Bacteriology 2: Host-Environment-Pathogen Flashcards
What is a host?
Any organism that support the survival and growth of microorganisms (parasites, viruses, bacteria)
What is a Saprocyte?
Organism that live on dead or decaying organic matter (environment).
**Usually not parasite but can occasionally live in/on animals causing disease
What is a parasite? does it cause harm?
Organism that lives on/within another living organism and derives nutrients from host
- May or may not cause harm. Must be under the right circumstances
Saphrocyte vs parasite
- Incomplete distinction
- Some organisms may live as one for the other
Define commensal
Organism that lives in/on host without causing disease
- Normal Flora
What is a pathogen?
Parasitic and saprophytic bacteria which have the potential to cause disease.
- Normal Flora
- Don’t always cause disease but can under the appropriate conditions
Carriers (Carrier state)
Animals with specific bacterial pathogens present in only part of the population
- May be causing subclinical disease or no disease BUT still shed
Pathogens VS Carrier state
- A pathogen on most animal = Normal Flora -Can’t eliminate
- A pathogen on few animals = Carrier animals -Can eliminate
Disease from Normal Flora?
Opportunistic
Characteristics of carrier animal diseases?
- Contagious
- CAN be eliminated if carriers are identified and culled/cured
Where in your body is the normal flora?
Skin- Everywhere, higher is folds, gramPOS dominate (i.e armpits)
Ear- Ear flap (pinna), vertical canal (fewer), horizontal canal (Fewer), gramPOS dominate
Udder- Around the streak canal (Fewer as advancing into udder)
Eye- Conjunctiva (Low number of bacteria, Cornea (VERY few), gramPOS dominate
Respiratory tract- Cranial to larynx, Some gramNEG
Reproductive tract- Distal to the cervix, Mixture of gramPOS and gramNEG
Urinary Tract- Urethra (Moving toward bladder = fewer and fewer bacteria), Mixture of gramPOS and gramNEG
Sterile sites
Post Tympanic membrane
teat cistern
Past cornea (inside eye)
Below the larynx sterile
Bladder
Uterus - past the cervix = sterile
How does sterile site respond infection?
Cleared rapidly by host defense
Do not induce imflammation
What is the significance of a sterile site?
-Influences form of sample collection
- Influences interpretation of bacteria
What is a disease
Any abnormal condition affecting an animal
What is an endogenous infection?
An infection arising from bacteria that live on the skin, mucus membrane as commensals
What is and Exogenous infection?
An infection from environmental bacteria. Occurs when impaired host defenses allow these bacteria to invade
What is a pathogen
Those bacteria capable of causing disease
What is pathogenicity?
The capacity of a bacteria to produce disease in a host
What is virulence?
The strength of pathogenicity
What is an obligate pathogen
Bacteria that must cause disease in order to be transmitted from one host to another
*Relatively less common
What is an opportunistic pathogen?
Bacteria that are normal flora or saphrocytes. Cause disease when the host is compromised
Factors that may allow opportunistic pathogens?
- Damage to tissues
-Introduction of microorganisms
-Disturbance of normal flora
What is infectivity?
Capacity of an organism to become established in a host.
Involves: Ability to penetrate tissues, survive host’s defenses, and multiply/disseminate within the host
How does the number of a potentially pathogenic bacteria present offbeat the development of a disease?
In general: the more bacteria present: the more likely a disease will occur
What is host tissue compromise usually due to?
- Damage of host tissues
- Impairment of innate immunity host defenses
What does it mean to be immune compromised?
Impairment of the ADAPTIVE immune system
Does compromise mean the same thing as immunocompromise ?
No
_____ amount of highly virulent bacteria will lead to disease
Small
______ amount of weakly virulent pathogen will cause disease
Large
E. Coli, Streptococci are highly virulent bacteria meanly they will be _____ isolated from infections
Commonly
Weakly virulent pathogens with be _____ isolate from infections
Rarely
What is the first line of defense?
Innate immunity
What is the second line of defense?
Adaptive immunity
Innate vs adaptive immunity
- Self-recognition
- Lag phase
- diversity
- Memory
See photo
Where is the innate immune system?
Skin/Mucus membranes
What type of cells does innate immunity use?
Phagocytes: macrophages, neutrophils
Can activating of the innate immune system cause damage?
Yes, leads to fever causing damage to host
What are the two divisions of the adaptive immune system?
- Antibody mediated immunity: Opsonization, neutralization, Lysis of bacteria
- Cellular mediated immunity: destruction of intracellular bacteria by cytotoxic t cells
What is another term for a predisposing factor leading to infection?
Stressor
What are examples of innate stressors?
Species, Sex, Age. (Aka. Key questions in outbreak investigation)
What are some external stressors?
Extreme temperatures, Nutritional deficiencies, overcrowding, transportation, change in feed, weaning
What are some internal host stressors?
- Tissue damage: trauma, other infections, allergies
- Host response: endocrine changes, immunosuppressive organism (viruses) or drugs
Why is it important to identify the stressor or predisposing factor?
To properly treat and CONTROL these disease. It will reappear if you don’t fix the cause
Host + host compromise+ bacteria +
Infection
What is a “good” pathogen infection?
Highly virulent + little host compromise
AKA
-Ability to attach and colonize
-Ability to gain access to the body (Invade)
-Ability to evade the innate immunity
-Ability to produce molecules that cause dysfunction or damage
How do you target a disease caused by a weakly virulent pathogen?
Aim to increase the host defense mechanisms
How do you treat a highly virulent pathogen?
Aim to attack the bacteria. Increasing host defense mechanisms won’t do much.
List 6 sources of bacteria
- Normal flora
- Animals incubating disease
- Animals with overt disease
4.Carrier animals with sub clinic or no clinical signs - Fomites
- Environment (Ex: saprocytes)
What is a host defense mechanism?
Stops the infection from developing AKA immune system (innate and adaptive)
Six routes of bacterial infection transmission
1.Inhalation
2.ingestion
3.Inoculation
4.Transplacental
5.Genital Tract
6.umbilicus
What is genetic variation of bacteria?
Coding for virulence factors.
- Phase variation
- May have random phase variation
- Genetic elements (Aka plasmids and phases)
- Being clonal or non-clonal
What is phase variation?
Virulence factors are not always expressed but turned on when needed
CAN also be random phase variation where this occurs randomly
Virulence factors for adhesions
- Fimbriae (pili): Present on some bacteria (Specifically gramNEG) and assist with adhesions through SPECIFIC interaction with cell surface receptors
- Adhesions: Weaker adhesions by physics-chemical attractions allow the bacteria to attach and colonized body sites
Virulence factors for Invasion
- Bacteria can ACTIVELY or PASSIVELY enter host
— Active entry via epithelium using specific molecules including exotoxins - Bacteria enter through compromised tissues
What is an exotoxin?
A toxin released by bacteria into its surroundings
Anti-phagocytic molecules
-Anti-phagocytic molecules (Evasion)
— Capsule, slime layer, biofilms
— Protect bacterial from ingestion and killing by phagocytic cells
What is the main strategy a body uses to overcome anti-phagocytic molecules?
Development of specific antibody and opsonization allowing phagocytosis
What is iron sequestration and when is it necessary?
Bacteria using siderophores that remove iron bound to lactoferrin/transferrin molecules or to RBC
—NEEDS iron to survive in the body
What does bacteria NEED to survive in the body?
Iron
Survival in protected sites
Extra cellular
Usually cleared by development of an antibody
Survival in protected sites- intracellular
Must be facultative intracellular parasite, obligate intracellular parasite
What does surviving within a cell allow the bacteria to evade?
Phagocytosis
Immune system (antibodies)
Antibiotics that act extracellular
Facultative intracellular parasites
Can live in or out of the cell
Some major pathogens: salmonella, brucella
Obligate intracellular parasites
MUST live within cells while in the host
- Less common
If you see a bacteria intracellular on a slide what does that mean?
It was:
A Facultative intracellular bacteria
A obligate intracellular bacteria
A phagocytosed bacteria
What is a toxin?
Virulence factor used for destruction of tissue
- Directly: on cell
-Indirectly: through lysis of phagocytes
- Specific dysfunction: without causing da,age to cell
- Inflammatory cascade: fever
What are the two categories of toxins
Endotoxins
Exotoxins
Endotoxin vs exotoxin
See photo
Factors that allow for survival in tissues
-Anti-phagocytic molecules
-Iron sequestration
-intracellular survival
