of pigs.
digestive system
normal microflora degrade ingested material in the?
✓ rumen of cattle and sheep
✓ caecum and colon of horses
✓ colon of pigs
what vitamins does microflora of the rumen synthesizes?
Vitamin K and Vitamin B
what body system does normal microflora primes?
immune system
When the community of commensals occupying a particular niche is in ecological balance, the bacteria utilize the resources they require from the host without causing any obvious adverse effects
When an equilibrium is disturbed or when the host is under severe stress, an indigenous member may escape from the restraining influences of the bacterial community and act as an?
opportunistic pathogen
Opportunistic pathogen occur in?
gastrointestinal tract following the administration of oral antibiotics
bacteria that can exist as a commensal in the rumen
Fusobacterium necrophorum
When Fusobacterium necrophorum transfer to the liver of feedlot cattle, what will happen?
it can act as a pathogen that causes HEPATIC ABSCESSES
For a microbw to act as a pathogen;
✓ must find an appropriate niche within a host
✓ must compete with the normal microflora to gain a foothold in that niche
✓ must evade normal host defences
✓ must express the genes that encode the factors that cause disease
the ability of a microbe to damage a host
pathogenecity
the relative capacity of a pathogen to damage a host
virulence
The bacterial traits that confer pathogenecity
virulence factors
Virulence Factors;
✓ adhesins
✓ toxins
✓ capsules
genes are expressed only when their products are required in a process
phase variation
are not uniformly distributed among all the strains of a particular bacterium
Genes encoding virulence factors
Genes that encode virulence factors are associated with a mobile genetic elements
bacteriophages, plasmids, and pathogenecity islands
arise when bacteria that live on the skin or mucous membranes as harmless commensals take advantage of impaired antimicrobial defenses of the host and behave as opportunistic pathogens
endogenous infections
Endogenous infections happens when?
- epithelial barriers are damaged
- immunity is weakened by drugs, radiation or exogenous pathogens
- ecological balance of the resident microbial community is disturbed by administration of antibiotics
- bacteria gain access to sites from which they are usually absent
occur after direct or indirect transmission from an infected animal or from the environment
Exogenous infections
Pathogens may enter a host through?
skin, conjunctiva, umbilicus, teat canal, main portals of the mucosae, gastrointestinal, respiratory and urogenital
determines the site of the initial interaction between pathogen and host and also the organs at greatest risk of infection
route of infection
are driven by microbial genes that express virulence factors and by host genes that are responsible for resistance to pathogens
subsequent interactions
in bacterial infections, the host may be damaged by BACTERIAL TOXINS, by the inflammatory response elicited by the bacteria or their toxins or commonly by both
toxins and inflammatory reactions
Two categories of Pathogens that are able to survive within host cells
✓ strict (obligate) intracellular pathogens
✓ facultative intracellular pathogens
2 obligate intracellular pathogens
Chlamydiae and rickettsiae
What are the facultative intracellular pathogens?
✓ Mycobacterium- phagocytic cells
✓ Brucella- uropathogenic E. coli
✓ Salmonella
✓ Listeria monocytogenes- non-phagocytic epithelial cells
play a significant role throughout the coarse of an infection
adhesins
what is the use of adhesins in Pathogens?
attach to host tissues and to resist the flushing action of body fluids
a transcription factor that moves to the cell nucleus where it up-regulates the expression of a number of pro-inflammatory genes
nuclear factor-kappaB
resistant to phagocytic cells because of its large size
biofilm
what is capsules?
help the bacterium to resist desiccation
composed of polyglutamic acid; it is anti-phagocytic and is regarded as an essential virulence factor
Bacillus anthracis
Two types of bacterial toxins
Exotoxins and Endotoxins
produced and secreted by viable bacteria
exotoxins
integral constituents of the bacterial cell wall not released until the microorganisms are lysed
endotoxins
Endotoxin composed of three parts;
hydrophobic glycolipid (lipid A)
hydrophilic polysaccharide
Opolysaccharide (O antigen)
released when bacterial cell walls are damaged by the complement system, phagocytes or antimicrobial drugs
Lipopolysaccharide
toll-like receptor 4 (TLR-4)
mononuclear phagocytes, neutrophils, platelets, dendritic cells and B lymphocytes
High concentrations of circulating endotoxin greatly increase the release of?
cytokines, interleukin-1, tumor necrosis factor-alpha
stimulate the production of prostaglandins and leukotrienes which are mediators of inflammation
cytokines
responsible for the deposition of thrombi in small vessels and for a dramatic drop in blood pressure, giving rise to life-threatening endotoxic shock
Lipopolysaccharide (LPS)
categories of exotoxins
✓ toxins that act on the extracellular matrix
✓ toxins that act on the plasma membrane of their target cells
✓ toxins that act inside the cells
✓ toxins that cause dysfunction of the immune system
toxins that cause dysfunction of the immune system
superantigens
